Publications by authors named "Lindsey J du Toit"

30 Publications

  • Page 1 of 1

Putative Effector Genes Distinguish Two Pathogenicity Groups of f. sp. .

Mol Plant Microbe Interact 2021 Feb 21;34(2):141-156. Epub 2020 Dec 21.

Washington State University Northwestern Washington Research and Extension Center Mount Vernon, Mount Vernon, WA 98273, U.S.A.

Fusarium wilt of spinach, caused by f. sp. , is an important disease during warm conditions in production regions with acid soils, yet little is known about what confers pathogenicity to spinach in f. sp. genetically. To identify candidate fungal genes that contribute to spinach Fusarium wilt, each of 69 geographically diverse isolates was tested for pathogenicity on each of three spinach inbreds. Thirty-nine isolates identified as f. sp. caused quantitative differences in disease severity among the inbreds that revealed two distinct pathogenicity groups of f. sp. . Putative effector gene profiles, predicted from whole-genome sequences generated for nine f. sp. isolates and five nonpathogenic, spinach-associated (NPS) isolates, distinguished the f. sp. isolates from the NPS isolates, and separated the f. sp. isolates into two groups. Five of the putative effector genes appeared to be unique to f. sp. , as they were not found in 222 other publicly available genome assemblies of , implicating potential involvement of these genes in pathogenicity to spinach. In addition, two combinations of the 14 known () genes that have been affiliated with host pathogenicity in other formae speciales of were identified in genome assemblies of the nine f. sp. isolates, either and or , , and . Characterization of these putative effector genes should aid in understanding mechanisms of pathogenicity in f. sp. , developing molecular tools for rapid detection and quantification of f. sp. , and breeding for resistance to Fusarium wilt in spinach.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.
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http://dx.doi.org/10.1094/MPMI-06-20-0145-RDOI Listing
February 2021

Three New Fungal Leaf Spot Diseases of Spinach in the United States and the Evaluation of Fungicide Efficacy for Disease Management.

Plant Dis 2021 Feb 1;105(2):316-323. Epub 2021 Jan 1.

Department of Plant Pathology, University of Arkansas, Fayetteville, AR 72701.

Leaf spot diseases of spinach, caused by , has become a major production constraint in several production areas, including Texas, in recent years. Leaf spot symptoms were observed in several fields in Texas in 2016 and 2017, with typical anthracnose-like symptoms and leaves with small, circular, and sunken lesions that appeared similar to injury from windblown sand. The lesions were plated on potato dextrose agar, from which fungal cultures were recovered. The fungi were identified based on morphology and sequence analysis of the introns of glutamate synthetase and glyceraldehyde-3-phosphate dehydrogenase (for isolates determined to be spp.) and the internal transcribed spacer ribosomal DNA (for isolates determined to be spp.). Based on foliar symptoms, fungal colony and spore morphology, pathogenicity tests of fungal isolates on the spinach cultivar 'Viroflay', and DNA sequence analysis of the isolates, the symptoms on spinach leaves for two sets of samples were caused by and , and leaf spots resembling damage from windblown sand were caused by . This is the first report of spinach leaf spot diseases caused by , , and in the United States. and caused severe symptoms on the spinach cultivar 'Viroflay', whereas caused symptoms of intermediate severity. Fungicide efficacy tests demonstrated that chlorothalonil, mancozeb, pyraclostrobin, fluxapyroxad + pyraclostrobin, and penthiopyrad were completely effective at preventing leaf spots caused by any of these pathogens when applied 24 h before inoculation of 'Viroflay' plants in greenhouse trials.
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http://dx.doi.org/10.1094/PDIS-04-20-0918-REDOI Listing
February 2021

Characterization of Leaf Spot Pathogens from Several Spinach Production Areas in the United States.

Plant Dis 2020 Jul 22;104(7):1994-2004. Epub 2020 May 22.

Department of Plant Pathology, University of Arkansas, Fayetteville, AR 72701.

Leaf spot diseases have become a major concern in spinach production in the United States. Determining the causal agents of leaf spots on spinach, their prevalence and pathogenicity, and fungicide efficacy against these pathogens is vital for effective disease management. Spinach leaves with leaf spots were collected from Texas, California, Arizona, and South Carolina from 2016 to 2018, incubated in a moist chamber, and plated on potato dextrose and tryptic soy agar media. Fungal and bacterial colonies recovered were identified based on morphology and sequence analysis of the internal transcribed spacer rDNA and 16S rRNA, respectively. Two predominant genera were isolated: (i) spp., which were identified to species based on sequences of both introns of the glutamate synthetase (-I) and glyceraldehyde-3-phosphate dehydrogenase (-I) genes; and (ii) spp., identified to species based on sequences of the and calmodulin () genes. Anthracnose () and Stemphylium leaf spot ( and ) were the predominant diseases. Additional fungi recovered at very limited frequencies that were also pathogenic to spinach included , , , and . All of the bacterial isolates were not pathogenic on spinach. Pathogenicity tests showed that , , and caused significant leaf damage. The fungicides Bravo WeatherStik (chlorothalonil), Dithane F-45 (mancozeb), Cabrio (pyraclostrobin), and Merivon (fluxapyroxad and pyraclostrobin) were highly effective at reducing leaf spot severity caused by an isolate of each of and , when inoculated individually and in combination.
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http://dx.doi.org/10.1094/PDIS-11-19-2450-REDOI Listing
July 2020

A phylogenetically distinct lineage of associated with chlorotic leaf spot of Brassicaceae in North America.

Plant Pathol 2020 Apr 22;69(3):518-537. Epub 2020 Jan 22.

Department of Plant Pathology Washington State University Mount Vernon WA USA.

Light leaf spot, caused by the ascomycete , is an established disease of Brassicaceae in the United Kingdom (UK), continental Europe, and Oceania (OC, including New Zealand and Australia). The disease was reported in North America (NA) for the first time in 2014 on spp. in the Willamette Valley of western Oregon, followed by detection in cover crops and on weeds in northwestern Washington in 2016. Preliminary DNA sequence data and field observations suggest that isolates of the pathogen present in NA might be distinct from those in the UK, continental Europe, and OC. Comparisons of isolates from these regions using genetic (multilocus sequence analysis, gene sequences, and rep-PCR DNA fingerprinting), pathogenic ( inoculation studies), biological (sexual compatibility), and morphological (colony and conidial morphology) analyses demonstrated two genetically distinct evolutionary lineages. Lineage 1 comprised isolates from the UK, continental Europe, and OC, and included the type specimen. Lineage 2 contained the NA isolates associated with recent disease outbreaks in the Pacific Northwest region of the USA. Symptoms caused by isolates of the two lineages on and differed, and therefore "chlorotic leaf spot" is proposed for the disease caused by Lineage 2 isolates of . Isolates of the two lineages differed in genetic diversity as well as sensitivity to the fungicides carbendazim and prothioconazole.
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http://dx.doi.org/10.1111/ppa.13137DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7074063PMC
April 2020

Genetic Diversity and Differentiation in Populations on Table Beet in New York and Washington States.

Plant Dis 2019 Jul 6;103(7):1487-1497. Epub 2019 May 6.

1 Plant Pathology and Plant-Microbe Biology Section, School of Integrative Plant Science, Cornell AgriTech at the New York State Agricultural Experiment Station, Cornell University, Geneva, NY 14456, U.S.A.

is an important seedborne pathogen of table beet worldwide that is capable of causing foliar, root, and damping-off diseases. Ten microsatellite and mating type markers were developed to investigate the genetics of populations in table beet root crops in New York and in table beet seed crops in Washington, from where table beet seed is predominantly sourced. The markers were used to characterize 175 isolates comprising five populations (two from New York and three from Washington), and they were highly polymorphic with an allelic range of 4 to 33 and an average of 11.7 alleles per locus. All populations had high genotypic diversity (Simpson's complement index = 0.857 to 0.924) and moderate allelic diversity (Nei's unbiased gene diversity = 0.582 to 0.653). Greater differentiation observed between populations from the two states compared with populations within the same state suggested that an external inoculum source, such as windblown ascospores, may be homogenizing the populations. However, most genetic diversity (87%) was among individual isolates within populations (pairwise index of population differentiation = 0.127; = 0.001), suggesting that local within-field inoculum source(s), such as infested field debris or infected weeds, may also be important in initiating disease outbreaks. Standardized index of association, proportion of compatible pairs of loci, and mating type ratio calculations showed evidence for a mixed reproduction mode in all populations. These findings could be useful in designing more effective management strategies for diseases caused by in table beet production.
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http://dx.doi.org/10.1094/PDIS-09-18-1675-REDOI Listing
July 2019

A New Subclade of Identified from .

Int J Mol Sci 2019 Apr 3;20(7). Epub 2019 Apr 3.

Department of Plant Science, University of Manitoba, 66 Dafoe Road, Winnipeg, MB R3T 2N2, Canada.

Blackleg (Phoma stem canker) of crucifers is a globally important disease caused by the ascomycete species complex comprising of and . Six blackleg isolates recovered from cv. Mizspoona in the Willamette Valley of Oregon were characterized as based on standard pathogenicity tests and molecular phylogenetic analysis. These isolates were compared to 88 characterized isolates from western Canada, 22 isolates from Australia, and 6 isolates from Idaho, USA using maximum parsimony and distance analysis of phylogenetic trees generated from the ITS rDNA (internal transcribed spacer rDNA) sequence, and the and gene sequences. The isolates derived from collected in Oregon formed a separate subclade based on concatenated gene sequences or a single gene sequence, regardless of the analyses. Pathogenicity tests showed that these isolates failed to infect either resistant or susceptible cultivars, but caused severe symptoms on three cultivars (Accession number: UM1113, UM1112, and UM1161), a var. (cabbage) cultivar (Copenhagen Market), and two cultivars (CBM, a common brown Mustard, and Forge). These findings demonstrated that the isolates derived from a crop in Oregon were genetically distinct from existing species of , and constitute a new subclade, herein proposed as 'americensis'.
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http://dx.doi.org/10.3390/ijms20071668DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6479289PMC
April 2019

Limestone-Mediated Suppression of Fusarium Wilt in Spinach Seed Crops.

Plant Dis 2017 Jan 19;101(1):81-94. Epub 2016 Oct 19.

Washington State University, Mount Vernon Northwestern Washington Research & Extension Center, Mount Vernon 98273-4768.

Fusarium wilt of spinach is caused by the soilborne fungus Fusarium oxysporum f. sp. spinaciae and occurs in most regions of spinach production. The disease is favored by acid soils and warm temperatures, and the fungus can survive extended periods as chlamydospores or by asymptomatic colonization of the roots of nonhost plant species. The 10- to 15-year rotation required to minimize losses to Fusarium wilt is the primary constraint on spinach seed production in the maritime Pacific Northwest, the only region of the United States suitable for this cool-season, daylength-sensitive crop. Raising soil pH with agricultural limestone (97% CaCO) results in a transitory, partially suppressive effect on spinach Fusarium wilt. A field trial was completed from 2009 to 2012 to assess the potential for annual applications of agricultural limestone at 0, 2.24, and 4.48 tons/ha for 3 years prior to a spinach seed crop to improve Fusarium wilt suppression compared with the level of suppression attained from a single limestone amendment at 4.48 tons/ha. Three proprietary female spinach lines were planted that ranged from highly susceptible to partially resistant to Fusarium wilt. Three successive annual applications of limestone at 4.48 tons/ha reduced midseason wilt incidence by an average of 20%, increased spinach biomass by 33%, and increased marketable spinach seed yield by 45% compared with plots amended once with the same rate of limestone in the spring of planting. The suppressive effect increased with increasing rate of limestone amendment, with the greatest difference observed when limestone was applied at between 0 and 2.24 tons/ha annually for 3 years. The effects on seed yield were greatest for the partially resistant female line, followed by the moderately susceptible and highly susceptible female lines. Overall, the results demonstrate that annual applications of agricultural limestone on acid soils of the maritime Pacific Northwest of the United States can enhance suppression of spinach Fusarium wilt, potentially reducing the required rotation interval by as much as 50%, thereby doubling the capacity for spinach seed production in the United States.
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http://dx.doi.org/10.1094/PDIS-04-16-0423-REDOI Listing
January 2017

Timing of Glyphosate Applications to Wheat Cover Crops to Reduce Onion Stunting Caused by Rhizoctonia solani.

Plant Dis 2016 Jul 7;100(7):1474-1481. Epub 2016 Mar 7.

Professor, Washington State University, Mount Vernon Northwestern Washington Research and Extension Center, Mount Vernon 98273.

Stunting caused by Rhizoctonia spp. is economically important in irrigated onion bulb crops in the semiarid Columbia Basin of Oregon and Washington, where cereal winter cover crops commonly are planted the previous fall to prevent wind erosion of soil. The cover crop is killed with herbicide application just before or shortly after onion seeding, so that the dead rows of cereal plants provide a physical barrier tall enough to protect onion seedlings against wind and sand blasting but not tall enough to shade onion seedlings. However, the cover crop also serves as a green bridge for Rhizoctonia spp. on cereal roots to colonize the onion roots, potentially resulting in severe stunting of onion seedlings. To determine the effect of timing of application of the herbicide glyphosate to reduce this green bridge effect and, subsequently, onion stunting, three herbicide application intervals preceding onion planting were evaluated in a grower's onion field in each of 2012 and 2014 in the Columbia Basin. The wheat cover crop was killed with a glyphosate application 27, 17, and 3 days before onion seeding in 2012 and 19, 10, and 3 days before seeding in 2014. As the interval between herbicide application and onion planting increased from 3 days to 19 and 27 days, the number of patches of stunted onion plants decreased by ≥55%, total area of stunted patches decreased by 54 to 63%, and patch severity index decreased by 59 to 65%. Similarly, the Rhizoctonia solani AG 8 DNA concentration in soil sampled from the dead cover crop rows declined as the interval between glyphosate application and onion seeding increased in the 2012 trial but not in the 2014 trial. R. solani AG 3 and AG 8 DNA concentrations in soil sampled from the cover crop rows were significantly positively correlated with the number of patches of stunted onion plants (r = 0.490 and 0.607 at P = 0.039 and 0.008, respectively), total area of stunted patches (r = 0.496 and 0.659 at P = 0.035 and 0.003, respectively), and patch severity index (r = 0.492 and 0.635 at P = 0.038 and 0.005, respectively) in the 2012 trial; however, these variables were only correlated significantly with R. solani AG 3 DNA concentration in the 2014 trial. Increasing the interval between herbicide application to the cover crop and onion planting provides a practical management tool for stunting in onion bulb crops.
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http://dx.doi.org/10.1094/PDIS-10-15-1234-REDOI Listing
July 2016

Pythium Species Associated with Damping-off of Pea in Certified Organic Fields in the Columbia Basin of Central Washington.

Plant Dis 2016 May 24;100(5):916-925. Epub 2016 Feb 24.

Washington State University Mount Vernon NWREC.

Organic vegetable production accounted for 19% of the total organic acreage in Washington State in 2013, with 1,700 ha of certified organic vegetable pea. However, production is challenged constantly with the threat of poor emergence after planting due to damping-off caused by Pythium spp. A survey of Pythium spp. in organic vegetable production areas of the semiarid Columbia Basin of central Washington was carried out in fall 2009 to identify species associated with damping-off during early spring planting. Of 305 isolates baited from soil sampled from 37 certified organic fields, 264 were identified to 16 Pythium spp. by sequencing the internal transcribed spacer region of ribosomal DNA. A soil DNA-CFU regression curve was developed using real-time quantitative polymerase chain reaction assays for each of the three predominant pathogenic species (Pythium abappressorium, the P. irregulare complex, and P. ultimum var. ultimum) found in soil sampled from the 37 fields. The P. irregulare complex, P. abappressorium, and P. ultimum var. ultimum were detected in 57, 78, and 100% of the fields sampled, respectively. A regression analysis was used to determine that P. ultimum var. ultimum ranged from 14 to 332 CFU/g of soil in the 37 fields, the P. irregulare complex ranged from 25 to 228 CFU/g of soil, and P. abappressorium DNA was below the quantifiable limit. In summary, P. ultimum var. ultimum was the most prevalent pathogenic Pythium sp. detected in certified organic fields in the semiarid Columbia Basin of central Washington but multiple Pythium spp. may be associated with damping-off in cool and wet, early spring planting conditions.
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http://dx.doi.org/10.1094/PDIS-07-15-0774-REDOI Listing
May 2016

Characterization and Pathogenicity of Rhizoctonia and Rhizoctonia-Like spp. From Pea Crops in the Columbia Basin of Oregon and Washington.

Plant Dis 2015 May;99(5):604-613

Professor, Washington State University Mount Vernon Northwestern Washington Research & Extension Center, Mount Vernon 98273.

Isolates of Rhizoctonia and Rhizoctonia-like spp. (n = 179) were baited selectively from soil and plant samples collected from irrigated pea crops in the semiarid Columbia Basin of Oregon and Washington from 2011 to 2013, and characterized to species, subspecies, and anastomosis groups (AG) based on sequences of the internal transcribed spacer region of ribosomal DNA. Rhizoctonia solani comprised 76% of all isolates, and included isolates of AG 4 (31% of all isolates), AG 2-1 (18%), AG 3 (10%), AG 8 (8%), AG 5 (5%), AG 10 (3%), and AG 9 (1%). The isolates of Ceratobasidium spp. (20%) comprised four AGs: AG K (11%), AG A (6%), AG I (2%), and AG I-like (1%). Waitea circinata isolates (4%) comprised two subspecies: W. circinata var. circinata (approximately 4%) and W. circinata var. zeae (<1%). Repeated pathogenicity tests of isolates of the 10 most frequently detected AGs and subspecies on 'Serge' pea at 15°C revealed that R. solani AG 2-1 caused the greatest reduction in pea emergence, followed by R. solani AG 4. R. solani AG 4 caused the most severe root rot, stunting, and reduction in pea seedling biomass, followed by isolates of AG 2-1. R. solani AG 8 did not affect emergence, plant height, and total biomass compared with noninoculated control plants; however, root rot caused by isolates of AG 8 was ranked the third most severe among isolates of the 10 Rhizoctonia subgroups, after that caused by isolates of AG 4 and AG 2-1. Isolates of other AGs and subspecies were either weakly virulent or nonpathogenic on pea. The most common AGs (AG 4 and AG 2-1) detected in pea fields in the Columbia Basin were also the most virulent. In a growers' pea crop grown for seed ('Prevail') planted 5 days after herbicide application and incorporation of a preceding winter wheat crop, severe stunting caused by Rhizoctonia spp. resulted in an average 75% yield loss within patches of stunted plants. In contrast, the yield of processing pea from a green pea crop of Serge did not differ significantly for plants sampled within versus outside patches of stunted plants; however, plants within patches were significantly more mature. In the Prevail seed crop, a greater frequency of R. solani AG 8 was detected than AG 2-1 or AG 4 from within patches of stunted plants, indicating that isolates of AG 8 may be associated with the root rot complex in some pea crops in the Columbia Basin.
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http://dx.doi.org/10.1094/PDIS-08-14-0803-REDOI Listing
May 2015

Stunted Patches in Onion Bulb Crops in Oregon and Washington: Etiology and Yield Loss.

Plant Dis 2015 May;99(5):648-658

Professor, Washington State University Mount Vernon NWREC, Mount Vernon 98273.

Onion stunting caused by Rhizoctonia spp. is an important soilborne disease on very sandy soils in the Columbia Basin of Oregon and Washington. From 2010 to 2013, 251 isolates of Rhizoctonia or Rhizoctonia-like spp. were obtained from soil and onion plant samples collected from inside and outside patches of stunted plants in 29 onion fields in the Columbia Basin. Sequence analysis of the internal transcribed spacer (ITS) region was used to identify the isolates, with 13 anastomosis groups (AGs) or subspecies detected. The most frequent was Waitea circinata var. circinata (25%), followed by Rhizoctonia solani AG 3 (17%), R. solani AG 4 (14%), Ceratobasidium sp. AG A (10%), R. solani AG 8 (7%), Ceratobasidium sp. AG K (6%), R. solani AG 2-1 (6%), W. circinata var. zeae (6%), R. solani AG 5 (4%), Ceratobasidium sp. AG G (2%), R. solani AG 11 (2%), and R. solani AG 1-1B and AG 10 (each <1%). However, the distribution of AGs and subspecies varied depending on whether soil or onion plants samples were collected within or adjacent to patches of stunted onion plants. In an attempt to predict the risk of onion stunting for a field prior to planting, DNA concentrations of AG 2-1, AG 3, AG 4, and AG 8 were quantified from bulk soil samples collected from each of nine growers' fields approximately 1 month before onion sowing in 2012. The preplant DNA concentrations did not show a significant association with the amount of stunting observed in the fields during the growing season. In contrast, the frequency of isolation and DNA concentration of R. solani AG 8 detected in soil samples collected during the growing season were greater from inside patches of stunted onion plants than from adjacent healthy areas of an onion crop sampled in 2012, but not for soil samples collected similarly from an onion crop in 2013. AG 2-1, AG 3, and AG 4 DNA concentrations did not differ significantly in soil sampled inside versus outside stunted patches in the fields sampled in 2012 and 2013. Relationships between the number of bulbs harvested or bulb weight versus severity of stunting were defined using correlation and regression analyses for six onion cultivars grown in seven fields surveyed in 2012 and 2013. Onion stunting reduced the average marketable bulb yield by 25 to 60% within stunted patches of the six cultivars. Stunting did not reduce onion plant stand but consistently reduced the size of bulbs, and yield reduction increased with increasing disease severity.
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http://dx.doi.org/10.1094/PDIS-05-14-0441-REDOI Listing
May 2015

A Soil Bioassay for Predicting the Risk of Spinach Fusarium wilt.

Plant Dis 2015 Apr;99(4):512-526

Washington State University Mount Vernon Northwestern Washington Research & Extension Center, Mount Vernon 98273-4768.

The maritime Pacific Northwest is the only region of the United States suitable for production of spinach seed, a cool-season, daylength-sensitive crop. However, the acidic soils of this region are highly conducive to spinach Fusarium wilt, caused by Fusarium oxysporum f. sp. spinaciae. Rotations of at least 10 to 15 years between spinach seed crops are necessary to reduce the high risk of losses to this disease. The objectives of this study were to develop a greenhouse soil bioassay to assess the relative risk of Fusarium wilt in fields intended for spinach seed production, and to identify soil chemical and physical properties associated with conduciveness to this disease. Preliminary bioassays established a protocol for growing spinach plants in a greenhouse environment and inducing Fusarium wilt symptoms so that the bioassay can be completed in <2 months. Test soils with a range of Fusarium wilt inoculum potentials, and three spinach inbred parent lines (highly susceptible, moderately susceptible, and moderately resistant to Fusarium wilt) were used to evaluate sensitivity of the bioassay to different levels of risk of Fusarium wilt. Then, from 2010 to 2013, spinach seed growers and stakeholders submitted soil samples from 147 fields for evaluation with the bioassay. The fields were each under consideration for planting a spinach seed crop, yet the bioassay revealed a wide range in Fusarium wilt inoculum potential among soil samples. Differences in susceptibility to Fusarium wilt of the three inbred lines were key to detecting differences in wilt risk among soils. Visits to spinach seed crops planted in fields evaluated in the bioassay, as well as test plots of the three inbred lines planted in growers' seed crops, confirmed the predictive value of the bioassay for Fusarium wilt risk. Correlation analyses for 23 soil properties revealed significant relationships of 15 soil properties with the Fusarium wilt potential of a soil, but the correlations were influenced significantly by susceptibility of the inbred line to Fusarium wilt (13, 10, and 8 soil properties correlated significantly with Fusarium wilt risk for the susceptible, moderate, and partially resistant inbreds, respectively). Multiple regression analyses identified different statistical models for prediction of Fusarium wilt risk depending on the spinach inbred line, but the best fitting model explained <34% of the variability in Fusarium wilt risk among 121 fields evaluated in the soil bioassay. Thus, no model was robust enough to replace the bioassay for the purpose of predicting Fusarium wilt risk.
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http://dx.doi.org/10.1094/PDIS-08-14-0804-REDOI Listing
April 2015

Quantitative Molecular Detection of Xanthomonas hortorum pv. carotae in Carrot Seed Before and After Hot-Water Treatment.

Plant Dis 2013 Dec;97(12):1585-1592

Oregon State University, Department of Botany and Plant Pathology, Corvallis.

Molecular assays to detect and quantify DNA from viable cells of the seedborne pathogen Xanthomonas hortorum pv. carotae in carrot seed were developed and evaluated for use on nontreated and hot-water-treated seed lots. Both a TaqMan real-time polymerase chain reaction (PCR) assay and a loop-mediated isothermal amplification (LAMP) dilution endpoint assay detected and quantified DNA from viable pathogen cells after treatment of carrot seed washes with the live-dead discriminating dye propidium monoazide (PMA). The detection limits of the assays were approximately 10 CFU for pure cultures of X. hortorum pv. carotae, and 10 to 10 CFU/g seed from naturally infested carrot seed lots. X. hortorum pv. carotae in and on carrot seed was killed by soaking the seed in hot water (52°C for 25 min), and a subsequent PMA treatment of these hot-water-treated seed washes suppressed detection of the pathogen with both the real-time PCR and LAMP assays. For 36 commercial seed lots treated with PMA but not hot water, regression of colony counts of X. hortorum pv. carotae measured by dilution plating on a semiselective agar medium versus estimates of pathogen CFU determined by the molecular assays resulted in significant (P ≤ 0.05) linear relationships (R = 0.68 for the real-time PCR assay and 0.79 for the LAMP assay). The molecular assays provided quantitative estimates of X. hortorum pv. carotae infestations in carrot seed lots in <24 h, which is a significant improvement over the 7 to 14 days required to obtain results from the traditional dilution-plating assay.
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http://dx.doi.org/10.1094/PDIS-03-13-0262-REDOI Listing
December 2013

Pathogenicity, Virulence, and Vegetative Compatibility Grouping of Verticillium Isolates from Spinach Seed.

Plant Dis 2013 Nov;97(11):1457-1469

Department of Plant Pathology, University of Arkansas, Fayetteville.

In 2005, Verticillium dahliae was first reported to be pathogenic to spinach seed crops in the Pacific Northwest, with symptoms only developing after initiation of the reproductive stage of plant growth, and to be prevalent on commercial spinach seed lots produced in Denmark, The Netherlands, and the United States. In this study, the genetic diversity, pathogenicity, and virulence were examined for a collection of isolates of Verticillium spp. from spinach as well as other hosts (alfalfa, cotton, lettuce, mint, peppermint, potato, radish, and tomato) from various countries and from different vegetative compatibility groups (VCGs). Of a total of 210 isolates of V. dahliae obtained from spinach seed produced in Denmark, the Netherlands, New Zealand, or the United States, 128 were assigned to VCG 4B (89% of 91 U.S. isolates, 86% of 42 isolates from the Netherlands, 19% of 43 Denmark isolates, and 8% of 13 New Zealand isolates), 65 to VCG 2B (92% of the New Zealand isolates, 79% of the Denmark isolates, 14% of the Netherlands isolates, and 9% of the U.S. isolates), and 3 to VCG 2A (2% of each of the Denmark and U.S. isolates, and 0% of the Netherlands and New Zealand isolates); 14 isolates could not be assigned to a VCG. Although little variation in the sequence of the internal transcribed spacer (ITS) region of ribosomal DNA was observed among isolates within each Verticillium sp., the ITS region readily differentiated isolates of the species V. dahliae, V. tricorpus, and Gibellulopsis nigrescens (formerly V. nigrescens) obtained from spinach seed. Greenhouse pathogenicity assays on spinach, cotton, lettuce, and tomato plants using isolates of V. dahliae (n = 29 to 34 isolates), V. tricorpus (n = 3), G. nigrescens (n = 2), and V. albo-atrum (n = 1) originally obtained from these hosts as well as from alfalfa, mint, peppermint, potato, and radish, revealed a wide range in virulence among the isolates. Isolates of V. tricorpus and G. nigrescens recovered from spinach seed and an isolate of V. albo-atrum from alfalfa were not pathogenic on spinach. In addition, isolates of V. dahliae from mint and peppermint were not pathogenic or only weakly virulent on the hosts evaluated. Although there was a wide range in virulence among the isolates of V. dahliae tested, all of the V. dahliae isolates caused Verticillium wilt symptoms on spinach, lettuce, tomato, and cotton. None of the isolates of V. dahliae showed host specificity. These results indicate that Verticillium and related species associated with spinach seed display substantial variability in virulence and pathogenicity to spinach and other plants but the V. dahliae isolates were restricted to three VCGs.
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http://dx.doi.org/10.1094/PDIS-01-13-0016-REDOI Listing
November 2013

Observations from a Quarter Century of Evaluating Reactions of Sweet Corn Hybrids in Disease Nurseries.

Plant Dis 2011 Dec;95(12):1492-1506

Terai Seeds, Greenville, MS.

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http://dx.doi.org/10.1094/PDIS-03-11-0236DOI Listing
December 2011

Verticillium Wilt of Skullcap and Potential for Pathogen Dissemination via Seeds and Stems.

Plant Dis 2011 Sep;95(9):1147-1152

Washington State University, Pullman.

A commercial skullcap (Scutellaria lateriflora, family Lamiaceae) crop with wilted and necrotic plants was examined in Washington State in 2008. Three fungal isolates were obtained and identified as Verticillium dahliae based on morphology and sequencing of the internal transcribed spacer DNA region. All three skullcap isolates caused typical Verticillium wilt symptoms on skullcap and two peppermint cultivars. Inoculations of skullcap with the V. dahliae isolates from skullcap and an isolate from peppermint resulted in severe symptoms and a 21 to 78% reduction in aboveground biomass. Isolates from skullcap caused severe symptoms on the susceptible peppermint 'Black Mitcham' and reduced yield by up to 82%. One skullcap isolate caused severe symptoms on the moderately resistant 'Redefined Murray' in three of four trials and reduced biomass up to 71% compared with noninoculated control plants. The pathogen was recovered from 43 to 69% of skullcap stems from plants inoculated with skullcap or peppermint isolates, and was isolated from 2.5% of seed harvested from skullcap plants inoculated with the peppermint isolate of V. dahliae. This is the first report of V. dahliae infecting skullcap, and the first demonstration of V. dahliae isolates from skullcap and peppermint causing symptoms on both hosts, as well as the seedborne nature of V. dahliae in skullcap.
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http://dx.doi.org/10.1094/PDIS-01-11-0014DOI Listing
September 2011

Greenhouse Evaluation of Seed and Drench Treatments for Organic Management of Soilborne Pathogens of Spinach.

Plant Dis 2009 Dec;93(12):1281-1292

Associate Professor, Washington State University Mount Vernon Northwestern Washington Research and Extension Center, 16650 State Route 536, Mount Vernon, WA 98273.

The efficacy of 14 seed and drench treatments for control of soilborne damping-off pathogens in organic production of spinach was evaluated in a greenhouse study. The efficacy of each treatment was compared with nontreated seed and seed treated with a conventional fungicide for control of Fusarium oxysporum f. sp. spinaciae, Pythium ultimum, and Rhizoctonia solani. Two experimental seed treatments, GTG I and GTG II (each comprised of a proprietary organic disinfectant and the latter also containing Trichoderma harzianum T22), provided equivalent control to the conventional fungicide, mefenoxam, against P. ultimum in one trial and significant reduction of damping-off in the second trial. Natural II and Natural X (Streptomycete products), and Subtilex (Bacillus subtilis) seed treatments each suppressed damping-off significantly in one of the two trials. For R. solani, GTG I and Natural II seed treatments reduced damping-off as effectively as a drench with the fungicide Terraclor (pentachloronitrobenzene). A soil drench with Prestop (Gliocladium catenulatum) suppressed postemergence wilt caused by F. oxysporum in both trials; a compost tea drench and seed treatment with Yield Shield (Bacillus pumilis) each suppressed postemergence wilt in only one of two trials. GTG I and GTG II significantly increased seed germination compared to nontreated seed. No treatment was effective against all three pathogens, and some treatments exacerbated damping-off.
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http://dx.doi.org/10.1094/PDIS-93-12-1281DOI Listing
December 2009

A Real-Time, Quantitative PCR Seed Assay for Botrytis spp. that Cause Neck Rot of Onion.

Plant Dis 2007 May;91(5):599-608

Associate Professor, Washington State University, Department of Plant Pathology, Pullman 99164-6430.

A real-time fluorescent polymerase chain reaction (PCR) assay was developed using SYBR Green chemistry to quantify the Botrytis spp. associated with onion (Allium cepa) seed that are also able to induce neck rot of onion bulbs, i.e., B. aclada, B. allii, and B. byssoidea. The nuclear ribosomal intergenic spacer (IGS) regions of target and nontarget Botrytis spp. were sequenced, aligned, and used to design a primer pair specific to B. aclada, B. allii, and B. byssoidea. Primers and amplification parameters were optimized to avoid amplifying the related species B. cinerea, B. porri, and B. squamosa, as well as Sclerotinia sclerotiorum and isolates of 15 other fungal species commonly found associated with onion seed. The primers reliably detected 10 fg of genomic DNA per PCR reaction extracted from pure cultures of B. aclada and B. allii. Conventional assays of surface-disinfested and nondisinfested seed on an agar medium were used to determine the incidence of neck rot Botrytis spp. associated with each of 23 commercial onion seed lots, and the real-time PCR assay was used to determine the quantity of DNA of neck rot Botrytis spp. in each seed lot. A linear relationship could not be found between the incidence of seed infected with the neck rot Botrytis spp. using the conventional agar seed assays and the quantity of DNA of the neck rot Botrytis spp. detected by the real-time PCR assay. However, the real-time PCR assay appeared to be more sensitive than the conventional agar assay, allowing detection of neck rot Botrytis spp. in 5 of the 23 seed lots that tested negative using the conventional agar seed assay.
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http://dx.doi.org/10.1094/PDIS-91-5-0599DOI Listing
May 2007

Iris yellow spot virus: An Emerging Threat to Onion Bulb and Seed Production.

Plant Dis 2006 Dec;90(12):1468-1480

Colorado State University, Fort Collins, USA.

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http://dx.doi.org/10.1094/PD-90-1468DOI Listing
December 2006

Carrot Purple Leaf: A New Spiroplasmal Disease Associated with Carrots in Washington State.

Plant Dis 2006 Aug;90(8):989-993

Mercer Ranch, Prosser, WA 99350.

During the growing seasons of 2003 and 2004, a disease occurred in several carrot crops in south central Washington with symptoms suggestive of infection by phytopathogenic mollicutes (phytoplasmas and spiroplasmas). In the fall, many affected carrot plants exhibited extensive purple or yellow-purple leaf discoloration, general stunting of shoots and taproots, and formation of bunchy, fibrous secondary roots. For detection of the putative causal agents, polymerase chain reaction (PCR) assays were performed using primers specific to phytoplasmas as well as primers specific to plant-pathogenic spiroplasmas. Restriction fragment length polymorphism (RFLP) analyses of PCR-amplified 16S rDNA sequences revealed that about 81% of affected plants showing dark purple or yellow-purple leaf symptoms tested positive for Spiroplasma citri. Of affected plants showing mild purple discoloration of leaf margins, 18% tested positive for a phytoplasma strain belonging to the clover proliferation group (16SrVI), subgroup 16SrVI-A, and 11% for another phytoplasma strain belonging to the aster yellows group (16SrI), subgroup 16SrI-A. Nucleotide sequence analysis of cloned 16S rDNA confirmed the phytoplasma group affiliations. Some symptomatic plants were co-infected with S. citri and either aster yellows phytoplasma or clover proliferation group phytoplasma. To our knowledge, this is the first documentation of spiroplasma infection of carrot in the United States.
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http://dx.doi.org/10.1094/PD-90-0989DOI Listing
August 2006

Seedborne Cladosporium variabile and Stemphylium botryosum in Spinach.

Plant Dis 2006 Feb;90(2):137-145

Vegetable Seed Pathologist, Washington State University - Northwestern Washington REC, 16650 State Route 536, Mount Vernon, WA 98273-4768.

Assays of 77 spinach (Spinacia oleracea) seed lots produced in the United States, Denmark, the Netherlands, or New Zealand in 2000 to 2003 showed that Stemphylium botryosum, causal agent of Stemphylium leaf spot, was present in every lot, at a mean incidence of 29.1% per lot. Either Cladosporium variabile, causal agent of Cladosporium leaf spot, or the morphologically similar species C. macrocarpum, was present in 37 of the 77 lots, at a mean incidence of 1.8% per lot. Some seed isolates of S. botryosum and C. variabile proved pathogenic on spinach. Nonpathogenic isolates resembling C. variabile were identified as C. macrocarpum by the absence of torulose aerial hyphae. Pathogenic isolates of S. botryosum were also detected in each of 12 seed lots stored for up to 11 years at 4.4°C and 60% relative humidity. C. variabile or C. macrocarpum was detected in only 2 of the 11 lots, which had been stored for 3 and 8 years. Component seed assays demonstrated that S. botryosum and C. variabile (or C. macrocarpum) were internal and external in spinach seed. S. botryosum was detected in 5 to 76% of the embryos of five seed lots, but the two Cladosporium species were detected in only 0 to 1% of the embryos of these lots. This suggests greater potential difficulty at eradicating S. botryosum than C. variabile from infected spinach seed using seed treatments.
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http://dx.doi.org/10.1094/PD-90-0137DOI Listing
February 2006

Efficacy of Hot Water and Chlorine for Eradication of Cladosporium variabile, Stemphylium botryosum, and Verticillium dahliae from Spinach Seed.

Plant Dis 2005 Dec;89(12):1305-1312

Former Graduate Research Assistant, Washington State University-Northwestern Washington Research & Extension Center, Mount Vernon 98273-4768.

Cladosporium variabile, Stemphylium botryosum, and Verticillium dahliae are seedborne and seed-transmitted pathogens of spinach. Spinach seed treatments in 1.2% NaOCl for 10 to 60 min, or hot water (40, 45, 50, 55, and 60°C) for 10 to 40 min, were evaluated for eradication of these fungi from seed. C. variabile and V. dahliae were largely eradicated by chlorine treatment for ≥ 10 min. Although chlorine treatment reduced the incidence of S. botryosum, this fungus was not eradicated after 60 min in chlorine. Seed germination was not affected adversely by chlorine treatment, even after 60 min. In contrast, germination was reduced significantly by hot water treatment at 50°C for ≥30 min or 55 or 60°C for ≥10 min. C. variabile was eradicated from seed treated in 40°C water for 10 min. V. dahliaewas eradicated from seed treated at 55°C for ≥30 min or 60 °C for ≥10 min. S. botryosum was eradicated from a lightly infected seed lot (5% incidence) by hot water treatment at 55 or 60 °C for ≥10 min, but could not be eradicated from two heavily infected lots (>65% incidence), even at 60°C for 40 min. Using precisely controlled parameters, chlorine or hot water seed treatments can be used to eradicate C. variabile and reduce the incidence of S. botryosum and V. dahliae in spinach seed without damaging germination.
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http://dx.doi.org/10.1094/PD-89-1305DOI Listing
December 2005

Bacterial Blight in Carrot Seed Crops in the Pacific Northwest.

Plant Dis 2005 Aug;89(8):896-907

WSU Extension Educator, Grant/Adams Counties, Ephrata 98823.

Carrot (Daucus carota subsp. sativus) seed crops in Oregon and Washington were surveyed in 2001-02 and 2002-03 for development of Xanthomonas campestris pv. carotae, causal agent of bacterial blight. For each state and season, 20 plants were sampled from each of 7 to 12 direct-seeded crops twice in the fall or winter and three times from spring to summer; and from each of 2 to 4 steckling (root-to-seed) crops three times from spring to summer. X. campestris pv. carotae was detected in 1 of 15 and 6 of 32 stock seed lots planted in the fall in Oregon and Washington, respectively, and in 2 of 6 steckling shipments planted in each state in the spring. The pathogen was detected at 10 to 10 CFU/g foliage in 1 of 22 and 10 of 14 direct-seeded crops within 2 months of planting in 2001 and 2002, respectively. The prevalence of X. campestris pv. carotae then increased through the season in most seed crops, although bacterial blight symptoms were not observed until April in Oregon and July in Washington in both seasons. In August 2002 and 2003, X. campestris pv. carotae was detected in all 10 and 13 crops surveyed in Oregon, respectively; and in 11 of 12 and 7 of 10 crops in Washington, respectively. The pathogen was typically less prevalent in steckling versus direct-seeded crops. X. campestris pv. carotae was detected in 20 of 22 and 19 of 23 harvested seed lots in Oregon and Washington, respectively, at populations ranging from 1.3 × 10 to 1.4 × 10 CFU/g seed. Airborne X. campestris pv. carotae, detected ≤1,600 m downwind of crops being threshed in Oregon in September of 2003 and 2004, may provide a source of inoculum for newly planted seed crops between overlapping biennial seasons for carrot seed production. Despite the prevalence of this pathogen in the Pacific Northwest, carrot seed lots free of X. campestris pv. carotae were detected, demonstrating the ability to produce clean seed in this region by adhering to recommended practices for management of bacterial blight.
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http://dx.doi.org/10.1094/PD-89-0896DOI Listing
August 2005

Verticillium Wilt in Spinach Seed Production.

Plant Dis 2005 Jan;89(1):4-11

Graduate Student, Washington State University, Northwestern Washington REC, Mount Vernon 98273-4768.

There are no previous reports of Verticillium wilt in fresh and processing spinach (Spinacia oleracea) crops in the United States. In 2002, a hybrid spinach seed crop in the Pacific Northwest developed late-season wilt symptoms. Assays of the harvested seed and stock seed of the male and female parents revealed 59.5, 44.0, and 1.5%, respectively, were infected with Verticillium dahliae. Assays of 13 stock or commercial seed lots grown in 2002 and 62 commercial lots harvested in 2003 in Denmark, Holland, New Zealand, and the United States revealed the prevalence of Verticillium spp. in commercial spinach seed. Sixty-eight lots (89%) were infected with Verticillium spp. at incidences ranging from 0.3 to 84.8%. Five spinach seed isolates of V. dahliae were pathogenic on each of three spinach cultivars by root-dip inoculation. V. dahliae was detected on 26.4% of the seed from 7 of 11 inoculated plants but on none of the seed from 6 control plants, demonstrating systemic movement of V. dahliae. Seed-to-seed transmission was also demonstrated by planting naturally infected seed lots. This is the first report of Verticillium wilt of spinach in the primary region of spinach seed production in the United States.
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http://dx.doi.org/10.1094/PD-89-0004DOI Listing
January 2005

Prevalence of Botrytis spp. in Onion Seed Crops in the Columbia Basin of Washington.

Plant Dis 2004 Oct;88(10):1061-1068

Washington State University, Grant/Adams Counties, Ephrata 98823.

Of 12 onion seed lots harvested in the semi-arid Columbia Basin of Washington in 1999 or 2000, 8 were infected and 10 infested with Botrytis aclada at incidences of 1 to 10% and 2 to 26%, respectively. Twenty to forty plants were sampled from each of nine direct-seeded, biennial seed crops in April, June, and July 2001 and assayed for Botrytis spp. Six direct-seeded crops were sampled in October and November 2001 and April, June, and July 2002. One bulb-to-seed crop was sampled in April, June, and July 2002. The incidence of B. aclada increased through each season, reaching 100% in most fields by July. Infections were primarily asymptomatic, with no apparent relationship between plant infection and infection of harvested seed. B, cinerea, B. squamosa, and B. porri were detected in 16, 4, and 4% of the fields, respectively, at lower incidences than B. aclada. Harvested seed from 15 of the fields were infected with B. aclada at <1 to 28%. B, cinerea, B. porri, and B. squamosa were detected in three, three, and none of the harvested lots, respectively.
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http://dx.doi.org/10.1094/PDIS.2004.88.10.1061DOI Listing
October 2004

Stewart's Wilt Reactions of an International Collection of Zea mays Germ Plasm Inoculated with Erwinia stewartii.

Plant Dis 2000 Aug;84(8):901-906

Department of Crop Sciences, University of Illinois, Urbana 61801.

Maize accessions were evaluated in 1997, 1998, and 1999 to identify additional sources of Stewart's wilt resistance and to determine if reactions differed among accessions collected from various regions of the United States and throughout the world. The distributions of Stewart's wilt reactions rated from 1 (no appreciable spread of symptoms) to 9 (dead plants) were relatively similar among groups of accessions from all regions of the world except for those from the Mid-Atlantic/Ohio River Valley region of the United States, the southern United States, and the northeastern United States. The mean and median Stewart's wilt rating for 1,991 accessions evaluated in 1997 was 4. The mean Stewart's wilt rating for 245 accessions collected from the Mid-Atlantic/Ohio River Valley region was 3.1, which was significantly lower than that for accessions from all other regions. The mean rating for accessions from the southern United States was 3.7, which also was lower than mean ratings for accessions from all other regions. Ratings from trials in 1997 and 1998 were highly correlated (r = 0.87) for 292 accessions and 15 sweet corn hybrid checks evaluated in both years. Of 20 accessions rated below 2 in 1997 and 1998, seven were from Virginia, seven were from the Ohio River Valley or central Corn Belt of the United States, four were from the northern or western Corn Belt of the United States, and two were from Spain. Ratings for these accessions ranged from 1.7 to 3.1 in 1999. Ratings ranged from 2.6 to 3.7 for F hybrids of these accessions crossed with one of two susceptible sweet corn inbreds, CrseW30 or Crse16, which were rated 5.7 and 5.4, respectively. Based on the reactions of this collection of germ plasm, it appears that high levels of Stewart's wilt resistance are prevalent only among accessions collected from areas where the disease has been endemic for several years, whereas moderate levels of resistance can be found in accessions collected from nearly everywhere in the world.
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http://dx.doi.org/10.1094/PDIS.2000.84.8.901DOI Listing
August 2000

Variation Associated with Silk Channel Inoculation for Common Smut of Sweet Corn.

Plant Dis 1999 Aug;83(8):727-732

Department of Crop Sciences, University of Illinois, Urbana 61801.

Efforts at breeding for resistance to common smut of maize (Zea mays), caused by Ustilago maydis, are hampered by the lack of a reliable and efficient method of inoculation. Silk channel injection is one of the most efficient methods of inoculating for ear galls but is less consistent than acceptable for accurate assessment of the response of genotypes. The objective of this study was to examine how the silk channel inoculation method can be modified to reduce variation while maintaining efficiency for large-scale field inoculations. Variation associated with inoculum concentration and variation among people inoculating were examined. Incidence and severity of symptomatic ears increased with inoculum concentration. Concentrations between 10 and 10 sporidia/ml are recommended. Variation among people was greater than variation among inoculum concentrations. Incidence and severity ratings were lower for people inexperienced at inoculating with U. maydis than for experienced people. Variation among people inoculating can be controlled by appropriate experimental design.
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http://dx.doi.org/10.1094/PDIS.1999.83.8.727DOI Listing
August 1999

Effects of Silk Maturity and Pollination on Infection of Maize Ears by Ustilago maydis.

Plant Dis 1999 Jul;83(7):621-626

Department of Crop Sciences, University of Illinois, Urbana 61801.

Host resistance is the most efficient method of controlling common smut of maize (Zea mays), caused by Ustilago maydis. Precise timing of ear inoculations with U. maydis relative to silk maturity and pollination may improve the ability to screen maize germ plasm for resistance. The objectives of this study were to determine the length of time maize kernels can be infected by U. maydis through silks, and to examine the effects of pollination on infection through silks. Two field studies were done in 1995, 1996, and 1997 at the University of Illinois South Farms. In the date-of-inoculation study, ears were inoculated at 2- to 3-day intervals from early silk emergence until 16 days after silk emergence. In the date-of-planting study, hybrids were planted on four dates and ears were inoculated on the same day for all planting dates. In each study, ear shoots were covered with shoot bags prior to silk emergence to prevent pollination, or ear shoots were left uncovered to allow silks to be pollinated normally. Maize ears were susceptible to infection by U. maydis from silk emergence until 8 to 14 days after silk emergence. During this period of susceptibility, incidence of ears with galls decreased as silks aged. Incidence of ears with galls on plants inoculated 7 days apart differed by as much as 70%. The period that maize ears were susceptible to infection by U. maydis was shorter and incidence of ears with galls decreased more rapidly when silks were exposed to pollen than when silks were not exposed. The silk channel method of inoculating for common smut does not appear to be practical for large-scale evaluations of numerous lines. The method is practical for evaluating a limited number of lines or for inducing ear galls for commercial production of huitlacoche (smut galls eaten at an immature stage).
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http://dx.doi.org/10.1094/PDIS.1999.83.7.621DOI Listing
July 1999

Reactions of Processing Sweet Corn Hybrids to Gibberella Ear Rot.

Plant Dis 1999 Feb;83(2):176-180

Department of Crop Sciences, University of Illinois, Urbana 61801.

Gibberella ear rot has increased in prevalence recently on late-season processing sweet corn grown in the Midwestern United States. Little information is available about the reactions of hybrids currently grown for processing. A total of 52 processing hybrids were evaluated in 1996 and 1997 for reactions to Gibberella zeae following one of two methods of inoculation: inserting an infested toothpick or injecting a spore suspension in the silk channel 7 days after the mid-silk growth stage. Ratings of ear rot severity ranged from 2.4 to 8 on a scale of 1 to 9. Severity of ear rot differed among hybrids, but none of the hybrids was highly resistant, nor did the hybrids display a great degree of variation for reaction to G. zeae. Severity of ear rot was consistently lower for cvs. Sprint and HMX 5372 than for the other hybrids. Ear rot ratings also were lower for cvs. GH 1834 and GH 2690 in three of four comparisons. Severity of ear rot was consistently higher for cv. GH 2628 in all comparisons and for cvs. Empire, Excalibur, GG 42, GH 1861, Jubilee, Rival, and WSS 3680 in three of four comparisons. Ranks of some hybrids changed between inoculation methods, years, or both, but most hybrids were ranked similarly in at least three of four comparisons. Coefficients of variation were approximately 5% higher for the injection method of inoculation in 1996 than for the other trials. The toothpick method of inoculation required less labor and ranked hybrids as consistently or more consistently than the injection method.
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http://dx.doi.org/10.1094/PDIS.1999.83.2.176DOI Listing
February 1999

Evaluation of an Aeroponics System to Screen Maize Genotypes for Resistance to Fusarium graminearum Seedling Blight.

Plant Dis 1997 Feb;81(2):175-179

Associate Professor, Department of Plant Pathology, University of Illinois at Urbana-Champaign, Urbana 61801.

A noncirculating aeroponics system was evaluated as a method for rapid screening of maize genotypes for resistance to Fusarium graminearum seedling blight/root rot. The system allows for nondestructive, repetitive sampling of seedlings for assessing disease progress and seedling growth. Shoot growth and root rot were assessed at 3-day intervals, and final shoot and root dry weight were determined 15 days after inoculation. The nine hybrids screened differed in severity of root rot as early as 6 days after inoculation, indicating differences in resistance to F. graminearum. Inoculation did not always significantly affect shoot growth, root dry weight, or shoot dry weight, but differences in these agronomic traits were observed among hybrids.LH119 × LH51 and Pioneer Brand 3379 showed the greatest resistance to root rot. Area under-disease progress curve and a critical stage of disease assessment (9 days after inoculation) gave similar rankings of hybrids for root rot resistance, indicating that a single disease assessment (versus multiple assessments) may be adequate in screening for resistance with this aeroponics system.
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http://dx.doi.org/10.1094/PDIS.1997.81.2.175DOI Listing
February 1997