Prabin Tamang

Document Type

Thesis - University Access Only

Award Date

2011

Degree Name

Master of Science (MS)

Department / School

Plant Science

Abstract

Cochliobolus sativus (Ito & Kuribayashi) Drechs. Ex Dastur (anamorph Bipolaris sorokiniana Sacc. (Shoemak.) is the causal agent of spot blotch (SB) and common root rot (CRR) in wheat. Cochliobolus sativus, therefore, is considered an economically important and devastating fungal pathogen to North American wheat production. Different pathotypes of C. sativus have been reported in the USA and elsewhere and information on pathogen population structure has potential implications for disease management and varietal development. However, the virulence pattern of C. sativus isolates in South Dakota has not been reported to date. The objectives of this study were to assess the virulence pattern of C. sativus collected from different wheat growing regions in eastern South Dakota, and to identify the novel sources of genetic resistance to spot blotch. Diseased root and leaf samples were collected from 77 commercial production fields, out of which C. sativus was isolated from 51. A total of 98 isolates were prepared and stored for later use. Fifty nine randomly selected isolates were evaluated for virulence patterns in the greenhouse on three cultivars of wheat (Chirya-3, Ning-8319, and Sonalika). Additionally, barley (ND Bl 12, Bowman, and ND-5883), and oat (Don, Jerry, and Stallion) were also included in the study. All isolates were inoculated once on all the host lines at the two leaf stage and disease assessment was made 10 days after inoculation using a 1 to 9 rating scale. Analysis of variance revealed that there were highly significant differences (P< 0.0001) among all Cochliobolus sativus isolates, host lines and their interactions. Five pathotypes were identified where pathotype 'O' was the least virulent on all cultivars and pathotype '7' was the most virulent on wheat cultivars. None of the isolates infected barley or oat lines used in this study except barley line ND-5883 with very few isolates. Results suggested variation is present among C. sativus isolates in eastern South Dakota. Virulent isolates were used to identify novel sources of resistances to SB in wheat genotypes and relative species. To achieve this objective, a total of 147 genotypes from South Dakota and USDA National Small Grains collection were evaluated at seedling stage in the greenhouse under controlled environment conditions. All genotypes were inoculated artificially at the two leaf stage and disease assessment was made 10 days after inoculation. Results indicated that 44 % of the total genotypes (n=147) were resistant and the remaining 56 % were susceptible to spot blotch. Of the 32 wheat genotypes and 115 wheat relatives, 14 and 51 genotypes were resistant, respectively. Six highly resistant genotypes included five wheat relatives (PI 265008, PI 348591, PI 348620, PI 348637, and PI 348638) and one wheat genotype (Albany). Resistance sources identified in this study could be used in wheat breeding program for developing spot blotch resistance.

Library of Congress Subject Headings

Cochliobolus -- South Dakota

Wheat -- Disease and pest resistance -- Genetic aspects

Fungal diseases of plants

Format

application/pdf

Number of Pages

79

Publisher

South Dakota State University

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