Date of Graduation

5-2012

Document Type

Thesis

Degree Name

Master of Science in Plant Pathology (MS)

Degree Level

Graduate

Department

Plant Pathology

Advisor

James Correll

Committee Member

Rick Cartwright

Second Committee Member

Yulin Jia

Third Committee Member

Vibha Srivastava

Abstract

Rice blast, caused by Pyricularia oryzae (teleomorph: Magnaporthe grisea), is one of the most economically important diseases of rice worldwide, including Arkansas. Rice blast has been severe the past few years on conventional cultivars and, more recently, has been observed on hybrid rice cultivars. The first objective of the current research was to examine the genotypic and phenotypic variation in the P. oryzae population in Arkansas during the 2009, 2010, and 2011 growing seasons and compare isolates from conventional cultivars with those from and hybrids. A total of 904 isolates were recovered from symptomatic rice cultivars in Arkansas and were examined for their genotypic and phenotypic diversity. The isolates were evaluated for vegetative compatibility, MGR586 DNA fingerprint diversity, SSR marker diversity, and virulence on a set of 40 commercial cultivars or advanced breeding lines as well as hybrid cultivars. Examination of isolates indicated that three and of the four known VCGs were present (VCGs US-01, 02, and 04) and that one VCG (US-01) predominated (>50%). Using SSR markers, MGR586 fingerprint, and virulence tests, the genotypic and phenotypic differences between lineages of P. oryzae from Arkansas were examined. Most of the isolates collected from hybrids showed a similar genotype and phenotype as the isolates recovered from conventional cultivars. Three atypical isolates, recovered from Plant Introduction accessions grown in Texas, had unique MGR586 fingerprints and could not be assigned to one of the known VCGs. One of the three isolates appeared to have a unique virulence phenotype and two of the isolates were not virulent on any of the rice germplasm tested. Population analysis could continue to provide a better understanding of pathogen virulence evolution, assist in screening for disease resistance, and help develop strategies to breed for durable resistance to blast disease. In addition, a second objective was to evaluate the stability of the AVR-Pita gene in-vitro. Previous research found structural variation of the AVR-Pita gene among field isolates. Examination of AVR-Pita over an eight week in-vitro experiment indicated that the AVR-Pita sequence were stable.

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