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United States Department of Agriculture

Agricultural Research Service

Research Project: RESPONSE OF DIVERSE RICE GERMPLASM TO BIOTIC AND ABIOTIC STRESSES Title: Examination of the rice blast pathogen population diversity in Arkansas, USA – Stable or Unstable?

Authors
item Correll, James -
item Boza, Edward -
item Seyran, E -
item Cartwright, Richard -
item Jia, Yulin
item Lee, Fleet -

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: October 30, 2008
Publication Date: April 6, 2009
Citation: Correll, J.C., Boza, E.J., Seyran, E., Cartwright, R.D., Jia, Y., Lee, F.N. 2009. Examination of the rice blast pathogen population diversity in Arkansas, USA – Stable or Unstable? In: Wang, X., Balent, B., editors. Advance in Genetics, Genomics, and Control of Rice Blast Disease. Springer, Berlin. p. 217-228.

Interpretive Summary: Blast disease has been a serious threat to Arkansas rice production. In the present study, several thousands of isolates of Pyricularia oryzae (= P. grisea) have been recovered from commercial rice fields in Arkansas over the past 17 years. Isolates of P. oryzae were characterized using a number of tests including DNA fingerprinting with MGR586, mitochondrial DNA RFLPs, mating type, vegetative compatibility, and virulence assay. Overall eight different MGR586 DNA fingerprint groups (A-H) were identified among contemporary and archived isolates of P. oryzae in the U.S. However, only 4 MGR586 DNA fingerprint groups (groups A, B, C, and D) were identified since 1991. The correlation between the four MGR586 DNA fingerprint groups (A-D) and the four distinct genetic vegetative compatibility groups (VCGs 01-04) was established. Furthermore, all isolates belong to a single mtDNA RFLP haplotype and all isolates within a given group are of a single mating type. In addition, some yearly samples have even shown that a single haplotype often makes up the majority of the isolates within a given fingerprint group or VCG. For example, over 60% of the isolates recovered in a given season belonged to 1 of 4 distinct clones. Thus, it is evident that the rice blast pathogen population in Arkansas has remained stable over the past 17 years. The data also suggest that the population is strongly influenced by host genotype. In particular, a distinct “shift” in virulence among field isolates to overcome the Pi-ta resistance gene has occurred among MGR586 group B isolates. The immergence of this “race-shift” has occurred among field isolates in MGR586 group B and structural variation of AVR-Pita is predicted.

Technical Abstract: Over the past 17 years, isolates of Pyricularia oryzae (= P. grisea) have been recovered from commercial rice fields in Arkansas. Annual samples have typically included 100–500 isolates recovered from 5 to 10 cultivars from 10 different counties with the majority of the isolates being recovered from neck blast samples. Isolates of P. oryzae were characterized using a number of tests including DNA fingerprinting with MGR586, mitochondrial DNA RFLPs, mating type, vegetative compatibility, and virulence. Although up to eight different MGR586 DNA fingerprint groups (A-H) have been identified among contemporary and archived isolates of P. oryzae in the U.S., only 4 MGR586 DNA fingerprint groups (groups A, B, C, and D) have been identified since monitoring the populations in Arkansas beginning in 1991. There is a complete correspondence between the four MGR586 DNA fingerprint groups (A-D) and the four distinct genetic vegetative compatibility groups (VCGs 01-04). Furthermore, all isolates belong to a single mtDNA RFLP haplotype and all isolates within a given group are of a single mating type. In addition, some yearly samples have even shown that a single haplotype often makes up the majority of the isolates within a given fingerprint group or VCG. For example, over 60% of the isolates recovered in a given season belonged to 1 of 4 distinct clones. Thus, it is evident that the rice blast pathogen population in Arkansas has remained stable over the past 17 years with regard to these four MGR586 DNA fingerprint groups. Although all 4 MGR586 groups can typically be found in the annual samples of the contemporary population, there appears to be a strong bias for group A isolates in more recent samplings (since 2000). Over 80% of the isolates recovered between 2000 and 2006 were in MGR586 group A, belonged to VCG US001, had a single mtDNA RFLP haplotype, and were a single mating type (mat1-1). The data indicate that the population is strongly influenced by host genotype. Evaluation of virulence indicates that isolates within a group are clearly more similar within a group than between groups; however, there is some virulence diversity within each of the genetic groups identified. In addition, a distinct “shift” n virulence among field isolates to overcome the Pi-ta resistance gene has occurred among MGR586 group B isolates. The immergence of this “race-shift” has occurred among field isolates in MGR586 group B and also can be generated experimentally in greenhouse selections among isolates in group B; this race shift is associated with changes in AVR-Pita.

Last Modified: 12/22/2014
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