Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/11/2007
Publication Date: 10/8/2007
Citation: Correll, J.C., Boza, E.J., Seyran, E., Cartwright, R.D., Jia, Y., Lee, F.N. 2007. Examination of the rice blast pathogen population diversity between 1990 and 2006 - Stable or unstable? 4th Intl. Rice Blast Conference, October 108-14, 2007, Changsha, China. p. 46. Interpretive Summary:
Technical Abstract: Over the past 17 yeas, isolates of Pyricularia grisea (P. oryzae) have been recovered from commercial rice fields in Arkansas. Annual samples have typically included 200-500 isolates recovered from 5-10 cultivars from 10 different counties with the majority of the isolates being recovered from the neck blast samples. All isolates were subsequently single-spored and stored desiccated on filter paper. Isolates of P. grisea were characterized using a number of tests including DNA fingerprint groups (A-H) which have been identified among contemporary and archived isolates; only 4 MGR596 DNA fingerprint groups (groups A, B, C, and D) have been identified since we have been monitoring populations beginning in 1990. These four DNA fingerprint groups correspond with four distinct genetic groups, or vegetative compatibility groups (VCGs). In addition, some yearly samples have shown that a single haplotype often makes up the majority of the isolates within a given fingerprint group. 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 4 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 recent samplings. Over 90% 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. A distinct shift in virulence among field isolates to overcome the Pi-ta resistance gene among MGR586 group B isolates is associated with changes in AVR-Pita.