Evaluation of N orth A merican isolates of S oybean mosaic virus for gain of virulence on Rsv ‐genotype soybeans with special emphasis on resistance‐breaking determinants on Rsv4

• Published in: Molecular plant pathology Vol. 13; no. 9; pp. 1077 - 1088
• Main Authors: Khatabi, B., Fajolu, O. L., Wen, R.‐H., Hajimorad, M. R.
• Format: Journal Article
• Language: English
• Published: 01.12.2012
• ISSN: 1464-6722; 1364-3703
• DOI: 10.1111/j.1364-3703.2012.00817.x

Summary Resistance to S oybean mosaic virus ( SMV ) in soybean is conferred by three dominant genes: Rsv1 , Rsv3 and Rsv4 . Over the years, scientists in the USA have utilized a set of standard pathotypes, SMV ‐ G1 to SMV ‐ G7 , to study interaction with Rsv ‐genotype soybeans. However, these pathotypes were isolated from a collection of imported soybean germplasm over 30 years ago. In this study, 35 SMV field isolates collected in recent years from 11 states were evaluated for gain of virulence on soybean genotypes containing individual Rsv genes. All isolates were avirulent on L 78‐379 ( Rsv1 ), whereas 19 were virulent on L 29 ( Rsv3 ). On PI 88788 ( Rsv4 ), 14 of 15 isolates tested were virulent; however, only one was capable of systemically infecting all of the inoculated V 94‐5152 ( Rsv4 ). Nevertheless, virulent variants from 11 other field isolates were rapidly selected on initial inoculation onto V 94‐5152 ( Rsv4 ). The P 3 cistrons of the original isolates and their variants on Rsv4 ‐genotype soybeans were sequenced. Analysis showed that virulence on PI 88788 ( Rsv4 ) was not associated, in general, with selection of any new amino acid, whereas Q1033K and G1054R substitutions were consistently selected on V 94‐5152 ( Rsv4 ). The role of Q1033K and G1054R substitutions, individually or in combination, in virulence on V 94‐5152 ( Rsv4 ) was confirmed on reconstruction in the P 3 cistron of avirulent SMV ‐ N , followed by biolistic inoculation. Collectively, our data demonstrate that SMV has evolved virulence towards Rsv3 and Rsv4 , but not Rsv1 , in the USA . Furthermore, they confirm that SMV virulence determinants on V 94‐5152 ( Rsv4 ) reside on P 3.