Oral: Virus-Host Interactions
Bean common mosaic virus isolate overcomes the bc-3 resistance allele in common bean: virus genetic determinants defining a novel pathogenicity group
X. FENG (1), J. Myers (2), A. Karasev (1) (1) University of Idaho, U.S.A.; (2) Oregon State University, U.S.A.
Bean common mosaic virus (BCMV) exists as a complex of strains that can be distinguished biologically, on a set of bean differentials, into pathogenicity groups (PG) numbered I to VII. Resistance against BCMV in Phaseolus vulgaris is governed by six recessive resistance alleles at four loci. One of these alleles, bc-3, is able to protect P. vulgaris against all BCMV strains and against other potyviruses; bc-3 was identified as the eIF4E allele carrying mutated eukaryotic translation initiation factor gene. We characterized a novel BCMV isolate, 1755a, that was able to overcome bc-2 and bc-3 alleles in common bean. Hence, it displayed a novel pattern of interactions with resistance genes in P. vulgaris, and was assigned to a new pathogroup, PG-VIII. The IVT7214 cultivar supporting the replication of BCMV-1755a was found to have the intact homozygous bc-3 CAPS marker. The complete genome of the 1755a isolate was sequenced and found to be a recombinant between the BCMV strain NL1 (PG-I) and an unknown BCMV strain. Analysis of the recombination patterns in the genomes of NL1 and US1 (PG-I), NY15P (PG-V), US10 and RU1-OR (PG-VII), and 1755a (PG-VIII), indicated that P1/HC-Pro cistrons of BCMV strains may interact with most resistance genes. This is the first report of a BCMV isolate able to overcome the bc-3 resistance in common bean.