Pyramiding genes for resistance to bean common mosaic virus

Markers linked to the bc-3 gene conditioning resistance to bean common mosaic potyviruses in common bean

“…Epistatic interactions occur between the different resistance genes when bean plants are inoculated with the NL 3 strain of BCMNV: bc-3 masks the effect of the I, bc-2 2 and bc-1 2 genes; and bc-2 2 masks the bc-1 2 gene (Kelly et al, 1995). Because of the epistatic interaction between bc-3 and I, the effect of the I gene cannot be detected phenotypically in the presence of the bc-3 gene.…”

“…The fourth recessive locus conditioning resistance is a strain nonspecific bc-u gene that is necessary for the full expression of all strain specific recessive genes in the absence of the I gene (Drijfhout, 1978). With the exception of the bc-2 locus, the other single recessive resistance genes are functional in the presence of the I gene (Kelly et al, 1995). Most of the resistance genes have been mapped to independent loci on the bean integrated linkage map (Freyre et al, 1998): The I gene maps to linkage group B2 (Freyre et al, 1998); the bc-1 2 allele maps to B3 (Freyre et al, 1998;Kelly et al, 2003;Miklas et al, 2000); the bc-u also resides on B3 due to its loose linkage with bc-1 locus (Strausbaugh et al, 1999); and the bc-3 gene maps to B6 (Gepts, 1999;Kelly et al, 2003).…”

“…The presence of the I gene in bean cultivars in Central and Eastern Africa where BCMNV strains exist has been such a serious problem that breeders in those regions select against the I gene (Silbernagel et al, 1986). Since dominant and recessive resistance genes have distinctly different mechanisms of resistance, bean breeders can utilize gene pyramiding as a strategy to enhance the durability of resistance (Kelly et al, 1995). Plant death resulting from the single I gene can be prevented by incorporating into new cultivars a series of recessive genes that confer resistance to the specific TINI strains of BCMNV (Kelly, 1997).…”

“…The dominant inhibitory I gene (Ali, 1950) conditions a classic hypersensitive resistance response whereas the recessive genes are constitutively expressed and act by restricting virus replication or movement within the plant (Kelly, 1997;Kelly et al, 1995Kelly et al, , 2003. The dominant form of resistance to BCMNV and BCMV conferred by the I gene has been a source of resistance against a wide range of BCMV strains for the last half century (Kelly, 1997).…”

“…Among the methods available to prevent virus infection in common bean, genetic resistance is the most cost effective and durable (Drijfhout, 1978;Kelly et al, 1995;Miklas et al, 2000). In East Africa where BCMNV is found in wild legumes (Sengooba et al, 1997;Spence & Walkey, 1995), the only effective way to control these viruses is to plant resistant cultivars, otherwise susceptible bean plants can become infected from alternate hosts, growing adjacent to bean fields .…”