Identification of RFLP markers linked to a major gene, sw1, conferring resistance to Stewart's wilt in maize

The objective of this study was to determine the genetic basis of resistance to Stewart's bacterial wilt (Erwinia stewartii Smith) and to map associated gene(s) in maize (Zea mays L.). It is known that two major dominant genes were involved in the resistance to Stewart's wilt and a single major gene conditions intermediate resistance. Recombinant inbred lines (RILs) were derived in Hawaii from resistant inbred Ki14 and susceptible inbred Hi31, and analyzed by restriction fragment length polymorphism (RFLP). Seventy-one RILs were evaluated for resistance to Stewart's wilt at Henderson, KY. The RILs segregated 1:1 and F ₁ hybrids showed intermediate resistance, indicating a single major resistance gene in this population. RFLP markers on the short arm of chromosome I showed the largest effect and suggested a major gene in this region. This gene, designated sw1, was mapped on the short arm of chromosome 1 between the RFLP markers umc167 and umc67. This region includes two resistance gene analogs (RGAs) and a major gene for resistance to maize streak virus, msv1, also revealed in RILs produced in Hawaii. In an inoculated trial at Urbana, IL, where disease developed poorly, marker data suggested that none of the more susceptible phenotypes had Sw1 alleles from the resistant parent, Ki14.