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 resistanc e to Stewart's bacterial wilt (Erwinia stewartii Smith) and to map associat ed gene(s) in maize (Zea mays L.). It is known that two major dominant gene s were involved in the resistance to Stewart's wilt and a single major gene conditions intermediate resistance. Recombinant inbred lines (RILs) were d erived in Hawaii from resistant inbred Ki14 and susceptible inbred Hi31, an d 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, indicat ing a single major resistance gene in this population. RFLP markers on the short arm of chromosome 1 showed the largest effect and suggested a major g ene 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 incl udes 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 i noculated 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.