A QTL on chromosome 5BL in wheat enhances leaf rust resistance of Lr46

Combinations of effective leaf rust resistance genes that condition resistance to many leaf rust races are key to the development of wheat cultivars with long-lasting resistance to leaf rust caused by Puccinia triticina. A population of F-6 recombinant inbred lines (RILs) derived from the cross 'Thatcher*3/Americano 25e' was evaluated for segregation of adult plant leaf rust resistance in three field plot tests and in a greenhouse test. A genetic map was constructed with 243 diversity array technology markers. Significant effects for reduction in leaf rust severity were found on chromosomes 1BL and 5BL. The sequence-tagged site marker csLV46, closely linked to Lr46, mapped to the logarithm of odds peak on chromosome 1BL, indicating that the RILs were likely segregating for this adult plant resistance gene. Lines with csLV46 had an average leaf rust severity of 35 % in the four tests. RILs with the resistance on chromosome 5BL designated as QLr. cdl-5BL had an average leaf rust severity of 47 %. RILs with both csLV46 and QLr. cdl-5BL had an average leaf rust severity of 22 %, close to the Thatcher*2/Americano 25e parental line. Lines that lacked both csLV46 and QLr-5BL had an average severity of 56 %. The QLr. cdl-5BL region enhanced the leaf resistance conditioned by Lr46 in an additive manner.