Leaf Rust Resistance in Wheat Line RL6062 is an Allele at the Lr3 Locus

RL6062, a 'Thatcher' backcross line of wheat (Triticum aestivum L.), has resistance to leaf rust (caused by Puccinia triticina Erikss.) derived from a line of common wheat from Iran. RL6062 has an intermediate infection type (IT) of small to moderate uredinia surrounded by distinct chlorosis. RL6062 was crossed with Thatcher and the F-2 seedlings and F-3 families segregated for a single leaf rust resistance gene. Bulk segregant analysis of homozygous resistant and homozygous susceptible F-3 families using diversity arrays technology (DArT) markers indicated that the leaf rust resistance was on chromosome 6BL. RL6062 was crossed with Thatcher lines with genes Lr9, Lr3a, Lr3b, and Lr3c that are also located on chromosome 6BL. The F-2 seedlings of RL6010-Lr9/RL6062 segregated for IT that ranged from immune response to high IT with large uredinia that lacked necrosis or chlorosis. The F-3 families derived from F-2 seedlings with high IT were homozygous susceptible or segregated for intermediate IT and high IT, confirming that resistance in RL6062 was not allelic to Lr9. The F-2 seedlings of RL6002-Lr3a/RL6062 segregated for IT that varied from flecks to moderately large size uredinia that lacked chlorosis or necrosis. The F-3 families derived from F-2 seedlings that had intermediate to high IT segregated for low IT of fleck to intermediate IT, and none of the seedlings had high IT. The lack of segregation for susceptible plants in the F-3 families indicated that the leaf rust resistance in RL6062 is an allele at the Lr3 locus. Alleles at the Lr3 locus had intermediate to recessive expression.