Detection and Introgression of Lr46 Gene-Conferring Partial Resistance to Leaf Rust (Puccinia triticina) in Wheat

Detection and introgression of slow leaf rust resistance gene, Lr 46 in seven parental wheat cultivars, i.e., Gemmeiza-9, Gemmeiza-11, Gemmeiza-12, Misr-1, Misr-2, Sakha-94 and Giza-171 and their F 1 and F 2 crosses was carried out at Bahteem Agricultural Research Station, Qaliobia governorate, Egypt. These tested cultivars varied in their reactions to leaf rust disease. The cultivars Misr-1, Misr-2, Sakha-94, and Giza-171 showed slow rust reaction meanwhile, Gemmeiza-9, Gemmeiza-11 and Gemmeiza-12 cultivars were fast rusting. Values of area under disease progress curve (AUDPC) run in a parallel line with its disease severity. Lr 46 gene was found in cultivars Misr-1, Misr-2, Sakha-94, and Giza-171 and absent in cultivars Gemmeiza-9, Gemmeiza-11, Gemmeiza-12 cultivars at 300 pb. Qualitative analysis of the obtained data showed that there were no segregations in the crosses Lr 46×Misr-1, Lr 46×Misr-2, Lr 46×Sakha94 and Lr 46×Giza-171 in the F 2 plants, indicating the presence of the Lr 46 in these cultivars. While, segregation was found in the crosses Lr 46×Gemmeiza-9 , Lr 46×Gemmeiza-11 , Lr 46×Gemmeiza-12 , indicating that these cultivars do not carry Lr 46 gene. Additionally, the heritability was above 94%, suggesting that the selection of genotypes resistant to leaf rust in the first generations (F 2 ) was feasible. However, this selection is more successful in later generations because the dominance effect is critical for the expression of this trait. Molecular detection proved that Lr 46 gene was inserted into Gemmeiza-9, Gemmeiza-11 and Gemmeiza-12 to have slow rust resistance in F 2 plants. This saves effort and time as it is possible to rely on molecular marker assisted selection in the early selection of plants carrying this gene. Mean of the yield components, plant height, number of spikes/plant, number of kernels/plant, 100-kernel weight, and grain yield/plant of the three F 2 crosses was higher than those of their parents. So, plant breeders should not rely on complete rust resistance, but should consider partial resistance, particularly slow rusting resistance genes.