Variation in Leaf Tip Necrosis and its effect on yield traits in wheat

Four leaf rust adult plant resistance genes (Lr34, Lr46, Lr67 and Lr68) are known to be associated with leaf tip necrosis (LTN). LTN caused by these genes is different from each other at phenotypic level. LTN associated with APR genes Lr34, Lr46 and Lr67 has been designated as Ltn1, Ltn2 and Ltn3. Seventy-seven CIMMYT genotypes were selected to find out the association between genotypic and phenotypic variability for LTN and its association with yield traits; 1000 grain weight, grain yield, leaf area and percentage of leaf tip necrosis in the flag leaf of main tiller. All the genotypes were screened for the presence of 3 APR genes with linked markers, csLV34 for Lr34; Xwmc44 and Xgwm259 for Lr46 and Xcfd71 for Lr67. The genotypes were grouped into 5 classes; only Lr34, only Lr46, only Lr67, Lr34+L46+Lr67 and genotypes lacking all three genes. Molecular analysis revealed that 7 genotype with Lr34 only, 6 with Lr46 only, 7 with Lr67 only, 13 with all the 3 genes, and 28 without any Lr gene. Phenotypic data of LTN percentage was compared and it was noted that maximum LTN % was observed for Lr67 (7.811%) followed by Lr46 (7.348%) and Lr34 (6.47%). Surprisingly, presence of all three genes reduced the LTN% (4.7055%) as compared with absence of all three genes (6.011%). It was also observed that the three genes simultaneously reduced 1000 grain weight and plot yield. All three genes increased leaf area highly significantly both when they are alone or together (34.7 to 44.7 cm2) in comparison to those genotypes (24.7 cm2) which lacks these Lr genes and also reduced 1000-grain weight and plot yield but non-significantly.