Variation and inheritance of leaf angle, and its association with spot blotch (Bipolaris sorokiniana) severity in wheat (Triticum aestivum)

One thousand four hundred and seven spring wheat germplasm lines belonging to Indian and CIMMYT wheat programs were evaluated for their leaf angle and resistance to spot blotch caused by Bipolaris sorokiniana during three consecutive crop seasons, 1994-95, 1995-96 and 1996-97. Disease severity was recorded at six different growth stages beginning from tillering to late milk stage. Three crosses (M 3109 x Sonalika, HP 1808 x K 9006 and HD 2662 x K 9006) were made between genotypes with erect and drooping leaves. M 3109 was resistant, Sonalika susceptible while the other three lines possessed moderate resistance to spot blotch. Individually threshed F-2 plants were used to advance the generations. Leaf angle and spot blotch resistance were recorded in parents, F-1, F-3, F-4 and F-5 generations. Leaf erectness in F-1 generation showed partial dominance. Evaluation of F-3, F-4 and F-5 progenies (120-150) revealed that leaf angle was under the control of few genes that appeared to be close to three. Germplasm lines with erect and semi-erect leaves displayed lower spot blotch severity than those having drooping and semi-drooping leaves. Lines homozygous for erect leaf posture in F-3, F-4 and F-5 generations showed significantly lower mean AUDPC than those with drooping leaves. A positive correlation (0.58) between leaf angle and AUDPC further indicated a positive influence of leaf erectness on severity to spot blotch disease.