Response to selection for grain yield under maydis leaf blight stress environment in maize (Zea mays)

Abstract

Maydis leaf blight (MLB), caused by Bipolaris maydis, is one of the most important diseases in maize. The objectives of this study were to quantify the progress for maydis leaf blight resistance improvement by estimating selection differential, expected and observed responses to selection after two cycles of $S _1$ line recurrent selection, and to estimate heritability for various morphological and yield traits in "Azam" composite maize population. This study was conducted at the research farm of Agricultural University, Peshawar, Pakistan during summer 2006 and 2007. In cycle-3 about one hundred $S _1$ lines while in cycle-4 196 $S _1$ lines of maize population Azam were evaluated under epiphytotic conditions along with their progenies in lattice square design with two replications. Highly significant variations were observed among the $S _1$ lines for grain yield, MLB, plant height, ear height, ear length, kernel rows $cob^ {-1}$, and maturity traits in two cycles. In cycle-3 the expected and observed responses for grain yield (432, 2144 kg $ha^ {-1}$), MLB (-0.53, - 0.65), plant height (1.65, 28cm), ear height (-0.43, 10 cm), ear length (0.78, 5 cm), kernel rows $cob^ {-1}$ (-0.29, 2), pollen shedding (-0.21, -5 days) and silking (-0.09, -4 days) were observed, while in cycle-4 expected and observed responses were (715, 2762 kg $ha^ {-1}$), (-0.01, -0.13), (1.15, 41 cm), (0.44, 23 cm), (1.17, 3 cm), (0.07, 1), (-1.23, -2 days) and (-1.39, -1 days) for the above traits, respectively. In both cycles the heritability values were estimated for grain yield (0.50, 0.64), MLB (0.84, 0.52), plant height (0.62, 0.79), ear height (0.63, 0.47), ear length (0.58, 0.55), kernel rows $cob^ {-1}$ (0.63, 0.62), pollen shedding (0.83, 0.83) and silking (0.72, 0.82). The increased performance of the progenies of selected $S _1$ lines manifests the efficiency of breeding program and suggests that $S _1$ line recurrent selection would be the most efficient method for improving MLB resistance and grain yield simultaneously in maize population Azam.