Inheritance of Resistance to Striga Hermonthica (Del.) Benth. In An Open Pollinated Maize Population, Tzl Composite ! Cl.

Abstract

The parasitic weed Striga hermonthica (Del.) Benth. of the Scrophulariaceae family constitutes one of the most economically important biological constraints in maize production in the sub-Saharan regions of Africa. The type of gene action involved in the inheritance of resistance to Striga hermonthica was investigated using the open-pollinated population, TZLComposite-1 Cl in a North Carolina design 1 scheme. Recombination were done among the best families and also the poorest performing families selected. Realized heritabilities were thus computed for important Striga related variables. This study also elucidated the rate and the extent at which resistance to Striga can be increased by using conventional population improvement methods. Comparison of the magnitude of the additive genetic variance (cr2a) and the dominance variance (a2d) showed that additive genetic variance was a major portion of the genotypic variance for characters like ear Striga rating (a2a = 0.41±0.15 and a 2d = - 0.20±0.23 ), yield of infested plants (a2a = 401564±172649 and a 2d= 571271315131), anthesis-silking interval of infested plants (a2a = 0.585±0.49 and a 2d = -0.38±0.93) and Striga rating at 8 weeks after planting (cr2a = 0.28+0.12 and c 2d= 0.03±0.21), whereas the number of Striga per host plants is controlled by non additive gene action (ci2a = 75.69±76.64 and a 2d = 211.47±134.48). Estimates of narrow-sense heritability (h2n) confirms the magnitude of the additive genetic variance in the total genetic variance for the traits ear Striga rating (h2n = 0.43+0.16), yield of infested plants (h2n = 0.31+0.13) and Striga rating (h2n = 0.33±0.15), which can be improved by selection. Estimates of realized heritability (h2 r) were highest for ear Striga rating (h2r = 0.34+0.37), yield of infested plants (h2r = 0.32±0.48) and for Striga rating (h2r = 0.27±0.57). Genetic correlations derived from the covariance of full-sib families (rg) and also genetic correlations obtained from correlated responses to selection (Rg) were estimated between the yield of infested plants and ear Striga rating (Rg = -0.50±0.38; rg = 0.88±1.28), Striga rating 1 (Rg = -0.52+0.43; rg = -0.92±0.93), Striga count 1 (Rg = -0.26±0.56; rg = - 0.22+0.46) and anthesis-silking interval (Rg = 1.76±0.09; rg = 1.05±1.30). Yield of infested plants was positively correlated to plant height of infested plants (rg = 0.61+0.54), and also to the number of ear harvested for infested plants (rg = 0.99+1.12). Anthesissilking interval of infested plants had a positive but low correlation with days to silk (rg = 0.45+0.85) and days to anthesis of infested plants (rg = 0.09+0.73). Anthesis-silking interval was negatively correlated to Striga rating at 8 weeks after planting (rg = 0.84+1.39). The results of this study indicate that resistance to Striga hermonthica in openpollinated maize varieties was shown to be controlled by polygenes . Recurrent selection (selection which involve recombination of superior genotypes to form a population for continued cyclic selection), using a selection index that includes the important traits with high level of additive genetic variance will lead to satisfactory results in selecting for Striga resistance in this open pollinated maize population.