Abstract
Weeds are the most widespread biotic production constraint of rice in Africa and one of the major factors limiting grain yield. An efficient breeding strategy could be particularly important for improving weed management in sub-Saharan Africa (SSA) because most smallholder rice farmers use few external inputs. To understand rice weed competitiveness, experiments on reciprocal interspecific crosses derived from FKR19 (Oryza sativa) and CG20 (Oryza glaberrima) were carried out to estimate gene effects and heritability of traits: plant height at five leaves, plant height 30 days after transplanting, plant height at maturity, number of tillers at 30 and 60 DAT, number of fertile tillers, width of leaves at 80 DAT and at maturity, and length of leaves at 80 DAT and at maturity for rice–weed competitiveness. Six generations – P1, P2, F1, F2, BC1F1 and BC2F1 – were raised and subjected to generation mean analysis. The lowest heterosis of F1 was obtained in both crosses (CG20/FKR19 and FKR19/CG20), except for plant height at 30 days after transplanting and leaf width at maturity in the CG20/FKR19 cross. The majority of traits displayed higher dominance gene effects (H5_L, H30 and L_80 for CG20/FKR19; W_mat and L_mat for FKR19/CG20) than additive gene effects; the latter were slight and non-significant for the majority of traits. Duplicate epistasis was observed for the number of tillers 30 days after transplanting and leaf length at maturity and plant height at maturity. Additive genetic variance values were higher in CG20/FKR19, revealing that the CG20 variety can be used as a donor parent. Plant height at maturity, length of leaves at 80 DAT and at maturity showed high narrow-sense heritability (hn2>0.70), influencing weed competitiveness. Key words: Additive, dominance, heritability, rice, variance components, weed competitiveness.
Highlights
Rice (Oryza sativa L.) is one of the most important crops in the world
The mean values of the ten traits for the F1 generation derived from the CG20/FKR19 cross were lower than the mean values for either parent, except for the trait W_mat, where it was higher than the mean value of both parents
Of the F1 generation derived from the FKR19/CG20 cross, the mean value was generally lower than the mean value for either parent, except for H30 where it was greater than the donor parent, and for the trait W_mat, where it was greater than both parents
Summary
Rice (Oryza sativa L.) is one of the most important crops in the world. It is the fifth most important cereal in Africa in terms of area harvested, and fourth in terms of production (FAO, 2008). Generation mean analysis (Mather and Jinks, 1971) or scaling tests have been widely used for genetic analysis (Fall, 1994; Kearsey and Pooni, 1996; Möhring and Piepho, 2010) This approach was used in the present research to estimate genetic parameters such as additive gene effects, dominance gene effects and narrow-sense heritability. Some previous studies of the genetic effects of wheat–weed competitiveness have shown that it is possible to combine high grain yield with high competitiveness in a single genotype (Gibson and Fischer, 2004) Applying this approach to rice has the potential to generate new knowledge about the nature and magnitude of gene effects and their contribution to the control of rice–weed competitive traits, and to assist in formulating an efficient breeding program. It measured ten main quantitative traits: plant height at five leaves (H5_L), plant height 30 days after transplanting (DAT) (H30), plant height at maturity (Hmat), number of tillers at 30 DAT (T30) and 60 DAT (T60), number of fertile tillers (Tfert), width of leaves at 80 DAT (W_80) and at maturity (W_mat), and length of leaves at 80 DAT (L_80) and at maturity (L_mat)
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