The genetic basis and effect of the few-branched-1 (Fbr1) mutant tassel trait on grain yield and seed production dynamics in maize

[摘要] English: Maize is among the most commonly bred crops in the world and maize breeding programmes are increasingly using molecular tools to enhance the efficiency and speed of developing productive cultivars. Breeding efforts of CIMMYT have focused on incorporating drought tolerance into elite germplasm. The incorporation of the Fbr1 gene into its elite germplasm was one such effort as the improvement of drought tolerance relies on manipulation of adaptive traits that limit yield under the target stress. The aim of this study was to find the genetic basis and effect of the Fbr1 tassel mutation on maize grain yield under stress and non-stress environments. A number of elite CIMMYT lines have been successfully converted to the Fbr1 mutation, and were homozygous for the 1074 SNP loci used, thus could be used in breeding programmes involving these new tassel mutants. The UPGMA cluster analysis revealed two discrete clusters of the inbred lines according to predefined CIMMYT heterotic groups. In the principal component analysis, the SNP loci were effective in characterising the maize inbred lines since they separated maize lines according to tassel size. Positive relationships between grain yield and pollen yield and its components were found, under drought conditions. However, the Fbr1 tassel trait did not have a positive effect on yield under stress and Fbr1 x Fbr1 hybrids had lower grain and pollen yield, and were less adapted to abiotic stress conditions. This raised questions on the value of incorporating such trait in breeding programmes targeting stress tolerance. Therefore, incorporation of the Fbr1 tassel trait should accompany selection for other traits associated with stress tolerance under low N and drought conditions, such as the 'stay green trait, factors associated with premature senescence, synchrony between male and female flowering and decreased barrenness if yield gain is to be realized. Estimates of genetic components of variance revealed importance of both additive and dominance components in the determination of grain yield, pollen yield and their components. Additive gene action was predominant in determining tassel size and pollen yield, thus progress can be made by selecting within segregating progenies when improving maize populations for the Fbr1 trait. The investigation of GxE interaction showed significant variation in stability of Fbr1 lines and hybrids as measured by mean yield and ASV. The AMMI and the GGE biplots ranked the best and poorest genotypes similarly in terms of yield performance and stability. The two classification models could be used simultaneously to make selection of genotypes more precise. Genetic distances were positively correlated with hybrid performance, SCA, and heterosis indicating that genetic distance could accurately predict hybrid performance in this set of germplasm. This study showed that yield is a complex trait and its improvement under stress should involve simultaneous selection of other traits associated with stress tolerance. The SNP markers are the marker of choice in genetic characterisation and determination of marker-based genetic distances because of their wide coverage of the maize genome. A number of lines homozygous for the Fbr1 tassel trait, has been identified in this study. These lines could be used in future research such as the developing of mapping populations aimed at tagging the Fbr1 trait, since the position of the Fbr1 gene in the maize genome is still unknown.

[发布机构] University of the Free State