Improvement strategies for yield potential, disease resistance and drought tolerance of Zimbabwean maize inbred lines

[摘要] English: Breeding for drought and low N tolerant genotypes in Zimbabwe is an important intervention that will see the country curbing the food in-security problem. Both CIMMYT and DR&SS maize germplasm was used in this study that was conducted in Zimbabwe in the 2009/10 and 2010/11 seasons. Evaluations were done under optimum, drought and low N conditions. One of the objectives was to estimate combining ability and heterosis for grain yield and other agronomic traits of white maize inbred lines under stress and optimal environments. Line x tester analysis of 23 inbred lines identified RS61P, NAW5885 (from DR&SS) and CML444, CML539, CML442, CML537 and CML548 (from CIMMYT) as having desirable GCA effects under both drought and low N conditions. Additive and nonadditive gene effects were important in the expression of traits across all environments; however non-additive gene effect assumed a more important role in the expression of traits under stress environments. The single crosses RS61P/CML444 and 2N3d/CML548 were identified as potential testers for the SC and N3 heterotic groups respectively. In the analyses of G x E and stability using AMMI and GGE biplot the same single crosses were identified as the most stable. There were three mega environments identified within the test environments and Agricultural Research Trust farm site was the most powerful in discriminating genotypes. Genetic diversity amongst the 23 inbred lines was examined using 14 morphological traits and 1 129 SNP markers. The morphological data revealed variability amongst inbred lines that could be manipulated through selection and hybridisation. Variability was further substantiated using PCA where the overall diversity could not be explained by a few eigenvectors and the major contributors were grain yield, texture, ear aspect, common rust, GLS and anthesis days. Euclidean and Rogers' dissimilarity matrices based on morphological and SNP data respectively clustered lines related by pedigree together in some cases. The SNP dendrogram had a high goodness of fit value (r=0.87) compared to the morphological dendrogram, which showed that it grouped the lines efficiently, although at times it was not in agreement with the known heterotic grouping that was previously established using testers. The assessment of correlation between genetic distances, F1 performance, heterosis and SCA revealed significant positive correlations and regressions between SCA, MPH, HPH and per se performance of hybrids. The HPH and MPH also showed significant positive association and linear regression along with high coefficient of determination with per se performance of hybrids, especially under drought conditions. Correlations of genetic distances with MPH and HPH were too low to be of predictive value. An average of 112.29% MPH and 76.40% HPH were realised across environments and this was an indication of the potential of these inbred lines for hybrid development. The segregating lines at F3 stage were testcrossed to group A (CML539/CML442) and B (CML444/CML395) testers and testcrosses containing lines derived from DR&SS lines K64r, RS61P, NAW5885, SC5522 and CIMMYT drought tolerant donors based on DTPWC9 were generally amongst the best performing testcrosses in early and late maturing trials. Three-way hybrid performance was predicted from 11 single cross hybrids and results showed that there was significant but weak correlation between the predicted and the observed grain yield means and this could be explained by epistatic and significant G x E interaction, which were not taken into account in the prediction equation. Three-way cross hybrids identified as having superior performance under drought and well-watered conditions included RA214P/CML538//RS61P, RS61P/ CML444//CML538 and RS61P/CML444//CML539. However, there is still need to evaluate these hybrids under low N conditions before they can be recommended for release.

[发布机构] University of the Free State