Combining ability and GXE analysis for grain yield performance among CIMMYT germplasm
Kamutando, Casper Nyaradzai
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The International Centre for Maize and Wheat Improvement (CIMMYT) develops inbred lines and hybrids yearly that have several breeding and commercial attributes. However, the recently developed inbred lines that are adapted to the mid-altitude climatic conditions have not yet been assessed for their combining abilities (GCA and SCA) and their corresponding hybrids have not yet been assessed for grain yield (GY) stability. Therefore, the objectives of this study were: to identify single-crosshybrids adapted to stress and optimum environments,to identify new inbred lines with positive GCA estimates for GY under drought, low N, random stress and across all these environments; and to identify hybrid combinations with the highest SCA effects for GY across all environments. Thirty (30) male lines where crossed with eight (8) female lines using the North Carolina Design II (NCII) mating design and 240 hybrids were generated. These hybrids were planted at eight (8) different sites, alongside 10 commercial and CIMMYThybrid checks. The experiments were planted using a50 X 10 alpha (0.1) lattice design. Individual sites analysis of variance (ANOVA) was done for all the traits evaluated and significant differences for most of the traits (p< 0.05) were detected. A combined ANOVA was done and the presence of GEI in the performance of the hybrids was noted for all the traits (p<0.001). The genotypegenotype x environment (GGE) scatter plot showed genotypes such as CZL0713 X CL106683 to be specifically adapted to the stress environments and CZL052 X CL115809 to be specifically adapted to the optimum environments. The NCII design analysis showed significant differences in the GCA effects of both the male and the female lines (GCAf and GCAm, respectively) for GY. The narrow-sense heritability (h2)for GY was 5.3%; however the largest h2 was 35.4% for anthesis date. CL115791 was the best line across all the sites and under optimum sites (GCA=0.599 tha-1 and 0.986 tha-1, respectively). CL106689 showed the best GCA attributes in managed drought sites (MDS) (GCA=0.995 tha-1), CL106508 was the best under low nitrogen (N) sites (GCA=0.829 tha-1) and CL115791 was the best under the random stress (RS) site (GCA=0.565 tha-1). The single cross hybrid, CL115801 X CML312 showed the highest SCA effects for GY across all sites. In conclusion; CIMMYT has new lines that have desirable adaptive attributes across most environmental stresses in the mid-altitude region, hence these can be adopted for hybrid, synthetic and OPV formation. Hence, the genetic resources are there to reduce most of the problems faced by farmers in sub-Saharan Africa. However, further testing of the lines under farmer conditions need to be done to validate these findings.