Evaluating families and breeding values of parental populations in sugarcane
Mbuma, Ntombokulunga Wedy
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Sugarcane is a complex crop which is under complex genetic control where chromosomes get eliminated after crossing, resulting in progeny performance deviating from the expected based mid-parent values. The early stage of sugarcane breeding is generally associated with low levels of precision and selection efficiency due to the significant genotype by environment interaction effects and competition among genotypes. The general aim of this study was to evaluate sugarcane families and assess the breeding values (BV) of genotypes to increase crossing and selection efficiency in sugarcane breeding programmes. The objectives were; to 1) determine the magnitudes of variability in family variance components, 2) broad-sense heritability (H) and to evaluate their implications in breeding for cane yield, 3) to evaluate BV of genotypes using best linear unbiased prediction (BLUP), 4) to determine the range of BV among the SASRI gene pool, 5) to investigate family by environment interaction and evaluate its implications in sugarcane varietal development breeding. Family data on stalk number, stalk height and stalk diameter were sampled from the first 20 genotypes per family plot across the SASRI regional breeding programmes and were used to calculate cane yield. Highly significant (P< 0.001) family and individual genotype variance in all the populations except CLCAP, indicated the existence of large genetic variability among the populations. Families produced larger variances and H estimates than individual genotypes, indicating that selection of superior families would be more effective than selecting among individual genotypes. The humic soil (68%), CLCHP (57%), CSCHP (57%) and irrigated (53%) populations had higher family H estimates for cane yield than sandy soil (42%), CLCAP (37%) and CSCAP (43%) populations, indicating the importance of family evaluation and the potential improved genetic gains through family selection, first followed by individual selection within those families in different ecological conditions and identification of location specific families. Low H estimates in sandy soil, CLCAP and CSCAP populations indicated a low proportion of genetic variability and thereby a potentially low selection efficiency among these populations. Significant (P < 0.05) female and male variances indicated that the presence of enormous genetic variability among progenies which was inherited from both the parents. Genotypes (82H0397, 85H0428, N52, B74713, 87W0629, 01G1662, 88W1323, 02K1657, 87L0573, 97E0474, N31, 93E0888, 03U1030, 06T3608, 96W0246, WI82498 and 79F0779) with high BV produced progenies with high cane yield when crossed with diverse genotypes, which indicate their general combining ability and these combiners can be utilised in base broadening programmes. Genotypes with high BV can be used to build a core germplasm /gene pool of best combiners that are known to produce high cane yielding progenies. The numbers of genotypes with high breeding values in CSCHP (29.4%), CLCHP (28.0%), humic soil and irrigated (26.0%) populations were higher compared to those in sandy soil (22.9%), CSCAP (21.0%) and CLCAP (18.4%) populations. Significant (P<0.01) family and family by location variance for cane yield, stalk number and diameter indicated the existence of location specific variability among families for these traits. The family by crop year and family by location by crop year interaction variances were non-significant (P>0.05). Evaluating families in multi-locations proved to be the need of the hour than its performance across ratoon crops. BLUP estimates identified elite families with significantly higher cane yield across locations and which were location specific compared to population mean. Results from this research could be used to guide future crossing (trait combinations) and selection at early stages of breeding thereby enhancing breeding efficiency.