Family evaluation for quality traits in sugarcane
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Family evaluation and selection has the potential to increase the selection efficiency, thereby improving breeding for quality traits at early stages of sugarcane breeding. Data from family evaluation trials can also be useful for quantifying the performance of parental genotypes that were used to produce families. The objectives of this study were to compare family to individual genotype evaluation and determine optimum sample size for estimating sucrose content; to determine family evaluation breeding parameters and phenotypic correlations for quality traits; to determine the proportions of families and parents producing significantly higher trait values compared to the trial mean for the coastal short cycle mini-line breeding programme. Data were collected from 20 genotypes within each family plot for hand held refractometer Brix %cane data (surrogate for sucrose content), estimated recoverable crystal (ERC) %cane, polarisation (Pol) %cane, Brix %cane, Brix dry matter (DM) %cane, purity %, fibre %cane and DM %cane. Data were analysed using statistical analysis system software (SAS). Both family and individual genotype variances were significant (P<0.01) suggesting selection for individual genotypes within selected superior families will increase efficiency of selection. Broad-sense heritability (H) values ranged from 0.74 to 0.77 for families and from 0.14 to 0.17 for individual genotypes. Families (7.06 to 12.72%) produced higher predicted selection gains (%Gs) than individual genotypes (2.42 to 5.47%). The higher H and %Gs indicated superiority of family selection compared to individual genotype evaluation. Response surface graphs showed four replications and 10 genotypes produced H values of 0.77 to 0.80 compared to 0.74 to 0.77 with sample size of 20 genotypes in three replications. Reducing the sample size from 20 to 10 genotypes will reduce data collection costs. ERC %cane, Pol %cane and fibre %cane had the largest H and %Gs values, suggesting that family evaluation was effective for these traits. Results showed strong associations among sucrose related traits (ERC %cane, Pol %cane and Brix %cane) with correlation coefficient values ranging from 0.80 to 0.99. The significant (P<0.05) negative correlation between sucrose related traits and fibre %cane (r>0.07) showed a decrease in sucrose content with an increase in fibre content. Results showed that Brix %cane had a high H, high %Gs and significant positive correlations with both ERC %cane and Pol %cane, suggesting that Brix %cane is a suitable trait for family evaluation. Brix %cane can be measured easily in the field using a hand held refractometer, providing data to quantify within family variability in early stages of sugarcane breeding. Results showed highly significant family, female and male variances, highlighting the existence of genetic differences and control among families. Results showed a lower proportion of families producing significantly higher best linear unbiased prediction (BLUP) values compared to the population mean. Results suggested the need to use breeding values to guide parent selection for breeding programmes.