Estimation of genetic parameters in agronomic characters and maturity index of sugarcane (Saccharum spp)

Varietal improvement in sugarcane is often targeted at high yield and sucrose quality. Effective genetic improvement of the crop requires understanding of the various attributes contributing to the existing diversity through genetic analysis. Hence, the objectives of this study were to evaluate sugarcane cultivars in the plant and ratoon crop cycles with a view to estimate the variance components, heritability and genetic gain of the characters and also to determine the association between them, both at phenotypic and genotypic levels. In the present investigation, twelve cultivars of sugarcane were evaluated in the two crop cycles in 2013 and 2014. The experiment was laid out in a randomized complete block design with three replications at Ibadan, Nigeria. Data were recorded on formative, vegetative and yield characters. Brix per cent (BP) was recorded at 9, 10, 11 and 12 months after planting (MAP) and denoted as BP9, BP10, BP11 and BP12. Data were subjected to analysis of variance for each crop and across crop cycles. Significant variations (p<0.001) existed among the cultivars, crop cycles and cultivars × crop cycles for all the formative, vegetative, yield characters and BP. Phenotypic variance for all the characters were higher than their respective genotypic variance. Estimates of heritability and genetic gain for the characters ranged from 23.3 % to 95.9 %, and from 10.4 to 23.0, respectively. However, days to flower initiation (DFI), stalk diameter (STD) and millable stalk (MBS) had high genetic gain across crop cycles. Additive gene action controlled inheritance of number of tillers and stalk, stalk diameter, total stalk at harvest, DFI, and brix per cent at 9 and 11 MAP, while both additive and non-additive genes governed inheritance of number of nodes, MBS, mean stalk weight and BP12. Phenotypic correlations in plant crop cycle were mostly positive and significant whereas both positive and negative correlations existed in ratoon crop cycle. Positive phenotypic and genotypic correlations existed among BP9, BP10 and BP11 in both crop cycles. The results of the study indicated that meaningful selection of genotypes for sugarcane improvement should be carried out at the formative growth phase or at maturity phase using yield and brix per cent attributes.