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Ratooning ability increases sugarcane production economics by reducing frequency of planting. During sugarcane breeding, indirect selection for pest resistance and direct selection for high ratoon yields increases ratooning ability. The objective of this study was to describe the simultaneous screening of genotypes for yield and ratooning ability in sugarcane breeding trials using analysis of covariance. Data for cane yield (tons ha -1 ) and stalk population (×10 3 ha -1 ) collected from five trials harvested from plant to fourth ratoon crops were analysed using the Statistical Analysis System (SAS). There were significant differences in parameters for yield (intercept) and ratooning ability (slope) among test genotypes indicating potential for simultaneous screening. Comparison of genotypes to a control with known ratooning ability identified higher yield and good ratooning genotypes. Graphical trends identified genotype differences in yield and ratooning ability. The economics of yield and ratooning ability of two varieties was compared providing a mechanism for variety choice at planting. The method described provided statistical tests that would increase genotype selection efficiency for ratooning ability. The decline in yield among genotypes is slowed by the increase in stalk population.

The causes of genotype × environment (G × E) interactions in sugarcane (Saccharum spp.) are unclear. The objectives of this study were to (i) investigate the G × E interactions and site similarity in two selection programs in South Africa, (ii) identify factors responsible for G × E interactions, and (iii) illustrate the integrated use of crop models and climatic data to better understand G × E interactions. Data from eight series of trials were analyzed using variance components, genotype plus genotype × environment (GGE) biplots, and additive main effects and multiplicative interaction (AMMI). Crop model simulations helped summarize environmental covariates before and after canopy closure. Environmental covariates and genotypic traits were correlated to AMMI scores and superimposed on biplots. The G × E interaction accounted for more variation than the main effect of genotype and the repeatable component of G × E was dominant across all series. Two sites were identifi ed as redundant and were recommended for removal. Sites from one program were characterized by higher rainfall and lower water stress compared with sites from the other. The enriched AMMI2 biplots allowed for identifi cation of factors that infl uenced genotypic traits and permitted biological interpretations and trait relations to be studied. This study has illustrated of harvest; TT, mean daily thermal time; TT1 and TT2, average daily heat units before and after canopy closure, respectively; WSI, water stress index; WSI1 and WSI2, water stress index before and after canopy closure, respectively.

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Initial sugarcane production in South Africa relied on imported varieties. When imported varieties succumbed to diseases, the industry established the South African Research Institute (SASRI) with the mandate to develop sugarcane varieties. The popular and highly successful varieties, NCo310 and NCo376 were selected from crosses imported from India. NCo310 and NCo376 were grown successfully in several countries across the world where they produced high yield and ratooning ability. Later, crossing was established at SASRI based on flowers initiated in the glasshouse and photoperiod house under controlled temperature and photoperiod conditions. A five stage program is currently being implemented in the variety development process. More than 60 varieties have been released from the breeding programs. Other achievements include development of germplasm that is currently being used to enhance sugar cane variety development in South Africa. Currently, high realised selection gains are evident in most of the advanced selection populations. The released varieties show genetic gains over time. Efforts to enhance the breeding program include introgression, family evaluation, selection models and use of molecular markers.