Cultivar Genetic Gains from 95 Years of Sugarcane Breeding and Implications on Sugarcane Production in South Africa

Cultivar genetic gains determine the efficiency of plant breeding and measure genetic improvements and effectiveness of recurrent breeding and selection cycles. South Africa Sugarcane Research Institute was established in 1925 to develop cultivars adapted to local growing environments after imported cultivars failed to adapt. The objectives of this study were to determine the genetic gains of South African cultivars developed over 95 years of sugarcane breeding and evaluate implications on progress and future breeding strategies. Data for cane yield, sucrose content, sugar yield, fibre content and purity were analysed using mixed models to compute means and linear regression to determine trends in trait values. Cultivar F-values were four to 16 times larger than cultivar by environment interaction F-values indicating high genetic differences. Cane yield genetic gains were 0.03 to 0.35 t/ha/year for irrigated, 0.19 to 0.48 (coastal) and 0.39 to 0.43 (midlands), while those for sugar yield ranged from 0.01 to 0.08 (irrigated), 0.03 to 0.07 (coastal) and 0.06 to 0.07 (midlands). The fibre % genetic gains were negative for irrigated and 0.02 to 0.06 for coastal and midlands. Sucrose % and purity % produced non-significant genetic gains indicating need to review breeding strategy. The new cultivars produced 12 to 17% (irrigated), 8 to 20% (coastal) and 16% (midlands) higher cane yield than old cultivars and 3 to 16% (irrigated), 8 to 22% (coastal) and 14 to 17% (midlands) higher sugar yields. The genetic gains for sugar yield were similar to those for cane yield. Planting new cultivars will increase sugar production by up to 22% in South Africa.