Quantifying Sugarcane Cultivar Genetic Gains in the Midlands Region of South Africa

Analyzing genetic gains of sugarcane cultivars provides a measure of performance for plant breeding programs. Previous studies in several countries showed yield of up to 150% in the last 50 yr. The objective of this study was to determine the genetic gains for cane yield, percent estimated recoverable crystal (ERC%) cane and sugar yield of cultivars grown in the humic and sandy soils of the Midlands region in South Africa. Data were derived from the final stage of cultivar testing. There was 0.40 Mg ha(-1) yr(-1) cane yield genetic gain in humic soils and 0.38 Mg ha(-1) yr(-1) in sandy soils. Sugar yield genetic gains were 0.051 Mg ha(-1) yr(-1) in humic soils and 0.047 Mg ha(-1) sandy soils. Genetic gains by sequence of release ranged from 1.70 to 2.45 Mg ha(-1) cultivar(-1) for cane yield and 0.23 to 0.27 Mg ha(-1) cultivar(-1) for sugar yield. Recently released cultivars produced genetic gains equivalent to 9 to 28% in cane and sugar yield. There were no genetic gains for ERC% cane. Significant cultivar x soil type interaction indicated that certain cultivars were not adapted to both soil types. Cultivars released after 2000 produced genetic gains equivalent to more than 14% increase in cane and sugar yield compared to older cultivars. Replanting 70% of current hectarage to newer and higher yielding cultivars will increase grower cane and sugar yield by 5 to 17%.