Location and seasonal effects on sugarcane smut and implications for resistance breeding in South Africa

Smut, Sporisorium scitamineum (Syd.) (formerly Ustilago scitamineum), is a major disease of sugarcane causing cane yield losses of 0.25 to 0.75% for every 1% of infected stools. Breeding resistant cultivars is part of integrated smut management. The objective of this study was to determine the effects of locations and seasons on smut infection genotype in irrigated sugarcane breeding trials. Data for smut-infected stools and smut whips collected from early and late season trials at Pongola (NPG) and Mpumalanga research stations (MP) were analysed using linear mixed models. There were significant (p < 0.001) location, season, location by season, genotype, genotype by location, genotype by season and genotype by location by season interaction effects for infected stools and whips. Broad sense heritability in late season trials averaged 0.89 compared to 0.61 in early season, while that for MP (0.79) was higher than for NPG (0.69) indicating higher selection efficiency for smut resistance in late season MP trials. Genotypes had significantly (p < 0.001) higher infected stools and whips at MP than at NPG and in late than early season trials. Smut-screening using MP late season trials will increase efficiency of breeding for smut resistance in South Africa.