The effect of rainfall and temperature on the preharvest sprouting tolerance of winter wheat in the dryland production areas of the Free State Province

Preharvest sprouting (PHS) is a risk factor in winter cereal farming in certain environments as even mild sprouting affects the suitability of wheat for end-use products. This is because even mild sprouting affects the suitability of wheat for end-use products. The extent of PHS is hard to predict. To establish a quantitative relationship between PHS and different climatic characteristics, eighteen winter wheat cultivars were planted in three regions representative of the wheat growing conditions of the Free State Province of South Africa over four years. Climatic characteristics during six environmental periods were investigated, namely planting to harvest (PH), anthesis to harvest (AH), grain filling (GF), 14 days prior to physiological maturity (14M) and 10 and 20 days prior to harvest (10H and 20H) respectively. These data sets were correlated with PHS resistance determined in a rain simulator to determine if climate during various stages of grain development had an effect on the expression of dormancy and Subsequent PHS. Principal component analysis (PCA) on mean PHS values identified three distinct groupings of cultivars, ranging from PHS susceptible to PHS resistant. A fairly strong positive correlation (r = 0.715, P = 0.008) was found between PHS and minimum temperature during grain filling. Large variations in PHS values were also observed between the various cultivars, indicating that certain cultivars, such as Caledon, Gariep, Limpopo, Matlabas, PAN 3118, PAN 3120, PAN 3377 and SST 334, are more sensitive to environmental effects than others and that the variation in cultivar PHS is not consistent across sites and years. (C) 2009 Elsevier B.V. All rights reserved.