Variation in the chemical composition of wheats grown in Western Australia as influenced by variety, growing region, season, and post-harvest storage

Abstract

Two experiments were conducted to examine varietal and environmental influences on physical characteristics and chemical content in a cohort of wheats grown in Western Australia. In Expt 1, a 3 × 3 × 2 factorial experiment examined the relationships between wheat variety (Arrino, Stiletto, and Westonia), growing region (high, medium, and low rainfall zone), and 2 harvest years (1999 and 2000). In Expt 2, the effect of storage for 6 months on the chemical composition of the wheats was examined. Wide variations in the content of crude protein (CP, CV 19.4%), total starch (CV 5.45%), total non-starch polysaccharides (NSP, CV 9.4%), insoluble NSP (CV 10.4%), and soluble NSP (CV 20.7%) were observed. The crude protein content of wheat was inversely related to total starch content (r = –0.779, P < 0.001). Variety influenced fast digestible starch (P < 0.001), acid detergent fibre (ADF, P < 0.01), total NSP (P < 0.05), insoluble NSP (P < 0.05), and in vitro extract viscosity (P < 0.05). The annual precipitation level (mm) irrespective of growing region was correlated to bushel weight (r = –0.683, P < 0.01), CP (r = –0.631, P < 0.01), total starch (r = 0.526, P < 0.05), ADF (r = –0.687, P < 0.01), lignin (r = –0.863, P < 0.001), soluble NSP (r = 0.826, P < 0.001), and free sugar contents (r = –0.795, P < 0.001), indicating the importance of annual rainfall for accumulation of protein, carbohydrates, and lignin in wheats. Harvest year had a strong influence on chemical composition (P < 0.05 to <0.001) and bushel weight (P < 0.001) of wheat. Storage for 6 months decreased soluble NSP (P < 0.01), ADF (P < 0.05), and lignin content (P < 0.01), and increased free sugar content (P < 0.001).