Test-weight and weathering of spring wheat

Abstract

Wet weather often delays harvest and results in a grade reduction of wheat because of a decrease in test-weight, an important grading factor in Canada. The objectives of this study were to assess the effect of delayed harvest on test-weight loss of 14 Canadian wheat cultivars representing three different classes, and to develop a screening strategy for retention of test-weight for breeding programs. Non-weathered test-weight (NWTWt), weathered test-weight (WTWt), and test-weight loss (TWtLoss; i.e. NWTWt – WTWt) in the field, averaged over five field locations and 2 yr were similar within the CPS, CWAD and CWRS wheat classes, although there were genotypic differences for all three variables. Because test-weight requirements for the top grades are higher in the CWAD class than in other classes, durum cultivars would be more susceptible to downgrading during wet harvests. Historical data from the Durum Wheat Co-operative Test also suggests that, since 1950, the mean test-weight of the genetic lines has decreased by 3.7 kg hL−1, and is now close to the minimum for grade #1 in the CWAD class. Most of the decrease in test-weight observed over several weeks in the field could be simulated by a single 5 – 10 min soaking of non-weathered seed in the laboratory. Linear regression analyses of both field and laboratory samples indicated that 90% of the genotypic variation in weathered test-weight could be attributed to differences in the NWTWt. These results suggest that the screening strategy for retaining test-weight should focus on selection for increased NWTWt. This is much simpler than screening for high WTWt or low TWtLoss, which requires soaking of the seed or field weathering. Key words: Triticum aestivum, Triticum turgidum, quality