2 MEASURES OF GRAIN FILLING IN SPRING WHEAT

Grain weight is a component of grain yield and duration of grain filling is a component of maturity. Both are important traits in applied plant breeding and both depend upon the grain filling process. Grain filling has been described by multi-point and two-point curves. Multipoint curves, based on repeated measurements of grain weight during the grain filling period, are much more demanding of labor and laboratory resources than curves based on records of anthesis, maturity, and final grain weight. To evaluate these two methods of measuring grain filling characteristics, we grew 11 spring wheat cultivars in irrigated and dryland field trials at Saskatoon, SK, Canada in 1989 and 1990. Final grain weight, time to 50% filled, and relative grain growth rate were estimated from logistic curves fitted to grain weights measured twice weekly from anthesis to maturity. Duration of grain filling and average filling rate (harvest grain weight/duration) were estimated from records of anthesis and maturity. Relative grain growth rate was not related to average filling rate (r = -0.01), and was less closely related than average filling rate to harvest grain weight (r = 0.08 compared with r = 0.93, P = 0.01). Estimated time to 50% filled was moderately correlated with observed duration (r = 0.66, P = 0.05) and, compared with observed duration, differences among cultivars were more consistent and less sensistive to environmental influence. Compared with two-point curves, logistic curves provided better estimates of inherent differences in rate and duration of grain filling. However, this advantage does not justify routine use of multi-point curves in plant breeding except where late season stress masks inherent differences in maturity.