GRAIN FILLING PARAMETERS AND PROTEIN-CONTENT IN SELECTED WINTER-WHEAT POPULATIONS .2. ASSOCIATIONS

Understanding the relationship between grain filling (GF) characteristics, earliness, and N accumulation would aid in improving grain size and grain protein content in wheat (Triticum aestivum L.). A significant association of early anthesis, long GF duration, low GF rate, and high protein concentration was found in a set of F-1 hybrids and their parents from a 4 x 4 diallel cross involving Chinese and U.S. cultivars. This association was also found in an FL population of a cross between an early hard red winter Chinese wheat and a late soft white winter U.S. cultivar. Expressing GF duration and rate on a temperature basis (degree days) removed the correlation between anthesis date and GF parameters and showed that the early parent with a longer GF duration in days actually required less degree days for GF than did the late-heading parent. Regardless of the way of expressing GF parameters, a significant negative correlation was found between rate and duration of GF, suggesting a physiological barrier in combining high values for both traits. Kernel weight was significantly correlated with GF rate but not with GF duration, opening the possibility of breeding early maturing cultivars with reduced GF period without sacrificing grain weight. Grain protein concentration was negatively correlated with GF rate and positively correlated with GF duration, regardless if GF parameters were expressed on a time or temperature basis. These results suggest that improvements in both grain size and grain protein concentration will be difficult but not impossible and that selecting for long GF duration might be beneficial in this respect. Expressing GF parameters on a temperature basis proved useful in removing the differential influence of temperature variation on plants of different earliness.