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

Understanding the relationship between grain filling (GF) characterist ics, earliness, and N accumulation would aid in improving grain size a nd grain protein content in wheat (Triticum aestivum L.). A significan t association of early anthesis, long GF duration, low GF rate, and hi gh protein concentration was found in a set of F-1 hybrids and their p arents 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 betwe en 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 pa rameters and showed that the early parent with a longer GF duration in days actually required less degree days for GF than did the late-head ing parent. Regardless of the way of expressing GF parameters, a signi ficant 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 no t with GF duration, opening the possibility of breeding early maturing cultivars with reduced GF period without sacrificing grain weight. Gr ain protein concentration was negatively correlated with GF rate and p ositively correlated with GF duration, regardless if GF parameters wer e 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 duratio n might be beneficial in this respect. Expressing GF parameters on a t emperature basis proved useful in removing the differential influence of temperature variation on plants of different earliness.