To study the grain filling traits in wheat, two winter cultivars and four spring cultivars were selected. The resulting Fl, F2, F3 and backcrosses were tested. The following measurements were made: a) Visual traits for physiological maturity (PM), b) Grain dry weight accumulation, c) Regression models for grain filling period, d) Chlorophyll content and spectra analyses in flag leaves, e) Sucrose content in top node of stems. Of the six visual traits noted, the complete loss of green color from glumes was the best indicator of physiological maturity (PM), however it did vary among the different genotypes tested. Measurements of chlorophyll content and shift in the second derivative spectra of chlorophyll offered a more accurate estimate of PM than any visual traits in a growth chamber. A shift in the second derivative spectra was earlier than PM under field conditions. There was a good agreement between the date when the sucrose content in the top node of wheat stem fell to the minimum level and PM; this date seems to be a good indicator of PM. The shift of band Ca 693 in the fourth derivative spectra during grain filling had different patterns in the hybrid suggesting that the shift be controlled by cytoplasmic factor(s). The linear model monitoring the linear phase of grain filling is better than the polynomial models monitoring the whole period of grain filling for estimating the rate and duration of grain filling. Additive and non-additive gene actions were both significant in inheritance of the grain filling rate, effective duration and grain weight. Additive gene action was more important for the grain weight and less important for the effective duration of grain filling than non-additive gene action. Narrow sense heritability estimates were low for the grain filling rate and duration and high for grain weight. Grain filling rate was positively correlated with grain weight and grain yield and negatively associated with the duration of grain filling. The effective duration of grain filling also had a positive direct effect on grain yield, however this relationship was obscured by strong negative relation between the rate and effective duration of gain filling.

The nature of inheritance and possible associations for traits influencing earliness and grain yield were investigated using a four parent diallel of winter and spring wheat cultivars. More genetic variability was observed for the traits measured in segregating populations resulting from crosses between winter and spring type wheats in contrast to spring x spring or winter x winter crosses. The one exception was plant height where more genetic variability resulted from spring x spring crosses. Narrow sense heritability estimates were high for time and duration of heading, anthesis, grain filling and physiological maturity and for plant height. Smaller values were noted for rate of grain filling, kernel number, harvest index, tiller number, kernel weight, whole plant dry weight and grain yield. Estimates of the coefficient of heritability and the parent-offspring correlation coefficient were similar in magnitude except for the traits grain yield, tiller number, kernel weight and whole plant dry weight where large variations due to the environment were encountered. Using the Jinks-Hayman model, no maternal effects were noted nor were any nonallelic interactions observed for total duration of grain filling and lag period. The actual grain filling period was influenced to some degree by such interactions. The spring cultivars also appeared to have more dominant genes for longer total duration of grain filling and lag period. In contrast the winter parents had more dominant genes for the longer actual grain filling period. Estimates of general and specific combining ability provided similar evidence in terms of the nature of gene action. Both additive and nonadditive gene action was present for all traits, the relative magnitudes depending on the specific trait. Based on individual combining ability effects, the winter x spring cross Yamhill x Siete Cerros would appear to provide the highest proportion of desired segregates when combining earliness and acceptable grain yield. From the direct and indirect associations of grain yield, it would appear that a shorter duration of grain filling along with a shorter lag period from heading to anthesis are important for higher rates of grain filling if negative associations between earliness and grain yield are to be avoided.

Concerns about the genetic control and environmental influence of various stages of development including the grain filling period, and the relationship between early maturity and grain yield prompted this study. The experimental material consisted of two facultative and two winter wheat cultivars. A dial!el cross, excluding reciprocals, was also developed to provide an Fl generation. Information was collected for 14 traits and subjected to statistical analyses. Genetic differences among varieties were found for time of heading, flowering and physiological maturity, duration and rate of the grain filling period, grain yield and yield components. The facultative types, AI Feng 2 and Selection CB 83-52, showed earlier heading, flowering and physiological maturity, longer lag period (period between heading and flowering), and longer duration and lower rate of grain filling, resulting in lower grain yield. The winter cultivars, Stephens and Yamhill Dwarf, in contrast had later heading, flowering and maturity, shorter lag period, and shorter duration and higher rate of grain filling, giving higher grain yield. For the developmental stages after heading, larger differences were observed in the lag period while differences in duration of grain filling period were relatively small among the cultivars. Depending on the specific Fl population, there was a tendency toward dominance for early heading, a range from no to complete dominance for early flowering and no dominance for physiological maturity. Long duration and fast rate of grain filling were generally dominant. Grain yield was positively associated with the number of days to heading, flowering and physiological maturity. Also positive associations of grain yield were obtained with tiller number, kernel weight, grain weight per spike, biological yield and rate of grain filling. Negative associations of grain yield were noted with lag period and duration of grain filling period. No clear associations between physiological maturity and the yield components were found. Grain filling duration showed no association with yield components while grain filling rate exhibited positive association with tiller number and kernel weight. There was negative association between duration and rate of grain filling period. According to heading responses from different planting dates, Stephens and Yamhill Dwarf had high sensitivity while Selection CB 83- 52 and AI Feng 2 showed low sensitivity to vernalization. Genotype X environment interaction was observed with each cultivar responding differently for several traits depending on the planting dates.

The need to develop a shorter life cycle wheat cultivar which would be more adapted to multiple cropping systems prompted this study. Thus the following information was obtained. Greatest variations in developmental patterns were found in the stem elongation, booting, inflorescence emergence and anthesis for five winter and five spring cultivars when planted at different dates. Differences among the ten winter wheat cultivars in time, duration and rate of grain filling was also observed. Generally later flowering cultivars had a more rapid rate of grain filling than early flowering cultivars with the net result being that physiological maturity was similar between the two groups. Actual grain filling period from flowering to physiological maturity varied among the cultivars, but larger differences were observed in lag period from heading to flowering. The duration of lag period contributed to the largest difference in total grain filling period from heading to physiological maturity. Changes in visual spike color of the glumes and main axis of a spike was satisfactory in identifying physiological maturity without destruction of the spike; however changes in kernel color was a more direct and precise method. Physiological maturity is a better measure of the optimum harvesting time to provide for maximum grain yield for planting sequential crops. Grain yield was positively associated with time of heading, flowering, physiological maturity, rate of grain filling and components of grain yield, but negatively associated with duration of grain filling period, lag period and harvest index. There was little association with the duration of the actual grain filling period and grain yield. However, a large association was observed between grain yield and the rate of grain filling. The direct effects of tiller number and rate of grain filling on grain yield were consistently positive and high. The indirect effects of rate of grain filling on grain yield were positive and high via time of heading, flowering and physiological maturity, components of yield and whole plant dry weight, but negative and high via duration of grain filling period, lag period and harvest index.