Observed duration and average and maximum grain filling rates in wheat genotypes of different earliness

Grain yields of wheat (Triticum aestivitm L) are influenced partly by final grain dry weight, which is largely determined by the rate and duration of the grain filling process. A study was undertaken to compare the observed final grain dry weight of five groups of wheat genotypes differing in earliness (extra early, medium early, medium late, late and a control group of high yielding NS cultivars) with the observed duration and average and maximum rates of grain filling in two different environments. Correlation coefficients were used to determine which grain filling parameter had more influence on final grain dry weight, in an environment common for our country (2002), final grain dry weight was strongly positively correlated with the average and maximum rates and strongly negatively correlated with the duration of grain filling. The medium late and control groups had the highest final grain dry weights. Correlations between final grain dry weight and the duration and average rate of grain filling were positive in an unfavorable environment (2001). The NS cultivars and extra early genotypes had the highest final grain dry-weights. The rate and duration of grain filling are usually negatively correlated. The influence of grain filling parameters on final grain dry weight is not the same in different environments, so the ability of the genotype to compensate for the low grain filling rate with grain fill prolongation in unfavorable environments might be more important. The observed average grain filling rate is probably more important as a parameter for describing these processes than the maximum one.