GENETIC ANALYSIS OF TIME TO EAR EMERGENCE IN HEXAPLOID WHEAT, TRITICUM AESTIVUM, USING INTERVARIETAL CHROMOSOME SUBSTITUTION LINES

Differences in days to ear emergence between the cultivars Chinese Spring and Hope, under long photoperiod, are under complex genetical control. A minimal estimate of ten genes of comparatively major effect and four of minor effect determine the difference in days to ear emergence under these conditions. The concept has been developed of the genetic control of time to ear emergence in wheat being determined by two types of gene action (i) a threshold response function and ((ii) a rate function. It appears that with vernalization response, at least, the threshold function is closely linked with, or a pleiotropic expression of, the rate function. The two chromosomes 7B and 5D of Hope in Chinese Spring appear to bear genes which exhibit strong expressions of these dual functions — 7B vernalization reducing and rate (to ear emergence) promoting and 5D vernalization promoting and rate retarding. However, in the case of chromosome 5D of Hope in Chinese Spring at least, the presence of a null allele for the gene for spring habit on 5D on Chinese Spring could mean that the retardation of development rate was a function of the rest of the genotype. Homoeologous group 5 possesses a distinctive role in the control of maturity of bread wheat. Intervarietal chromosome substitution in wheat, particularly for chromosomes 5A and 5D and in addition chromosomes 3B and 7B could play a significant role in breeding for altered time to ear emergence.