Thirty-eight spring wheat genotypes of north temperate or low latitude origin, all reasonably well adapted to the English environment, were grown in controlled environments providing the four combinations of 10 and 14 h photoperiods and temperatures of 8 and 16 °C for 6 weeks. They were then transferred to a glasshouse to assess their responses to these treatments. In separate experiments the responses of the genotypes to vernalization for 2 and 4 weeks at 2 and 8 °C were compared with unvernalized controls. The genotypes were also compared in field experiments from early, intermediate or late sowing over 3 years.

Both high temperatures and long days hastened ear emergence. At the higher temperature more leaves and spikelets were produced on the main stem while in long days the plants had fewer leaves and spikelets.

Most genotypes of north temperate and low latitude origin were responsive to photoperiod but not to the vernalization treatments. As a group, the low latitude ones were as responsive as the north temperate group. Five genotypes of north temperate origin were responsive to vernalization but not to photoperiod and were designated as ‘winter’ ones. Pitic 62 and Hork, from low latitudes, were responsive to vernalization and Hork was unique in also being responsive to photoperiod. The main difference between the north temperate and low latitude genotypes was in time to ear emergence and it is suggested that these differences were due to the effects of earliness genes as distinct from those determining photoperiodic response.

Taking all genotypes individually there were no correlations between yield or its sensitivity to sowing date and any of the attributes measured in controlled environments. However, considering class means, the winter genotypes were the latest to reach ear emergence in the field, and their yields, while greatest from the earliest sowings, were proportionally more depressed by late sowing than the others of the north temperate origin. Thus, it may be unwise for plant breeders to incorporate a vernalization response in spring wheat varieties unless genes for ‘earliness’ are also included. The low latitude class gave only slightly lower yields than the north temperate class.

It is concluded that genes other than those controlling responses to photoperiod, temperature and vernalization were more important determinants of the differences in yield among this set of genotypes.