SOME ASPECTS OF PHOTOPERIODISM IN WHEAT AND ITS WILD RELATIVES

Experiments with plants grown in controlled environment conditions exa mine three aspects of photoperiodism in wheat. A survey of the floweri ng responses of 20 genotypes of diploid, tetraploid and hexaploid whea t cultivars and wild relatives to growth under three daylengths (8, 12 , 16 h) after three durations of vernalisation (0, 4, 10 weeks at 2 de grees C) showed that all were long-day plants and many responded to ve rnalisation. The requirement for long days was most stringent among th e diploid progenitors and most relaxed among the hexaploid cultivars. However, not even the earliest flowering spring wheat cultivars (among eight) were entirely daylength-neutral. Minimum times to inflorescenc e initiation appeared to be determined independently of the responses to daylength. Whereas leaf initiation and appearance rates were hardly influenced by daylength, the rate of spikelet initiation responded to it from the beginning of floral induction, well before the appearance of double ridges. Comparison of the times to double ridges among near -isogenic lines of four spring wheat cultivars (Ciano 67, Yaqui 50, Re scue and April Bearded) showed that each of the three dwarfing genes R ht1, Rht2 and Rht3 advanced inflorescence initiation but without chang ing the response to daylength.