Pre-anthesis development and number of fertile florets in wheat as affected by photoperiod sensitivity genes Ppd-D1 and Ppd-B1
Lengthening the late reproductive phase (LRP) of stem elongation in wheat (Triticum aestivumL.), by changing its photoperiod sensitivity independently of the preceding phases, would improve the yield potential through increasing spike weight and the number of fertile florets at anthesis. This paper presents results of a two-year field experiment designed to determine the impact of Ppd-D1and Ppd-B1on (i) the duration of three pre-anthesis developmental phases, and (ii) spike weight and the number of fertile florets at anthesis under two photoperiods during the LRP (natural and an extension of six hours over that). Near isogenic lines of Mercia and single chromosome recombinant lines of Cappelle Desprez were used. Under natural photoperiod, Ppd-D1hastened time to anthesis ca. 500∘C d in both backgrounds by reducing each of the three pre-anthesis phases. Ppd-B1hastened the time to anthesis under natural photoperiod by 178∘C d, mainly by reducing the early reproductive phase. The response to photoperiod of the LRP under extended daylength depended on the Ppdlocus present: Ppd-D1was insensitive while Ppd-B1and the recessive controls were sensitive. For all lines, photoperiod treatments and years, the number of fertile florets was associated with spike dry weight at anthesis (R 2≅ 80%, p< 0.01) which, in turn, was positively related to the intercepted radiation accumulated during the LRP (R 2 45%, p< 0.05). Changing the duration of the LRP through extended photoperiod or through Ppd-D1produced similar results in both backgrounds and years. Thus, altering the duration of the LRP by manipulating photoperiod sensitivity may be an alternative to changing the fertile floret number in wheat. Nevertheless, as no particular allele was responsible for the photoperiod sensitivity only during the LRP, new alleles should be studied to identify the control of photoperiod sensitivity of individual phases to fine-tune the pre-anthesis wheat development.