Duration of developmental phases, and dynamics of leaf appearance and tillering, as affected by source and doses of photoperiod insensitivity alleles in wheat under field conditions

Variation in photoperiod sensitivity in wheat plays a major role in the crop adaptation to wide agronomic environments. Photoperiod insensitivity is provided by Ppd-Aa, Ppd-B1a and Ppd-D1a alleles. Effects of the genome, doses and source of the particular Ppd-1a alleles on time to anthesis has not been analysed simultaneously in the same experiments, even less under field conditions; and the effects on particular phases rather than on considering only the total time to anthesis and on phyllochron have not been considered for this range of allele combinations. We carried out field experiments during two consecutive growing seasons to assess differences in time to anthesis, in its component phases, in final leaf number, phyllochron and tillering across wheat isogenic lines differing in specific Ppd alleles and homoeoalleles. In addition to confirming that the introgression of Ppd-1a alleles advanced anthesis time (on average by 307, 251 and 191 degrees C d if there were 3, 2 or 1 insensitivity alleles introgressed, respectively), we found that the variation between photoperiod insensitive genotypes was largely dependent on the varietal source of Ppd-B1a which could be stronger or weaker than Ppd-D1a depending on the donor considered. All components of time to flowering: the particular sub-phases (P < 0.001) as well final leaf number (P < 0.001) and phyllochron of late-appearing leaves (P < 0.05) were sensitive to Ppd-1a alleles, but the strength of particular alleles on particular components was different, so that similar adjustments in time to anthesis could be achieved with different partitioning of developmental time between the considered phases. We also found that although they did not affect phyllochron of the first 7 leaves, that of the leaves appearing later was consistently reduced in lines carrying Ppd-1a. Tillering was sensitive too, but not final number of spikes due to compensations between tillering and tiller mortality.