Effect of Gibberellic Acid on Growing-Point Development of Non-Vernalized Wheat Plants under Long-Day Conditions

The goal of this study was to determine whether the application of gibberellic acid (GA₃) to seeds of common wheat varieties with different vernalization and photoperiod requirements affects the transition from vegetative to generative stage. Three varieties of wheat with different photoperiod sensitivities and vernalization were selected for the experiment—the winter varieties, Mironovskaya and Bezostaya, and the spring variety, Sirael. Seeds were treated with different concentrations of GA₃ and plants were grown under long-day conditions with monitoring of their photosynthetic activity (F_v/F_m, P_n, E, g_s). We monitored the activity of the photosynthetic apparatus by checking the plants to see if they were growing properly. The phenological stages of the wheat species were checked for indications of a transition from the vegetative to the generative stage. Selected concentrations of GA₃ had no effect on the compensation of the vernalization process (transition to the generative phase). Chlorophyll fluorescence was one of the factors for monitoring stress. The variety, Bezostaya, is similar to the spring variety, Sirael, in its trends and values. The growth conditions of Bezostaya and Sirael were not affected by the activity of the photosynthetic apparatus. The development of growing points in winter varieties occurred at the prolonged single ridge stage. The spring variety reached the stage of head emergence after sixty days of growth (changes to the flowering phase did not appear in winter wheat). Application of GA₃ to the seeds had no effect on the transition of the growing point to the double-ridge generative stage. The present study highlights the priming effect of GA₃ on seeds of common wheat varieties with different vernalization and photoperiod requirements as it affected the transition from vegetative to generative stage.

Effect of Ppd-A1 and Ppd-B1 Allelic Variants on Grain Number and Thousand Kernel Weight of Durum Wheat and Their Impact on Final Grain Yield

The main yield components in durum wheat are grain number per unit area (GN) and thousand kernel weight (TKW), both of which are affected by environmental conditions. The most critical developmental stage for their determination is flowering time, which partly depends on photoperiod sensitivity genes at Ppd-1 loci. Fifteen field experiments, involving 23 spring durum wheat genotypes containing all known allelic variants at the PHOTOPERIOD RESPONSE LOCUS (Ppd-A1 and Ppd-B1) were carried out at three sites at latitudes ranging from 41° to 27° N (Spain, Mexico-north, and Mexico-south, the latter in spring planting). Allele GS100 at Ppd-A1, which causes photoperiod insensitivity and results in early-flowering genotypes, tended to increase TKW and yield, albeit not substantially. Allele Ppd-B1a, also causing photoperiod insensitivity, did not affect flowering time or grain yield. Genotypes carrying the Ppd-B1b allele conferring photoperiod sensitivity had consistently higher GN, which did not translate into higher yield due to under-compensation in TKW. This increased GN was due to a greater number of grains spike-1 as a result of a higher number of spikelets spike-1. Daylength from double ridge to terminal spikelet stage was strongly and positively associated with the number of spikelets spike-1 in Spain. This association was not found in the Mexico sites, thereby indicating that Ppd-B1b had an intrinsic effect on spikelets spike-1 independently of environmental cues. Our results suggest that, in environments where yield is limited by the incapacity to produce a high GN, selecting for Ppd-B1b may be advisable.

Dynamics of leaf and spikelet primordia initiation in wheat as affected by Ppd-1a alleles under field conditions

Wheat adaptation is affected by Ppd genes, but the role of these alleles in the rates of leaf and spikelet initiation has not been properly analysed. Twelve near isogenic lines (NILs) combining Ppd-1a alleles from different donors introgressed in A, B, and/or D genomes were tested under field conditions during two growing seasons together with the wild type, Paragon. Leaf initiation rate was unaffected by Ppd-1a alleles so the final leaf number (FLN) was reduced in parallel with reductions in the duration of the vegetative phase. Spikelet primordia initiation was accelerated and consequently the effect on spikelets per spike was less than proportional to the effect on the duration of spikelet initiation. The magnitude of these effects on spikelet plastochron depended on the doses of Ppd-1 homoeoalleles and the specific insensitivity alleles carried. Double ridge was consistently later than floral initiation, but the difference between them was not affected by Ppd-1a alleles. These findings have potential for selecting the best combinations from the Ppd-1 homoeoallelic series for manipulating adaptation taking into consideration particular effects on spikelet number.