Objectives Our previous work confirmed that grain number per unit area could been maintained through delaying sowing date. This study further investigated the development characteristics of florets and compared their differences in differentiation and degradation under different sowing dates, and analyzed the relationship between photosynthate accumulation and distribution and floret development and grain setting. The purpose was to provide references for wheat high-yield cultivation.
Methods Field experiments were conducted during the 2014−2015 and 2015−2016 at the Experimental Station of Dongwu Village (35°57′N, 117°3′E), Shandong Province, China. Two wheat cultivars of Tainong18 and Jimai22 were planted as the experimental materials. Winter wheat was sowed on September 24, October 1, 8, 15 and 22, respectively. Binocular microscope was used to record the dynamics of differentiation and degeneration during the floret development. The final grains number, the dry matter and nitrogen accumulation of spikes and stems at anthesis were investigated, and the accumulation rate of dry matter and nitrogen in the whole plants and spikes during the floret degeneration stage were calculated.
Results Among the five sowing date treatments, the number of fertile florets and final grains per unit areas were maintained same, but the maximum number of differentiated florets per unit area was significantly reduced, and the survival rate of florets was significantly increased. When the sowing date was delayed, the degenerated rate of florets was significantly reduced. The accumulation of dry matter and nitrogen in the whole plants and spikes were significantly accelerated during the floret degeneration stage, thus ensure the constant spike dry weight and the ratios of dry matter and nitrogen between spikes and stems at anthesis. The number of fertile florets at anthesis exhibited significant and positive correlations with spike dry matter weight, the ratios of dry matter weight and nitrogen accumulation of spike/stem, and the accumulation rate of dry matter and nitrogen in the whole plants and spikes and survival rate of fertile florets, respectively. The number of degenerated florets per square meter produced by effective stems and ineffective tillers significantly reduced as a response to delay sowing date, and the number of degenerated florets per square meter produced by ineffective tillers was even more significantly decreased. Enhanced the proportion of the main shoots in the population of photosynthate can be in favor to maintain the number of fertile florets and decrease the number of degenerated florets, and reduce the depletion of florets death. In addition, the growing degree day production efficiency of fertile florets increased and the growing degree day production efficiency of degenerated florets reduced as a result of delaying the sowing date.
Conclusions Delayed the sowing date could increase the survival of florets through inhibiting the floret degeneration. The maintenance of the number of fertile florets is closely related to the photosynthate metabolism of plant. Delaying the sowing date could increase the proportion of the main stem in the plant population, which is beneficial to reduce the invalid consumption and improve the utilization efficiency of resource.
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