Effects of Plant Density on Grain Number and Grain Weight at Different Spikelets and Grain Positions in Winter Wheat Cultivars

Abstract

Seed-setting traits and grain weight are influenced by either genetic factor or cultivation environment in wheat (Triticum aestivum L.), such as plant density. Due to the unbalanced development of a spike, grain number and grain weight at different spikelets and grain positions are largely different. Although their distributions have been described in earlier reports, the effect of plant density is not clear. This study focused on the effect of plant density on the grain number and grain weight of two wheat cultivars (Lankao Aizao 8 of large-spike type and Zhoumai 18 of medium-spike type) at different spikelets and grain positions. The grain number, spikelet weight, and grain weight with the spikelets positions from the bottom to the top increased first and then decreased. The differences of seed-setting traits between two cultivars were significant. Meanwhile, seed-setting traits of main sipke were superior than that of tillering spike. Under low sowing density, the seed setting characteristics and grain weight in Lankao Aizao 8 were more superior than those in Zhoumai 18, and those of main stem spike were more superior than those of tillering spike. The effects of spikelet and grain positions on the weight of individual grain varied with the grain number of spikelet. For the basal and middle spikelets, the grain weight was higher at second grain position than at the first one, whereas it was inverse for the upper and top spikelets. The grain weight was lower in the third grain position than in the first and second grain position, and the least in the fourth grain position. In conclusion, appropriate plant density is important for high yield of different spike-type cultivars, and in wheat production we should properly increase the proportion of tillering spike on the basis of ensuring main stem spike number; increase grain weight on the basis of ensuring fertile grain number especially for basal spikelet; and develop the potential of grain weight in the third and fourth grain positions on the basis of ensuring that in the first and second grain positions of spikelet.