GRAIN-YIELD VS SPIKE NUMBER IN WINTER-WHEAT IN A HUMID CONTINENTAL CLIMATE

Wheat (Triticum aestivum L.) yields often are closely related to spike number per unit ground area. This study was conducted to determine whether, for soft white winter wheat in a region with a humid continental climate, this relationship is determined primarily by changes in total dry weight accumulation (TDW), harvest index (HI), or both. The study involved several field experiments in which seeding density varied from 6 to 24 g m-2, sowing dates ranged from 14 September to 1 November, alternate rows were removed in May and early June, row spacing varied from 0.16 to 0.32 m, a growth regulator (chloroethyltrimethylammonium chloride) was applied at 9.6 kg a.i. ha-1, and 11 genotypes (both gibberellic acid sensitive and insensitive) were used. These treatments were used to create a range of final spike numbers. Grain yields ranged from 180 to 570 g m-2, and increased with spike numbers per m2. Total dry weight, which ranged from 720 to 1670 g m-2, also increased with spike numbers per m2, such that HI remained unchanged as spike number per unit area increased. Harvest index, however, decreased with spike number per plant, and was related to kernel weight but not to kernel number per spike. Positive relationships of grain yield to spike number per unit land area thus seem to arise from increased TDW rather than enhanced HI. Examination of the reasons for high dry matter production at high spike numbers appears worthwhile for subsequent research.