The effect of soil fertility on the contribution of main stem, tillers and kernel position to grain yield and grain protein content of wheat

Abstract

The relative contribution of main stems and tillers, as well as the relative contribution of first, second and third kernels in spikeiets to grain yield and grain protein content, is seldom quantified. The grain yield of main stems, tillers and relative mass of kernels in the spikelet by floret position were determined in a long-term fertilization and irrigation experiment at the University of Pretoria. A randomized complete block design in a split-plot arrangement with three replicates was used. Main plots consisted of two different soil fertility levels and subplots were assigned to four cultivars. Mean grain yield of main stem (MS), first tiller (T1) and second tiller (T2) for the cultivar Kariega was 1.26 g, 0.98 g and 0.53 g respectively, 1.29 g, 0.78 g and 0.40 g for Carina, 1.63 g, 0.69 g and 0.09 g for Inia and 1.71 g, 1.10 g and 0.51 g for SST 86. Within a cultivar, the respective ears (MS, T1 and T2) did not differ in mean grain protein content, but significant differences were observed among the cultivars with Kariega averaging 16.2% while SST 86 and Inia averaged 14.5%. Main stems contributed on average 68.6%, first tillers 24.8% and second tillers 4.4% of the mean yield per unit area. Main stems produced on average 44.1 grains, first tillers 28.9 grains and the second tillers 15.3 grains. Main stems constituted 51.7% of the total ear number per unit area, first tillers 30.3% and the second tillers 14.4%. First kernels were on average 9.3% larger than second kernels, and 26.5% larger than third kernels, but did not differ in grain protein content. Increasing soil fertility increased fertile ear number per unit area, grain yield of main stem and first tiller, decreased that of second tiller but did not affect grain number of main stem or first tiller, while kernel mass and grain protein content was increased slightly by relative position in the spikelet. Significant interactions between soil fertility and cultivar were observed for ear grain number and protein content, and grain protein content in different floret positions. Under the experimental conditions, grain yield was largely contributed to by main stems and first tillers, and especially first and second kernels in the spikelet.