Spatial variation in seed size and seed set on spikes of some Canadian spring wheat cultivars

Abstract

The seed size (mass) distribution of grain on individual spikes of four Canadian wheat cultivars (Glenlea, HY320, Pitic 62 and Neepawa, Triticum aestivum L.) was determined on plant samples from two replicates of the 1984 High Yielding Wheat Cooperative trial grown at Ellerslie, Alberta. Specific grain mass was determined for individual floret locations on all spikes of each plant, and sterile floret locations were also determined. For all four cultivars the maximum amount of seed size variation from the samples was attributable to variation at the floret level, accounting for 92% of the seed size variance of Pitic 62, down to 74% for Neepawa. Neepawa differed from the other three cultivars in demonstrating a high (20%) and significant variance in seed size attributable to spikelet position. Pitic 62 was the only cultivar of the four that demonstrated significant variance (12%) due to plant differences within replicates. Consistent with previous literature, approximately 50% of total plant yield was accounted for by the mainstem spike, decreasing to 8 to 15% on the third spike. The mean number of seeds spike−1 on the mainstem was 26.8 (Neepawa), 35.9 (Glenlea), 46.8 (HY320) and 48.6 (Pitic 62), but this number decreased in response to tiller order, as did seed mass and floret fertility. Quadratic functions were calculated fitting seed mass to floret position (1 proximal to 4 distal), and were significant in all cases, with R2 values of 63% for Neepawa, 56% for Glenlea, 82% for Pitic 62 and 89% for HY320. The fitted quadratics suggest an optimization of seed size at floret site 2 for some cultivars, with a rapid decrease in seed size at floret sites 3 and 4, especially for the high-yielding cultivars Glenlea and Pitic 62. Fourth florets of the latter cultivars were shown in frequency distributions to produce seeds smaller than the mean seed size of the Neepawa seed size expected at Florets 1, 2 and 3. Large negative skewnesses for seed size for Glenlea, HY320 and Pitic 62 also underscored the tendency for the high-yielding cultivars to produce relatively large numbers of small seeds. Although determined in only one site-year, these differences in seed size distribution pattern amongst cultivars are of major significance to visual identification systems. Large-seeded, high-yielding wheats in pure stand can be expected to produce a significant number of small-seeded kernels that might be confused by visual inspection with CWRS seed type. Key words: Grain, grading, cultivar registration, seed identification, high-yielding wheats