The extent and significance of seed size variation in New Zealand wheats

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Abstract
The mean 1000 seed weight of machine-dressed seed lines of seven New Zealand wheat cultivars varied from 27 to 57 g over three seasons, depending on both cultivar and season. Seed size distribution tended to follow a normal distribution. When equal numbers of seeds per unit area were sown, large seed outyielded small seed by 3–17% through the production and maintenance of more ears per unit area. No other yield components were significantly affected. The ability of large seed to produce and retain more ears arose from greater emergence and greater vigour of the seedlings produced. When seed was sown on a constant weight basis, the yield from large seeds was equal to or less than that from small seeds because there were fewer ears per unit area. When sowing on a constant weight basis, no advantage is gained from the use of large seed. Sowing on a seed number basis, which is beginning to be used to achieve optimum plant populations, will exploit the advantages of large seed.