Components of Yield in Diploid, Tetraploid and Hexaploid Wheats (Triticum spp.)

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Abstract
Twenty-nine accessions of Triticum including ancestral diploids and primitive and modern tetraploid and hexaploid froms were examined for differences in yield components. Mean whole plant and main shoot harvest index for the ploidy groups exhibited significant (P < 0·01) increascs from the diploids to the tetraploids and from the tetraploids to the hexaploids. Mean biological yield per plant for the ploidy groups increased significantly (P < 0·01) from the diploid to the hexaploid but declined significantly (P < 0·01) from the tetraploid to the hexaploid level. There were marked reductions in shoot number and percentage of infertile shoots per plant and increases in grain number per spikelet and grain size from diploid what (Triticum monococcum) to the early tetraploids. Yield component variation in early and recent Australian wheats revealed that the semi-dwarf (gibberellininsensitive) wheats were significantly higher in whole plant and main shoot harvest index over normal height (gibberellin-sensitive) wheats.