Grain Size and Seedling Growth of Wheat at Different Ploidy Levels

A study was made of the influence of grain size variation within and between diploid, tetraploid and hexaploid wheat, on a number of seedling growth characters. Differences in grain size within the three ploidy levels appeared to be related to total photosynthetic area and dry weight accretion in the seedling. In the diploids there was a positive correlation between seed size and total photosynthetic area (r = +0·99, P < 0·01) and total dry weight (r = +0·84, P < 0·05) of the seedling at 10 weeks after emergence. In the tetraploid and hexaploids, seed size was negatively correlated with both total photosynthetic area (r = −0·69, P < 0·05 and r = −0·33, P < 0·05 for the tetraploids and hexaploids respectively) and total dry weight (r = −0·69, P < 0·05 and r = −0·59, P < 0·05 for the tetraploids and hexaploids respectively), of the seedlings 10 weeks after emergence. The main physiological distinction between the tetraploids and hexaploids appeared to be the superiority of the hexaploids in rate of leaf appearance and the lower ratio of expanded to unexpanded leaves in the seedling 10 weeks after emergence. The tetraploids, in turn, appeared to be superior to the diploids in these two characters.