Physiological Basis of Genetic Differences in the Growth of Grains of Six Varieties of Wheat

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Abstract
The physiological basis of genetic variation in rate of accumulation of dry matter (growth) in wheat grain has been investigated by culturing ears of six different varieties on solutions of sucrose. Differences between varieties in accumulation of dry matter in the cultured ears were similar to those for grains growing in the field. Intracellular concentration of sucrose was positively correlated with increases in dry matter in treatments within varieties, but was not related to differences between varieties. In comparisons between varieties, high intracellular levels of sucrose were more often associated with low rates of accumulation of dry matter than with high rates. It is concluded that, within the varieties investigated here, genetic variation in the rate of deposition of dry matter in the endosperm is not attributable to variation in supply of assimilate to the grain. No single or simple parameter of the growth of the grain at anthesis, or in the succeeding 2 weeks, was related to the grain's subsequent rate of growth. The weight of ethanol-insoluble material in the endosperm itself at day 19 was not indicative of the amounts of this fraction deposited in the endosperm in the week that followed day 19. Significant variation between the varieties was observed in the relationship (viz. the slope) between the intracellular amounts of sucrose and the rate of accumulation of ethanol-insoluble dry matter (mostly starch), a relationship which is presumed to reflect kinetic properties of the process(es) converting sucrose to starch. In the six varieties investigated, all the observed differences in grain growth rate could be attributed to variation in the slope defined above, and/or in day 19 endosperm dry matter. It is suggested that these two parameters reflect two independent physiological determinants, accounting for much of the genetic variation in the rate of growth of wheat grain.