Performance of Near‐Isogenic Genotypes of Rice Differing in Growth Duration. II. Carbohydrate Partitioning During Grain Filling1

Abstract

The distribution of non‐structural carbohydrates during grain filling was compared for a near‐isogenic pair of rice (Oryza sativa L.) genotypes that differed by 18 days in their vegetative growth duration. The objective was to determine the effect of the longer vegetative growth period on the production of assimilates that would later be remobillzed and used in grain filling. The percentage of total sugars in all measured vegetative plant parts declined after 17 days of grain filling of EDT, the earlier genotype. Sugar percentages did not decline from heading to full maturity for ‘Calrose 76,’ the later genotype. Starch percentage at the start of grain filling was greater for Calrose 76 than for EDT. At maturity, Calrose 76 had 33.6, 12.5, and 2.3% starch, respectively, in the third internode, second internode and sheath, and first internode and sheath. At maturity, ED7 was essentially devoid of starch in these same plant parts. Calrose 76 also used some of the vegetatively stored starch during grain filling. The apparent contribution of preheading stored nonstructural carbohydrates to grain filling of the two genotypes was about the same for the early sown (11 May) comparison. The same comparison for the later sown (21 May) trial showed ED7 with 15.6% and Calrose 76 only 6% apparent contribution to grain filling. Increased rates of N fertilizer enhanced the apparent contribution to grain filling of both genotypes sown early but not for the later sown trial. Daily rates of starch accumulation in the panicles averaged for the two genotypes began to decline by the 17th day after heading. The daily rates of sugar accumulation were nearly the reciprocal of daily rates of starch accumulation in the panicle. In an environment of full sun and warm days during grain filling, cultivars with longer growth periods probably can support larger panicles than those with shorter growth periods.