Cultivar and environmental effects on quality characters in wheat. I. Starch

Abstract

The composition of starch in wheat is an important determinant of grain quality, especially for white-salted noodles. Starch consists of 2 types of polymer, amylose and amylopectin, and occurs in predominantly larger A-type and smaller B-type granules. High starch pasting peak viscosity is desirable for white-salted noodles, and is influenced by the waxy genes coding for granule-bound-starch synthase (GBSS), which are involved in the synthesis of amylose. To study cultivar and environmental effects on the proportion of A-type granules, the proportion of amylose in starch, starch pasting peak viscosity, and grain hardness, 7 cultivars were grown in 15 environments which differed for temperature during grain filling. These cultivars varied in grain hardness classification and for the presence of GBSS coded by the Wx-B1 locus. Cultivars null for Wx-B1 GBSS had higher pasting viscosity than those with Wx-B1 GBSS, verifying the null requirement for cultivars suitable for white-salted noodles. However, the relationship between amylose concentration and pasting viscosity was complex, indicating that Wx-B1 influences pasting viscosity beyond its influence on the proportion of amylose and amylopectin. Environments with a high level of accumulated temperatures above 30ºC during the first 14 days after anthesis produced grain with a high proportion of A-type granules, even when irrigated. The proportion of amylose also increased with increasing accumulation of temperatures above 30ºC during the first 14 days, but was not influenced by temperature to the same extent as granule type. Environmental variation in pasting peak viscosity was large, but not related to high temperature. The hardness of grain was related to accumulated temperatures above 30ºC during the second 14 days after anthesis, with the increase in hardness much greater in soft-grained than hard-grained cultivars.