CULTIVAR AND ENVIRONMENTAL-EFFECTS ON QUALITY CHARACTERS IN WHEAT - I- STARCH

The composition of starch in wheat is an important determinant of grai n quality, especially for white-salted noodles. Starch consists of 2 t ypes of polymer, amylose and amylopectin, and occurs in predominantly larger A-type and smaller B-type granules. High starch pasting peak vi scosity is desirable for white-salted noodles, and is influenced by th e waxy genes coding for granule-bound-starch synthase (GBSS), which ar e involved in the synthesis of amylose. To study cultivar and environm ental 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 temperatu re during grain filling. These cultivars varied in grain hardness clas sification and for the presence of GBSS coded by the Wx-B1 locus. Cult ivars null for Wx-B1 GBSS had higher pasting viscosity than those with Wx-B1 GBSS, verifying the null. requirement for cultivars suitable fo r white-salted noodles. However, the relationship between amylose conc entration and pasting viscosity was complex, indicating that Wx-B1 inf luences pasting viscosity beyond its influence on the proportion of am ylose and amylopectin. Environments with a high level of accumulated t emperatures above 30 degrees C during the first 14 days after anthesis produced grain with a high proportion of A-type granules, even when i rrigated. The proportion of amylose also increased with increasing acc umulation of temperatures above 30 degrees C during the first 14 days, but was not influenced by temperature to the same extent as granule t ype. Environmental variation in pasting peak viscosity was large, but not related to high temperature. The hardness of grain was related to accumulated temperatures above 30 degrees C during the second 14 days after anthesis, with the increase in hardness much greater in soft-gra ined than hard-grained cultivars.