Potential for increasing rate of grain growth in spring wheat. I. Identification of genetic improvements

Abstract

Cultivars that can fill their grain quickly may have an advantage in environments with short, hot, dry grain-filling periods, but this hypothesis needs to be tested by selecting in breeding populations. The rate and duration of grain growth of 13 introductions and three local, standard cultivars were measured in nine environments over 3 years to identify new germplasm with faster grain growth and shorter durations of grain growth. Duration of grain growth was calculated from the cumulative daily average temperatures between anthesis and physiological maturity, and rate of grain growth was calculated from the mean kernel weight and duration. The loss of green colour from the peduncle was used as an indicator of physiological maturity. The aim was to identify parents to use in a subsequent breeding program. Genotypes were identified with improvements in grain growth characters over the standard cultivars. Kansu No. 32, SA 42, NIAB 75-509 and Maya 74 had the fastest rates of grain growth, e.g. 75, 84, 79 and 70 8g/kernel �C day respectively, compared with 64 for Aroona, the best standard cultivar, at sites with short periods of grain growth. Kansu No. 32 developed heavy kernels quickly, and differed from other genotypes in that it had a short duration of grain growth that was consistent regardless of environmental conditions. SA 42, NIAB 75-509 and CEP 8058 also developed grain quickly, with the flexibility to develop grain in a shorter time than the standard cultivars in hot grain-filling conditions, but similar time in favourable conditions. These four genotypes had less kernels/m2 associated with the increased grain growth rate. Yu Mai 7, Maya 74 and V763-251 had smaller increases in rates of grain growth, but only a slight reduction in kernel numbers. Rate of grain growth is more important than duration as a selection criterion to improve kernel weight and grain yield in Western Australian conditions, as duration is influenced to a much greater extent by environment. Growth rate was negatively associated with number of kernels/m2, so these two characters must be considered simultaneously in selection, to ensure grain numbers are maintained while improving rate of grain growth.