Manipulation of the availability of assimilates for kernel growth in wheat in Japan: Effects of crop thinning and planting geometry

摘要

Wheat often overproduces kernels when grown in favorable environments, resulting in low kernel weight with high kernel screenings. This indicates that photoassimilation after heading would not be sufficient to support the growth of a large number of kernels. The objective of this study was to examine the effects of crop thinning at heading (experiment 1) and double-row planting (compared with equidistant row spacing; experiment 2) on kernel weight and yield of Japanese wheat cultivars under differentlevels of soil fertility. In experiment 1, elimination of aboveground competition for radiation by thinning increased yield by up to 32%, mainly due to increased kernel weight. In experiment 2, double-row planting increased kernel weight significantly (by 4-10%) without yield loss by moderately suppressing maximum stem number (by 7-14%) and spike and kernel number (by up to 14%) under high fertility. In both experiments, the effect of crop thinning or row configuration on wheat yield and kernel weightwas negligible under low fertility because of little competition for radiation. The results suggested that control of vegetative growth and kernel production would help avoid the shortage of assimilates for kernel growth in fertile environments. For further increasing wheat yield under favorable conditions in Japan, the appropriate crop management options (e.g., planting geometry) should be combined with the suitable varieties having a more communal ideotype (sparse tillering with upright posture) thana competitive phenotype (profuse tillering with lax posture) to enhance photoassimilation after heading.