Middle portion of the wheat culm remobilizes more carbon reserve to grains under drought

In a semi‐arid climate, heat and drought stress can significantly reduce photosynthesis during grain filling hence, the remobilization of stored carbon reserves from stems becomes important to wheat (Triticum aestivum L.) yield. A 2‐year field study was conducted to better understand the contributions of different internodes to grain yield. We measured remobilization of stored carbon reserves in eight wheat genotypes under irrigated and dryland conditions. For each genotype, plant samples consisting of ten culms were collected between anthesis and physiological maturity. There was no difference in single stem weight loss between two water levels, but the stem loss contribution to yield was higher in dryland wheat (54.4%) than that in irrigated wheat (38.5%). Among the genotypes, the stem loss contribution to yield ranged 38.9%–58.1% in the relatively wet season of 2017 and 36.5%–62.5% in the dry season of 2018. The amount of stem loss showed a strong relationship with grain yield, especially under the dryland condition. At each sampling date, length as well as the dry weight of peduncle (first internode from the top) was greater than the other internodes; however, more stem loss (in weight and percentage weight) occurred in the third internode, followed by second and fourth internodes. Results suggest that the stem loss contribution to yield is greater under dryland than irrigated condition and occurs mainly in the middle portion of the culm.