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Rice (Oryza sativa L.) is highly sensitive to cold stress, which leads to large reductions in rice yield at the booting stage. In this study, Kongyu131 and Kenjiandao6 rice cultivars with different levels of cold stress sensitivity were sprayed with diethylaminoethyl hexanoate (DA-6) concentrations of 500, 200, 20, 2, 0.2, and 0 mg/L one day before undergoing cold water stress (CWS). We analyzed changes in yield and its factors, dry matter production, stem characteristics, and physiological and biochemical characteristics of the rice plants. The results showed that DA-6 increased peroxidase activity, delayed nitrogen and chlorophyll degradation, maintained soluble protein and potassium contents, and suppressed the accumulation of malondialdehyde in the leaves of both cultivars under CWS. DA-6 also increased the phosphorous content and superoxide dismutase activity in Kenjiandao6 under CWS; however, in Kongyu131, DA-6 increased the soluble sugar content. In addition, DA-6 treatment increased the weight of the panicle at maturity, and of the leaf, panicle, and stem-sheath at heading in both cultivars. The lengths of the panicle, the top first internode, the export rate of stem-sheath, translocation rate of stem-sheath, and export of stem-sheath from heading to maturity were increased in Kenjiandao6; however, in Kongyu131, DA-6 increased the dry weight ratio of panicle to total plant and reduced the dry weight ratio of stem-sheath to total plant at maturity. Furthermore, DA-6 improved yield in both cultivars, mainly by increasing the grain weight in the inferior grains (IG) and middle grains (MG) under CWS. DA-6 increased the grain weight in the IG and MG in Kenjiandao6 mainly by enhancing the seed setting rate and number of filled grains (NFG) in the IG and MG, and in Kongyu131 by improving the NFG in MG and IG. The optimal concentration of DA-6 to alleviate CWS was 2 mg/L. In conclusion, exogenous DA-6 was effective for maintaining dry matter production and physiology in two early japonica rice cultivars under CWS at booting, thereby improving cold tolerance and enhancing yield. The less cold-tolerant cultivar Kenjiandao6 was more sensitive to the effects of DA-6 and displayed better results than the more cold-tolerant cultivar Kongyu131. [ABSTRACT FROM AUTHOR]

Rice (Oryza sativa L.) plants are most sensitive to chilling injury at booting, where cold affects a substantial decline in the seed‐setting rate (SSR). 6‐Benzyladenine (6‐BA) alleviates cold stress in seedlings; however, little is known about the effects of 6‐BA on alleviating cold stress at booting. Plants of early japonica rice cultivars Kenjiandao6 (K6) and Kongyu131 (K131) were sprayed with 6‐BA at concentrations of 0, 0.2, 2, 20, 200, and 500 mg L−1 at booting and were then subjected to cold water stress (16 °C) for 5 d. The optimal 6‐BA concentration was found to be 20 mg L−1. 6‐Benzyladenine treatment improved the peroxidase (POD) activity in two cultivars and superoxide dismutase activity in K6, delayed chlorophyll degradation, maintained the K, P, and N contents in the two cultivars and the soluble protein content in K6, and suppressed the accumulation of malondialdehyde (MDA) under cold stress. 6‐Benzyladenine increased the N and P contents and POD activity to greater degree in K6 than in K131. 6‐Benzyladenine increased yield in K131, mainly by improving the SSR in the distal and middle parts of the panicle, and the number of filled grains (NFG) from the middle and basal parts of the panicle. However, 6‐BA increased yield in K6 mainly by improving the SSR and the NFG per panicle. Exogenous 6‐BA is effective for maintaining rice physiology and yield under cold stress at booting. The less cold‐tolerant cultivar K6 was more sensitive to the effects of 6‐BA and displayed better results than did the more cold‐tolerant cultivar K131. Core Ideas: The optimal 6‐benzyladenine concentration was found to be 20 mg L−1 under cold stress in early japonica rice at booting.6‐Benzyladenine at 20 mg L−1 effectively reduced the physiological and metabolic damage in rice due to cold stress at booting.6‐Benzyladenine increased the cold resistance of 'Kongyu131' mainly by improving the peroxidase activity, chlorophyll, N, P, and K contents.6‐Benzyladenine enhanced a resistance of 'Kenjiandao6' mainly by improving superoxide dismutase and peroxidase activities, soluble protein, chlorophyll, N, P, and K content.The effect of 6‐benzyladenine was higher in the less cold tolerant variety Kenjiandao6 than in Kongyu131 under cold stress. [ABSTRACT FROM AUTHOR]