High temperatures are a major concern that limit rice germination and plant growth. Although previous studies found that melatonin can promote seed germination, the physiological regulation mechanism by which exogenous melatonin mediates high temperature tolerance during rice seed germination is still largely unknown. In order to overcome these challenges, the present study investigates the effects of melatonin on the characteristics of rice seed germination as well as on antioxidant properties, under different high temperature conditions. The results show that 100 μM melatonin seed-soaking treatment under high temperature conditions effectively improves the germination potential, the germination index, and the vigor index of rice seeds; increases the length of the shoot and the root; improves the activity of the antioxidant enzymes; and significantly reduces the malondialdehyde content. The gray relational grade of the shoot peroxidase activity and the melatonin soaking treatment was the highest, which was used to evaluate the effect of melatonin on the heat tolerance of rice. The subordinate function method was used to comprehensively evaluate the tolerance, and the results show that the critical concentration of melatonin is 100 μM, and the critical interactive treatment is the germination at 38 °C and followed by the recovery at 26 °C for 1 day + 100 μM. In conclusion, 100 μM of melatonin concentration improved the heat resistance of rice seeds by enhancing the activity of the antioxidant enzymes.

The lodging resistance of rice is a prerequisite for ensuring yield and rice quality. An in-depth analysis of key traits affecting rice lodging resistance is crucial for guiding the cultivation of excellent rice varieties and field production. Given consumer demand for high-quality rice and frequent extreme weather conditions, this study focused on six high-quality conventional rice varieties and compared the main stem internode physical traits, stem and sheath plumpness traits, main stem mechanical properties, yield-related traits, and panicle characteristics of the plants based on field phenotype measurements. Among them, three varieties showed lodging resistance in the field, while the other three varieties all experienced varying degrees of lodging susceptibility. The results showed that lodging-resistant varieties exhibited a more reasonable internode structure, lower plant height, gravity center height, and relative gravity center height, as well as shorter and thicker second internodes (N2). Additionally, they had higher sheath phimosis degree, greater bending stress, internode-breaking moment, and plant-breaking moment, along with a lower lodging index compared to lodging-susceptible varieties. Specifically, lodging-resistant varieties had 0.83–9.61% lower plant height, 4.11–16.10% lower gravity center height, and 0.09–12.68% lower relative gravity center height than those of lodging-susceptible varieties. Their N2 internode length was 8.96–44.69% shorter, while stem and sheath weight ratios were 16.37–268.58% and 8.27–165.01% higher than those of lodging-susceptible varieties, respectively. At the same time, lodging-resistant varieties exhibit the ability to stabilize yield while reducing their own risk of lodging by increasing effective panicles and reducing single panicle weight. In addition, NX42, LD3, and SY17 were ultimately evaluated as low-risk lodging varieties in this study. This study aims to address the lodging problem of high-quality conventional rice and analyze the key mechanisms underlying its lodging resistance. The research provides important theoretical support for genetic improvement of high-quality conventional rice.

The aim of this study was to investigate the impact of soil thickness on seedling growth in rice machine transplanting. Zhongzu 53 was selected as the test variety, and three different soil thickness treatments were applied: 0 cm (CK), 0.5 cm (T1), and 1 cm (T2). The emergence rate, plant height, root length, leaf age, number of green leaves, total root length, projected area, root surface area, and total root volume were measured. The results demonstrated that, compared with the CK treatment, the seedling emergence rate of the T1 treatment increased significantly by 68.6%, while no significant difference was observed in the emergence rate between the T1 and T2 treatments. The plant height, root length, and leaf age of the T1 treatment were significantly higher than those of both the CK and T2 treatments. In terms of root morphological indicators, the total root length, total root projected area, and number of root tips in the T1 treatment were significantly greater than those in the CK and T2 treatments. Correlation analysis revealed that the seedling emergence rate was extremely significantly positively correlated with the total root number (p < 0.01) and significantly positively correlated with the number of white roots, number of root tips, and total root length (p < 0.05). Grey correlation analysis indicated that the total root number had the highest correlation degree with the seedling emergence rate. Principal component analysis (PCA) results showed that the cumulative contribution rate of PCA1 and PCA2 reached 67.5%. Membership function analysis revealed that the T1 treatment had the highest average membership value, whereas the CK treatment exhibited the poorest performance. In conclusion, an appropriate cover soil thickness can effectively improve the growth performance of mechanically transplanted rice seedlings.