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Direct seeding of rice has become a main planting method due to the low labor input and high economic benefit in South China. Dry direct seeding (DDS) has been widely used for single-season rice planting establishment. However, few studies have examined the performance of early-season indicarice under mechanical dry direct seeding. A two-year field experiment was conducted with two indicarice cultivars (i.e., Zhongjiazao 17 and Zhuliangyou 819) to study lodging characteristics and grain yield formation under DDS, flooded direct seeding (FDS) and wet direct seeding (WDS) patterns. The results showed that the annual grain yield in DDS was higher by 14.42–26.34% for cultivar ZLY819 and 6.64–24.58% for cultivar ZJZ17 than in WDS and FDS, respectively, and these increases were mainly attributed to the improvement of the panicles. The DDS pattern significantly increased the seedling emergence rate of early indicarice cultivars, and increased total dry weight and crop growth rate. Meanwhile, shorter basal internodes, better stem diameter and stem wall thickness and lower lodging index were found in DDS in contrast to FDS and WDS. In particular, DDS improved the stem lodging resistance. Our results suggested that the appropriate direct seeding method was beneficial for improving the grain yield and lodging resistance of early indicarice.

Xanthine dehydrogenase (XDH) is a crucial enzyme involved in purine metabolism. To evaluate the effect of XDH deficiency on rice growth during dark treatment, wild type (WT) Nipponbare (Oryza sativaL.) and two independent transgenic lines with severe RNAi suppression (xdh3and xdh4) were used in the present experiment. Under normal growth conditions, chlorophyll levels and biomass were indistinguishable between WT and the two RNAi transgenic lines, but XDH enzyme activity and ureide levels were suppressed in XDHRNAi transgenic lines. When XDHRNAi transgenic lines were subjected to dark treatment, chlorophyll content and biomass were significantly decreased, while O2–· production rate and malonaldehyde (MDA) were significantly increased compared to WT. The spraying test of exogenous allantoin raised chlorophyll content and biomass and reduced O2–· production rate and MDA in WT and both transgenic lines, and it also simultaneously reduced differences between RNAi and WT plants caused by XDH deficiency in growth potential and anti-oxidative capacity under dark treatment. These results suggested that fully functional purine metabolism plays an important role in reducing the sensitivity of rice seedlings to dark stress.