Besides genetic improvement for developing stress-tolerant cultivars, agronomic management may also add considerable tolerance against different abiotic stresses in crop plants. In the present study, we evaluated the effect of six different spacing treatments (S1: 10 × 10 cm; S2: 15 × 10 cm; S3:15 × 15 cm; S4:20 × 10 cm; S5: 20 × 15 cm; S6: 20 × 20 cm (row-row × plant-plant)) for improving submergence tolerance in rice. A high yielding submergence intolerant rice cultivar IR64 was tested against its SUB1 QTL introgressed counterpart (IR64-Sub1) for 12 days of complete submergence for different spacing treatments in field tanks. Relatively wider spaced plants showed higher individual plant biomass and early seedling vigour, which was particularly helpful for IR64 in increasing plant survival (by 150% in S6 over S1) under 12 days of submergence, whereas the improvement was less in IR64-Sub1 (13%). Underwater radiation inside the plant canopy, particularly beyond 40 cm water depth, was significantly greater in wider spacing treatments. Leaf senescence pattern captured by SPAD chlorophyll meter reading and chlorophyll fluorescence imaging data (Fm, Fv/Fm) taken at different time intervals after stress imposition suggested that there was lesser light penetration inside the canopy of closer spaced plants, and that it might hasten leaf senescence and damage to the photosynthetic system. The initial content of total non-structural carbohydrate (NSC) was higher in wider spaced plants of IR64, and also the rate of depletion of NSC was lesser compared with closer spaced plants. In contrast, there was not much difference in NSC depletion rate under different spacing in IR64-Sub1. Further, higher antioxidant enzyme activities in wider spaced plants (both IR64 and IR64-Sub1) after de-submergence indicated better stress recovery and improved tolerance. Taken together we found that wider spacing (row-row: 20 cm and plant-plant: 15 cm and more) can significantly improve submergence tolerance ability in rice, particularly in submergence intolerant non-Sub1 cultivar like IR64, perhaps due to better underwater light penetration, delayed leaf senescence and slower depletion of NSC reserve.

中文翻译：

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株距的改变通过更好的光拦截和胁迫下的有效碳水化合物利用提高了 Sub1 和非 Sub1 水稻（cv. IR64）的耐淹性

除了开发抗逆品种的遗传改良外，农艺管理还可以增加作物对不同非生物胁迫的相当大的耐受性。在本研究中，我们评估了六种不同间距处理的效果（S1：10 × 10 cm；S2：15 × 10 cm；S3：15 × 15 cm；S4：20 × 10 cm；S5：20 × 15 cm； S6: 20 × 20 cm (row-row × plant-plant)) 用于提高水稻的耐淹性。在田间水箱中针对不同间距处理的 SUB1 QTL 渐渗对应物 (IR64-Sub1) 对高产不耐淹水稻品种 IR64 进行了 12 天的完全淹水测试。间距相对较宽的植物表现出更高的个体植物生物量和早期幼苗活力，这对于 IR64 在 12 天淹没下提高植物存活率（S6 比 S1 提高 150%）特别有帮助，而 IR64-Sub1 (13%) 的改善较少。植物冠层内的水下辐射，特别是超过 40 厘米水深，在更宽的间距处理中明显更大。SPAD 叶绿素计读数和叶绿素荧光成像数据（Fm，Fv/Fm）在胁迫施加后不同时间间隔拍摄的叶片衰老模式表明，距离较近的植物冠层内的光穿透较少，可能会加速叶片光合系统的衰老和损害。与间隔较近的植物相比，IR64 间隔较宽的植物中总非结构碳水化合物（NSC）的初始含量较高，NSC 的消耗率也较小。相比之下，IR64-Sub1中不同间距下的NSC消耗率没有太大差异。更远，去淹没后更宽间距植物（IR64和IR64-Sub1）中更高的抗氧化酶活性表明更好的胁迫恢复和更高的耐受性。综上所述，我们发现更宽的间距（行-行：20 厘米，植物-植物：15 厘米及以上）可以显着提高水稻的耐淹能力，特别是在不耐淹的非 Sub1 品种（如 IR64）中，这可能是由于更好的水下光照渗透、延迟叶片衰老和较慢的 NSC 储备消耗。