Floods are major constraints to crop production worldwide. In low-lying, flood-prone areas of the tropics, longer-term partial submergence (stagnant flooding [SF]) greatly reduces rice yield. This study assesses shoot growth and several physiological mechanisms associated with SF tolerance in rice. Five rice genotypes with contrasting responses to SF were evaluated in field ponds. Following transplanting, floodwater was gradually increased at a rate of ～2 cm day?1 to reach a final depth of 50 cm and then maintained until maturity. Although plants were not fully submerged, the yield was reduced by 47 % across genotypes compared with those grown under control conditions (6.1 vs. 3.3 t ha?1). This reduction was mainly attributed to the reduction in biomass caused by reduced light interception and leaf growth above the water. Stagnant flooding also reduced panicle number per unit area by 52 % because of reduced tillering. Shoot elongation rate kept pace with rising floodwater and correlated positively with leaf growth and biomass production. Conversely, stem non-structural carbohydrate (NSC) concentration correlated negatively with shoot elongation rate, suggesting that fast-elongating genotypes actively consume NSCs to avoid complete submergence. Moderate shoot elongation rate strongly and positively correlated with grain yield under SF; however, elongation at rates 2.0 cm day?1 was associated with reduced harvest index due to a smaller panicle size and increased lodging. Tolerant varieties were found to be either inherently tall or elongate moderately with rising floodwater. Our studies suggest that to improve tolerance of SF an appropriate phenotype should combine both of these traits. Fine-tuning for optimum shoot elongation with rising floodwater is, therefore, a priority for future work.
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机译：洪水是全球农作物生产的主要制约因素。在热带低洼，易发生洪水的地区，长期的部分淹没（停滞洪水[SF]）大大降低了水稻产量。这项研究评估了水稻的苗长和与SF抗性相关的几种生理机制。在田间池塘中评估了五种对SF反应不同的水稻基因型。移栽后，洪水以〜2 cm d ？1 的速率逐渐增加，最终达到50 cm的深度，然后一直保持到成熟。尽管植物没有完全被淹没，但与在对照条件下生长的基因型相比（6.1 vs. 3.3 t ha ？1 ），该基因型的单产降低了47％。该减少主要归因于光拦截的减少和水面上叶片的生长而导致的生物量减少。由于分flood减少，积水也使单位面积的穗数减少了52％。枝条伸长率与洪水增加保持同步，并与叶片生长和生物量产生正相关。相反，茎的非结构性碳水化合物（NSC）浓度与枝条伸长率呈负相关，这表明快速伸长的基因型会主动消耗NSC以避免完全淹没。 SF条件下适度的枝条伸长率与籽粒产量成正相关。然而，由于穗直径较小和倒伏增加，以＞ 2.0 cm day ？1 的速率伸长与收获指数降低有关。人们发现，耐性品种要么较高，要么随着洪水的增加适度地伸长。我们的研究表明，要提高对SF的耐受性，适当的表型应将这两个特征结合起来。因此，随着洪水的增加，微调以最佳地延长芽的生长是未来工作的重点。
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