Lafitte H R, Yongsheng Guan, Yan Shi, Li Z-K
International Rice Research Institute, Los Baños, Philippines.
J Exp Bot. 2007;58(2):169-75. doi: 10.1093/jxb/erl101. Epub 2006 Sep 22.
Most high-yielding rice cultivars developed for irrigated conditions, including the widely grown lowland variety IR64, are highly susceptible to drought stress. This limits their adoption in rainfed rice environments where there is a risk of water shortage during the growing season. Mapping studies using lowland-by-upland rice populations have provided limited information about the genetic basis of variation in yield under drought. One approach to simultaneously improve and understand rice drought tolerance is to generate backcross populations, select superior lines in managed stress environments, and then evaluate which features of the selected lines differ from the recurrent parent. This approach was been taken with IR64, using a range of tolerant and susceptible cultivars as donor parents. Yields of the selected lines measured across 13 widely contracting water environments were generally greater than IR64, but genotype-by-environment effects were large. Traits expected to vary between IR64 and selected lines are plant height, because many donors were not semi-dwarf types, and maturity, because selection in a terminal stress environment is expected to favour earliness. In these experiments it was found that some lines that performed better under upland drought were indeed taller than IR64, but that shorter lines with good yield under drought could also be identified. In trials where drought stress developed in previously flooded (lowland) fields, height was not associated with performance. There was little change in maturity with selection. Other notable differences between IR64 and the selected backcross lines were in their responses to applied ABA and ethylene in greenhouse experiments at the vegetative stage and in leaf rolling observed under chronic upland stress in the field. These observations are consistent with the hypothesis that adaptive responses to drought can effectively allow for improved performance across a broad range of water environments. The results indicate that the yield of IR64 under drought can be significantly improved by backcrossing with selection under stress. In target environments where drought is infrequent but significant in certain years, improved IR64 with greater drought tolerance would be a valuable option for farmers.
大多数为灌溉条件培育的高产水稻品种，包括广泛种植的低地品种IR64，对干旱胁迫高度敏感。这限制了它们在雨养水稻环境中的应用，因为在生长季节存在缺水风险。利用低地与高地水稻群体进行的图谱研究，提供了关于干旱条件下产量变异遗传基础的有限信息。一种同时提高和理解水稻耐旱性的方法是构建回交群体，在可控胁迫环境中选择优良品系，然后评估所选品系的哪些特征与轮回亲本不同。已针对IR64采用了这种方法，使用一系列耐旱和敏感品种作为供体亲本。在13个广泛的水分条件变化环境中测量的所选品系产量通常高于IR64，但基因型与环境的互作效应很大。预计IR64与所选品系之间会有所不同的性状包括株高，因为许多供体不是半矮秆类型；还有成熟度，因为在终端胁迫环境中的选择预计会有利于早熟。在这些实验中发现，一些在旱地干旱条件下表现较好的品系确实比IR64高，但也能鉴定出在干旱条件下产量良好的矮秆品系。在先前淹水（低地）田块出现干旱胁迫的试验中，株高与表现无关。选择后成熟度变化不大。IR64与所选回交品系之间的其他显著差异在于，在营养生长阶段的温室实验中它们对施加的脱落酸和乙烯的反应，以及在田间长期旱地胁迫下观察到的叶片卷曲情况。这些观察结果与以下假设一致，即对干旱的适应性反应能够有效地在广泛的水分环境中实现性能提升。结果表明，通过在胁迫下进行回交选择，IR64在干旱条件下的产量可得到显著提高。在干旱不常发生但在某些年份影响显著的目标环境中，耐旱性更强的改良IR64对农民来说将是一个有价值的选择。
