Evaluation on drought tolerance in sweet potato and cassava

本研究旨在探讨甘薯和木薯根系发育和可塑性与其耐旱性的关系。在迄今开发或收集的大量遗传资源中，为每个物种选择了几个基因型进行研究。具体而言，我们进行了一系列盆栽和根箱试验，评估了两种植物在不同生长阶段、不同时期和不同程度的高根区温度胁迫和干旱胁迫下的根系发育情况。结果表明：1)高根区温度促进了新梢的生长，总体上抑制了整个根系的发育，但促进了高分枝阶（2、3）侧根的发育；2)两种植物对干旱胁迫都非常敏感，干旱胁迫普遍降低了茎和根的生长。干旱后复水尤其促进了高分枝目侧根的发育；3)不同品种对干旱的反应也存在基因型差异。在干旱条件下，每个物种都有一个维持或促进根系生长的基因型(cv。VSP-2用于甘薯和cv。PSR-74用于木薯)。此外，我们还访问了菲律宾Leyte的4块种植不同甘薯品种的农民田，调查了根系发育和土壤理化状况，验证了盆栽试验的结果。此外，目前正在进行实地试验，以评价其耐旱性，包括田间水分关系和根系发育。为此目的，目前正在建造一个避雨棚。因此，在本研究中，我们展示了根系对土壤胁迫的发育和响应，这是根系作物中研究最少的部分。仍在继续努力完成实验和调查，并整理数据发表。

This study aimed to examine the root system development and plasticity in sweetpotato and cassava in relation to their drought tolerance. Among the huge genetic stock developed or collected so far, several genotypes for each species were selected for this study. Specifically, we have conducted a series of pot and root box experiments to evaluate the root system development in both species under high root-zone temperature stress and drouht stress imposed at different growth stages, for various periods and degrees. Major findings were : 1) high root-zone temperature promoted the shoot growth, while it inhibited the whole root system development in general, but development in the lateral roots of high branching orders (2nd and 3rd) was promoted ; 2) both species were very sensitive to drought stress which generally reduced shoot and root growth. However, rewatering after drought promoted especially the development of lateral roots of high branching orders ; 3) genotypic differences were also noted in the responses to drought. There was a genotype in each species that maintained or increased root growth under drought (cv. VSP-2 for sweetpotato and cv. PSR-74 for cassava). Besides, four farmers' fields in Leyte, Philippines, planted with different sweetpotato varieties were visited, in which we surveyed the root system development and soil physical and chemical conditions so that the results of the pot experiments be verified. In addition, field experiments are now being attempted to evaluate the drought tolerance including water relations and the root system development in the field. For the purpose, a rain shelter is being constructed at the moment. As such, in this study, we showed the development and responses of the root system to the soil stresses which are the least-studied part of the root crops. Efforts still continue to complete the experiments and survey, and organize the data for publication.