Abstract
Drought is one of the major factors limiting rice yield worldwide. A total of 46 hybrid rice varieties were chosen to investigate their root distribution and their response to drought. A field experiment was carried out in a dry shed building to evaluate the drought tolerance capacity of hybrid rice varieties on the basis of CTIRDE (complex tolerance index of rice under drought environment) values. Next, the experiment was conducted in a specially designed pot system and seed bags to analyze the root distribution and activity of antioxidant enzymes in different rice varieties. Moreover, the DEEPER ROOTING 1 (DRO1) gene was sequenced to elucidate its role in the root distribution of typical rice varieties. On the basis of CTIRDE values, the 46 hybrid rice varieties were classified as tolerant (CTIRDE ≥ 0.75), semi-tolerant (0.75 > CTIRDE > 0.65), or sensitive (CTIRDE ≤ 0.65) to drought stress. The tolerant varieties (Chuanguyou208 and Deyou4727) displayed a significantly larger length, had higher number and weight of roots in the 30–50 cm soil layer, and exhibited a significantly higher activity of Superoxide dismutase (SOD) and Peroxidase (POD) enzymes in roots during the drought stress period. The DRO1 gene sequencing results revealed that the tolerant and sensitive varieties exhibited a single-nucleotide polymorphism (SNP) in the 3-exon region, and the tolerant varieties (Chuanguyou208 and Deyou4727) exhibited a larger root growth angle with the horizontal axis, hence developing a deeper root system as compared with the other two group varieties. A significant correlation was found not only between the DRO1 gene and root distribution but also between DRO1 and the activity of SOD and POD enzymes. Conclusively, as a key feature, a deep root system enabled tolerant rice varieties (Chuanguyou208 and Deyou4727) to avoid drought stress by absorbing more water stored in deep soil layers. The root distribution, activity of POD and SOD enzymes in roots, and DRO1 gene can be used to screen tolerant rice varieties that can survive better under drought stress during the seedling stage of rice growth.
Highlights
As one of the serious stress factors for rice growth, drought has caused a 25.4% reduction in rice yield over the last 20 years [1]
When rice is exposed to drought stress, it shows a reduction in plant height, wilting, leaf rolling, leaf senescence, stomatal closure, decreased leaf elongation, and lower dry matter production [6,7,8,9]
These findings indicated that the DEEPER ROOTING 1 (DRO1) gene has a sound correlation with the root distribution, with deep root distribution
Summary
As one of the serious stress factors for rice growth, drought has caused a 25.4% reduction in rice yield over the last 20 years [1]. When rice is exposed to drought stress, it shows a reduction in plant height, wilting, leaf rolling, leaf senescence, stomatal closure, decreased leaf elongation, and lower dry matter production [6,7,8,9]. These variations differ significantly among different rice varieties [6,7,10,11]; it is difficult to identify resistant rice varieties by any one of these agronomic traits
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