Physiological and genetic analysis for lodging resistance in rice

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Lodging is a common problem especially in rice (Oryza sativa). It can reduce yield, quality of production, and mechanical harvesting efficiency (Weber and Fehr, 1966 ; Kono, 1995). From the point of view of dynamics, lodging resistance in a plant is determined by two main factors, the weight of the upper part (ears and upper leaves and stems) and the pushing resistance of the lower part (Mulder, 1954). Pushing resistance was used as the index of lodging resistance in maize and rice. We identified a new locus responsible for increased pushing resistance of the lower part of rice (Oryza sativa) and analyzed its physiological function to understand how to improve lodging resistance in rice. Quantitative trait loci (QTLs) controlling pushing resistance of the lower part were analyzed in a population of backcross inbred lines of japonica Nipponbare x indica Kasalath plants cut out at 40 cm to exclude the effect of the weight of the upper parts. Five QTLs for pushing resistance were detected … More ; only one QTL from Kasalath on chromosome 5 (pr15) had a positive effect. The likelihood odds ratio curve of pr15 echoed that for lodging resistance by typhoon. We selected three near-isogenic lines (NILs) in which the chromosomal region of pr15 was substituted with that of Kasalath in the Nipponbare background. The dry weights and densities and the contents of accumulated carbohydrate in stems below 40 cm (lower stems) in each NIL were significantly higher than those of Nipponbare. There was no difference between Nipponbare and the NILs in yield, root characteristics, or the weights of the upper parts. Pushing resistance of the lower part and lodging resistance in the NILs were up to twice as high as in Nipponbare. These results suggest that pr15 might affect the characteristics of the lower stems of the NILs, thus increasing lodging resistance. The results of this study strongly suggest that pushing resistance of the lower part could be a new target for improving lodging resistance in rice. We have shown that pr15 can improve lodging resistance without negative effects on other traits (e.g.yield and plant height); therefore, it might be suitable for introduction into modern rice cultivars. Less