Study On Resistance And Physiological And Biochemical Mechanism Of Different Rice Varieties To Rice Leaffolder Cnaphalocrocis Medinalis (Güenée) Infestation

In recent years, rice leaffolder Cnaphalocrocis medinalis (Güenée) outbreaks in China have resulted in serious damage to rice. However, causes of the outbreaks not been understood.Therefore, understanding of C. medinalis outbreak mechanisms is of important significance for sustainable control of the pest. This paper reviewed the occurrence and outbreak causes of the pest, and resistance of rice to the pest.The present investigation is to examine physiological and biochemical restance of the several rice varieties commonly cultivated in production to the pest, and the objective is to provide scientific information for breeding of resistant rice variety and sustainable management of the pest and the method of screening of resistant variety according to physiological and biochemical indices of rice plant. Experimental results are as follows:1. Life-table parameters of a semi-natural population of cnaphalocrocis medinalis (Güenée) on different rice varieties and changes in sugar content in rice plants after insect infestationLife-table parameters of C. medinalis on five extended rice varieties, Yangjin 9538, Huidao 9, Yangfujin 8, Yangdao 6, and Shanyou 63, were compared under a semi-natural population,i.e., potted rice plants covered with a big cage (1.5 m length×1 m width×1 m height) under exclusion of natural enemies.These parameters were survival rate,fecundity,and index of population trend(Ⅰ).Experimental results showed that the index of population trend of C. medinalis that fed on Huidao 9 was the lowest among the five varieties, indicating that Huidao 9 was resistant to the insect. That on Yangfujin 8 was the highest. TheⅠvalue for Yangfujin 8 was 3.56 times higher than that for Huidao 9. The survival rate of different developmental stages, ratio of female adults to male adults (♀/♂), pupa weight, number of eggs laid by female adults, and percentage damage of rice leaves varied with rice varieties. In addition, this study measured changes in biochemical substances in rice plants after pest infestation. The result demonstrated that soluble sugar content in plants on which C. medinalis larvae fed was not significantly different for different varieties, but was significantly different compared to control (non-feeding) plants. The reduced sugar content in plants was significantly different among the five varieties.2.Comparison of physiological and biochemical response of different rice varieties to rice leaffolder infestationThe rice leaffolder, C. medinalis(Güenée) infestation has led to serious threat to rice production. Application of rice resistant variety has been demonstrated as one of the most economic and effective management for rice leaffolder population. But resistance and tolerance differentiation of rice varieties to rice leaffolder attack and its physiological and biochemical mechanism has few been investigated, which will hinder the establishing of screening methods and breeding of resistant varieties. Hence, based on five extended rice varieties ( Yangjin 9538, Huidao 9, Yangfujin 8, Yangdao 6, and ningjin 1), measurement of silicon cells and the contents of wax layer for the leaves, the change of physiological and biochemical parameters of leaffolder-infested plants, and probing behaviour of leaffolder on different varieties were carried out. These parameters were chlorophyll content, malondialdehyde (MDA) levels, free proline content and activity of protective and antidotal enzymes.The result demonstrated that observation of silicon cells, the contents of wax layer, chlorophyll content, and activity of protective and antidotal enzymes in ningjin 1 on which C. medinalis larvae fed were significantly higher than other varieties, in contrast, malondialdehyde (MDA) levels was the lowest, indicating that ningjin 1 was resistant to the insect, and percentage damage of rice leaves is the lowest. But on Yangfujin 8 and Yangjin 9538 were the highest. These parameters of rice leaves varied with rice varieties.The findings of this study will be provide scientific information for the screening of leaffolder - resistance and tolerant varieties and realization of leaffolder sustainable management.