A Review on the Hyper-Susceptibility of Chinese Hybrid Rice to Insect Pests

Highly susceptible Chinese hybrid rice gave significant impact on the insect pest ecology. The brown planthopper (BPH), Nilaparvata lugens, and the whitebacked planthopper (WBPH), Sogatella furcifera, have raised as the most prominent outbreak-prone pests of Chinese hybrid rice. Although WBPH was only a secondary insect pest of rice in China before 1970s, it increased greatly in the hybrid rice areas in 1980s. WBPH also became an economic insect pest of japonica rice in Central China due to its massive displacement from hybrid rice area in South China. BPH was temporally suppressed by the hybrid rice with the Bph 1 gene for BPH-resistance. However, the BPH adapted to them by shifting biotype, when the resistant hybrid rice spread over the insect migration zone in South- and Central China. After 1990, previously BPH-resistant hybrid rice became highly susceptible to BPH. Lack of major genes for resistance does not account enough for the hyper- susceptibility of Chinese hybrid rice to the planthoppers. Heterotic vigorous growth of hybrid rice might be partially responsible for the enhanced fecundity of the planthoppers. Hyper-susceptibility of Chinese hybrid rice to the rice planthoppers is primarily inherited from the WA-CMS lines. Thus, CMS lines are needed to improve insect pest resistance in hybrid rice. Utilization of durable and multi-resistant IR varieties like IR64 as restorer lines might be an alternative approach to improve hyper-susceptibility of Chinese hybrid rice to insect pests.The striped stemborer, Chilo suppressalis and the yellow stemborer, Scirpophage incertulas also increased on Chinese hybrid rice, which is more favorable as their food plants and more tolerant to their infestations than inbred rice. Yield loss assessments, with special reference to the plant compensation to the stemborer infestation, and ecological interactions between stemborers and hybrid rice are needed to evaluate actual impact of and practical field resistance to stemborers in hybrid rice.