Integrating gene deployment and crop management for improved rice resistance to Asian planthoppers

This review examines the effects of crop management on the efficiency and durability of planthopper resistant rice in Asia. Historical evidence and selection experiments indicate that the proportion of virulent individuals in planthopper populations is normally sufficiently high for populations to overcome major resistance genes within 12-15 generations. Pyramiding resistance may prolong durability, but will depend on avoiding concurrent deployment of monogenic and pyramided lines that share resistance genes, and on the capacity of planthoppers to maintain virulence to >= 2 genes. Combining major genes with quantitative resistance will increase durability. Planthopper population size is likely to be the main contributor to virulence adaptation during the early stages of varietal adoption. High fertilizer inputs increase the availability of soluble proteins, thereby increasing rice susceptibility to planthoppers. Resurgence insecticides can directly increase host plant susceptibility, increase planthopper fecundity, and/or deplete natural enemy abundance, leading to rapid increases in planthopper densities. Nevertheless, comparative experiments indicate that the relative fitness of planthoppers on resistant and susceptible varieties is often maintained across gradients of fertilizer and insecticide applications. However, densities of planthoppers will increase in response to high inputs thereby enhancing the potential for populations to overcome resistance. Avoiding excessive fertilizer applications and resurgence insecticides, rotating rice varieties, increasing rice genetic diversity in the landscape, and maintaining generalist natural enemies will slow planthopper population growth, enhance resistance and has the potential to prolong durability. Because insecticides reduce the profitability of using resistant varieties, host plant resistance must be accompanied by a concomitant decline in insecticide use if it is to achieve its goals as an efficient, economic and environmentally friendly pest management option.