Current utility of the BPH25 and BPH26 genes and possibilities for further resistance against plant- and leafhoppers from the donor cultivar ADR52

This study examines the resistance of recently developed near-isogenic rice lines (NILs) with BPH25 and BPH26 genes and the resistance donor cultivar ADR52 against Philippine populations of the brown planthopper, Nilaparvata lugens (Stål). Monogenic and pyramided lines with BPH25 and BPH26 were largely ineffective against the planthopper in a series of laboratory bioassays. In previous studies, BPH25 and a pyramided BPH25 + 26-NIL had been effective in reducing the fitness of N. lugens collected in Mindanao (Philippines); however, the virulence of the planthopper appears to have developed recently in Mindanao so the NILs are now ineffective. ADR52 showed marginal resistance against N. lugens, was more generally resistant against the white-backed planthopper, Sogatella furcifera (Horváth), and had strong resistance against the green leafhopper, Nephotettix virescens (Distant). Resistance against the latter two species was not derived from either BPH25 or BPH26, indicating that the cultivar possesses other resistance genes. For all three insect species, egg laying was constant on ADR52 as the plants aged; however, resistance against nymphs of all three insects increased as ADR52 aged. ADR52 had generally high tolerance against all three insects, which increased under high nitrogen conditions. The results of this study indicate ADR52 is a potential source of further resistance genes against leafhoppers and planthoppers. However, the results also indicate the need to carefully manage resistance genes to avoid adaptation by target insects as has occurred with BPH25 and BPH26.