Effect of plant age, larval age, and fertilizer treatment on resistance ofa cry1Ab-transformed aromatic rice to lepidopterous stem borers and foliage feeders

The resistance of vegetative, booting, and flowering stage plants of a vari ety of an aromatic rice, Oryza sativa L., transformed with a Bacillus thuri ngiensis Berliner cry1Ab gene under control of the maize phosphoenolpyruvat e carboxylase (PEPC) promoter was evaluated against four lepidopterous lice pests-the stem borers Chilo suppressalis (Walker) (Lepidoptera: Crambidae) and Scirpophaga incertulas (Walker) (Lepidoptera: Pyralidae), and the foli age feeders Cnaphalocrocis medinalis Guenee (Lepidoptera: Pyralidae) and Na ranga aenescens Moore (Lepidoptera: Noctuidae). Plants of the cry1Ab-transf ormed line (no. 827) were more resistant to young, larvae of S. incertulas. C. suppressalis, and C. medinalis than control plants at the vegetative st age but not at the flowering stage. Survival of 10-d-old stem borer larvae did not differ on cry1Ab plants and control plants at either the vegetative or flowering stage, but the development of 10-d-old C. suppressalis larvae was retarded on the vegetative stage cry1Ab plants. Immunological analysis also showed an apparent decline in Cry1Ab titer in leaf blades and leaf sh eaths at the reproductive stage. In experiments comparing three fertilizer treatments (NPK, PK, and none), there was a significant interaction between fertilizer treatment and variety on larval survival only in whole-plant as says at booting stage with C. suppressalis. On cry1Ab plants, larval surviv al did not differ significantly among the three fertilizer levels, whereas on control plants survival was highest with the NPK treatment. cry1Ab plant s tested at the sixth and seventh generations after transformation were mor e resistant than control plants to N. aenescens and C, suppressalis, respec tively, suggesting that gene silencing will not occur in line 827. The resu lts of the experiments are discussed in terms of resistance management for B. thuringiensis toxins in rice.