Protease inhibitors have been reported to confer insect resistance in transgenic plants, except for a rice protease inhibitor that conferred drought tolerance in transgenic rice plants. We have cloned a protease inhibitor of tobacco that is expressed under treatment with ABA, hydrogen peroxide, methyl jasmonate and wounding. The cDNA codes for a six-domain serine protease inhibitor with a deduced sequence of 396 amino acids. We have generated transgenic tobacco plants expressing the protease inhibitor constitutively under the 35S promoter. When analyzed in the T(2) generation, these transgenic plants exhibited tolerance to sodium chloride, variable pH and sorbitol, together with the expected resistance to the insect pests Spodoptera litura and Helicoverpa armigera. The transgenic plants showed enhanced seed germination, root length and root-shoot ratio, significantly enhanced total chlorophyll content and reduced thiobarbituric acid-reactive substances under stress. Under sodium chloride treatment, the transgenic plants have enhanced protease inhibitor activity. The transgenic plants exhibited a higher potassium content and an optimum Na+/K+ ratio. To our knowledge, this is the first report of transgenic plants with constitutive protease inhibitor expression showing tolerance to a wide range variable pH in the culture medium along with other stresses.

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This study examines aspects of virulence to resistant rice varieties among planthoppers and leafhoppers. Using a series of resistant varieties, brown planthopper, Nilaparvata lugens, virulence was assessed in seedlings and early-tillering plants at seven research centers in South and East Asia. Virulence of the whitebacked planthopper, Sogatella furcifera, in Taiwan and the Philippines was also assessed. Phylogenetic analysis of the varieties using single-nucleotide polymorphisms (SNPs) indicated a clade of highly resistant varieties from South Asia with two further South Asian clades of moderate resistance. Greenhouse bioassays indicated that planthoppers can develop virulence against multiple resistance genes including genes introgressed from wild rice species. Nilaparvata lugens populations from Punjab (India) and the Mekong Delta (Vietnam) were highly virulent to a range of key resistance donors irrespective of variety origin. Sogatella furcifera populations were less virulent to donors than N. lugens; however, several genes for resistance to S. furcifera are now ineffective in East Asia. A clade of International Rice Research Institute (IRRI)-bred varieties and breeding lines, without identified leafhopper-resistance genes, were highly resistant to the green leafhopper, Nephotettix virescens. Routine phenotyping during breeding programs likely maintains high levels of

A series of experiments was set up to examine the effects of nitrogen on rice (Oryza sativa L.) resistance against Nilaparvata lugens (Stål) and Sogatella furcifera (Horváth). Egg laying by N. lugens was reduced on the indica variety IR60. Nymph biomass (N. lugens and S. furcifera) was also lower on IR60: this was associated with low honeydew production and a high proportion of xylem-derived honeydew in N. lugens but not in S. furcifera. Nitrogen increased egg-laying by S. furcifera and increased N. lugens nymph biomass on all varieties tested. Oviposition and egg mortality in both planthopper species were examined on plants at 15, 30 and 45 days after sowing (DAS). Sogatella furcifera laid more eggs on plants at 15 DAS, but laid few eggs during darkness; N. lugens continued to lay eggs on older rice plants (30 DAS) and during darkness. Egg mortality was high on cv. Asiminori, highest at 45 DAS, and higher for S. furcifera than for N. lugens. Mortality of S. furcifera eggs was associated with lesions around the egg clusters. These were more common around clusters laid during the day and suggested induction by Asiminori of an ovicidal response. Egg mortality declined under higher soil nitrogen levels. Results are discussed in the light of improving rice resistance against planthoppers and reducing rates of planthopper adaptation to resistance genes.