Interaction of acid exudates in chickpea with biological activity or cry toxins from Bacillus thuritgiensis berliner against Helicoverpa armigera (hubner)

The H armigera egg and larval numbers before and after sprays of B. rhuringiensis (Bt) formulation ~iole~w'e re low on the chickpea genotypes ICC 506 and ICCV 10 across BI concentrations as compared to those on L 550 and C 235 during vegetative and flowering stages. Leaf feeding and pod damage were lowest on ICC 506, followed by ICCV 10 across Bt concentrations as compared to that on L 550 and C 235. During the 2005-06 post-rainy season and first planting during the 2006-07 post-rainy season, highest grain yield was recorded in case of ICCV 10. In the second planting, the genotypes ICCV I0 and ICC 506 recorded the highest total grain yield. There were no significant d~fferences between the genotypes and Bt concentrations for grain yield. Significantly lower leaf damage was recorded on ICC 506 across Br concentrations in detached leaf assay under laboratory conditions. Larval survival and larval weights were lower in ICC 506, ICCV 10. and C 235 across Br concentrations as compared to that of L 550. Survival and development of H. armigera on ICC 506, ICCV 10, and C 235 sprayed with different concentrations of Bt differed significantly with that of the unsprayed plants of these genotypes. At higher concentrations of Br (0.1.0.2. and 0.5%), there was no survival of the armigera larvae. At lower concentrations of Br (0.05%), the larval survival and larval and pupal weights were lower on the sprayed (0.05%) plants than those on the unsprayed plants of different chickpea genotypes. Larval and pupal periods were prolonged on plants sprayed with Bt. There was a significant reduction in fecundity of H armigera reared on chickpea plants sprayed with Br. At the vegetative and flowering stages, ICC 506 had the highest amounts of oxalic acid on dry weight and leaf area basis. At the podding stage, ICCV 10 had the highest amount of oxalic acid on dry weight basis. On dry weight basis, ICCV 10 had the highest amount of malic acid at the vegetative, flowering, and podding stages. On leaf area basis, ICCV 10 had the highest amount of malic acid at the vegetative stage, whereas C 235 had the highest amount of malic acid at the flowering and pcdding stages. Fumaric and citric acids were recorded at the podding stage only. The genotype C 235 had the highest amounts of fumaric and citric acids. There was no citric acid in ICC 506. The survival and development ofH armigera larvae reared on artificial diet with leaflpod powder of different chickpea genotypes and Br were significantly lower as compared to that on the standard artificial diet, and the diets without Br. Larval survival, larval and pupal weight, and pupation and adult emergence were lower on the resistant genotypes than on the susceptible ones, and the standard artificial diet. Oxalic and malic acids in the artificial diet increased the biological activity of Br toxins on the H armigera, and resulted in reduced larval weight, prolonged development, and reduced longevity and fecundity. The food, midgut, and faecal matter samples of larvae fed on diet with different amounts of organic acids and BI indicated the conversion of protoxin to toxin, and binding to the brush border membrane vesicles (BBMV) of midaut. Due to the conversion of p rot ox in to toxin and binding to the BBMV, the amount of Bl toxin in the midgut samples w& greater as comaared to that in the food sam~lesT. here were no significant differences in the amounts of Bt p;otein present in the midgutsamples of the larvae-fed on diet with different amounts of oxalic and malic acids and BI toxin, indicating that the organic acids did not influence the conversion of protoxin to toxin. The amounts of protein in the BBMV preparations ranged from 0.131 to 0.326 mg c&". The amount of protein estimated from the BBMV of larvae fed on diets with Bt was higher as compared to the amounts in the BBMV of the larvae fed on diet without Bt, indicating the binding of the BI protein to the BBMV, which resulted in increased protein content in the BBMV. The insecticidal activity of BI endotoxins depends on the amounts of food ingested by the target insects. The organic acids (oxalic and malic acids) also act as antifeedents, and therefore, may reduce the effect of B1 as less amounts of food will be consumed by the larvae. However, the amounts of oxalic and malic acids impregnated in to the diet did not effect th

Interaction between host plant resistance and biological activity of Bacillus thuringiensis in managing the pod borer Helicoverpa armigera in chickpea

The legume pod borer, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) has developed high levels of resistance to conventional insecticides, and therefore, efforts are being made to develop transgenic chickpea expressing toxin genes from the bacterium, Bacillus thuringiensis (Bt) for controlling this pest. However, there is an apprehension that acid exudates in chickpea might interfere with biological activity of Bt. Therefore, we studied the biological activity of Bt (BiolepR) on four chickpea genotypes with different levels of resistance to H. armigera under field conditions, and by incorporating lyophilized lead and pod tissue into the artificial diet with and without Bt. The pH of the acid exudates varied from 2.1 to 2.90, and malic and oxalic acid were the major components of the acid exudates in different chickpea genotypes. There was no survival of H. armigera larvae in chickpea plants spayed with 0.1, 0.2 and 0.5% of Bt. There was a significant reduction in larval survival, larval and pupal weights and fecundity, and prolongation of larval and pupal periods in chickpea plots sprayed with Bt (0.05%) as compared to the unsprayed plants. Biological activity of Bt was lower on artificial diets with leaf or pod powder of chickpea genotypes, which might be because of a low intake of Bt toxins due to antifeedant effects of acid exudates in the chickpea or reduction in biological activity of Bt due to the interaction of biochemical constituents in chickpea with the Bt toxins. Larval survival, larval and pupal weights, pupation and adult emergence were significantly lower on diets with leaf or pod powder of the H. armigera-resistant genotypes than on the susceptible check. Chickpea genotypes with resistance to H. armigera acted in concert with Bt to cause adverse effects on the survival and development of this insect. The results suggested that development of transgenic chickpeas expressing toxin genes form Bt will be quite effective for controlling of the pod borer, H. armigera

Effects of hydroxycinnamic acid esters on sweetpotato weevil feeding and oviposition and interactions with Bacillus thuringiensis proteins

Sweetpotato weevil (SPW) pest management is challenging because the pest target is sub-terranean, so the application of pesticides is impractical and usually ineffective. Host plant resistance and the genetic transformation of sweetpotatoes to produce entomotoxic Bt proteins offer potential for environmentally benign pest control. Resistance can be conferred by naturally occurring hydroxycinnamic acids which protect against oviposition by adults, but these compounds are restricted to the root surface so do not protect against the cortex bound larvae where the greatest damage occurs. Resistance could be enhanced if combined with expression of Bt proteins in transformed plants but interactions between hydroxycinnamic acids and Bt proteins remain unknown. Here the bioactivity of Cry7Aa1 protein and hydroxycinnamic acid esters was evaluated individually and in combination against SPW larvae and mortality determined. Low and high concentrations of hydroxycinnamic acid esters alone caused significantly higher mortality of both weevil species in all experiments compared to the control. SPW larval mortality was greater when tested as a combination of hydroxycinnamic acid esters and Bt protein but this effect was additive not synergistic. Although we report no evidence of antagonistic interactions the antifeedant effects of the plant compounds conferring host plant resistance could have reduced consumption of the Bt protein in our assays leading to a lower efficacy when combined. Further work is required to determine if the toxic effects of Bt proteins function alongside host plant resistance in sweetpotato under field conditions