Production of Spore-δ-entotoxin of Bacillus thuringiensis strains and studies on cross-resistance of Cry1Ac and Bt-based biopes.pdf

1、The present study elaborates on the results of cross-resistance of Cry1Ac and Bt-based biopesticide resistant Helicoverpa armigera (Hübner) to various Bt strains (HD-1, HD-4, HD-8, HD-57, HD-133, HD-234, HD-263, HD-282,

2、 HD-551,HD-744 and Bt-based biopesticide. In this.study, all the bioassays were done on larvae of 55th, 60th and 61st Cry1Ac and 58th, 64th, and 65th Bt-based biopesticide selected generations of H. armigera. The resista

3、nce ratios (RR) among Cry1Ac and Bt-based biopesticide selected generations varied from 417 fold in 46th generation to 172 fold in 55th generation of Cry1Ac selection and from 21 fold in 58th generation to 15 fold in 67

4、generation of Bt-based biopesticide selection.Cry1Ac selection exhibited minimum resistance ratio (2.722, 2.756) against HD-1and HD-8 among all the HD strains tested and the slopes for HD-1 and HD-8were highly significan

5、t (1.49 and 1.31 respectively). The test insect also showed low resistance ratios 3.959 and 4.385 for HD-551 and HD-57 respectively with highly significant slopes 1.18 and 2.36 accordingly. The spore-crystal toxins of st

6、rains of HD-1, HD-8 and HD-263 and Bt-based biopesticide caused significant reduction in larval wt.(％)with regressions y=0.011x+93.912, R2=0.7269, df=4,p＜0.05, and y=0.03x+85.332, R2=0.6982, df=4, p＜0.05, y=0.0458x+79.58

7、,R2=0.7271, df=4,p＜0.05, and y=0.0776x+59.169, R2=0.8273, df=4, p＜0.05,respectively against Cry1Ac selection. Significant slopes 1.49, 1.31, 2.36, 1.67,1.18, 1.12 and 2.09 were observed for HD-1, HD-8, HD-57, HD-263, HD-

8、551,HD-744 and Bt-based biopesticide respectively which indicated fast interaction between spore-crystal toxins of Bts and the Cry1Ac resistant insect. Bt-based biopesticide selection of H.armigera showed low resistance

9、 ratios (1.12, 1.10, 1.82,1.95,2.09, and 1.55 for spore-crystal toxins of HD-1, HD-8, HD-133, HD-263, HD-282,and HD-744 respectively). The linear regressions between larval wt. Reduction(％) and toxin concentrations were

10、significant for HD-263, HD744 and Bt-based biopesticide with equations y= 0.0937x+82.891, R2 =0.7832, df=2, p＜0.05, y=0.0421x+92.930 R2=0.8869, df=4, p＜0.05,and y=01163x+44.382, R2=0.7975, df=2, p＜0.05) respectively.

11、Previous studies conducted by other workers indicated synergistic impact between spores and crystals of Bt strains against resistance insects. Our results suggest that the spore-crystal complex (perhaps due to synergisti

12、c interaction between or among the spore and crystal components) may have caused synergism due to which a Cry1Ac selection was knocked down and spore-crystal complex-based formulations of Bts can be developed for use as