Selection and characterization of Bacillus thuringiensis strains from northwestern Himalayas toxic against Helicoverpa armigera

Abstract

In this study, we present the selection and the characterization of Bacillus thuringiensis (Bt) strains with respect to their cry/cyt gene content and toxicity evaluation toward one of the most important polyphagous lepidopteran pest, Helicoverpa armigera. Fifty‐six Bt isolates were obtained from 10 different regions of northwestern Himalayas, recording a total B. thuringiensis index of 0.62. Scanning electron microscopy revealed presence of bipyramidal, spherical, flat and irregular crystal shapes; SDS‐PAGE analysis of spore‐crystal mixtures showed the prominence of 130, 70, and 100 kDa protein bands in majority of the isolates; PCR analysis with primers for eight cry and cyt gene families and 13 cry gene subfamilies resulted in isolates showing different combinations of insecticidal genes. Strains containing cry1 were the most abundant (57.1%) followed by cyt2 (46.42%), cry11 (37.5%), cry2 (28.57%), cry4 (21.42%), cyt1 (19.64%), cry3 (8.9%), and cry7, 8 (7.14%). A total of 30.35% of the strains did not amplify with any of the primers used in this study. Median lethal concentration 50 (LC50) estimates of spore‐crystal mixtures of Bt‐JK12, 17, 22, 48, and 72 against second instar larvae of H. armigera was observed to be 184.62, 275.39, 256.29, 259.93 μg ml−1, respectively. B. thuringiensis presents great diversity with respect to the presence of crystal protein encoding genes and insecticidal activity. Four putative toxic isolates identified in this study have potential application in insect pest control. B. thuringiensis isolate JK12 exhibited higher toxicity against H. armigera than that of B. thuringiensis HD1, hence can be commercially exploited to control insect pest for sustainable crop production. The results of this study confirm the significance of continuous exploration of new Bt stains from different ecological regions of the world.

Characterization and Evaluation of Indigenous Bacillus thuringiensis Isolate T352 against Fall Armyworm, Spodoptera frugiperda (J.E. Smith)

“…Similarly, Bt isolate RM11 expressed the toxicity on Plutella xylostella with 4.51 µg/ml[32]. Lone et al[41] reported two isolates, JK12 and JK17 with LC 50 value of 184.62 and 275.39 µg/ml against Helicoverpa armigera. Soares Figueiredo et al[42] found that synergistic effect of Vip3 and Cry1 proteins expressed more toxicity on S. frugiperda.…”

Biotoxicity assessment of cloned cry 11 protein gene from Bacillus thuringiensis 9NF

“… Lone et al (2017) reported that the toxic isolates have a remarkable use in the pest control. So, commercially abused to control insect pest and revealed the confirmed significance of innovative Bt .…”

Isolation, characterization, and bio-insecticidal efficiency of Ethiopian isolates of Bacillus thuringiensis against Galleria mellonella L. (Lepidoptera: Pyralidae) and tomato whitefly, Bemisia tabaci (Genn.) (Hemiptera: Aleyrodidae)

“…Likewise, Woldetenssay and Ashenafi (2008) isolated a total of 213 Bacillus-like colonies from 503 soil samples collected from the different agro-ecological zone of Ethiopia. Another study showed that about 89 Bacillus-like colonies were isolated from 207 soil samples of different sites (Lone et al 2017). Captivatingly, soil environment could be inhabited by diverse microbial community and preferred as the main source for Table 4 Bioassay evaluation of Bacillus thuringiensis against whitefly, Bemisia tabaci the isolation of Bacillus species in general and Bt in particular (Soares-da-Silva et al 2015).…”