Abstract
Two populations (CS19 and CS20) of entomopathogenic nematodes were isolated from the soils of vegetable fields from Bijnor district, India. Based on morphological, morphometrical, and molecular studies, the nematodes were identified as Steinernema surkhetense. This work represents the first report of this species in India. The infective juveniles (IJs) showed morphometrical and morphological differences, with the original description based on longer IJs size. The IJs of the Indian isolates possess six ridges in their lateral field instead of eight reported in the original description. The analysis of ITS-rDNA sequences revealed nucleotide differences at 345, 608, and 920 positions in aligned data. No difference was observed in D2-D3 domain. The S. surkhetense COI gene was studied for the first time as well as the molecular characterization of their Xenorhabdus symbiont using the sequences of recA and gyrB genes revealing Xenorhabdus stockiae as its symbiont. These data, together with the finding of X. stockiae, suggest that this bacterium is widespread among South Asian nematodes from the "carpocapsae" group. Virulence of both isolates was tested on Spodoptera litura. The strain CS19 was capable to kill the larvae with 31.78 IJs at 72 hr, whereas CS20 needed 67.7 IJs.
Highlights
Two populations (CS19 and CS20) of entomopathogenic nematodes were isolated from the soils of vegetable fields from Bijnor district, India
For a high efficiency as biological control agents against insect pests, Entomopathogenic nematodes (EPN) should be adapted to local environmental conditions (Gal et al, 2001; Chen et al, 2009)
During the survey of EPNs in Uttar Pradesh, India, two nematode isolates belonging to the genus Steinernema Travassos, 1927, were recovered from soil samples of eggplant (Solanum melongena L. (Solanales: Solanaceae)) and cauliflower (Brassica oleracea L. (Brassicales: Brassicaceae)) fields of district Bijnor
Summary
Nematode isolation: Entomopathogenic nematodes were isolated from soil samples taken during the month of June in 2013 from eggplant and cauliflower fields of Bijnor district of Western part of Uttar Pradesh, India, located in between 298 29 and 298 589 North and 788 09 to 788 579 East at an altitude of 115 m using the Galleria mellonella L. (Lepidoptera: Pyralidae) baiting technique (Bedding and Akhurst, 1975). Cadavers of G. mellonella recovered from the trap were disinfected in 0.1% NaOCl solution, washed in ddH2O, and transferred onto White trap (White, 1927). The IJs were isolated from White traps, washed twice with ddH2O, disinfected with 0.1% NaOCl, and stored into tissue culture flask at 158C 6 18C. Steinernema surkhetense from India: Bhat et al 93 of G. mellonella 1 d after infection with S. surkhetense CS19 following Akhurst (1980) methodology. All PCR products were sequenced and deposited in GenBank under the following accession numbers: KY489779 (16S sequence), KX826948 (recA sequence), KX826949 (gyrB sequence). Scanning electron microscopy: For the scanning electron microscope, lukewarm water killed IJs were washed three times with 0.1 M phosphate buffer (pH 7.2) followed by fixing in 4% glutaraldehyde buffered with phosphate buffer (pH 7.2) at 48C overnight and washed with 0.1 M phosphate buffer. Sequence alignment and phylogenetic analyses: The sequences were edited and compared with those deposited
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