Studies on a Pasteuria isolate from an entomopathogenic nematode, Steinernema pakistanense (Nematoda: Steinernematidae)

Nematology , 2005, Vol. 7(4), 637-640 Short communication Studies on a Pasteuria isolate from an entomopathogenic nematode, Steinernema pakistanense (Nematoda: Steinernematidae) Harish K. B AJAJ ∗ and Kum Kum W ALIA Mycelial and endospore-forming bacteria belonging to the genus Pasteuria are obligate parasites of several plant- parasitic nematodes. Three species of this bacterium, Pas- teuria penetrans , P. thornei and P. nishizawae , parasites of Meloidogyne , Pratylenchus and Heterodera species, respectively, are being explored as biocontrol agents for the management of their specific nematode hosts. Ento- mopathogenic nematodes (EPN) are being increasingly advocated for the management of insect pests in several countries. As infective stages of EPN and plant-parasitic nematodes inhabit soil, concerns have been expressed about whether EPN are hosts of Pasteuria species, and whether a Pasteuria isolate can infect both plant-parasitic nematodes and EPN (Mohotti et al. , 1998; Somasekhar & Mehta, 2000). Soil samples analysed from the rhizosphere of Zizyphus jujuba from the horticultural farm of CCS Haryana Agri- cultural University, Hisar (India) for plant-parasitic nema- todes also revealed the presence of infective juveniles (IJ) of EPN (Heterorhabditis indica and Steinernema pakista- nense). Microscopic studies of IJ of S. pakistanense re- vealed heavy infestation of about 17% of the IJ, with Pasteuria spores present inside the pseudocoelom and/or attached to the body cuticle. Pratylenchus microstylus , present in one sample, was also infected with Pasteuria spores. Therefore, aspects of the interaction of the Pas- teuria isolate infecting S. pakistanense were studied. Infective juveniles of S. pakistanense were extracted from soil obtained from around the roots of Z. jujuba from an orchard of CCS Haryana Agricultural Univer- sity by Cobb’s decanting and sieving technique followed by a modified Baermann’s funnel technique. After careful microscopic examinations (× 400), they were divided into three groups: i) healthy; ii) with Pasteuria spores attached; Department of Nematology, CCS Haryana Agricultural University, Hisar-125 004, India ∗ Corresponding author, e-mail: [email protected] Received: 20 April 2005; revised: 12 June 2005 Accepted for publication: 23 June 2005 Keywords: encumbrance, Galleria mellonella, Heterodera cajani , Meloidogyne javanica , Pasteuria penetrans , Pasteuria thornei , Pratylenchus gibbicaudatus. and iii) infected with Pasteuria spores. The groups were transferred separately to cavity blocks containing sterile distilled water. Pratylenchus gibbicaudatus infected with Pasteuria were collected from soil/roots of vetiver (Vetive- ria zizanioides) growing wild near a water canal at CCS Haryana Agricultural University Campus. For host range studies soil samples from around the roots of Z. jujube containing IJ of S. pakistanense in- fected with Pasteuria , and of vetiver containing Pas- teuria -infected P. gibbicaudatus , were processed through a 400 µ m mesh sieve by Cobb’s sieving and decanting technique followed by modified Baermann’s funnel tech- nique to recover sympatric species of nematodes. The worms were examined microscopically for species iden- tification and infection with Pasteuria spores. Cross en- cumbrance of Pasteuria spores originating from S. pakis- tanense , P. gibbicaudatus , Heterodera cajani and Meloi- dogyne javanica was tested in cavity blocks containing spore suspension in sterile distilled water. For this purpose 30 IJ of Pasteuria- infected S. pakistanense and P. gib- bicaudatus were crushed separately to liberate spores in sterile water in cavity blocks. Spore suspensions of Pas- teuria isolates of M. javanica and H. cajani were ob- tained by crushing five infected females (obtained from glasshouse cultures) in sterile distilled water. The number of endospores of each isolate was adjusted to 1 × 10 5 per ml. To each cavity block containing 2 ml of spore sus- pension were added 20 specimens each of IJ of S. pakis- tanense , Pasteuria -free specimens of different stages of P. gibbicaudatus recovered freshly from soil, and freshly hatched second-stage juveniles (J2) of H. cajani and M. javanica . There were three replications of each treatment. Observations on spore encumbrance were recorded after 72 h. © Koninklijke Brill NV, Leiden, 2005 637 Also available online - www.brill.nl