THE NEMATODES OF CHILLI PLANTS OF SINDH: ABUNDANCE, DIVERSITY AND THE ASSEMBLAGE

Abstract

Fifteen chilli growing areas of Sindh (University of Karachi, Malir I, Malir II, Asoo Goth, Memon Goth I, Haji Ghafoor Goth, Memon Goth II, Gulshan-e-Iqbal, New Karachi, National Nematological Research Centre (NNRC, Univ. Karachi), Gadap, Ghotki, Khairpur, Larkana and Sukkur) were studied for soil and plant nematodes. Fifty two species (33 genera) of nematodes, including three new species (Helicotylenchus Siddiqii n. sp., Paratylenchus (P) karachiensis n.sp. and Bitylenchus. capsicumi n. sp.), were encountered during this survey. As evident from the literature survey, some 34 species were migratory ectoparasite. There were four endoparasite species. Bacteria / fungi feeders were five. There was one predatory carnivorous species (Mylonchulus sp.). There were three saprophytic species. Several of the ectoparasitic species were endoparasitic at their later stages of life. All Helicotylenchus spp. were obligatory parasites, Hemicriconemoides and Hoplolaimus species were obligatory root parasites. Ten species viz. Aporcelaimellus paracentrocercus, Acrobeloides sp., Cephalobus sp., Dorylaimus sp., Discolaimus sp., Ecuminicus monohystera, Geomonhystera sp. Moshajia sp. Mylonchulus sp. and Rhabditis sp. appeared to be free living bacteria. Rhabditis sp. was also entomopathogenic and Tylenchulus semipenetrans, a semi-endo-parasitic species. Frequency and density (abundance) of nematode species was highly variable from field to field and within a field. A substantial number of species (15 in number; c 29 % of the total species) occurred in one sample site each. Cephalobus sp. and Dorylaimus sp. occurred in 11 and 10 sites, respectively. By count, 48 species had less than 50% frequency in the sample sites. The mean density of a nematode species amounted to 15.93 ± 1.794 individuals varying by 81.74%. The nematode assemblage size of a site averaged to 200.67 ± 29.67 individuals per site. The population size varied greatly among the sites by 57.25%. The largest assemblage size build up was observed in Ghotki (415 individuals per 100g soil) followed by Sukkur (346). The population size was the lowest at Memon Goth (II). In other sites it ranged from 123 to 263 individuals per site. The number of nematode species recorded from various sites varied from 5 (Haji Ghaffor Goth of Malir) to 20 in another Malir field. The number of species per site averaged to 11.67 ± 1.18 varying substantially (CV= 39.22%). Different species were differentially successful. In 15 sites studied, on the basis of density, nine species of nematodes attained the rank of leading dominant, 12 species were second dominant and 11 species attained the status of the third dominant. Longidorus elongatus, was first dominant in two sites (University of Karachi and Ghotki), Acrobeles sp., a free living nematode was leading dominant in Malir, Memon Goth I and Gadap. And Cephalobus sp, another freeliving nematode, was leading dominant in Haji Ghafoor Goth, Memon Goth II and Larkana chilli fields. Helicotylenchus siddiqii predominated in Malir, Tylenchorhynchus annulatus dominated in Gulshan-e-Iqbal, Rotylenchus reniformis in New Karachi and Xiphinema basiri and Acrobeloides sp. predominated in Asoo Goth (Malir) and Khairpur, respectively. Meloidogyne javanica was the leading dominant of chilli plants of NNRC (Karachi) and Sukkur. The structure and organization of the assemblages of different sites was simple as species diversity of the sites was low and the dominance concentration was high. On the basis of information theory function (H?), species diversity was comparatively higher in Sukkur, Ghotki, Gadap, Memon Goth and Malir I. Equitability was lower in Khairpur and maximum in Sukkur. The relative abundance pattern of the species in sample sites was geometric as was evident by the linear plots of densities on log scale. In present studies, Species richness appeared to control diversity relatively more than the equitability. The cluster analysis of the data indicated five discrete groups of the sites, on the basis of compositional similarity: Group A.: an agglomeration product of nine sites and comprised of four sites dominated by free-living Acrobeles sp., Cephalobus sp. with subordinates such as free-living Dorylaimus sp. or parasitic subordinates such as Tylenchorhynchus brassicae, Filenchus butteus in varying proportions. The other five sites were dominated by Longidorus elongatus in association of subordinate free-living Aphelenchoides sp., Helicotylenchus siddiqii, Tylenchorhynchus annulatus, T. brassicae, Rotylenchus reniformis or Filenchus filiformis. Group B: comprised of sites from NNRC (Karachi) and Sukkur. The dominant nematode species was Meloidogyne javanica in the two sites sub-ordinated by Tylenchorhynchus annulatus, Helicotylenchus pseudorobustus and a free-living species, Ecuminicus monohystera. Group C: comprised of two sites – Asoo Goth and Gadap dominated by Xiphinema basiri sub-ordinated by Meloidogyne incognita, Longidorus elongatus, Rotylenchulus reniformis and a free-living nematode, Acrobeloides sp. Group D: This was solely represented by the Khairpur site predominated by Acrobeloides sp, a free living species . Tylenchorhynchus tuberosus and Tylenchulus semipenetrans were the second and the third dominant species. Group E: represented by Ghotki site was predominated by three parasitic species – Longidorus elongatus, Aphelenchus avenae and Tylenchulus semipenetrans.