Diversity of plant parasitic nematodes in pulses.

Abstract

Pulses, such as chickpea (Cicer arietinum), pigeonpea (cajanus cajan), common bean (Phaseolus vulgaris), mung bean (Vigna radiata), urd bean (Vigna mungo) and lentil (Lens culinaris), are an excellent source of dietary protein as well as forming part of a cholesterol-free diet for millions of people around the world. Numerous plant parasitic nematodes attack pulse crops and the prominent among them are Meloidogyne spp., Heterodera spp. and Paratylenchus spp., the endoparasites, Rotylenchulus spp., the semi-endoparasites, and Tylenchorhynchus spp. and Helicotylenchus spp., the ectoparasites. These nematodes have diverse methods of attack. Meloidogyne causes galling on roots, accompanied by a change in cell morphology, leading to the formation of giant cells in the cortical region of root upon which they feed; Heterodera form syncytia in the steler region and have a pearly appearance on the root; Pratylenchus form necrotic lesions on the root; Rotylenchulus reniformis cause dirty root disease and the mature females attached to the roots have a kidney-like appearance (seen under a microscope), hence the name reniformis. Tylenchorhynchus and Helicotylenchus are ectoparasites, but are considered of lesser importance than endoparasites or semi-endoparasites. They cause mechanical injury by feeding primarily on the epidermal cells of roots. Host range, length of life cycle and soil temperature and moisture for survival vary with nematode genera and species. Economic Threshold Level (ETL) also varies from crop to crop, as for chickpea it is estimated 1-2 J₂ of M. incognita/cm³ of soil or 0.031 P. thornei/cm³ of soil or 1 egg of H. ciceri/cm³ of soil or 1 premature female of R. reniformis/gm of soil, whereas in the case of pigeonpea it is 1 J₂ of M. javanica/gm of soil or 1-2 J₂ of H. cajani/gm of soil or 1.4 premature female of R. reniformis/gm of soil. During parasitism, nematodes have an adverse effect on the normal physiology, growth and development of the host plant. Ultimate harm caused to pulse crops are in the form of reduction in yield and quality. Average yield losses caused due to plant parasitic nematodes on a worldwide basis have been estimated as 13.7% in chickpea, 13.2% in pigeonpea and 10.9% in common bean. Different approaches for the management of these nematode pests include cultural, biological, botanical, host plant resistance and chemicals. These approaches need to be tested by research workers to develop integrated nematode management (INM) strategies at farm level in order to achieve maximum yield and better quality of crop.