ROOT KNOT NEMATODE REPRODUCTION AND GALLING SEVERITY ON THIRTEEN VEGETABLE CROPS

Proceedings: International Symposium on Prospects of Horticultural Industry in Pakistan 28 th to 30 th March, 2007 Institute of Horticultural Sciences, University of Agriculture, Faisalabad ROOT KNOT NEMATODE REPRODUCTION AND GALLING SEVERITY ON THIRTEEN VEGETABLE CROPS Safdar Ali Anwar*, Nazir Javed, Amjad Zia, Muhammad Kamran, Hussain and Makky Javed Department of Plant Pathology, University of Agriculture, Faisalabd, Pakistan *Email: safdar_uaf2006@yahoo.com Abstract The root knot nematodes (RKN) (Meloidogyne incognita and M. javanica), are widespread and serious pathogens of vegetables throughout the vegetable production areas of Pakistan, impacting both the quantity and quality of marketable yields. In addition, root-knot nematodes interaction with other plant pathogens, result in increased damage caused by other diseases. The objective of this study was to compare the RKN resistance or susceptibility of several vegetable crops grown in the Punjab. The vegetable crops including bitter gourd, carrot, chillies, cowpea, cucumber, eggplant, garden pea, okra, pumpkin, spinach, sponge gourd, tomato, and turnip, were evaluated in a field naturally infested with RKN. Two species of root knot nematode including Meloidogyne incognita and M. javanica were identified on the basis of perineal patterns from all the crops. Meloidogyne incognita was identified on 85% and M. javanica on 15% of total samples examined. The population of second stage juveniles in soils and roots was variable depending on the type of crop and field sampled. The incidence of RKN [Number of samples with RKN total samples 100]. The RKN incidence was lowest (0%) on spinach and highest (95%) on cucumber with an average of 57% on test crops. The root gall severity was based on galling indices (GI) measured on 0 to 5 scales [0-GI = 0%; 1-GI =10 to 20%; 2-GI = 21 to 50%; 3-GI = 51 to 80%; 4-GI = 81 to 100%., 5-GI = > 100%] on roots. The severity ranged from 0 to 100% with an average of 68%. The size of galls varied from crop to crop. The gall size was small on roots of chilies, large on roots of sponge gourd, and intermediate on roots all other 11 vegetable crops. Our findings demonstrate that RKN is a damaging pathogen of vegetables. Key words: Galls, incidence, Meloidogyne incognita, M. javanica, nematodes, severity INTRODUCTION Nematodes are tiny, thread-like eelworms belonging to phylum Nematoda. Twenty five percent of nematodes are free-living saprophytes, which contains 90% microbial feeders preying on bacteria, fungi, yeast and diatom. These nematodes cause biodegradation of toxic compounds and play major role in recycling of nutrients (Freckman, 1988). Marine and fresh water nematodes make 50%, whereas animal parasites are 15% which cause animal and human disease. The insect 310

parasitic nematodes regulate the insect populations. Plant parasites are only 10% that can retard plant growth and diminish yields. The vegetable crops are attacked by several other than root knot nematodes including spiral, Helicotylenchus spp.; columbia lance, Hoplolaimus spp.; cyst, Heterodera spp.; stunt, Tylenchorhynchus spp.; dagger, Xiphenema spp.; false root knot, Nacobbus aberans; reniform, Rotylenchulus reniformis; stem and bulb, Ditylenchus dipsaci; potato cyst, Globodera rostochiensis and G. Pallida; root-lesion, Pratylenchus spp.; burrowing, Radopholus similis; sting, Belonolaimus longicaudatus; needle, Longidorus, and stubby, Trichodorus spp. and Paratrichodorus spp. Three nematode genera including Heterodera, Rotylenchulus, and Globodera are sedentary, whereas most of the others are the migratory that are mobile in the soil and move from feeding site to feeding site on the host plant. The root knot nematode most damaging pest of vegetable crops will be focus of our discussion. These nematodes are obligate sedentary-vascular endoparasites that feed on roots resulting in the formation of galls or knots on plant roots. It becomes difficult for the galled roots to take up water and other nutrients leading to stunted plant growth (Anwar and Din, 1986). There are several pathogenic species of this nematode but the two most commonly found associated with our vegetable crops in Pakistan are M. incognina (85%) and M. javanica (15%) (Anwar, 1989; Maqbool et al., 1988). Root Knot Nematode Behavior The infectious stage of this nematode is the second stage juvenile (J2), which occurs free in the soil. The J2 penetrates between and through cells to a position at the center of the root usually near the growing tip and migrate to the vascular tissue, establish feeding sites and become sedentary. An enzyme is released from esophageal glands, which causes the plant cells surrounding the head region to enlarge, forming giant cells which serve as a source of nourishment for the female root knot nematodes (Hussey and Mims, 1990). The female nematodes swell until they become pear-shaped or oval by going through series of molts and enlarge. Mature females are about 1/16 inch in size. Adult matured female deposits 300-500 eggs in a protective jelly-like matrix at the root surface on the galls. After hatching, J2s over wintering stage, move a short distance to locate a favorable plant root and begin feeding. Four weeks are required to complete the life cycle, so several generations can develop in one cropping season. Host Vegetable Crops Eleven vegetable crops including bitter gourd, carrot, chilies, cow pea, cucumber, egg plant, okra, garden pea, sponge gourd, pumpkin, and tomato have been found good host, whereas spinach and turnip as poor host of root knot nematodes. Symptoms Root-knot nematode symptoms on plant roots are dramatic. As a result of nematode feeding, large galls or "knots" can form throughout the root system of infected plants. Severe infections result in reduced yields on numerous crops and can also affect consumer acceptance of many plants (Roberts, 1987), including vegetables like carrot (Figure 1). The degree of root galling generally depends on the magnitude of nematode population density, Meloidogyne species and host plant species and even cultivar. Increase in the nematode population density in a field results in an increase in the number of galls per root system. The roots of sponge gourd were found with a gall index of 5 [=100% severity] with 35 per g of root. Generally the fast growing annuals like sponge gourd exhibit large sized galls compared to woody perennials like chilies, which had small hard galls (Figure 1). Each vegetable crop responds differently to root-knot nematode infection (Figure 1). Carrots typically undergo severe forking with galling predominantly found on lateral roots (Figure 1), Root-not nematode galls on sponge gourd, pumpkin are very large (Figure 1). On cow pea and cucumber, galls are usually of medium size. Depending upon the root knot nematode incidence and the severity of infection, these symptoms can often result in significant economic losses to growers (Barker and Olthof, 1976). 311

Damage Root-knot nematodes damage crops by attacking the young root tips. Their entry and feeding can stimulate visible galls within 15 days. These galls interfere with the roots ability to absorb water and nutrients, and provide locations for other disease-producing organisms, such as fungi or bacteria, to readily enter the plan (Powell, 1971). Most damage to crops results from the physiological changes in the root tissue as root-knot nematodes feed. Giant cells formed during the feeding process disrupt the development of the root's vascular system and impair the root's ability to remove water and nutrients from the soil efficiently (Anwar and Din, 1986). Also, sugars and carbohydrates produced in the leaves are diverted to the nematodes' feeding sites rather than to the developing fruit (Anwar, 1995; McClure, 1977). Plants with damaged root systems result in poor foliage growth and consequently yield is reduced. The extent of damage ranges from no visible damage to significant damage depending on the species and density of nematodes present, the susceptibility of the crop being grown, and environmental conditions. Many plants can tolerate moderate densities of plant-parasitic nematodes without sustaining significant losses in production. When nematodes are a problem, patches of poor plant growth often become evident within a field that otherwise may appear normal. The quality of the marketable product is reduced by nematode infestations that cause tissue breakdown, deformation, or discoloration. Root systems may be deformed, and underground organs such as potato tubers and carrot taproots may be damaged and unmarketable (Roberts, 1987; Sikora and Fernandez, 1990). Assessment of Galling in the Field When root-knot susceptible crops are planted in the same field every year, an assessment for root-knot galls at the end of the season provides valuable information on the level of nematode infestation and the likelihood of nematode damage in the next year. The field incidence of root knot nematode was assessed as Number of samples with RKN total samples 100. The RKN incidence was lowest (0%) on spinach and highest (95%) on cucumber with an average of 57% on other test crops. The root gall severity was based on galling indices (GI) measured on 0 to 5 scales [0-GI = 0%; 1-GI =10 to 20%; 2-GI = 21 to 50%; 3-GI = 51 to 80%; 4-GI = 81 to 100%., 5-GI = > 100%] on roots. The severity ranged from 0 to 100% with an average of 68%. The size of galls varied from crop to crop. The gall size was small on roots of chilies, large on roots of sponge gourd, and intermediate on roots of all other 11 vegetable crops. The number and size of the galls provides an indication of the degree of root-knot nematode infestation (Barker et al., 1985). SUMMARY Our findings contribute important information on the association of two root knot nematodes species namely M. incognita and M. arenaria with commercially planted vegetable crops. The incidence of occurrence of these nematodes, severity of infection, gall size, and numbers of galls varied from crop to crop and field to field. High incidence and severity demonstrate that root knot nematodes are damaging pathogens of vegetables. The feeding activities of nematodes reduce root growth and render them unfit to absorb sufficient water and nutrients from soil to meet the foliage requirements leading to poor plant growth and ultimate harvested yield is reduced (Barker and Olthof, 1976; Davis et al., 1976). REFERENCES Anwar, S. A. 1989. Investigations on nematodes associated with field, vegetable and fruit crops. Technical Bulletin. Barani Agricultural College, Rawalpindi, Pakistan. Anwar, S.A. 1995. Influence of Meloidogyne ingconita, Paratrichodorus minor and Pratylencus scribneri on root-shoot growth and carbohydrate partitioning in tomato. Pakistan Journal of Zoology 27:105-113. Anwar, S.A., and G.M. Din. 1986. Nematodes: Biotic constrains to plant health. Proceeding of Parasitology 3:48-53. 312

Barker, K.R., and T.H.A. Olthof. 1976. Relationships between nematode population densities and crop responses. Annual Review of Phytopathology 14:327-353. Barker, K.R., D.P. Schmitt, and J.L. Imbriani. 1985. Nematode population dynamics with emphasis on determining damage potential to crops. In: Sasser, J. N. and C. C. Cater, eds., An Advanced Treatise on Meloidogyne, Vol. 1. Biology and Control. North Carolina University Graphics, Raleigh, North Carolina, pp.135-148. Davis, R.F., H.J. Earl, P. Timper. 2003. Interaction of root-knot nematode stress and water stress in cotton. 2002 University of Georgia Cotton Research and Extension Report, pp.312-315. Freckman, D.W. 1988. Bacterivorous nematodes and organic-matter decomposition. Agricultural Ecosystem and Environment 24:195-217. Hussey, R.S., and C.W. Mims. 1990. Ultrastructure of esophageal glands and their secretary granules in the root-knot nematode Meloidogyne incognita. Protoplasma 165:9-18. Maqbool, M.A., S. Hashmi, and A. Ghaffar. 1988. Problem of root knot nematode in Pakistan and strategy for their control. In: M.A. Maqbool, A.M. Golden, A. Ghaffar and L. R. Krusberg, eds., Advances in Plant Nematology, Karachi, Pakistan, National Nematological Research Centre, University of Karachi, pp.229-240 McClure, M.A. 1977. Meloidogyne incognita: A metabolic sink. Journal of Nematology 9:88-90. Powell, N.T. 1971. Interaction between nematodes and fungi in disease complex. Annual Review of Phytopathology 9:253-274. Roberts, P.A. 1987. The influence of planting date of carrot on Meloidogyne incognita reproduction and injury to roots. Nemtologica 33:335-342. Sikora, R.A., and E. Fernandez. 1990. Nematode parasites of vegetables. In: M.R. Luc, A. Sikora, and J. Bridge (eds.). Plant Parasitic Nematodes in Subtropical and Tropical Agriculture. CAB Bioscience, Egham, UK. pp.319-392. 313

Figure 1: Galls on roots of vegetable crops produced by root knot nematodes. 314