A preliminary study on root-knot nematodes , Meloldogyne species and their bacterial hyper-parasite , Pasteuria penetrans associated with Spinach in Matara District

A survey was undertaken to investigate, the species composition and distribution of Me 10idogyn e nematodes and the prevalence of Pasteuria penetrans, a group of bacterial hyper-parasite of Meloidogyne nematodes, associated with spinach in Matara district. A total of 11 localities, i.e., Dandeniya, Denipitiya, Diyalape, Kirimatimulla. Malitnbada, Malara, Mirisisa, Pasgoda, Radampola, Talalla and Welipitiya representing spinach growing regions were selected for the survey. At least 10 root systems of mature spinach plants were sampled from each locality. Roots were assessed for the percentage of root system galled and a gall index (0-5) was assigned. AI least 20 mature females were checked for the species identification and infection of P. penetrans. Species identification was based on the perineal pattern morphology. Meloidogyne nematodes were recovered from the roots of spinach crops grown at 9 localities, i.e., except, Radampola and Diyalape. Three Meloidogyne species, i.e., M incognita. M. javanica and M arenaria were detected. However, M. incognita and M javanica were found with the highest frequencies of occurrence, i.e., 88%for each, while M. arenaria was found in a low frequency, i.e., 2%. In general, mixed populations were detected. Associations of M. incognita and M javanica were common. Sometimes, M javanica, M incognita and M. arenaria occurred together. Only at one locality, i.e., Talalla, single population, i.e., M javanica, was prevalent. About 16% of the individual root systems inspected showed more than 50% (gall index: 5 and 6) of galling while 43% of the roots showed 26-50% (gall index: 4) and the remaining 41% showed 125% (gall index: 1, 2 and 3) galling. Pasteuria penetrans was recovered from only three localities, Welipitiya, Denipitiya and Malimbada with the frequencies of occurrence, 12%, 85% and 4%, respectively. This survey showed that M incognita and M javanica were predominant Meloidogyne species associated with spinach in Matara district. Introduction Spinach (Spinacia oleracea) is an economically important leafy vegetable crop in Sri Lanka. It is cultivated in small-scale farms and backyard gardens in southern Sri Lanka. Apart from their importance as food, it earns cash for the farmers who sell their products in urban areas. Several plant-parasitic nematodes have been reported on spinach and among these, root-knot nematodes, Meloidogyne spp. are one of the most common and damaging nematodes (Ekanayake, & Toida, 1997; Castillo & Jimenez-Diaz, 2003). The primary symptom of root-knot nematode infection is the formation of typical root galls on the roots. Nutrient and water uptake are reduced because of the damaged root system, resulting in weak and poor yielding plants (Abad et al., 2003). Pasteuria penetrans (Thome) Sayre and Starr is an obligate spore-forming group of bacterial parasite of several genera of plant parasitic nematodes (Sturhan, 1988). Only the spore stage is exposed to the soil environment and Meloidogyne nematodes become infected when endospores of P. penetrans adhere to the cuticle of infective juveniles (Ils) in the soil. Once Us invade the roots and initiate feeding, germination of the spores starts (Sayre & Wergin, 1977). Pasteuria penetrans has a high potential for reducing Meloidogyne populations (Stirling, 1984; Gowen & Tzortzakakis, 1994) via destroying the reproductive capacity of females (Mankau, 1980) and preventing invasion of roots by Us (Mankau & Prasad, 1977; Stirling 1984). Several studies confirmed prevalence of P. penetrans in Sri Lanka, too (Silva et al., 1996; Mohotti et al., 1998, Mohotti et al., 2002). Meloidogyne infestations often overlooked by growers and confused with nutrient deficiencies and other causes. Most of the vegetable growers in southern Sri Lanka are not aware of nematode damage on their crops and as a result it goes unnoticed in their fields. To date, only investigations have been conducted on nematodes associated with vegetable crops in the southern Sri Lanka. Hence, knowledge on Meloidogyne species composition, damage levels, distribution as well as their natural enemies, associated with vegetable crops including spinach is still fragmentary. This information is vital to establish successful management practices against these nematodes. Therefore, the primary objectives of this study was to investigate the species