Investigation on root-knot nematode Meloidogyne graminicola and their bacterial parasite - Pasteuria penetrans associated with rice in Matara, Badulla and Hambantota districts.

Abstract

Rice is the most widely consumed food in Sri Lanka. Rice root nematode, Meloidogyne graminicola causes considerable yield losses on rice in many south Asian countries. In this investigation, prevalence of M. graminicola infestations associated with three developmental stages of rice plants, grown at five localities, namely, Hangunnawa, Kital Ella, Ella, Kumbalwela, Keppetipola, Uduwara in the upcountry (in Badualla district) and two localities, Welihinda (in Matara district) and Kattakaduwa (in Hambanthota district) in low-country (and Matara districts) was determined, during January - November 2008. In addition to the prevalence, the disease severity was also investigated using rootlet infestation, gall formation and density of females within the root tissues. Moreover, infection levels of M. graminicola by Pasteuria penetrans, a bacterial parasite was assessed to find out the natural suppression. At each locality least 25 rice plants were sampled with respect to each developmental stage. Out of the eight localities surveyed, three localities i.e., Uduwara, Kattakaduwa, Welihinda were positive for the M. graminicola infestation. No M. graminicola infestation were found at Hangunnawa, Krtal Ella, Ella, Kumbalwela, Keppetipola in Badulla district. The percentage infested rice plants with respect to localities, rice variety and the developmental stage of rice plants. As a whole, maximum infestation, 27%, was detected at Welihinda. At all the localities, rice plants' sampled at the seedling stage showed the highest percentage of M. graminicola infestation. Out of the six rice varieties included in the trial, only three varieties, i.e., T-56 (in Uduwara), BG-red (in Welihinda) and AT-362 (in Hambanthota) were susceptible for M. graminicola. The highest mean percentage infested rootlets per root system, i.e., 10.7%, was recorded at Uduwara at the seedling stage. Significant differences in percentage infested rootlets per root system were found among the three developmental stages of rice plants at Welihinda. All the times only one root-knot was found on one infested rootlet. The highest number of galls, i.e., 6, per root system was recorded at Welihinda with respect to the flowering stage while the minimum was recorded in Uduwara at the harvesting stage. The total number of females found per root system ranged 2-7. However, number of egg-bearing females remained low. Pusturia penetrans infection was recorded at all the three M. gruminiola positive localities. However, level of infection differed with the locality and the developmental stage of rice plants. Most of the times, the level of female infection exceeds 20%. The weed species, Echinochloa colonum was found as an important alternative host plant for M. graminiola.