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.
