Incidences of root-knot nematodes on selected three leafy-vegetable species in Hambantota district and nematicidal properties of aqueous extract of ripe “Goraka” fruits.

Abstract

In the first part of this research project, Meloidogyne infestations on three leafy-vegetable species, i.e., Centella asiatica, “Gotukola”; Ipomea aquatica, “Kangkung”; Alternanlhera sessilis, “Mugunuwenna” in Hambantota district of Southern Sri Lanka were investigated during February 2006 - July 2007 via a survey. Eleven sites representing small-scale leafy-vegetable growing fields in Hambantota district were sampled. At least 50 individual root systems of each leafy-vegetable species were checked for the presence of galling. At least 10 root systems with galls were selected and number of galls present on each root system was recorded. Each root system was teased off and at least 30 Meloidogyne mature females were removed and their perineal patterns were examined. The identification was done using perineal pattern morphology. Of the three leafy-vegetable species tested Meloidogyne infestations were detected only on two species, i.e., “Kangkung” and “Mugunuwenna”. No Meloidogyne infestations were recorded on “Gotukola” at any of the field surveyed. Meloidogyne infestations were identified in twenty seven percent of “Kangkung” and sixty four percent of the “Mugunuwenna” fields sampled. Three Meloidogyne species, namely M. incognita, M. javanica and M. arenaria, were recovered from the root systems of leafy-vegetables sampled. However, prevalence of the nematode species differed with leafy-vegetable species tested. Most of the times, the three nematode species occurred as a mixed population. However, frequency of occurrence of Meloidogyne species differed significantly. Meloidogyne incognita showed significantly higher frequency of occurrence compared to other two species. In the second part of the project, the nematicidal properties of aqueous extract of ripe “Goraka” fruits on second-stage juveniles (J2s) of Meloidogyne incognita was tested at five concentrations, 20%, 40%, 60%, 80% and 100%. They were prepared using the stock solution (S) of “Goraka” fruits. One-day old juveniles of M. incognita were used. The J2s in 1 ml sterile distilled water (SDW) were exposed to 1 ml of test extract for 48 hours at the ambient temperature (30°C ± 2). SDW was used in untreated controls. Significant differences in mortality of Ts between the untreated controls and all the other concentrations of “Goraka” extract were found. Moreover, significant differences were recorded among the mortality of Ts in five concentrations tested and mortality was dependent on dose rates. Highest J2 mortality was detected at high concentrations and considerable mortalities were recorded at low concentrations too. The LC50 value was found at 41.90% S. In addition, significant correlation was detected between the percentage mortalities of

J2s and the concentration of the “Goraka” extract. The results showed that “Goraka” fruit extract has a nematicidal potential and this property could be used in nematode management systems.