Evaluation of the nematicidal potential of some botanicals against root-knot nematode, Meloidogyne incognita infected carrot: In vitro and greenhouse study

Abstract

In this study effort was made to manage the root-knot nematode, Meloidogyne incognita by the utilization of selected plants such as Coccinia grandis, Commelina benghalensis, Leucas cephalotes, Phyllanthus amarus and Trianthema portulacastrum. During the in vitro experiment, the second juveniles (J2s) of M. incognita directly treated with aqueous extracts of the plant leaves at 1000, 2000, 3000, 4000 and 5000 ppm concentrations. As a result, the 5000 ppm concentration was found most toxic against the survival of second stage juveniles of M. incognita compared to other concentrations. Maximum mortality of 91% was observed in 5000 ppm extract of P. amarus after 72 h of exposure with LC50 value 2084.49 ppm while minimum mortality of 6.2% was found in 1000 ppm extract of T. portulacastrum after 24 h with LC50 value 9484.18 ppm. The percent mortality of juveniles calculated the LC50 values of all the treatments after 24, 48 and 72 h. Similarly, the in vitro tests showed a gradual decrease in the rate of egg hatching of M. incognita with the increasing concentrations of aqueous leaves extracts of plants, i.e., 1000 ppm to 5000 ppm and exposure period. Maximum inhibition in egg hatching was found at 5000 ppm (86.5%) after seven days in the extract of P. amarus while least was observed in T. portulacastrum at 1000 ppm (10.6%). The findings indicate that the plant extracts were found lethal to J2s and also inhibit egg hatching. In pots under greenhouse conditions, the plants treated with both the doses (50 and 100 g/pot) of fresh chopped leaves of the selected botanicals significantly experienced the reduced infestations in relation to root gall index, egg masses/root system and nematode population/250 g soil. The P. amarus treated at 100 gm / pot showed highest nematicidal efficacy with the maximum reductions in all the pathological parameters as compared to the untreated uninoculated control simultaneously resulted in maximum increase of growth and physiological parameters of carrot such as shoot and root lengths, shoot and root fresh weights, shoot and root dry weights, chlorophyll and carotenoid contents and nitrate reductase activity (NRA). The information derived from this study suggests that the leaves of P. amarus plant can be used for the management of M. incognita and could be a possible replacement for synthetic nematicides. Keywords: Aqueous extract, Chopped leaves, Egg hatching, Mortality, LC50M.incognita