EVALUATION OF ROSELLE (HIBISCUS SABDARIFFA) LEAF AND POMEGRANATE (PUNICA GRANATUM) FRUIT RIND FOR ACTIVITY AGAINST MELOIDOGYNE INCOGNITA
Keywords:gongura, Hibiscus sabdariffa, management, Meloidogyne incognita, natural products, plant extracts, pomegranate, Punica granatum, root-knot nematode, roselle, soil amendments
AbstractPomegranate (Punica granatum) fruit and roselle (Hibiscus sabdariffa) leaves have been used in traditional medicine, including as anthelmintics. Methanolic extracts from these plants were investigated for activity against the southern root-knot nematode (RKN), Meloidogyne incognita. Dried, ground powders were prepared from pomegranate fruit rinds and from roselle leaves. In in vitro assays, methanolic extracts from both powders, dried and dissolved in water, inhibited egg hatch and viability of second-stage juveniles (J2). Some of the effect of these extracts on J2 was nematostatic, depending on the extract concentration. The pomegranate extract (pH 3.4 to 3.8) was effective at the tested concentrations of 0.45% to 1.8% (volume extract per volume water), reducing egg hatch up to 93.9%, and killing more than 30% of the J2. Roselle extract concentrations of 4.5% and higher (pH 2.8 to 3.6) suppressed egg hatch by up to 97.4%, and 100% J2 mortality occurred in concentrations of 22.5% and 45.0% extract. Pomegranate and roselle extracts with pH adjusted to higher values (5.9 and 5.0, respectively) were also active against RKN. Pomegranate extract, pH 5.9, resulted in 96.5% to 99.7% egg hatch suppression and 100% J2 mortality at concentrations of 22.5% to 33.8%. Pomegranate fruit rind powder was also tested as a soil amendment in greenhouse trials, and was phytotoxic to cucumber seedlings at application rates of 5.0% and 10.0% (weight dried pomegranate rind/weight dried soil), resulting in plant death. Shoot heights and fresh weights were reduced at 0.25%, 0.5%, and 1.0% powder application rates, and root fresh weights also tended to be lower at these concentrations. The numbers of galls per root system and galls per g root fresh weight were suppressed in the 1.0% application rate. Amendment with pomegranate fruit rind powder resulted in rapid growth of Rhizopus sp. and Aspergillus sp. on the soil. Suppression of RKN egg hatch and J2 activity by extracts from pomegranate fruit rinds and roselle leaves indicate that these plant-derived products are potential candidates for future studies of nematode-antagonistic compounds.