Antagonistic potential of Pasteuria penetrans based oil dispersion formulation against Meloidogyne incognita in medicinal coleus, Coleus forskohlii

Abstract

Medicinal coleus (Coleus forskohlii) is an important herbal plant of Indian Medicine. Root-knot nematode, Meloidogyne incognita. is the predominant pest of medicinal coleus that causes yield reduction upto 72 per cent. Nematode affects the medicinal property of the tubers by producing root-knot galls on them. Chemical nematicides are not suitable as the molecule, forscholin is extracted from the tubers. Biological control is the only suitable solution to prevent pesticide residual issues. Pasteuria penetrans is a potential antagonistic bacterium of M. incognita. The current investigation, an oil dispersion formulation (ODF) of P. penetrans was developed and tested for its effectiveness against M. incognita. The formulation was water soluble and the spores were viable at 60 days of incubation that was confirmed through juvenile parasitization. Various concentrations of this formulation were prepared and screened against M. incognita infection in C. forsksholii under glasshouse conditions. Soil drenching of the formulation at the rate of 400 µL in 1000 mL of water recorded 86 per cent reduction in egg mass production. P. penetrans endospores were recovered from treated plants that confirms the efficiency of the formulation. Based on this result, field trials were conducted to evaluate the efficacy of ODF for two seasons. The results showed that the application of ODF @ 4 L/ha in 200L of water significantly reduced nematode infection to a tune of 74.9–84.8% and 61-66.5% reduction in egg mass production and gall index. The same formulation promoted tuber yield, that was 16.7–21.5 per cent increase over control.