Biocontrol and growth promotive potential of <i>Streptomyces</i> spp. in black pepper (<i>Piper nigrum</i> L.)

Abstract

Actinomycetes isolated from the rhizosphere of black pepper and from vermicompost were tested for their antagonistic effect against <em>Phytophthora capsici</em> and <em>Radopholus similis</em>, the causal agents of foot rot and slow decline diseases of black pepper. Based on <em>in vitro</em> evaluations, four isolates were shortlisted (IISR Act2, IISR Act5, IISR Act6, and IISR Act9) and subjected to<em> in vivo</em> evaluation for <em>Phytophthora</em> infection by challenge inoculation and also greenhouse evaluation for growth promotion in black pepper. Rooted plants of black pepper were raised in soil amended with Actinomycetes strains individually and in combinations in portray and were transplanted into earthenware pots containing potting mixture amended with respective actinomycetes keeping un-amended plants as control. Observations were recorded on growth parameters like plant height, root weight, shoot weight and root infection by nematodes. Besides, soil was also analyzed for pH, dehydrogenase activity, EC and NPK content to know the influence of actinomycetes on soil microflora as well as on nutrient status. The results showed that consortia are more effective than individual isolates. Consortia holding IISR Act5+IISR Act9 were found highly effective in enhancing all the growth parameters followed by IISR Act2+ IISR Act9 and IISR Act2 + IISR Act5. The dehydrogenase activity was found higher in these consortia showing the higher microbial metabolic activity. Root lesions were also negligible in these treatments. Being effective in growth promotion as well as antagonistic activity, the isolates were tested for plant growth promotion and biocontrol traits. Among the isolates, IISR Act9 was found highly efficient in IAA production (119μg/ml) when compared to IISR Act2 (36.25μg/ml) and IISR Act5 (32.4μg/ml). Hence based on the growth promotive and pathogen suppressive effect, the consortia of either IISR Act5+IISR Act9 , IISR Act2+IISR Act9 or IISR Act2+IISR Act5 can be effectively used in black pepper for growth promotion and biological control of foot rot and slow decline diseases. The potential actinomycetes were identified as <em>Streptomyces</em> spp. as per Bergey’s manual and rpoB gene sequence similarity of which IISR Act2 is identified as <em>Streptomyces</em> sp., IISR Act9 as <em>Streptomyces</em> <em>albus</em> and IISR Act5 as <em>Streptomyces</em> sp.