Plant growth promotion and fungal antagonism of endophytic bacteria for the sustainable production of black pepper (Piper nigrum L.)

Abstract

In this study, one hundred and six endophytic bacteria were isolated from the roots of black pepper (Piper nigrum L.) cultivated in the central highlands of Vietnam, which is the largest region of black pepper production in the country. Among these, there were sixteen potent isolates selected for further screening. After the screening, four promising isolates were selected: EB.CP32, which possessed the highest nitrogen fixation of 12.02 µg/ml, EB.CS30, which had the highest phosphate solubilization of 8.61 µg/ml, EB.DC16, which was able to produce the highest IAA (33.64 µg/ml), and EB.EK2, which possessed high three activities. The isolates and their complexes were applied to black pepper seedlings to evaluate their effectiveness in a greenhouse. The results showed that the bacteria were able to improve the soil fertility in areas such as a 5–15% increase in N; a 100–150% increase in available phosphorous; and an increase in leaf nutrient uptake (5–7% N, 30–60% P, and 70–90% Zn), thereby enhancing the disease resistance of black pepper. These isolates promoted the growth of black pepper up to approximately a 100% increase compared to the control. From a bioassay in the greenhouse, RB.CS30 and RB.EK2 were selected for analysis. Further investigation found seven potent antifungal compounds from the culture broth of RB.EK2 by LC–MS: 1-cyclohexyl-2-(3-methyl-2-propan-2-ylbutyl) guanidine (C1); dibenzoylacetylene (C2); 6-N,7-dimethylquinoline-5,6-diamine (C3); 2-(1,3-dihydroisoindol-2-yl)-N,N–diethylethanamine (C4); piperazine 1-butyl-4-(1-phenylpropan-2-yl) (C5); 10-(2,6-diphenylpyran-4-ylidene) anthracen-9-one (C6); and 3-methyl-2-naphthalen-1-yl-2-(2-piperidin-1-ylethyl) pentanenitrile (C7). Therefore, RB.CS30 and RB.EK2 were found to be promising endophytic bacteria for the plant growth promotion and biocontrol of black pepper.