Bio-fertilizer application: molecular and biochemical changes in infected cucumber with Phytophthora melonis

Abstract

In this work, the effects of two commercial bio-fungicides Biosubtil (Bacillus subtilis) and the bio-fertilizer Biophosphorus (Pseudomonas species), was assayed on the disease incidence, changes in the defensive enzyme activity, the total phenolic content and the expression level of some defense-related genes using real-time PCR method. Biochemical and molecular changes were measured at four time point: 24, 48, 72 and 96 hours post inoculation (hpi) of cucumber plantlets with Phytophthora melonis. The disease incidence decreased through applications of both antagonists. The highest disease reduction (60%) was noted for Biosubtil application compared to control plants. Biochemical analysis showed that both bio-fertilizers are able to increase total protein and phenolic compounds in infected cucumber plants. A maximum increase was observed with biophosphorus application at 72hpi. High activity of Peroxidae )PO) and β-1,3-glucanase enzymes were noted for biophosphorus application at 72 hpi while maximum increase of Polyphenol oxidase (PPO) was observed at 96 hpi for this application. Altered transcript levels of various resistance genes including cucumber pathogen-induced 4 (Cupi4), Lipoxygenase (Lox), Phenylalanine ammonia lyase (PAL) and Galactinol synthase (Gal) were recorded in both treatments. A high expression level (9.5 fold) among the treated genes was observed for Lox gene at 72 hpi and an high expression level for other genes was noted at 48 hpi when cucumber plants treated with Biophosporus. The results suggest that both bio-fertilizers are able to enhance disease resistance in cucumber through induce of resistance mechanisms and could be used as a resistance inducer in the greenhouse condition.