In‐vitro and in‐vivo assessment of biological control potential of nematode symbiont Xenorhabdus nematophila against Pseudomonas syringae, the causative agent of angular leaf spot of cucumber.

Bacterial diseases cause colossal losses in vegetable crops and are considered major limiting factors for the commercial production of vegetables around the globe. Among bacterial diseases, angular leaf spot of cucumber caused by Pseudomonas syringae is one of the most economically important diseases that cause substantial economic loss to the cucumber crop. In this study, the in‐vitro and in‐vivo effects of different strains (X1–X15) of the nematode symbiotic bacterium Xenorhabdus nematophila was determined on the growth of P. syringae in different selected media (TB, SB, SOB, SOC, YT and LB) and at different pH levels (6.5, 7.5 and 8.5) and on the incidence of angular leaf spot disease on potted cucumber plants. According to the results, maximum growth inhibition of P. syringe (25 mm) was observed in the case of strain X12, followed by strains X10 (23 mm), X8 (21 mm) and X6 (20 mm), while maximum colony growth was observed in the control. Moreover, this P. syringae growth inhibition by the X12 strain of X. nematophila was significantly maximum in SB medium and at pH 7.5. Results of the in‐vivo experiment with potted plants showed a maximum incidence (90%) of angular leaf spot disease in control plants, while a minimum disease incidence (15%) was observed for the plants treated with two times dilution of X. nematophila culture, followed by ten times (23%) and fifty times (35%). The overall results of this study demonstrate the inhibitory effect of X. nematophila on the growth and incidence of P. syringae and underscore its putative role in the biological management of plant pathogenic bacteria. [ABSTRACT FROM AUTHOR]