Abstract
This study aimed to evaluate the efficacy of endophytic bacterium to control common bean rust disease under greenhouse conditions. Endophytic bacterium Pseudomonas putida ASU15 was isolated from fresh asymptomatic common bean, identified using biochemical and molecular characteristics. In vitro, the inhibitory effect of different concentrations of P. putida (1 × 104, 1 × 105 and 1 × 106), as well as fungicide ortiva (0.01%) on uredospores germination of Uromyces appendiculatus were tested using water agar medium. The concentration showing the highest reduction of uredospores germination was at 1 × 106, while there was complete inhibition of uredospores germination associated with using ortiva. Scanning electron microscope exhibited the ability of P. putida cells to attack the cell wall of the fungal uredospores germ tubes of U. appendiculatus, causing obvious cell wall breakdown. The activities of chitinase, lipase, and protease produced by P. putida ASU15, in vitro, were evaluated spectrophotometrically. Chitinolytic, proteolytic, and lipolytic activities were exhibited, contributing 55.26, 3.87, and 26.12 U/mL, respectively. Under greenhouse conditions, treated plants with P. putida ASU15 (two days before pathogen inoculation or at the same time of pathogen inoculation) or fungicide reduced the disease severity, compared to the control. Applying P. putida ASU15 at the same time of pathogen inoculation showed reduction in disease severity (69.9%), higher than application before pathogen inoculation (54.9%). This study is considered the first report that demonstrates the mycoparasitic strategy of P. putida for controlling U. appendiculatus. In conclusion, our results revealed that P. putida ASU15 affords a significant disease reduction that may be attributed to direct suppression of pathogen spores germination.
Highlights
Common bean (Phaseolus vulgaris L.) is one of the most important vegetable food legumes in Egypt for local consumption and exportation [1]
The uredospores of U. appendiculatus were obtained from heavily infected bean plants in El-Menia Governorate, Egypt
We collected the uredospores from uredial lesions of the naturally infected bean leaves and used them to re-infect bean plants cultivated in the greenhouse of Assiut University
Summary
Common bean (Phaseolus vulgaris L.) is one of the most important vegetable food legumes in Egypt for local consumption and exportation [1]. Ex Pers.), is one of the most destructive, yield-limiting, worldwide diseases of common bean [2]. It causes yield losses ranging from 25 to 100%. The use of fungicides had been practiced and its success depends mainly on the high repetition of applications; fungicides were recently restricted in many countries for use against bean rust due to their adverse effects on non-target species, environmental pollution, and development of fungicide resistant strains, in addition to the harmful aspects they cause to humans and climate [7]. The wide variability of U. appendiculatus represents an obstacle to breeders aiming at the development of common bean cultivars with durable resistance to rust [8]
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