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.

Background Green mold disease on citrus caused by Penicillium digitatum is the most serious and destructive disease. It is causing 90% of production losses during post-harvest handling. Results In this study, the activity of seven yeast isolates from lemons against P. digitatum, a fungal pathogen that causes the green mold disease in lemons, was isolated and examined. In vitro experiments showed that isolate three significantly reduced pathogen growths and were later identified as Schwanniomyces vanrijiae. In addition, 3% ethanolic extracts of propolis (EEP) caused a strong mycelial growth inhibition with inhibition halos of 1.4 cm. The use of S. vanrijiae treatments to protect lemon fruits from green mold has been reported (55%); however, reports describing the application of EEP are limited (40%). Thus, the effectiveness of the combination of S. vanrijiae and 3% EEP in an antagonistic mixture for protecting lemon fruits from P. digitatum was examined. EEP and S. vanrijiae treatments were applied alone and in combination in both in vitro and in vivo conditions. The combined application of 3% EEP + S. vanrijiae on lemon fruits significantly reduced the severity and incidence of green mold (80 and 93.7%, respectively) with much higher efficacy than either treatment alone. Lemon fruits treated with both S. vanrijiae and 3% EEP showed increased levels of antioxidants, peroxidase (POD), polyphenol oxidase (PPO), and phenol than the untreated control. Conclusion The results indicated that the combination of S. vanrijiae + 3% EEP can strongly protect lemon fruits from green mold compared with the sole application of either bioagent.

The aim of this study is to assess the effect of extracts of Nerium oleander, Eucalyptus chamadulonsis and Citrullus colocynthis against bacterial spot disease of tomato and to investigate the induction of resistance by tomato (Solanum lycopersicum) in order to promote a sustainable management system. The antibacterial activity of aqueous and ethanol plant extracts was tested against Xanthomonas axonopodis pv. vesicatoria, isolate PHYXV3, in vitro and in vivo. The highest antibacterial activity in vitro was obtained with C. colocynthis, N. oleander and E. chamadulonsis, respectively. In vivo, ethanol extracts of N. oleander and E. chamadulonsis were more effective than aqueous extracts in reducing pathogen populations on tomato leaves. Under greenhouse conditions, application of the plant extracts at 15% (v/v) to tomato plants significantly reduced disease severity and increased the shoot weight of ‘Super Marmande’ tomato. In most cases, plant extracts significantly increased total phenol and salicylic acid content of tomato plants compared to either healthy or infected ones. In addition, C. colocynthis and E. chamadulonsis extracts significantly increased peroxidase activity while only E. chamadulonsis increased polyphenol oxidase after infection with the causal agent. The results indicated that the plant extracts showed promising antibacterial activity and could be considered an effective tool in integrated management programs for a sustainable system of tomato bacterial spot control.

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Background The red palm weevil (RPW), Rhynchophorus ferrugineus (Coleoptera: Curculionidae), overruns date palm ranches in most Oases of Saudi Arabia and causes massive economic losses. Integrated pest management (IPM) of the RPW by biocontrol agents of bacterial isolates was the primary aim of the present study. Results Thirty-seven bacterial isolates were isolated from the larvae of R. ferrugineus, which were collected from infested Phoenix dactylifera trees growing in different parts of Saudi Arabia. 16S rDNA sequencing showed that the isolated bacteria were: Serratia marcescens, Klebsiella pneumoniae and Bacillus thuringiensis. The potential of these isolates was tested against R. ferrugineus in the laboratory. The use of these three isolates showed significant mortality percentages against R. ferrugineus. The highest reduction in mortality was recorded at the concentration of 1 × 108 CFU/ml; B. thuringiensis isolate displayed the highest potency in mortal percentage rate (100%), 4 days post-treatment, followed by S. marcescens isolate after 5 days, and then K. pneumoniae isolate after 6 days. Conclusions These results suggest that the use of these bacterial isolates was very useful in in vitro experiments, and it may consider those bacterial strains of interest as a potential biocontrol agent of R. ferrugineus.

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Background Bacterial wilt caused by Ralstonia solanacearum is considered one of the most important diseases that cause economic losses to many economic crops and spread in many regions around the world, especially in the subtropical tropics and some warm temperate regions of the world. In this study the aqueous plant extract of Rosemarinus officinalis and Pseudomonas fluorescens for their antagonistic activity against bacterial wilt in vitro, greenhouse and population of R, solanacearum in plants was study. Results Following intensive screening studies, aqueous plant extract of R. officinalis and P. fluorescens was selected to study their effectiveness against bacterial wilt of potato plants and their antimicrobial activity or induction of systemic resistance in plants. In greenhouse, all soil drenching treatments on potato plants significantly reduced disease incidence of potato bacterial wilt than infected control. R. officinalis, P. fluorescens mixture between plant extract and endophytic bacteria and streptomycin reduced profoundly the disease severity by 75.51, 65.0 77.9 and 81.00%, respectively, than the infected control (83.71%). The plant extract and microorganism significantly increased fresh and dry weight of potato plants (g) per plant compared to non-treated control plants. R. officinalis, P. fluorescens mixture between plant extract and endophytic bacterium and streptomycin increased fresh weight from 100.1 to 169.9 compared to infected control also increased dry weight from 68.4 in streptomycin to 170.4% in mixture of plant extract and endophytic bacterium. The populations of bacterial pathogen R. solanacearum were lowest in stem of potato plants treated with plant extracts than in inoculated control plants (50%). In general, the total phenols increased in both inoculated and non-inoculated potato plants. Conclusions Ralstonia officinalis and P. fluorescens showed a strong in vitro activity in relation growth limitation of R. solanacearum as well as limiting the development of bacterial wilt disease on potato plants under greenhouse conditions.