Pseudomonas oryzihabitans: a potential bacterial antagonist for the management of bacterial fruit blotch (Acidovorax citrulli) of cucurbits

Chemicals used for plant health may have negative impacts on humans, animals and environment, thus antagonistic microorganisms have become popular for the control of plant diseases. Acidovorax citrulli (Ac)-induced melon bacterial fruit blotch (BFB) disease poses serious threats worldwide to the production of cucurbits, especially melon (Cucumis melo) and watermelon (Citrullus lanatus). In this study, effects of 14 different antagonistic bacteria isolated from the phyllosphere of melon and watermelon were tested against BFB through seed treatments under growth chamber conditions and through foliage sprays under greenhouse conditions. When seeds were treated with antagonistic bacteria, seven of them reduced disease incidence by over 50% and disease severity by about 70%. Then, these seven antagonists were sprayed on melon leaves twice (1 and 15 days after transplanting) under greenhouse conditions and disease development was monitored weekly for five weeks. As compared to the control, Pseudomonas oryzihabitans Antg-12, isolated from watermelon leaf, reduced both disease severity (55.85%) and the area under the disease curve (AUDPC) (66.85%), and increased yield by about 41%. In the present study it was shown that certain bacterial biocontrol agents can substantially reduce disease and, when added into integrated management of BLB, may well provide very useful solutions to disease control. To further prove this, studies using the antagonists under open field conditions are planned

IDENTIFICATION OF XANTHOMONAS SPP. DISEASE AGENT/S AND THE EFFECT OF CHEMICAL SEED TREATMENTS TO CONTROL BACTERIAL SPOT OF PEPPER

Bacterial leaf spot caused by the xanthomonads is a destructive disease of both tomato and peppers. This paper aimed to identify the causative bacterial spot agent/s of pepper in Kayseri Province of Turkey. Plants of pepper with leaf lesions picked up among pepper plants in fields. Xanthomonad-like yellow pigmented 12 bacterial strains obtained from infected leaf samples. These strains were identified using phenotypic features like gram reaction, oxidative metabolism, growth at 40 degrees C and on YDC medium, amylolytic and pectolytic activities. The molecular identification completed with species specific primers. All strains were gram negative, oxidative metabolism and grew at 40 degrees C, produced yellow mucoid colonies on YDC medium and showed strong amylolytic activity, while all did not have any pectolytic activity. All strains characterized as Xanthomonas euvesicatoria according to phenotypic and molecular characterization. The study concluded that X. euvesicatoria is the prevalent causal agent of pepper bacterial spot in Kayseri province. The second aim of the study was to evaluate the potential use of chemical seed treatments including sodium hypochlorite, cupric acetate, streptomycine sulphate, acetic, citric and lactic acid in the elimination of pepper bacterial spot disease. Two experimental groups were thus designed: 1) efficacy of treatments on the survival of X. euvesicatoria on pepper seeds was observed 2) the effects of seed treatments on germination and disease development on seedlings at chamber room conditions were evaluated. The treatments were used in both experiments were negative (with water only) and positive (only pathogen) control, immersion seeds into sodium hypochlorite (3%, 1, 3 or 5 min), streptomycine sulphate (0,02 g per liter), cupric acetate (0,2% 1, 3 or 5 min), acetic and citric acid (1% 1, 3 or 5 min) and lactic acid (2% 1, 3 or 5 min). All treatments were statistically significant. The efficacies of treatments on disease incidence and severity were greater than 89%. Additionally, these treatments had no adverse effect on seed germinations. The study recommended seed treatments with sodium hypochlorite (3%, 3 and 5 min), copper acetate (0.2%, 3 and 5 min), acetic and citric acid (1%, 1, 3 and 5 min) and lactic acid (2%, 1, 3 and 5 min) as the most suppressive treatments to control bacterial spot disease symptoms on pepper. The seed treatments have potential to control the disease in nurseries