ویژگی‏های فنوتیپی، بیماری‏زایی و مولکولی Pseudomonas spp. عامل بلایت هاله‌ای لوبیا در ایران

Beans are among the crops that are widely grown in tropical and subtropical regions of the world. According to the FAO statistics in 2022, the area under cultivation of beans in Iran was 86,129 ha, the production of this crop in the country was 160,000 tons. Iran is ranked 30th among different countries in terms of bean production. There are numerous pathogens affecting beans, causing substantial damage to the crop annually. In the surveys conducted in some provinces of the country i.e. Fars, Isfahan, and Kohgiluyeh-Boyer-Ahmad, various symptoms including small and water-soaked lesions with a yellow halo were observed on the leaves and pods of beans. Symptomatic plants were collected and brought to the laboratory for further studies. The samples were surface sterilized with dipping in a 0.5 % sodium hypochlorite solution and washed twice by sterile distilled water (SDW). A piece of each sample was cut using a sterile scalpel and macerated in 10-20 ml of SDW using a sterile mortar and pestle. A loopful of the resulting suspensions was streaked on NAS medium, plates were incubated at 25-27°C for 48-72 h. The creamy white colonies, flat and circular with 1-3 mm in diameter and entire margins were grown on NAS medium and produced fluorescent pigment on the KB medium. LOPAT tests including levan formation, oxidase reaction, potato soft rot, arginine dihydrolase, and tobacco hypersensitive were conducted following the methodology described in the bacteriology. All isolates were able to induce hypersensitive reaction on tobacco plants. However, the results of other tests differed from one strain to another. Four out of 20 strains, were negative for levan production, but were positive for oxidase, potato rot and arginine dihydrolase. By amplifying the 558 bp fragment using D21/D22 primer, it was determined that all the bacterial strains belong to Pseudomonas spp. To provide a precise and reliable insight into the taxonomic status and phylogenetic position of the strains, two housekeeping genes (gyrB and gltB) were sequenced. Based on the phylogenetic analysis, 15, four, and one of the 20 strains were identified as P. syringae pv. phaseolicola, P. aeruginosa, and P. syringae pv. atrofaciens, respectively. Pathogenicity of the bacterial strains were evaluated on bean plants in greenhouse conditions. In pathogenicity tests, water-soaked spots were appeared on the leaves 10–12 days’ post inoculation. The results of this study showed that various bacteria of the genus Pseudomonas are pathogenic on beans. As a preventive measure against disease, it is crucial to ensure the use of healthy seeds in cultivation practices.