دامنه میزبانیXanthomonas hortorum pv. pelargonii عامل سوختگی باکتریایی شمعدانی

The bacterium Xanthomonas hortorum pv. pelargonii is the causal agent of leaf spot and blight on geranium. This bacterium is transmitted to distant areas through infected cuttings. In the greenhouse as well as in the open space, water splashing (overhead watering) from the surface of infected plants can spread bacteria to healthy plants. During 2020 and 2021 across various provinces in the country, 22 bacterial strains were isolated from infected Pelargonium zonale showing leaf spots and blight symptoms. The results of biochemical, molecular, and pathogenicity tests showed that these 22 strains belong to the bacterium that causes geranium blight. Knowledge of bacterial distribution and host range is crucial for disease management and preventing the spread of bacteria. Therefore, in this study, to investigate the host range of bacterial blight, four different species of geranium plants including P. zonale, P. grandiflorum, P. peltatum and P. graveolens were investigated under greenhouse conditions. The bacterial suspension was prepared from 24-h old culture grown on YDC medium. The plants described above were inoculated by two methods of injection into leaves and stems and spraying of bacterial suspension on the aerial parts. All the inoculated plants periodically monitored for symptoms development until 28 days post-inoculation. Control plants were inoculated using sterile distilled water. A wide range of symptoms i.e. leaf spots with a yellow halo, V-shaped sympoms on the margins of leaves, rotting and blackening of stems were appeared in different geranium species. When the bacterial suspensions were sprayed over the aerial portions of geranium plants, only P. zonale and P. peltatum showed a leaf spot with a yellow halo on the upper and lower surface of the leaf. Subsequently, leaf spots turned to necrotic lesions and in some cases became coalescent at the ends of the leaves and formed a large necrotic area. On the other hand, P. grandiflorum and P. graveolens did not show any symptoms with the bacterial spray method. In these two plant species, by injecting bacteria into the leaves, V-shaped symptoms with a yellow halo were formed, which increased in size over time and the leaves of the plants dried up. The same symptoms appeared by injecting the bacteria into the leaves of P. zonale and P. peltatum. However, when the bacterial suspension was injected into the stem, stem rot, wilting, and gradual death of the plants were observed. The results of this study indicated that two species of geranium plants including P. zonale and P. peltatum were highly susceptible to bacteria, exhibiting typical disease symptoms after each injection and spraying of bacterial suspension.