دامنه میزبانی Xanthomonas alfalfae subsp. alfalfae عامل لکه برگی یونجه

Seedborne phytopathogenic bacteria act as primary inoculum source for many important plant diseases. Infested seeds are responsible for the re-emergence of diseases of the past, movement of pathogens across international borders, or the introduction of diseases into new areas. Xanthomonas alfalfae subsp. alfalfae is a seed-born bacterial and the causal agent of bacterial leaf spot on alfalfa that has been recently reported from southern Iran. Primary symptoms consisted of water-soaked lesions and small leaf spots, with a dark-brown border surrounded by a chlorotic halo. The spots increased in size over time and they became coalescent and in the case of severe infections, the leaflets became almost entirely dried. In order to determine the host range of bacterial, plants from the Solanaceae family including bell pepper (Capsicum annuum cv. Sereno), chili pepper (Capsicum frutescens cv. Aziz), eggplant (Solanum melongena cv. Emami), tomato (Solanum lycopersicum cv. Sunseed 6189) and also plants from Fabaceae family including, clover (Trifolium resupinatum), common bean (Phaseolus vulgaris cv. Sadri), mung bean (Vigna radiata cv. Mashhad), faba bean (Vicia faba cv. HBP-B), soybean (Glycine max cv. Katool), onobrychis (Onobrychis sativa) and pea (Pisum sativum) were grown under greenhouse conditions. The bacterial suspension consisting of 1 × 108 CFU/ml was prepared from 48 h old culture grown on YDC medium. Bacterial suspensions were sprayed onto the fully expanded leaves, petioles and stems of plants. The inoculated plants were maintained in greenhouse conditions with 90–95% relative humidity. No symptoms were observed on the inoculated solanaceous plants, including eggplant, chili/bell pepper, and tomato. Nevertheless, common bean, faba bean, mung bean, pea, and soybean plants showed different symptoms on the inoculated leaves at 25–30 dpi. On common bean, marginal necrotic areas surrounded by chlorotic halos appeared, while on mung bean necrotic spots with grayish white central areas were observed. Inoculated pea plants showed small and dark necrotic spots on the edges of the leaflets. Faba bean showed dark necrotic spots without chlorotic halos on the leaves. On soybean, only tiny necrotic spots were observed. Bacterial isolates were re-isolated from all symptomatic plants as well as from the asymptomatic clover and onobrychis plants at 30–35 dpi. Confirmation of the re-isolated bacteria was made assessing morphological traits of the isolates on YDC medium, and by detecting them using Xanthomonas-specific PCR primer Xc-lip-F2/Xc-lip-R2. These results are important from epidemiological point of view as leguminous crops such as common bean are cultivated on a large scale in Iran with potential threat of infection by this pathogen.