oa Morphological and genetic diversity of Rhizoctonia solani isolated from different vegetable crops in Qatar

The soil borne fungus Rhizoctonia solani is a pathogen of many plants and causes severe damage in crops around the world. It primarily attacks below ground plant parts such as the seeds, hypocotyls, and roots, also capable to infect above ground plant parts (e.g. pods, fruits, leaves and stems). The most common symptom of Rhizoctonia disease is referred as “damping-off” characterized by non-germination of severely infected seed whereas infected seedlings can be killed either before or after they emerge from the soil. The study of the diversity of the isolates of R. solani in Qatar allows the structure of the populations to be determined and adapte control strategies against this pathogen to be established. R. solani attack many crops leading to great yield losses and to the downgrading of production. Six isolates of Rhizoctonia solani (R7, R8, R9, R10, R11 and R12) were obtained from different plant types (tomato, cucumber, eggplant, common bean and broad bean) and different locations in Qatar representing major agro ecological zones like Al-Shamal, Rod Rasheed, Shahnia and Omsalaal. They were cultured in 3 different media (water agar, corn meal agar and potato dextrose agar), there were no significant differences among isolates on water agar and corn meal agar whereas all isolates showed different characteristics on the potato dextrose agar i.e. color of the mycelium, density of the mycelium and sclerotia formation. The microscopic examination of the isolates was done. The angle of the mycelium (right angle or acute angle) was recorded. Internal transcribed spacer (ITS region) of the rRNA was amplified using the universal ITS-1 and ITS-4 primers that anneal to the flanking 18S and 28S rRNA gene Direct sequencing of the amplification products was carried out in both directions using the universal ITS-1 and ITS-4 primers. Comparison of partial rRNA ITS nucleotide sequence of all isolates showed 91% sequence homology between R8 and R10, 73% similarity between R7 and R11, R9 showed 63% homology between the other two subgroups, meanwhile isolate R12 showed 36% similarity with all other isolates. Molecular markers are important tools for the characterization of genetic diversity in fungal pathogens where morphological features are either absent or not sufficient to allow intraspecific characterization.