PATHOGENICITY OF Rhizoctonia solani TOWARDS DISTINCT VARIETIES OF CULTIVATED STRAWBERRY PLANTS IN MOROCCO

In this study, the pathogenicity of Rhizoctonia solani recovered from diseased strawberry plants was evaluated on three strawberry varieties. Isolates H1, G1, R1 and For de R. solani were significantly highly pathogenic by inducing symptoms on the roots and crowns of inoculated plants. The severity index was maximal (100%) in Fortuna plants inoculated with H1, those of R1 and For reached 75% while those of M1 and G1 were the lowest (50%). The indexes were greater than 50% on Festival variety in response to all isolates with the exception of R2 (25%). With regard to infection ratings, the Fortuna variety was more affected by H1, R1 and For, assigned with scores of the crown rot ranging from 3 to 4. In addition, reduced development of root system of Festival variety was also observed in reponse to H1 with a disease score of 0. All the growth parameters decreased after the inocultaion experiments of the three strawberry plant varieties by the seven tested isolates of R. solani in comparison with non inoculated control plants. The infectivity reaction of strawberry plants to isolates H1, G1 and For was extensive leading to plant death after 3 weeks of inoculation. The rosette diameter of variety Fortuna inoculated by H1 was reduced to 13 cm, 14 cm by R1 and 16. 3 cm by M1 compared to 32.8 cm for control. A significant reduction in size of root part was noted in Fortuna plants inoculated with different isolates. It attained respectively 9.3 cm and 12.3 cm for G1 and H1 against 48.3 cm for control plants. Moreover, the re-isolation percentage of R. solani from roots, crown and soil for the three varieties of strawberry plants were greater than 60%, 80% and 62.5% respectively.