Responses of Tomato to Rhizoctonia solani Infection under the Salinity Stress

Ten isolates of Rhizoctonia solani Kuhen were obtained from the roots and crown of different cultivars of tomato (Solanum lycopersicum L.). The phenotypic and microscopic characteristics of these isolates were examined. The pathogenicity of each isolate to tomato seedlings was evaluated via a pot experiment. Results showed that the isolates had varying pathogenicity. Ten isolates were identified, four of which exhibited severe pathogenicity. The effects of three salinity levels (2, 6 and 12 dS m-1 NaCl) on fungal growth, and the effects of the interaction between pathogenicity and these salinity levels on the germination indicators, phenotypic growth and biochemical characteristics of three varieties of tomato, namely, Salimah, Bushra and Yassamen both in the field and the laboratory were assessed. The combined stress of the pathogenic fungus R. solani with the increase in NaCl concentration had a stronger pathogenicity to the tomato plant than individual stress alone. As a result, the germination indicators and all phenotypic traits of the plants substantially decreased. As salt concentration increased, the contents of chlorophyll a, b and total chlorophyll decreased. By contrast, the contents of carotenoids and anthocyanins increased and those of carbohydrates and proline in the leaves considerably increased. Analysis of the interactions between the R. solani treatments and the salinity levels revealed a strong correlation between the salinity levels and H2O2 accumulation. Our findings proved that the pathological effect of R. solani was observed to be more significant on tomato varieties under salinity treatments. © 2021 Friends Science Publishers