Impact of some biocontrol agents and essential oils on strawberry root rot caused by Rhizoctonia solani

Rhizoctonia solani is one of the most important soilborne pathogens which threatens strawberries and may cause significant losses in yield. In this study,the pathogenicity test of ten isolates of R. solani isolated from soil and different plant species i.e. cucumber, mint, bean, pear, citrus, tomato and strawberry was carried out on strawberry plants and they were all pathogenic. Molecular characterization of R. solani isolates by sequencing conducted by the partial rDNA internal transcribed spacer (ITS) revealed 99% homology among the isolates. R solani isolates belonged to three different AG groups. The isolates sequences clustering supported the genetic basis of the anastomosis groups. Five isolates belonging to AG-G, four isolates belonging to AG-F and one isolate belonging to AG-3. In vitro investigation of ten isolates of suppressing R. solani mycelia growth revealed potential suppressive effects. T. longibrachiatum (T4) strain showed the highest suppressive effect (72.22 %).While,mint and clove oils at 0.5% concentration showed a reduction of R. solani 71.11 and 67.77%, respectively. In greenhouse experiments, T. longibrachiatum (T4) was the most effective in reducing root rot incidence followed by Mint, Clove oils at 1% concentration then Pseudomonas stutzeri, being 5.33, 8.33, 10.67and 14.33, respectively. Biochemical studies revealed that mint oil significantly increased peroxidase, polyphenol oxidase and chitinase activity in strawberry roots planted in infested soil.