TWO TRICHODERMA SPECIES AND BACILLUS SUBTILIS AS BIOCONTROL AGENTS AGAINST RHIZOCTONIA DISEASE AND THEIR INFLUENCE ON POTATO PRODUCTIVITY

Stem canker and black scurf caused by Rhizoctonia solani is a problem facing potato production. In this work, under greenhouse conditions, three compatible bioagents i.e., Trichoderma koningii and T. harzianum (in mixture) and Bacillus subtilis ATCC®11774™ were evaluated individually and in combinations for disease suppression and further effect on plant growth of potato plants. Radial growth of R. solani was inhibited by the two Trichoderma strains and B. subtilis in dual Petri plate assay. In two experiments, significant plant protection was achieved when either B. subtilis added to tubers or Trichoderma mixture was added to the soil. However, soil application with Trichoderma either singly or in combination with tuber bacterization demonstrated the greatest suppression of cankers on potato plants. With respect to plant growth promotion, the greatest proportional increases in plant height were elicited by tuber bacterization combined with soil application of Trichoderma mixture. Dual tuber treatments by Trichoderma mixture with soil applications of bacteria led to the highest increase of plant stolons and leaf numbers in both experiments. Both combined applications and sole soil application by T. mixture recorded the same significant effect in increasing shoot fresh and dry weights of potato plants as well as improved tuber yield and some biochemical parameters (chlorophyll content, total phenol, peroxidase and polyphenoloxidase contents) significantly. This research suggests incorporation of such bioagents to suppress Rhizoctonia diseases and increase the productivity of potato. S