Eco-Friendly Microbial Fungicide of Bacillus spp., Trichoderma album, and Saccharomyces cerevisiae on Rhizoctonia solani, the Causal Agent of Potato Black Scurf Disease

Microbial biocontrol agents against Rhizoctonia solani (Rh), the causal agent of potato black scurf disease investigated. Endophyte Bacillus subtilis (Bac1 and Bac2), the fungal bioagents Trichoderma album , and Saccharomyces cerevisiae (yeast) were tested for their ability to inhibit the growth of R. solani using the dual culture technique. Four isolates of R. solani from infected potato tubers were collected from different areas in Alexandria and Behira governorates. All fungal isolates were identified by microscopy and confirmed with distinct morphologies. Molecular identification, DNA isolation, and ITS amplification were carried out on the tested R. solani isolates. The pathogenicity test of the R. solani isolates approved their ability to inhibit radish seeds germination on the water agar media compared to the control treatment in which the % of seed germination was 100%. Pathogenicity on potato plants also confirmed the isolates' potential. Isolate R. solani (Rh1) outperformed the others in terms of pathogenicity, severity on Cara and Spunta cultivars were 87.5% and 81.25%, respectively. As well, the Rh1 isolate exceeds the other isolates in increasing the colored area of potato leaves of the Cara cultivar. Co-culturing B. subtilis and R . solani isolate on PDA resulted in high inhibition rates for all isolates. T. album exhibited inhibition of all R . solani isolates tested on PDA at the rate of 2 according to the scale of Bell et. al., 1982. Scanning electron micrographs showed that T. album hyphae aggregated, penetrated, and deformed the hyphae of R. solani. S. cerevisiae was demonstrated to inhibit all isolates of R. solani on PDA medium when compared to the control treatment, which had a rate of inhibition of 0.00%. Thus, the current study demonstrated the efficacy of endophytes B. subtilis , T. album , and S. cerevisiae in limiting R. solani growth in vitro .