Biological control of sesame charcoal rot by gamma-irradiated mutants of Trichoderma aureoviride and their RAPD-PCR fingerprinting

The potential of Trichoderma spp. for biocontrol of phytopathogenic fungi has been well documented. In this study, the wild-type isolate of Trichoderma aureoviride (Tv59) was treated with the target dose of 250 Gy as the optimum dose. Twenty-six mutants were preliminarily screened based on better growth rates. In vitro, antagonistic evaluation of the 26 mutants and wildtype was performed against two Macrophomina phaseolina isolates (F33 and H7). Six mutants (Tv2(4), Tv20(6), Tv25(6), Tv3(3), Tv4(5), and Tv3(4)) showed remarkable inhibitory activity and were selected for further examination in greenhouse trials. Greenhouse assessment of the selected mutants against M. phaseolina isolates revealed Tv20(6) and Tv25(6) as the most highly effective treatments screened for the measured indices. Moreover, the total genomic DNA of the wild-type isolate and its 26 corresponding mutants were analyzed to determine their genetic variability through the RAPD technique. Five RAPD primers generated different banding patterns and yielded a total of 178 amplified fragments, 172 amplicons (96.62%) were polymorphic. While the dendrogram obtained by UPGMA cluster analysis of combined RAPD fingerprints differentiated the wild-type from its mutants at approximately 40% similarity level, the mutants were categorized into two clusters. Based on Jaccard similarity coefficients, eight mutants (Tv25(6), Tv1(5), Tv14(5), Tv20(6), Tv3(4), Tv40(6), Tv33(6), and Tv14(6)) showed the lowest genetic similarities with the parental isolate. The possibility of improvement in biocontrol effectiveness of T. aureoviride through random mutagenesis and detection and differentiation of genetic changes induced by gamma rays using RAPD analysis was successfully proved in the present study.