Agricultural production is greatly influenced by diseases caused by fungi. Penicillium digitatum is a common fungus that causes blue mold in citrus fruits. In addition, Fusarium and Phytophthora species are also recognized as citrus pathogens, involving in root rot and fruit rot. Currently, the use of microbial bioproducts to control fungal pathogens is always prioritized for an organic and sustainable agriculture. Trichoderma species are considered as safe filamentous fungi that antagonize against many fungal plant pathogens. In this study, 10 strains of Trichoderma were isolated and monitored for their antagonistic capacity towards the citrus pathogen P. digitatum. The strains Trichoderma Tr.6, Tr.7 and Tr.8 exhibited inhibitory efficacy of 95-100% against P. digitatum. Additionally, these three strains also strongly suppressed the growth of two other common plant pathogens Fusarium oxysporum and Phytophthora capsici. Based on the morphological characteristics and the sequence analysis of the internal transcribed spacer (ITS) region of rDNA, all three strains Tr.6, Tr.7 and Tr.8 were identified as Trichoderma asperellum. These Trichoderma strains represent promising potentials for applications in the production of bioproducts for the control of pathogenic fungi infecting citrus and other crops.
Penicillium chrysogenum is a well-known filamentous fungus for production of penicillin and some valuable secondary metabolites. In this study, we indicated that two strains VTCC-F1170 and VTCC-F1172 identified as P. chrysogenum, which are preserved at Vietnam Type Culture Collection (VTCC) of Vietnam National University Hanoi, exhibited the ability of antibiotic production to inhibit the tested bacterium Staphylococcus aureus on the agar plates by diffusion assays. Additional analyses of the morphological characteristics and the rDNA ITS (internal transcribed spacer) sequence confirmed that the identification of both strains as P. chrysogenum was completely accurate. These important evidences guaranteed that the fungal strains are reliable for the researches on genetic engineering of P. chrysogenum. Experimental assays of antibiotic susceptibility showed that the growth of both strains VTCC-F1170 and VTCC-F1172 was completely inhibited by nourseothricin at 50 μg/ml and phleomycin at 150 μg/ml. Using the Agrobacterium tumefaciens-mediated transformation method, we have succesfully transferred the nourseothricin resistance marker into the genome of the VTCC-F1170 strain.
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