Molecular characterization and screening of selected antagonistic microorganisms against major maize and bean pathogens

Abstract

Various plant diseases (Fusarium ear rots, bean anthracnose and damping off of seedlings) caused by phytopathogenic agents are known to cause considerable crop losses to agricultural yield all over the world. The use of antagonistic microorganisms in controlling maize and bean pathogens is an area of great potential in order to increase yield, thereof mitigate food insecurity. The aim of this study was to characterize and screen selected tropical fungi and bacteria for antimicrobial activity against maize pathogens (Fusarium moniliforme, Fusarium graminearum) and bean pathogens (Colletotrichum lindemuthianum, Pythium ultimum). A total of 87 tropical fungi were collected from Kakamega tropical rain forest. Two bacterial isolates; B1 and B5 (which had already been identified as Bacillus amyloliquefaciens), were obtained from groundnuts and mushroom respectively. Isolation and culturing of the microorganisms was done in different media of varying pH. Extraction, amplification and purification of the tropical fungi deoxyribonucleic acid-DNA, was done using BIO BASIC EZ-10 spin column DNA mini-prep kit. Molecular characterization was done through sequencing using the internal transcribed spacer region and ß-tubulin primers. Preliminary screening of the tropical fungi against test organism; Bacillus subtilis and Mucor plumbeus was done. Fermentation and extraction of secondary metabolites was also done on the active tropical fungi isolates. Anti-microbial activity of the selected tropical fungi and bacteria against the four phytopathogens was studied in vitro using the dual culture assay and the resulting inhibition zones analyzed using analysis of variance. A total of 64 tropical fungi were isolated into pure and axenic cultures. The cultures grown on potato dextrose agar at pH 5.6 ± 0.2 showed better mycelial growth compared to Mueller Hinton agar, Sabouraud Dextrose Agar and Yeast Malt Glucose agar. Eight tropical fungi were active against B. subtilis and two were active against M. plumbeus. Majority of the isolates were from the genus Xylaria (10), Psathyrella (8) and Fusarium (7). F. solani had the highest inhibition of 64% while Phaeomarasmius sp. had the lowest inhibition of 19.1% both against F. moniliforme. Epicoccum sp. inhibited the mycelial growth of P. ultimum by 38% and also inhibited C. lindemuthianum by 58%. None of the fungal antagonists inhibited the mycelial growth of F. graminearum. Bacillus amyloliquefaciens (B1 and B5) suppressed the mycelial growth of the four phytopathogens. The results of this study indicate the potential of antagonistic tropical fungi and bacteria as possible biocontrol agents against maize and bean fungal pathogens.