Arbuscular Mycorrhizal Fungi as a Biocontrol Agent for Angular Leaf Spot Disease of Common Beans (Phaseolus vulgaris L.)

Angular leaf spot disease caused by Phaeoisariopsis griseola is the most important disease which caused yield losses up to 80% of common beans. This study aims to induce natural defense of common bean against angular leaf spot disease by mycorrhization. The samples of Phaeoisariopsis griseola were collected in the field of 02 different agro-ecological zones considered as major bean production area in Cameroon. The Phaeoisariopsis griseola were isolated on PDA solid medium, and identified based on morphological. A pot experiment was carried out using a bifactorial device. The first factor was two varieties of common bean (GLP 195-C and PNG). The second factor consisted of eight treatments, namely T0 : absolute control, T1 : mycorrhizal treatment with Acaulospora tuberculata, T2 : mycorrhizal treatment with Gigaspora gigantea, T3 : mycorrhizal treatment with Entrophospora infrequens, T4: Terazeb synthetic fungicide treatment (positive control), T5 : mycorrhizal treatment with Acaulospora tuberculata and Gigaspora gigantea combination, T6 : mycorrhizal treatment with Acaulospora tuberculata and Entrophospora infrequens combination, T7 : mycorrhizal treatment with combination of Gigaspora gigantea and Entrophospora infrequens. Incidence, severity of angular leaf spot disease and biochemical parameters were assessed. The results showed that pots treated with the mycorrhizae Entrophospora infrequens, Gigaspora gigantea, Acaulospora tuberculata and combinations of mycorrhizae Acaulospora tuberculata and Gigaspora gigantea, Acaulospora tuberculata and Entrophospora infrequens, Gigaspora gigantea and Entrophospora infrequens contributed significantly to improved amino acid content from 44% to 70%, proline content from 20% to 33%, total phenol content from 36% to 60%, protein content from 16% to 41%, flavonoid content from 27% to 82%, tannin content from 60% to 298%, polyphenoloxidase content from 15% to 74% and peroxidase content from 31% to 109% compared with the control in the two common bean varieties. Similarly, the mycorrhizae treatments and the mycorrhizae combination significantly reduced the development of angular leaf spot disease by 20 to 80% compared with the control in both common bean varieties. This work shows that Arbuscular Mycorrhizal Fungi made a significant contribution to reducing the development of angular leaf spot disease in the pots while improving common bean grain yield.