Effect of Rhizophagus irregularis and Trichoderma harzianum on the Induction of Natural Defense in Cassava (Manihot esculenta Crantz) against Anthracnose

Abstract

Background: Cassava (Manihot esculenta Crantz) is a major staple food crop in Côte d’Ivoire. It contributes significantly to food security and serves as a source of income for farmers. However, cassava production is affected by phytopathogens. Aims: This study was conducted to evaluate the effects of two biostimulants, Rhizophagus irregularis (RI) and Trichoderma harzianum (TH) on photosynthetic pigment synthesis, peroxidase and chitinase activities, and anthracnose control in cassava. Place and Duration of Study: The two-month in vivo studies were conducted at the Ecology Research Center in Abidjan. A second study, focusing on defence compounds, was carried out at the Biocatalysis and Bioprocesses Laboratory at Nangui Abrogoua University, Côte d’Ivoire. Methodology: Three cassava cultivars, YACE, 9620A, and TMS4(2)1425, were grown in vivo, with RI and TH treatments applied at planting. These fungi were applied individually and in combination (RI+TH). Plants treated with RI and TH were inoculated with the pathogen Colletotrichum gloeosporioides, 48 days after sowing. Results: The results showed that, for each cassava cultivar, the RI+TH co-treatment showed the strongest inductive effect. For photosynthetic pigments, the highest Chl a and Car values were 38.89 and 9.60 µg/g FW, respectively, for the YACE cultivar; 32.54 and 9.69 µg/g FW for 9620A; and 36.08 and 9.02 µg/g FW for TMS4(2)1425. For enzyme activities, leaf peroxidase levels ranged from 0.90 to 0.98 ΔOD/min/mg prot., while root levels ranged from 1.54 to 1.69 ΔOD/min/mg prot. For chitinases, the highest activities were 103.01 mmol NAG/min/mg prot. in the leaves and 110.08 mmol NAG/min/mg prot. in the roots of the plants. Regarding anthracnose symptoms, the necrotic area caused by C. gloeosporioides in infected plants was reduced by 45 %, 47 %, and 49 % in YACE, TMS4(2)1425, and 9620A, respectively. Conclusion: The application of R. irregularis and T. harzianum induced resistance to anthracnose in cassava.