Resistance inducers and biochemical mechanisms in the control of anthracnose in cowpea

Different responses are observed in plants after infection by pathogens. The usage of systemic inducers, whether biotic or abiotic, has the function to increase the enzymatic production of the plant defense system. In that sense, our present research aims to evaluate the disease severity of anthracnose in the cowpea cultivar "sempre-verde" infected with Colletotrichum lindemuthianum URM 5771 and subjected to both biotic and abiotic resistance inducers, as well as evaluate the enzymatic activity of plant defense. The experiment was performed in a greenhouse with a completely randomized splitplot design with six treatments: four abiotic plant resistance inducers, acibenzolar-S-methyl, beta-aminobutyric acid, chitosan, and salicylic acid; one biotic inducer, the filamentous fungi Trichoderma aureoviride URM 5158; and a control with only water. The plant leaves were sampled at four time points, 4, 8, 12 and 20 days after inoculation with the plant pathogen, to measure the enzymatic activity of beta-1,3-glucanase, catalase, peroxidase, polyphenoloxidase, and protease. The abiotic inducers acibenzolar-S-methyl, beta-aminobutyric acid, and chitosan and the biotic inducer presented the highest potential in reducing the anthracnose caused by C. lindemuthianum URM 5771 in cowpea plants by showing the lowest values of injury severity over time. The disease progression showed a proportionate shift in enzymatic activity in that the inducers salicylic acid and T aureoviride URM 5158 promoted the highest enzymatic activity when compared to the other inducers. High correlations between the enzymatic activity of peroxidase and polyphenoloxidase and anthracnose severity were observed in cowpea plants. The use of abiotic and biotic resistance inducers presents high potential for anthracnose control in cowpea plants; however, more studies should be carried out covering different environments, plant cultivars and climatic conditions.