Indução de resistência em feijão-caupi com fontes de fosfito

Abstract

Cowpea (Vigna unguiculata (L.) Walp.) is a crop of socioeconomic importance to farmers. However, its production is compromised by the occurrence of phytopathogens and the salinity of irrigation water. Seeking to reduce losses, phosphite sources have been used as inducers of resistance to these stresses. The objective of this work was to evaluate the efficiency of different phosphite sources as inducers of resistance to biotic and abiotic stresses in cowpea plants. To determine the efficiency of different doses and sources of phosphite in the in vitro control of Fusarium sp. and in inducing resistance in the crop, copper, magnesium, calcium, manganese, Ranger®, and Titanium® phosphites were used at doses of 0, 150, 300, 450, 600, 750, and 900 mg P2O5 L-1, respectively, and an additional treatment with the fungicides was applied. In the in vitro experiment, the mycelial growth rate index, the percentage of mycelial growth inhibition, sporulation, and the percentage of sporulation inhibition were evaluated. In the in vivo experiment, seeds were treated, inoculated, and sown, remaining for 31 days for evaluation of morpho-agronomic and physiological characteristics, infection rate, and activity of the enzymes peroxidase, polyphenol oxidase, and phenylalanine ammonia-lyase. In the second experiment, the application of calcium phosphite, copper, manganese, and Titanium® sources as inducers of resistance to biotic and abiotic stresses in cowpea, a control, and fungicides were evaluated. Seeds were treated and inoculated with Fusarium sp. and sown; the treatments were also applied via foliar application. The pH and electrical conductivity of the drained water, morpho-agronomic and physiological characteristics, enzymatic activity, infection rate, and productivity were evaluated. In the third experiment, the effect of different phosphites used in the first experiment, on the induction of anthracnose resistance in cowpea was evaluated. The experiment was carried out in the Chã-de-Jardim experimental area during the 2023 and 2024 growing seasons. The treatments were applied only via foliar application. Physiological parameters, enzymatic activity, and anthracnose severity were evaluated at flowering, with measurements taken every seven days after the natural appearance of the first symptoms, and productivity was assessed at the end of the cycles. In the in vitro experiment, Titanium® was effective in inhibiting mycelial growth and sporulation of Fusarium sp. In the in vivo experiment, phosphite sources were effective in reducing the infection rate of plants inoculated with Fusarium sp., and copper and calcium phosphite showed an increase in peroxidase activity when compared to the fungicide control treatment. In the second experiment, plants irrigated with water with a conductivity of 3.0 dS m-1 and inoculated with Fusarium sp. showed reduced chlorophyll activity, chlorophyll fluorescence, and higher peroxidase enzyme activity. Plants inoculated and treated with calcium phosphite, manganese phosphite, and Titanium® showed higher peroxidase enzyme activity. In the field, Ranger® and magnesium phosphites increased productivity values in both growing seasons, all phosphite sources showed potential for controlling anthracnose severity, and copper, Ranger®, and manganese phosphites showed higher peroxidase activity.