Uso de discos de folhas de cajueiro-anão no estudo do oídio e da antracnose em condições controladas

Abstract

The cashew tree (Anacardium occidentale) has great economic and social importance for the Brazilian Northeast; however, its productivity is limited by important diseases, notably powdery mildew, caused by the fungi Erysiphe necator and E. quercicola, and anthracnose, caused by Colletotrichum spp. The development of management strategies based on genetic resistance and chemical control requires time, resources, and infrastructure, making the development of rapid and low-cost laboratory methodologies for preliminary assays highly relevant. In this context, this study aimed to evaluate the use of the leaf disc method for bioassays of E. quercicola and Colletotrichum spp. infections in dwarf cashew. In the first experiment, the curative and eradicative effects of systemic and contact fungicides on E. quercicola infection were evaluated using young leaf discs of clone CCP 76. The treatments tested were water (control), sulfur (Kumulus®), difenoconazole (Score®), and trifloxystrobin + tebuconazole (Nativo®), applied at 1, 4, and 7 days after pathogen inoculation. Evaluations of the incubation period, latent period, and conidial quantification showed that delayed applications reduced fungicide efficiency, except for Nativo®, which was the most effective treatment at all application times, delaying disease development and preventing sporulation. In the second experiment, a bioassay was developed to study the interaction between Colletotrichum spp. and dwarf cashew, using four inoculation methods (mycelial discs and conidial suspension, with and without wounding). The conidial suspension resulted in greater disease severity, shorter incubation and latent periods, regardless of wounding, demonstrating higher efficiency in inducing anthracnose under in vitro conditions. The bioassay allowed consistent characterization of the onset of the infection process in leaf discs and proved suitable for pathosystem studies and genetic resistance screening. Both experiments confirm that the leaf disc technique is a viable, reproducible, and efficient methodology for phytopathological studies involving powdery mildew and anthracnose in dwarf cashew, enabling advances in the development of management strategies and in the preliminary evaluation of fungicides and resistant genotypes.