Changes in polyphenol oxidase and guaiacol peroxidase enzymes and the expression of pathogenesis-related genes in benzothiadiazole, mycorrhiza-induced or genetic resistance of sunflower plants affected by Sclerotinia sclerotiorum

Abstract

White rot, a major disease in sunflower cultivation caused by Sclerotinia sclerotiorum is difficult to control, with no completely resistant cultivars currently available. Different studies have shown that the application of benzothiadiazole (BTH) and arbuscular mycorrhizal fungi (AMF) can effectively control this disease. It has also been reported that both induced and genetically inherited resistance, elevated polyphenol oxidase (PPO) and peroxidase enzyme (POX) activities, and resistance-related genes expression. This study aimed to elucidate the biochemical and genetic responses of sunflower plants under white rot infection and different treatments by measuring the ROS-scavenging enzymes PPO and POX activities in healthy or infected sunflower plants, as well as identifying some defense genes. Sunflower cultivars with different levels of resistance to Sclerotinia sclerotiorum were used. Pregerminated seeds were soaked in an aqueous solution of BTH before being sown into trays and placed in a greenhouse. Before sowing, AMF was also applied to the substrate. Twenty-one-day-old plants were then inoculated with Sclerotinia sclerotiorum. Our results demonstrated that BTH and AMF induced some degree of systemic resistance in sunflower against white rot, especially combined. Even though the amount of pathogen detected in plants only varied between cultivars, not changing when inducers were applied, disease severity was reduced, demonstrating that treatments were effective against white rot. In addition, the activation of defense-related genes correlated well with the degree of resistance observed in plants. Therefore, our results provide insights for a better understanding of the mechanisms underlying induced-resistance to sunflower white rot infections.