Evaluation of anthracnose-resistant greater yam and the mechanism of abscisic acid-mediated disease resistance

The greater yam (<italic>Dioscorea alata</italic> L.) is a major food crop in tropical and subtropical regions, particularly in Africa. However, anthracnose disease, caused by <italic>Colletotrichum</italic> spp., significantly threatens greater yam production. Identifying anthracnose-resistant greater yam varieties is therefore of great importance. In this study, we evaluated the anthracnose resistance of 46 greater yam varieties using <italic>in vitro</italic> leaf inoculation with <italic>C. alatae</italic> isolated and identified at Jiangxi Agricultural University (Nanchang, China). We examined the physiological and biochemical indices, including stomatal density and opening, activities of peroxidase (POD), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL), as well as abscisic acid (ABA) levels, in leaves of varieties with different resistance levels. Compared with susceptible varieties, immune and resistant varieties exhibited lower stomatal density and higher leaf wax content. Following infection, immune and resistant varieties rapidly increased POD and PAL activities, along with the expression of their encoding genes. Stomata in immune and resistant varieties closed, whereas those in susceptible varieties opened, facilitating pathogen invasion and resulting in rapid growth and accumulation of anthracnose mycelia in susceptible varieties. Resistant varieties maintained higher leaf ABA levels than the susceptible varieties during the early stages of inoculation. Additionally, the exogenous application of ABA enhanced the resistance of susceptible varieties. Our findings suggest that resistant greater yam varieties may improve resistance by increasing endogenous ABA levels and inducing stomatal closure, thereby hindering the invasion of anthracnose pathogenic mycelia. These results provide important insights for breeding anthracnose-resistant greater yam varieties and developing sustainable disease management strategies.