Quantitative Resistance of Papaya Fruit to Anthracnose Is Associated With Surface Topography, Timely Defences and Reduced Susceptibility Factors

Anthracnose disease, caused by Colletotrichum spp., leads to significant postharvest losses in papaya fruit. In this study, we identified a papaya genotype with quantitative resistance to anthracnose and investigated the mechanisms underlying this resistance using microscopy, fruit physicochemical analyses and transcriptomics. The resistant genotype exhibited several beneficial traits compared to a susceptible genotype, including a thicker cuticular layer, lower stomatal density, greater firmness and lower total soluble sugars. These characteristics can be considered preformed barriers or constitutive defences, or correlate with reduced susceptibility factors. We also found that the resistant genotype responds more rapidly to fungal presence by synthesising components that maintain surface and cell wall integrity, such as cutin and cuticular elements, and by depositing callose. In contrast, the susceptible genotype accumulated more susceptibility factors, including elevated sugar content and activation of cell wall‐degrading enzymes. While the susceptible genotype had a more robust immune response at the later stages of infection, the combination of susceptibility factors and a delayed response to the pathogen was insufficient to control the disease. This study highlights the need to characterise potential susceptibility factors and physicochemical traits to better understand fruit–pathogen interactions. Such knowledge can provide breeding programmes with strong targets for developing crop varieties that are less susceptible to fungal diseases yet maintain quality traits that consumers expect.