Histological and Molecular Characterization of the Musa spp. x Pseudocercospora musae Pathosystem

Yellow Sigatoka, caused by the fungus Pseudocercospora musae, represents one of the most challenging diseases in bananas, which is aggravated due to the genetic variability of this pathogen. The main objective of this study was to characterize the infection process of P. musae in two banana cultivars with different levels of resistance and to quantify the expression of resistance genes. Inoculated and non-inoculated leaf samples of the two cultivars, Yangambi km 5—resistant and Grande Naine—susceptible, were investigated by light microscopy, histochemistry, scanning electron microscopy, and RT-qPCR. The cultivar Grande Naine showed early signs of P. musae infection, including the production of lipophilic substances and phenolic compounds, while the cultivar Yangambi km 5 was not affected. In the Grande Naine cultivar, the protein kinase gene was upregulated, while in the Yangambi km 5, it was repressed. The WAK2 gene was initially upregulated in both cultivars; however, in Grande Naine, it was subsequently repressed, while in Yangambi km 5, it remained downregulated. These findings have the potential to contribute to more effective management strategies in the control of yellow Sigatoka and the development of banana varieties resistant to yellow Sigatoka.