Résumé
Studies on disease progress at the within-leaf scale remain scarce, though they are critical to understand mechanisms, improve models, and identify management options. We investigated the within-leaf progress of Black Leaf Streak Disease (BLSD) of banana, a crop with some of the largest leaves among cultivated plants. Disease progress was monitored under natural infection on nine leaves, each divided into seven predefined spatial compartments and 22 fragments (3512 mm2 each) within these compartments. The diseased area was assessed in these fragments twice a week. Functional principal component analysis was used to model disease progress. Clustering of the disease progress revealed distinct patterns that were linked to the predefined leaf compartments through a correspondence analysis. This helped redefine leaf compartments based on similar disease behavior. We identified four disease behaviors: (i) fragments with an early and fast disease progress, (ii) fragments with a delayed and fast disease progress, (iii) fragments with a delayed start and a moderate disease progress, and (iv) fragments with a delayed start and a slow disease progress. Disease progress showed strong heterogeneity at the within-leaf scale, with an earlier and faster disease progress at the apex of the leaf, whereas the bottom exhibited slower disease progress, both partly explained by initial number of lesions. Variable disease behaviors were observed in other leaf sectors. This study indicates that other factors different from the lesions densities can modulate disease progress at the leaf scale and highlights that BLSD management should be implemented at leaf sectors scale.