Morpho-anatomical and physiological characterization of rose genotypes in relation to powdery mildew disease resistance

Powdery mildew remains a significant challenge in rose cultivation, necessitating the development of disease-resistant rose cultivars to reduce fungicide dependency. The identification and characterization of physiological and structural basis of host-plant defense provide a quantifiable framework for screening germplasm and integrating durable resistance into high-yielding rose lines. This study evaluates eight rose genotypes categorized by their disease reactions: Immune (IIHRR 13-4), Resistant (R. indica, Arka Nishkant, Knock Out), Moderately Susceptible (IIHRR 4-15-12), and Susceptible (R. multiflora, Arka Swadesh, Arka Parimala) to powdery mildew. Analysis reveals that immunity and resistance are closely tied to restricted pathogen entry through thick leaves and regulated gas exchange. Notably, Knock Out combines extreme leaf thickness (190.67 μm) with the lowest observed stomatal conductance (0.26 mol (H₂O) m^-2 s^-1), while IIHRR 4-15-12 though "Moderately Susceptible," presents a valuable breeding base due to its synergistic combination of leaf thickness (134.33 μm) and low stomatal conductance (0.28 mol (H₂O) m^-2 s^-1).