Austropuccinia psidii infection changes stomatal dynamics and leaf gas exchange of guava leaves: A physio-histopathological assessment

This study aimed to characterise the life cycle of Austropuccinia psidii, the causal agent of myrtle rust, in guava cv. Paluma and to determine how this pathogen affects gas exchange in diseased leaves. The pathogen formed appressoria on ordinary epidermal cells and intercellular hyphae and intracellular branched lobe-shaped haustoria in parenchyma cells. In the stem, hyphae grew in the cortical region and crossed between tracheary cells, reaching the medullary region. In the leaf, hyphae colonised the intercellular spaces of the main vein and mesophyll and the substomatal chamber. Colonisation of the substomatal chamber by A. psidii changed the stomatal dynamics and leaf gas exchange. The stomatal response to light was slower and had a smaller amplitude in diseased guava leaves. Consequently, impaired stomatal movement induced by A. psidii is an additional factor changing the performance of plants under abiotic stress.