Morphological and molecular characterization of Podosphaera xanthii, causal agent of powdery mildew in husk tomato and watermelon

Objective: To determine the causal agent of powdery mildew in husk tomato and watermelon, as well as its morphological and molecular characterization. Design/methodology/approach: Leaves with powdery mildew symptoms were collected from husk tomato (Physalis ixocarpa) and watermelon (Citrullus lanatus) in Iguala, Guerrero, Mexico in 2018. From two isolates (Phyxa1 and Phyxa2) of husk tomato and two of watermelon (Citrus1 and Citrus2), the morphological characterization was carried out by assembling morphological structures and visualizing them under an optical microscope. For molecular characterization, the ITS region was amplified with the use of primers ITS1 and ITS4, PCR was performed and the products obtained were sequenced in the company Macrogen®. A phylogenetic analysis was performed with the resulting sequences and they were compared with other sequences available in GenBank. Results: It was determined that there is morphological and genetic variability between isolates from husk tomato and watermelon. The largest sizes of conidiophores and conidia were from Phyxa1 and Phyxa2 isolates, the smallest sizes were found in Citrus1 and Citrus2. The isolates presented a tendency to group according to the host, the Phyxa1 and Phyxa2 isolates were associated with Solanacea isolates, while the Citrus1 and Citrus2 isolates were grouped with isolates of the Cucurbitaceae family. Findings/conclusions: Podosphaera xanthii was shown to be the agent associated with powdery mildew in husk tomato and watermelon. The morphological and genetic variability of P. xanthii was determined, which was associated with the host of origin.