Archivio Journal of Plant Pathology

Abstract:

In July 2014, a white fungal efflorescence was observed on the stems and both surfaces of mature and young leaves of a caper plant (Capparis spinosa) growing in the Campus of the University of Bari. Light microscope observations revealed the presence of simple or branched conidiophores emerging through leaf stomata, and bearing conidia singly or in short chains. Primary (pyriform) and secondary (cylindrical) conidia, typical of the anamorphic stage of Leveillula taurica (Lév.) G. Arnaud, causal agent of powdery mildew (Palti, 1988), measured on average 62.2×20.2 μm (±7.23×±2.18 μm standard deviation). The teleomorphic stage was not observed during three months of observation. A 630-bp PCR amplicon obtained with the ITS1/ITS4 primer pair was sequenced (BMR Genomics, Italy) and deposited in GenBank under the accession No. KP164030 (isolate designated CSP-PUG1). The sequence shared up to 99% homology with several accessions of L. taurica, including the one previously reported on caper (AB045002), and other species of the genus. The Koch’s postulates were met with a successful pathogenicity test on caper. It is worth noting that, besides this plant, I have never observed powdery mildew on spontaneous caper plants in different Apulian (southern Italy) sites, even when they were growing close to highly susceptible plant species such as Convolvulus arvensis. Therefore, the sporadic pathogen occurrence on this plant might be due to microclimatic conditions unusual for caper. Indeed, the diseased plant had grown under a prolonged shading near a building, but caper normally grows in sun-drenched places like stone walls and rocky cliffs. To the best of my knowledge, this is the first report of L. taurica on caper in Italy.