First report of Phaeomoniella chlamydospora pycnidia as petri disease inoculum sources in South African vineyards.
Phaeomoniella chlamydospora is an important fungal pathogen associated with esca and Petri diseases of grapevine (Vitis vinifera) worldwide. Infected propagation material has been identified as a major means of spread, but little information is available about the vine-to-vine spread of P. chlamydospora. The existence of a pycnidial state was known from in vitro inoculation of P. chlamydospora on carnation leaves and moist incubation of infected grapevine canes. Naturally occurring P. chlamydospora pycnidia were first reported in Australian vineyards, but artificial infection attempts with conidia failed. Airborne spores of P. chlamydospora were found throughout the year in French and Californian vineyards, but the origin of this inoculum was not confirmed. Vineyards showing decline symptoms (stunted growth, vascular streaking) were sampled in the Western Cape Province (South Africa) during May 2011. Cordons, trunks, and old pruning wounds were collected. Pycnidia were found in the crevices, cracks, and on pruning wounds and on bark of 35-year-old Pinotage vines in Stellenbosch. Aggregations of 1 to 50 conidiomata were often found on bark surfaces. Morphological observations, molecular data (sequence analysis of the DNA extracted from the mycelium and the internal transcribed spacers 1 and 2 as well as the 5.8S rRNA gene) and pathogenicity test confirmed the causal agent as P. chlamydospora. This is thought to be the first report of the occurrence of P. chlamydospora pycnidia in South African vineyards and the first report to prove the capability of conidia from pycnidia to infect pruning wounds and cause vascular streaking typical of Petri disease.