Epidemiology, biology and detection of Phaeoacremonium spp. and Phaeomoniella chlamydospora Vine Decline (black measles or esca and Petri disease (syn: Young vine decline) in California
Esca and Petri disease have been documented in all of the major viticulture production regions of California. Diseases caused by the vascular pathogen, Phaeomoniella chlamydospora, is more likely responsible for Petri disease, but esca can be caused by both P. chlamydospora and numerous species of Phaeoacremonium. These fungi are also responsible for poor vineyard establishment in many newly-planted vineyards. In these cases, the young vines may have been infected prior to planting, but it is not known from whence the pathogen comes. The infection courts for these fungi are generally the xylem parenchyma and vessels of mature grapevine xylem and we suspect that nursery infection is occurring through these structures. It is suspected that the pathogens may be passed from mother vines to progeny vines via spores carried either in the sap flow or by external contamination of bark by the release of ascospores from perithecia.
Currently, it is known that these fungi are present in propagation material coming from mother plants in nurseries. A detection method using nested-PCR was developed to provide a rapid and sensitive test to determine the presence of these fungi in grapevine material throughout the propagation process.
It was demonstrated that pruning wounds are susceptible to infection by conidia of both T. minima and P. chlamydospora. Spores of several Phaeoacremonium species and P. chlamydospora were trapped in infected vineyards. Also propagules of both fungi were found on the surface of clusters, leaves and trunks of grapevine in infected vineyards in California. Perithecia of T. minima have been identified on moist incubated infected grapevine woods in California and Australia. Natural perithecia were also found in the deep cracks and wounds in infected vineyards throughout California.
Two other species which have been reported only once before on grapevines in California, Pm. angustius and Pm. Mortoniae, were also found to be somewhat common in California. After confirming the presence of Togninia spp. and Pa. chlamydospora in nursery propagation wood and as overwintering structures in California vineyards, we have begun to examine different applications for disease management. Liquid lime sulfur has been shown to be effective in killing the spores inside the pycnidia of Pa chlamydospora and the ascospores inside the perithecia of T. minima. Additional dormant applications need to be conducted in the next few years to determine the effect of lime sulfur and other tested fungicides on disease expression in infected vineyards. This work will require long term studies to take into account the discontinuity of the disease. Our results indicated that pruning wounds were susceptible to several fungal pathogens responsible for shoot dieback of grapevine, and we also have recovered several of these fungi in concert from wood cankers. Therefore, we are now testing the ability of boron-based material in comparison to other fungicides to control several wood decay fungi of grapes including E. lata, Botryosphaeria rhodina, B. dothidea, B. obtusa, B. sarmentorum, Phaeomoniella chlamdospora, Phaeoacremonium aleophilum and Pleurostomophora richardsiae
