Study of the Endophytic Nature of Phaeoacremonium and Phaeomoniella spp. In Grapevines

Petri disease (young vine decline) and esca (black measles) are increasing in importance in California vineyards. Our research investigates the endophytic biology of the causal organisms, focusing on the capacity of penetration and invasion of grapevine tissues and on the effect of stress factors in the pathogenic response of these fungi e.g. what triggers the pathogen to become pathogenic.Isolation results and scanning electron microscopy observations showed that P. inflatipes and P. aleophilum are capable of penetrating uninjured roots and shoots of tissue-cultured plants. Their mode of penetration, whether through direct penetration of the cuticle or through natural openings, is still under investigation. Root inoculation of grapevines in the greenhouse showed that the fungus was able to colonize the scion, cane and upper stem of both water-stressed and non-stressed vines. Recovery of P. inflatipes did not differ among treatments. There was vascular discoloration in the crown, scion, and upper stem but foliar symptoms characteristic of young vine decline have not yet occurred. The lack of differences in infection is not surprising nor is the lack of symptom development. Field evaluation of the effect of stress factors ? root configuration, early fruiting, fertilizer treatments, and water deficit are still in progress in Napa and Sonoma County and in Davis. Comparison of the effect of sap from water stressed and non-stressed vines showed that the sap from stressed vines enhanced the growth of P. inflatipes in vitro. Preliminary results indicated pronounced differences between the protein content of stress vs. non-stressed plants. Protein separation by 2D Gel electrophoresis indicated qualitative differences in the sap protein content. The identity of these proteins is being determined. Studies on infection of grape berries by phaeoacremonium spp. Showed that young berries were occasionally infected in the absence of injury. Occasional breaks in the cuticle were observed by light microscopy and this was probably the point of entry of the pathogens. In general, however, injury is necessary for penetration and infection. While scanning electron microscopy observations showed the organisms growing on the fruit furface and penetrating the lenticels, light microscopy observations of paraffin sections failed to show conclusively that the organisms are able to penetrate the fruit through the lenticels or undamaged cuticle. Shaking of fruit clusters inside plastic bags with carborandum dust before inoculation induced interveinal chlorosis that resembled naturally occurring leaf symptoms of esca. The symptoms appeared on leaves that are attached to the fruiting stem but not exposed to carborandum or inoculum. The inoculated organisms were reisolated from the inoculated berries but not from the symptomatic leaves thus indicating the possibility that leaf symptoms were induced by toxins produced in the fruit. Fruit clusters, covered with paper bags to determine if the causal organism or causal factor(s) of esca are introduced from the outside, showed symptoms of esca. This result, however, is preliminary since we have a limited number of observations. Washings from berries confirmed previous finding s in our laboratory that P. inflatipes, P. aleophilum, and P. chlamydospora are present on the surface of berries throughout the growing season.