Control of Eutypa Dieback of Grape
Three objectives were investigated in 1997, the primary short term objective of this research is to find an effective control of Eutypa dieback, caused by the fungus Eutypa lata. Field trials were performed in different production areas in 1997 in Yolo and San Joaquin Co. Dormant grape cvs (Cabernet Sauvignon, Grenache, Petite Sirah, Semillon) were pruned to 2 or 3 buds at different timings in each trial. Pruning wounds were protected with fungicides (1%Benlate, 20%Boric acid, 20%Soap, Nectec Paste, Proguard C and Proguard Gel) and biocontrol agents (Fusarium lateritium, Cladosporium herbarum) and inoculated 1 day later with Eutypa lata mycelium growing on agar or floating in water. In addition, Benomyl, Fusarium lateritium and Cladosporium herbarum were inoculated 7 and 14 days after treatment. The same fungicides were also tested in vitro by dipping grape wood blocks into the material and measuring the percent of wood blocks colonization by Eutypa mycelium and percent reisolation from wood blocks. The fungicide work has shown that generally, lab and field studies have given similar results. Nectec paste and 1%Benlate in vitro prevented 100%Eutypa reisolation from wood blocks, also resulted in a high rate of protection of pruning wounds in each field trial. At the least, the lab screening can be used to quickly evaluate potential fungicides to be used in field trials. Thus, Nectec and Break EC have shown promising in vitro control efficacy against Eutypa dieback. The second objective was to study plant/pathogen interaction in order to understand the physiological and biochemical processes of grapevine infection and colonization. Thus, better control of the disease could occur in the field, and cvs susceptibility differences may be better understood. In vitro tests have shown that no cv. difference have been observed when Eutypa mycelium was placed on autoclaved dead wood from one tolerant (Merlot) and one susceptible cultivar (Cabernet Sauvignon). Also, tests conducted on 4 phenolic compounds which naturally occur in reaction to pruning induced an inhibiting effect on the growth of Eutypa lata. Trans-Cinnamic acid has completly inhibited the growth of the fungus at the 3 pH is tested, while trans-Stilbene has no effect. Para-hydroxy-Benzoic acid and m-Coumaric acid show their maximum inhibitory effect to be at pH=5.4 and their lowest effect at pH=5.7. The third objective concern the study of Eutypa population which will offer insights into whether we are dealing with one or more sites of ascospore production and whether we might be dealing with other inoculum types. Collection of Eutypa isolates from various sources and sites was begun in 1996. Isolates had been also obtained from grapes in the East coast (Michigan), Italy, France and also from Rosaceae plants (apricot, cherry…). The technique of DNA extraction from Eutypa lata isolates has been completed and DNA has been extracted from all the isolates in the collection. All the isolates have a DNA molecular weight of 23 kb.