The screening for potential fungal and bacterial epiphytes and endophytes recovered from grapevine pruning wounds to use as a biocontrol agents continued. Fifty isolates of fungi and bacteria were isolated from grapevines of different ages and cultivars growing in California and were identified based on morphological characteristics and via PCR. The retrieved isolates were tested both in vitro and in planta as potential antagonists against Botryosphaeria sp. and Eutypa lata. The preliminary screening for antagonistic isolates was performed in vitro considering inhibition of mycelial growth, inhibition of spore germination, and production of volatile antifungal compounds. Among those tested, one bacterial isolate (bp1) and two Trichoderma viridae isolates (UCD1 and UCD2) showed a strong inhibitory effect in vitro against Botryosphaeria spp. and Eutypa lata. Macroscopic and microscopic observations suggested that the inhibition of pathogens growth by both the bacterial isolate and the Trichoderma viride could be due by the secretion of antifungal metabolites. A direct mycoparasitism was also observed shortly after the pathogens were put in contact with the fungal antagonist. Further in vitro experiments were conducted using French squared bottles to assess the ability of the biocontrol agents, as well as of new experimental products, to protect grape wood chips from pathogen colonization. Standard fungicides normally used in the control of grape canker diseases such as myclobutanil (Rally) and thiophanate methyl (Topsin M) were used as reference controls. Preliminary results showed that wood chips treated with biocontrol suspension (bp1, UCD1 and UCD2) exhibited the same level of protection as the fungicide mixture (Rally + Topsin) used as controls. Overall, fungal growth on wood chips was prevented with Bp1, UCD1 and UCD2 and experimental product mixture for a longer incubation time than wood chips treated with Rally and Topsin. These promising in vitro results were confirmed by in planta evaluation conducted in two field trials. Pathogens were not recovered from the pruning wounds treated with Bp1 bacterial suspension. Visual observation indicated no phytotoxicity on buds and leaves treated with Bp1. However, bp1 is a known human pathogen in compromised individuals so we are dropping the species from the testing. We are though still trying to see if the metabolites produced by this bacterium might be used for control. Both Trichoderma strains are currently under field investigation. Based on the obtained results we have been able to assess the optimal application time of biological agents in order to guarantee an adequate protection of the pruning wounds. In fact, the antagonist organisms need to fully colonize the pruning wound surface in order to function against canker pathogen infections. We are also evaluating dormant fungicide treatments using spray applications by tractor for canker disease prevention under ?natural? disease pressure. A fungicide trial (third year) is being conducted in a vineyard in Napa County as a five year study to asses this objective.
/wp-content/uploads/2017/09/AFV-Header-Logo.png 0 0 AVF /wp-content/uploads/2017/09/AFV-Header-Logo.png AVF2011-10-16 05:51:572017-10-16 05:52:51Grapevine Canker Diseases in California