WINETECH Technical Yearbook 2020

the Okanagan Valley over two years. The first spore release was detected at the end of winter (when daily temperatures raised above zero to 5°C or higher) and was often correlated with rainfall, though not always. The saprophytic colonisation of Neofu- sicoccum species of grapevine bark was investigated by a group in New Zealand. They found that Neofusicoccum species remained latent in the bark, when the cane was wounded, the pathogen progressed to- wards the wound. Also they could observe, with microscopic images, the pathogen entering through a lenticel (no wound- ing). This shows that Botryosphaeriaceae pathogens don’t need a wound to be able to infect. The role of clean rootstocks was confirmed with various studies. In Uruguay, rootstock mother plants were analysed for the occurrence of trunk disease pathogens. Of five different rootstock varieties investigated (SO4, Gravesac, Paulsen 1103, 3309 Couderc and RR101-14), the infection levels ranged from 6 to 38% close to the base of the cane and 4 to 18% on the upper part of the cane. The occurrence of the Botryosphaeriaceae on grapevine and alternative hosts and pos- sible implications were presented from our own research. The study concluded that 22 woody hosts in close proximity to Western Cape vineyards harboured Botryosphae-

period. Several such vineyards were visited and although most of these vines are still infected, their lifespan has been increased to such an extent that producers can make the re-plant arrangement and still produce grapes. Infected vines all show internal brown necrosis and black-brown vascular occlusions. HIGHLIGHTS FROM THE SCIENTIFIC PROGRAMME GETTING A BETTER UNDERSTANDING OF TRUNK DISEASES LIFE CYCLES Various studies investigated spore dis- persal patterns of the major trunk dis- eases in their region. The identification of conditions that favour spore release and consequent infection periods is important in developing control measures. In Aus- tralia, Eutypa dieback and Botryosphaeria dieback pathogens were monitored in four wine growing regions over three years. The results showed that the spore dispersal was sporadic and varied between regions, season and year. In South Australia, spores were primarily detected in late winter and early spring, while in New South Wales, a high number of spores were trapped over summer. Spores were generally recorded during or immediately after rain, but not all rain events resulted in spore detection. In British Columbia, the spore dispersal of Botryosphaeria dieback was followed in

riaceae species. In total, more than 20 Botryosphaeriaceae species occurred on these hosts of which 15 were also found on grapevine. One of these species, Neo- fusicoccum stellenboschiana , frequently occurred on grapevine, as well as many of the other woody hosts. A population genet- ic study showed that identical genotypes were found on grapevine, as well as these alternative hosts, which support the notion that these hosts act as inoculum sources. DISEASE MANAGEMENT An economic assessment of the potential gains from adopting preventative pruning practices and vine surgery was conducted in California vineyards. They found that preventative practices (like pruning wound protection) adopted early (≤5 years old) and vine surgery adopted in mature vine- yards (>10 years old) significantly reduced yield losses, raised revenue and extended vineyard profitable lifespan. The adoption of preventative practices in year 10 had very little economic value. They recom- mended preventative practices in young vineyards and vine surgery after symptoms appear in approximately 20% of vines of before year 15. New developments in terms of host resis- tance were also reported at the workshop. A study in Nebraska, USA, examined 25 20-year-old hybrid grapevine cultivars for the occurrence of trunk disease symp-

toms. Two cultivars, ‘Norton’ and ‘Brianna’, showed less symptoms and would have potential as tolerant to trunk diseases. ‘Norton’s’ ancestry in Vitis aestivalis was speculated as contributing to this toler- ance. A double-grafted vine was proposed by a research group from Colmar. Above the rootstock, a more tolerant interstem vine is grafted using for example Vitis sylvestris and then on top of this, the Vitis vinifera scion cultivar. Grafting trials that have been done, seem to hold promise. Several presentations and posters were presented on the use of biocontrol or- ganisms for the control of GTDs. In the nursery context, several contributions were made. In Spain, Streptomyces , Pythium oligandrum and Trichoderma atroviride were applied by soaking of one-year-old dormant grafted plants for 24 hours and applying two additional drenches with drip irrigation. They found significantly reduced fungal incidence of both black foot and Petri disease pathogens. However, there was no effect on shoot weight and root weight were significantly lower in all BCA treatments in comparison to the control. In Italy, products of T. asperellum and T. gamsii were applied at hydration, planting and additional three drenches in the field. These treatments reduced the occurrence of P. chlamydospora up to 70%. In another study in Italy, Trichoderma atroviride SC1 was applied during the nursery process

WINETECH TECHNICAL YEARBOOK 2020 47