Grapevine Trunk Diseases (GTD) are major limiting factor to grapevine production systems because they decrease the profitable lifetime expectancy of vineyards. Standard business models for vineyards are based on 25 years or more of maximum productivity. Affected vineyards often witness a decrease in productivity at around 10 years old, which often manifests by initial loss of spur position and decreased vigor (Figure 1). As vineyards age, the diseases progress causing cordon dieback and eventually vine death (Figure 2). The drop in productivity is also accompanied with a decreased in fruit quality and marketability. This condition implies that for growers the break-even point is reached at a later time than projected in the business model and that profits are eroded. Trunk diseases are caused by a set of taxonomically unrelated Ascomycota fungi that are soilborne (e.g., black foot disease, Armillaria root rot), airborne (e.g., Eutypa dieback, Botryosphaeria canker), or both (e.g., esca). Pathogenic fungi infect plants during the propagation phase in nurseries or in vineyards during the production phase. Most vascular fungal pathogens form spore-bearing structures on infected wood that are released in free-water (rain, irrigation, snow, dew). Fungi use wounds (natural, mechanical, pruning) as a point of entry to the plant vascular system, colonize the host and decay the wood, causing a irreversible loss of function of the xylem and phloem elements that results in the dieback symptoms (Figure 3). Foliar (dwarfing, stunting, necrosis, chlorosis) and fruit symptoms (blemished fruit, raisining, slow-maturing) caused by fungal phytotoxins and the decrease of vascular hydraulic conductivity can also be observed (Figure 4).
Figure 1: Grapevine affected by GTD. Note the wood dieback and decrease of vine vigor.
Figure 2: Grapevine affected by GTD. Note the apoplexy (vine collapse) caused by over cropping and heat shock.
Figure 3: Grapevine affected by GTD. Note the wood necrosis in the cordon of a mature vine (left) and in the wood cutting of a nursery plant (right).
Figure 4: Grapevine affected by esca disease, one of the GTD. Note the 'tiger-striped' patterns on the leaves and (left) and blemished fruits (right).