At anytime of the day or night, you can be sure that someone somewhere is enjoying a glass of fruity Sauvignon Blanc, an oaky Chardonnay, or a full-bodied Pinot Noir (Fig. 1).
This all-time beverage of choice for ancient Romans, aspiring sommelier’s and your average Joe alike, has become a ubiquitous joy for many. Whether complimenting a decadent meal at a five-star restaurant, or being the central star in a binge drinking session among college students, wine has evolved as an integral part of life, culture and diet since time immemorial.
Being home to what many wine critics consider the world’s best Sauvignon blanc, New Zealand burst into the global wine scene in the late 1980s. Over the last 30 years, new wine companies have been mushrooming from Northland to Central Otago, with today’s ranks swollen to over 600; creating an exciting atmosphere of new faces, new labels and new tastes (Fig. 2). Riding alongside this growth has been a substantial increase in the value of New Zealand wine exports; skyrocketing from $NZ18 million in the late 1980s, to $NZ1.5 billion in 2015. Given the clear economic value of this industry, we can argue with relative ease that any dangers which pose a threat to production and quality require serious consideration.
More specifically, I’m talking about infections caused by plant pathogens. Those pesky and occasionally disastrous infections that may reduce or entirely wipe out an entire vineyards production capacity. Of the myriad of plant pathogens capable of this, fungi are perhaps the largest and most devastating group.
Some well-known examples of these pathogens include black rot (Guignardia bidwellii), noble rot (Botrytis cinerea) (Fig. 3) and powdery mildew (Uncinula necator). Although in some cases, such as with B. cinerea, there’s a silver lining in fungal infection that allows for the production of wine with higher sugar content (i.e. dessert wine), for the majority of cases, fungal infection spells disaster for the grower.
Despite the effective control of several prominent fungal pathogens through the use of cultural (e.g. host resistance), chemical (e.g. fungicides) and biological (e.g. bio-fungicides) management strategies, new pathogens are becoming problematic. For instance, only recently have a family of Botryosphaeriaceous fungi been recognised as another significant pathogen for grapevines globally. Earlier research overlooked this family in favour of other, more prominent pathogenic agents. Recent research has decisively shown that this family is the cause of numerous disease symptoms such as shoot, spurs and branch dieback, in addition to severe internal wood necrosis and general loss of vigour. To put these symptoms in perspective with wine production, Botryosphaeriaceous infection can result in stunted growth, lower yields, incomplete graft unions and mortality, clearly highlighting the disastrous consequences this pathogen may have if left unchecked!
A prerequisite to understanding how to effectively manage a pathogen population is to first, and foremost, identify the pathogen at hand, followed by its modes of dissemination and area of distribution. While the mode of dissemination may remain common between fungal species (i.e. spore dispersal via wind/water), the identity and distribution must be individually confirmed for each pathogenic agent. This is because species diversity alongside their pathogenic severity may vary significantly between countries, if not between wine-growing regions.
A study by Lincoln University’s, Dr. Eirian Jones and Dr. Hayley Ridgway, set out to do just this in New Zealand. Their primary aim was to investigate the prevalence and identity of Botryosphaeriaceous dieback pathogens in necrotic grapevine tissues in New Zealand vineyards, and other woody hosts growing nearby.
Using both conventional (e.g. agar cultures and colony morphology) and more sophisticated DNA-based identification techniques, they identified six Botryosphaeriaceous species (Fig. 4) from grapevine and non-grapevine woody hosts; Neofusicoccum parvum, N. luteum, N. australe, Diplodia mutila, D. seriata and a Dothiorella sp. They discovered that in New Zealand vineyards, N. parvum was the most frequently isolated species, followed by N. luteum, D. mutila and N. australe, with the least common being D. seriata. Surprisingly, in contrast to this, D. seriata was the most frequently isolated species in France, New South Wales, Western Australian and Californian vineyards; confirming my previous statement on the variability of pathogenic agents between countries!
Secondary research goals included identifying species associated with dieback symptoms, and to determine their relative pathogenicity (i.e. ability to cause disease and severity of infection) to one another. The researchers did this by infecting excised plant material (i.e. trunk sections) and live plant specimens from a variety of vineyard favourites (e.g. Cabernet sauvignon, Chardonnay, Pinot noir, Riesling and Sauvignon blanc), to find out how pathogenic each Botryosphaeriaceous species was relative to one another (Fig. 5). Unsurprisingly they found that all species (except D. seriata) were pathogenic, irrespective of host source; indicating a potentially disastrous situation for vineyard productivity if optimal conditions for pathogen growth arise.
Expanding on these findings, the researchers were able to recognise that while the most severe trunk fungal symptoms were associated with older vines, the ease with which relatively young tissues of potted vines became infected and developed lesions illustrated how these may act as additional infection sources in a vineyard and further exacerbate disease spread; a feat not commonly observed in other plant pathogens.
In summary, this study highlighted the presence, symptoms and potential for Botryospaeriaceous fungal species to act as grapevine pathogens in New Zealand. So, next time you’re lounging in front of that fireplace with a glass of Cabernet Sauvignon blanc, or on a bar-leaner with an ice-cold bottle of Chardonnay, take a thought on the adversity vineyards have, and will continue to face in the hopes that their juices will grace your tongue.
Something to mull about, yes?
The author Kai Lewis is a postgraduate student in the Master of Science taught at Lincoln University. He wrote this article as part of his assessment for ECOL 608 Research Methods in Ecology.
- Amponsah, N. T., Jones, E. E., Ridgway, H. J., & Jaspers, M. V. (2011). Identification, potential inoculum sources and pathogenicity of Botryosphaeriaceous species associated with grapevine dieback disease in New Zealand. European Journal of Plant Pathology, 131(3), 467.