9 minute read
Research Microvine’s max potential
Max potential for microvine
Year-round supply, boutique “super grape” breeding, disease-resistant varieties and sustainable production on a small scale.
This is just some of the commercial potential and versatility of a new microvine developed by CSIRO scientists.
What began as a project almost 20 years ago looking at French wine grape variety Pinot Meunier now underpins a breeding program which sees the CSIRO scientists creating disease-resistant wine grape varieties.
More recently, though, they’ve successfully crossed the microvine with table grape varieties to produce seedless grapes with a range of
flavours and colours.
“The project started in the early 2000s with work by two CSIRO scientists, Mark Thomas and Paul Boss,” CSIRO project lead Ian Dry said. “They were aware that the old French variety Pinot Meunier, which is used for champagne production, had a naturally occurring mutation in the layer of cells that cover the plant – this is called the L1 or epidermal layer.
“They took Pinot Meunier and they put it through tissue culture, and they were able to to regenerate a grapevine only from cells from the epidermal layer, rather than the entire Pinot Meunier plant.”
The team discovered a few interesting things about the L1 plant.
Firstly, it had very short internodes which meant it was dwarf in stature. So it was named the microvine.
Secondly, the plant flowered very quickly.
“Normally if you took a grapevine and grew it from seed, for example, it would take two–three years for it to show flowers, but this flowered as quite a small plant,” Ian said. “So you get flowers from three–four months, and then fruit on it within six months – it had no juvenile period like you find with most woody perennial crops.”
Thirdly, every tendril on the vine was floral – instead of just the lower one–two tendrils on each shoot.
“As the shoot grew, it just continually produced bunches instead of tendrils! You would get more flowers and more bunches, so if you grow a continuous shoot, you would have a continuous series of bunches,” Ian said.
Interestingly, the genetic mutation which causes the phenotypic change in the microvine goes by the name of the “green revolution gene”, which dates back to the evolution of cereal production in the 1960s.
“They actually discovered some naturally occurring mutations in the cereal population that had short stalks, and when they discovered these, they used these in the breeding program because it meant that there was much less chance of “lodging” which is when the plant collapses under the weight of its grain. This is why cereals are now short, rather than tall and wavy,” Ian said.
Ian said the gene was involved in the perception of one of the plant hormones – gibberellic acid (GA) which table grape growers use for berry elongation.
In the case of the microvine, Ian said the gene has mutated so the plant no longer perceives the GA, meaning rather than cell elongation occurring, the opposite occurs, with a dwarf plant forming.
However, quite unexpectedly, Ian said this mutation also had a major impact on flowering in the microvine.
“What it told us was that GA has quite a significant role in regulating flowering and fruiting in grapevine, quite separate from its role in cell elongation, which table grape growers use to change berry size,” Ian said. “ GA actually has a very important role in the suppression of flowering in grapevine.”
Having used the microvine to speed up wine grape breeding, the initial researchers started looking for other opportunities.
“We’ve been using it as a breeding tool to speed up wine grape breeding and then, having done that, Mark then thought ‘I wonder whether there’s an opportunity here to utilise these interesting characteristics for a paradigm-shift in table grape production, particularly undercover cropping or indoor farming’,” Ian said.
Despite the convenience of being grown in a pot and hydroponically, the phenotype of the microvine still requires the normal growing conditions so that it won’t go into dormancy.
So CSIRO researchers then set about transforming the original microvine, which was derived from a wine grape variety, into a table grape by introducing traits like seedlessness, large berries, flavours and sugar and acid balance, to produce black, red and white seedless grapes.
By crossing the microvine with Crimson Seedless, for example, the progeny picked up the microvine phenotype, but also inherited the characteristics from its table grape parent.
“So now we have plants that combine all of those things together and we’ve got what we would almost term a table grape version of the microvine,” Ian said. “It still shows the same characteristics, like dwarf stature and rapid and continuous flowering, but now it also shows more table grape characteristics like seedlessness, large berries and flavours and aromas you would associate with table grapes.
This capability meant the CSIRO could take existing table grape varieties and cross them with powdery and downy mildew-resistant microvine parents that had been developed as part of the wine grape breeding program, to produce disease-resistant table grapes.
Ian also said they were also producing grapes with red flesh, which had the potential to be marketed from a health perspective as a “super food”. “We’ve also been making some rather interesting table grape varieties that have really high levels of anthocyanin (a flavonoid which creates the red pigment in fruit),” Ian said. “I guess there might be an opportunity to market that from a health perspective, because anthocyanins act as antioxidants, which are quite important for health, so they could be marketed as a super grape.”
Regardless of whether it’s a super grape, a disease-resistant variety (beneficial in a time of La Niña), or simply the ability to grow grapes anywhere in the world, all year round, CSIRO’s microvine could mean maximum potential. v
This page and opposite: CSIRO scientists have developed a potted or hydroponically grown microvine which can be crossed with table grape varieties to create new varieties and disease-resistant strains of existing varieties. Images: CSIRO
High priority exotic pest threats
It’s earned the title of Australia’s number one priority plant pest, so Xylella fastidiosa (xylella) needs very little introduction.
Pierce’s disease is a serious disease of grapevines caused by the xylella bacteria, which lives in the water conducting system (xylem) of the grapevine.
Xylella can be spread by xylemfeeding leafhoppers like the glassywinged sharpshooter (Homalodisca vitripennis, GWSS).
While the GWSS causes direct damage to grapevines through its feeding activities, the greatest threat posed by this pest is its ability to efficiently spread xylella.
Neither xylella nor GWSS are found in Australia.
Symptoms of Pierce’s disease
Plants infected by Pierce’s disease show symptoms of water stress, which include browning and loss of
leaves, lignification of canes and fruit raisining.
The characteristic symptom, leaf scorch, is seen in late summer and autumn and includes marginal leaf scorch (browning) that is frequently bordered by a red or yellow halo. The outer leaf area may dry suddenly while the rest of the leaf remains green. Affected leaves are less vigorous and smaller than healthy leaves. Ultimately, entire leaves may turn brown and drop, leaving the petioles attached to the plant.
Shoot growth of infected plants progressively weakens, and the tips of canes and roots may die back. Symptoms are usually more obvious in grapevines that are stressed by high temperatures or drought conditions.
Flower clusters on infected grapevines may set berries, but they usually dry out before reaching maturity.
Diseased stems often mature irregularly with patches of green and brown tissue, known as “green islands”, becoming visible. Symptoms of Pierce’s disease can be confused with chloride (salt) toxicity, drought symptoms or herbicide injury. Appearance and signs of GWSS
Adult GWSS are about 12–14 mm long, dark brown to black with a lighter underside. The upper parts of the head and back are stippled with ivory or yellowish spots, with wings that are partly transparent with reddish veins. Watery excrement often collects on either side of the insect, appearing as large white spots.
While feeding causes no visible signs of damage, copious amounts of liquid is excreted that can make leaves, stems and fruit appear white-washed when dry.
Clutches of up to 27 eggs are laid on the underside of leaves in a sideby-side arrangement. The clutches are dusted with a layer of whitish powder. After hatching they change in appearance from green watery blisters to tan to brown scars on the leaves.
Egg masses are usually found on recently expanded foliage, while older foliage has the distinctive scars left after the eggs have hatched.
Protecting your vineyard
Xylella is transmitted by grafting infected propagation material onto healthy rootstocks and by xylemfeeding leafhoppers like the GWSS.
Adult GWSS are strong fliers and can move rapidly from plant to plant. Nymphs are wingless but can walk and jump through the canopy or drop from plants and walk to new hosts. However, most rapid and longdistance movement occurs through the transfer of eggs on nursery stock of either crop or ornamental plants.
To protect your vineyard against Pierce’s disease:
- ensure all staff and visitors adhere to on farm biosecurity and hygiene practices
- source high health status (preferably certified) plant material from reliable and accredited suppliers - check your vineyard frequently for the presence of new pests and investigate any sick grapevines for unusual symptoms
- make sure you are familiar with common grapevine pests so you can tell if you see something different
- report anything unusual.
If you have noticed anything unusual in your vineyard call the Exotic Plant Pest Hotline 1800 084 881. v
This series from Plant Health Australia features exotic pests that would survive, spread and establish in Australian vineyards should they get through border quarantine controls. Growers should be familiar with their appearance and symptoms so that they can distinguish them from the pests that they normally encounter.
Xylella is just one of 240 plant pests and diseases of concern identified in the new Biosecurity Plan for Viticulture Industries. Recently endorsed by the table grape, dried fruit and wine grape peak industry bodies, the plan is a roadmap designed to prepare industry for plant pest incursions and improve on-farm biosecurity practices.
Opposite page: Adult glassy-winged sharpshooter on leaf surface. Image: Johnny N. Dell, Bugwood.org
This page, left: “Green islands” on a grapevine cane, surrounded by brown necrotic lesions caused by Pierce’s disease infection. Image: John Hartman, University of Kentucky, Bugwood.org
Right: Pierce’s disease reduces productivity and eventually results in the death of the infected grapevines. Image: Alex. H. Purcell, University of California – Berkeley, Bugwood.org
