Dwarf grapes may revolutionise viticulture

Australian scientists have discovered a mutation in grapevines equivalent to the dwarfing mutation in cereals discovered in the 1960s that was the basis of the "green revolution", which saw an increase in wheat yields.

The mutation results in a dwarfed variety of grapes that is much more fruitful, suggesting that the mutation might be useful in developing new varieties for viticulture.

Dr Mark Thomas, who was co-author of a paper describing the mutation in the April 25 issue of Nature, said the first clue to the identification of the gene was discovered when the researchers found that cells in the skin or the L1 layer of the grapevine contained a mutation that wasn't found in the L2 layer, or in the rest of the plant.

The Pinot Meunier strain is a sport variety derived from the Pinot Noir strain more than 400 years ago. Pinot Meunier is similar to Pinot Noir but has a "hairy" appearance to its young leaves. Both varieties are used in the production of champagne.

When plants were separately derived from these two layers by vegetative propagation techniques, the L2-derived plants resembled Pinot Noir grapes, while the L1-derived plants were semi-dwarfed, as well as having the hairy leaves found in Pinot Meunier.

Thomas and his co-author Paul Boss looked for the gene responsible and found that it was the grapevine homologue of the "reduced height -1" gene responsible for dwarfing in wheat. It was also equivalent to the GAI or gibberellic acid (GA) insensitive gene found in Arabidopsis.

"Mutated forms of the GAI genes are known as 'green revolution' genes and have been used to improve crop yields since the 1960's," said Thomas, who is a researcher at CSIRO Plant Industry in South Australia.

"In the normal situation this gene allows the plant to respond to GA," said Thomas, explaining that GA is an important plant hormone involved in the control of plant growth.

When the GAI gene was mutated, he said, the plant could no longer respond to GA and thus a dwarf phenotype was seen.

A more complicated effect of the mutation was the increased fruitfulness of the L1-derived strain. In grapevines, GA normally inhibits flowering, but this inhibition is prevented in the mutant variety, so the grapevines produce more flowers and thus more fruit.

"We need to do a bit more work to see how useful this phenotype is," said Thomas.

Potential benefits of the variety included its reduced vigour and increased fruitfulness, both of concern to viticulturists.

He said that they had started using the variety in breeding experiments and needed to evaluate the potential usefulness of this variety to growers.

"New knowledge about hormone response genes may allow us to fine-tune both the vegetative architecture of grapevines, and how many bunches of grapes they produce," said Dr David Smyth of the Monash University School of Biological Sciences, in an accompanying News and Views article for Nature.

Thomas said that the work was funded by the CRC for Viticulture as well as by the Grape and Wine Research and Development Corporation and the Dried Fruits Research and Development Council.

For more information:

Paul K Boss and Mark R Thomas, "Association of dwarfism and floral induction with a grape 'green revolution' mutation." Nature 416, 847-850 (25 April 2002)

David Smyth, "Champagne Surprise." New and Views, Nature 416, 801 (25 April 2002)