Image caption Many grape varieties have been around for centuries - is it time for some new ones?

The future of wine-making depends on developing new varieties of grape, scientists say - and maps of the grape genome can help provide them.

Disease is a constant issue for growers; but new regulations are likely to curb the use of chemical treatments.

US researchers have made genome maps of more than 1,000 vine samples.

Writing in Proceedings of the National Academy of Sciences (PNAS), they say this type of data plots the way to disease-resistant grape varieties.

The grape varieties whose wine we like to drink - merlot, chardonnay, semillon, riesling and the rest - have mainly been developed from one species, Vitis vinifera vinifera.

It was probably "domesticated" about 5,000 years ago, in or close to what is now Turkey.

Since then, it has become the staple for wine-making as far from its homeland as Australia, Chile, the US and South Africa.

We can't just go on using the same cultivars for the next thousand years Sean Myles

Vinifera has been honed into hundreds of varieties, red and white; but the grapes are all still members of the same species, with limited cross-breeding between different varieties.

"The degree to which that was done seems to have been extremely limited," said Sean Myles, lead author on the new study.

"Once we found good cultivars that were working for us, we adopted them and as a result they're sitting ducks for pathogens," he told BBC News.

Dr Myles is affiliated to Stanford University School of Medicine, but was based at Cornell University while this project - also involving researchers from the US Department of Agriculture (USDA) and Italian instutitions, and funded by the USDA - was running.

Chemical curbs

Just as the grapes travelled from the shores of Europe across the world, diseases have travelled in the other direction.

Powdery mildew, for example, evolved in North America.

Vinifera grapes have no natural resistance; and in Australia alone, dealing with this disease costs an estimated $100m per year, largely through the fungicidal chemicals that are used to protect vines.

Seventy percent of fungicides used in US agriculture are sprayed in vineyards.

Image caption The powdery mildew fungus is one of a number of major grape diseases

But as the EU - which still produces nearly 70% of the world's wine - seeks to improve the environmental footprint of its farm sector, the bloc is trying to reduce the use of such chemicals.

One proposal from the European Commission would heavily restrict spraying on "non-essential" crops from 2013.

Scientists from several institutions have been trying to develop new grape varieties that are immune to infection, either through cross-breeding with resistant species or through manipulating the genes that make plants susceptible to infection and damage.

But conventional cross-breeding is costly and laborious for grapes.

Plants have to be grown for three or four years until they fruit.

Then wine has to be made, tasted and assessed before growers know whether they have something viable; and even if they do, there is no guarantee that people will take to the taste over their preferred varieties.

What the Cornell/Stanford team has done is to produce genomic maps of more than 1,000 samples, which link the presence of genetic "markers" (sequences of DNA) to traits such as acidity, sugar content, or disease resistance.

"If you know the genetic markers associated with these traits, you can plant them out as seedlings, look at its DNA as soon as you get the first leaf tissue, and say for example 'we'll keep these five because we know their genetic profiles are associated with the traits we're interested in'," said Dr Myles.

"That'll save an enormous amount of time and money.

"But you do need to have genome-wide data from lots of individual plants - on the other hand that's getting increasingly cheap, so that compared with the method we used you can now do it 100 times cheaper."

Although commercial factors tended to make wine-making a conservative profession, he said change must come.

"We can't just go on using the same cultivars for the next thousand years."

The good news is that more experimentation should in principle produce a wider variety of wines.