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Grape study gives clues to threat from climate

Researchers in Australia say they have pinpointed key factors in the early ripening of grapes, providing potential answers for wine growers threatened by global warming.

Until now, no one has sorted out how the variables - warming, sunlight, soil moisture and vineyard management - each play a role in grape maturation.

A team led by Leanne Webb at the CSIRO looked at 10 sites in southern Australia where there were highly-detailed records, stretching from 1985 to 2009, for all of these factors.

Only at one site - at Margaret River on Australia’s south-western tip - did the grapes ripen later. For the others, maturation occurred six to 34 days earlier.

The most common driver of earlier ripening was higher temperature, deemed a significant factor at seven sites.

Lower soil moisture, particularly in the drought-stricken south-east, was a major factor for earlier harvests at five sites. Drier soils lead to higher levels of a stress hormone called abscisic acid in vine roots, which drives the plant’s fruit to earlier ripening.

But vineyard management was also important. In four sites, pruning and fertilisation methods that lowered crop yields contributed strongly to earlier maturation. And other technological innovations, such as improved disease and pest control, could have been a factor, the study says.

The authors of the study, published online on Sunday in the journal Nature Climate Change, say by increasing irrigation, or laying down mulch, growers can manage soil moisture and by changing their pruning regime, they can alter crop yields.

By choosing root stocks that are less sensitive to plant stress hormones, or trimming leaves, growers can also alter the response of the vine to lower humidity, the paper suggests.

Other crops facing the uncertainties of climate change could be helped by this analytical approach, the study says.

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