Experimental ‘Cool Climate’ HWT Trials Promise Healthier

25 October, 2006

The reduction of fungal infection in grapevines has moved a step closer with promising results from experimental trials using a hot water treatment (HWT) programme adapted to suit New Zealand’s cool climate viticulture.

The trials, carried out by Corbans Viticulture Ltd’s research and development manager, Anna Graham, showed modified hot water treatment of grapevine cuttings resulted in reduced vine losses in the nursery and enhanced vine health.

Standard HWT in warmer countries is to immerse cuttings in hot water at 50 degrees Celsius for 30 minutes to get rid of fungal, viral and bacterial pathogens (disease- causing organisms). In New Zealand, the standard practice has resulted in unacceptably high losses.

The mortality was significantly less after modified treatment, compared with losses in New Zealand following standard HWT of cuttings before grafting. The incidence of the fungus responsible for young vine decline, or Petri disease, Phaeomoniella chlamydospora, also decreased to a level comparable to cuttings treated at the standard HWT temperature of 50 degrees Celsius.

Fungal disease in the woody tissue of grapevines is a worldwide problem and of increasing importance to the viticulture industry, but this is the first time that HWT methods, adapted specifically to cool climate viticulture, have been scientifically studied in New Zealand.

The trials at Corbans Viticulture’s nurseries, supported by a Technology to Business Growth grant from the Foundation for Research, Science and Technology, compared standard HWT of cuttings with treatment using modified temperatures and times more suited to New Zealand cool climate viticulture.

Initially, the cuttings were from sauvignon blanc and 101-14 rootstock, but other varieties were included in subsequent trials.

Corbans Viticulture began studying HWT methods in 2003 as part of its ongoing programme to reduce pathogen levels in all its vines to benefit winegrowers and the industry. The research aims to develop a more effective protocol to treat grapevine cuttings which reduces vine loss while killing harmful pathogens.

Anna, who recently completed research for submission for her University of Auckland doctorate in assessment of grapevine quality, says she is currently taking tissue samples from the trial vines to test for fungi and bacteria.

“We are examining how effective our method is in reducing pathogen levels – that’s where the rubber really hits the road. The results are looking very promising and have the potential to benefit the whole industry,” she said.

While many New Zealand nurseries have used hot water treatment, the international standard of 50 degrees Celsius doesn’t work in this climate. Research suggests, says Anna, that vines in hotter climates survive that temperature because of the accumulation of heat shock proteins which protect them.

“Our challenge was first of all to see if we could reduce the presence of pathogens in the rootstock as well as grafted vine mortality – and we have had promising outcomes.”

Six months after modified HWT, pathogen levels remained significantly lower in the treated grafted vines than in the untreated vines and were repopulated with harmless and potentially beneficial fungal endophytes.

Anna says vines grafted with modified hot water treated cuttings grew at least as well as untreated vines during the first year of growth. The next step of the project is to assess the graft strength, stem diameter and root mass of the treated vines which will be compared with untreated vines.