PGRs offer potential to control ripening

Giving viticulturists the power to regulate grape ripening is a step closer to reality thanks to researchers at the CSIRO working on an AGWA-funded project.

They have completed laboratory and field trials to highlight the potential to either delay or promote veraison, and thus the timing of harvest, by manipulating the plant growth regulators (PGRs) that co-ordinate berry development.

The use of PGRs is common in horticulture, and in some other areas of agriculture, and has enormous appeal in the wine industry given that the impacts of climate change are already being felt across the country.

Grapes of all varieties are ripening earlier, often causing ‘seasonal compression’ and winery bottlenecks that can lead to wastage, higher costs and reduced wine quality.

The research team, led by Dr Chris Davies from the CSIRO Agriculture, set out to better understand the ripening process and the specific role of a variety of different PGRs. Their major focus was on those that can delay ripening – ethylene and, in particular, auxins.

‘Although the pathways targeted by auxins are yet to be determined, a detailed knowledge of auxin metabolism, both biosynthesis and breakdown, has been developed. We now know much about how auxin levels are controlled and why some auxins are more effective than others in controlling the timing of veraison,’ their report says.

‘New tools have been developed to study the effects of auxins, which have led to the possibility of novel, fit-for-purpose, synthetic versions.’

When the results were tested in a commercial vineyard, ‘substantial and predictable’ delays in ripening were demonstrated in both red and white wine cultivars in different vineyards, seasons and climatic conditions.

‘Apart from delaying harvest, other benefits have included an increase in the synchronicity of berry ripening,’ the report says.

Research into the use of aminoethoxyvinylglycine, a naturally occurring amino acid, confirmed its ability to advance ripening by inhibiting the production of auxin and ethylene.

When studying PGRs that don’t affect the timing of veraison but influence other aspects of berry development, the researchers found at least one that appears to be involved in controlling some aspect of the mid/late stages of berry ripening with the potential to be important to wine flavour and aroma.

The relationship between sugar levels, hang time and berry composition was also studied. Importantly these showed that while extending hang time may not improve the positive aspects of wine flavour, it will reduce the concentration of negative flavours.

The project’s report can be downloaded from here. A new AGWA project has commenced to follow up on these promising findings.

RD&E April newsletter article PGRs to offer potential to control ripening