Exploring the potential to regulate grape ripening

New research by the CSIRO has highlighted the potential to regulate grape ripening by manipulating the plant growth regulators (PGRs) that co-ordinate berry development.

This opens up the way for grapegrowers to control the timing of veraison and/or harvest to maximise fruit quality and better suit production schedules.

Controlling harvest timing also could alleviate some of the issues associated with increasing temperatures due to climate change.

The initial findings of the four-year study, co-funded by AGWA, suggest that the manipulation of berry character independent of yield could increase grape and wine value without the need to reduce production levels.

“Possible benefits include the easing of harvest season compression problems, improved winery intake scheduling, optimisation of harvest timing for maximum fruit quality, reduced fruit wastage and the manipulation of fruit composition,” said research leader Dr Chris Davies.

PGRs are small bioactive molecules that occur naturally in grapes and affect all aspects of berry development from flowering through to ripening. Some also are involved in the plant’s response to stress.

However, PGRs also can be applied to deliberately advance or delay ripening, and their use to control fruit development and to aid fruit storage is common in horticulture and sometimes in other areas of agriculture.

The CSIRO study has demonstrated in both white and red skinned Vitis vinifera cultivars that they can be used successfully without detrimental effects on wine flavor or aroma.

PGRs that promote ripening include abscisic acid, castasterone and the gas ethylene, which is more conveniently applied as a synthetic ethylene-releasing compound.  Another group of PGRs, auxins, delay the onset of berry ripening.

The researchers used sensory and chemical analysis to test for any effects on wine flavor but found this to be minimal in most cases, even when harvest was delayed for a significant time.

They also noted that the cost of PGR reagents was relatively modest and that some were already registered for used in grapes.

The project is due for completion at the end of June. Many of the findings have already been published in scientific journals and there are more papers in progress.

Dr Davies is also happy to talk with anyone interested in the research. He can be contacted at Christopher.Davies@csiro.au.

Effect of auxin treatment in delaying Shiraz berry ripening. The bunch on the left is a control (treated with a wetting agent only). The bunch on the right has been treated with an auxin plus wetting agent.
Effect of auxin treatment in delaying Shiraz berry ripening. The bunch on the left is a control (treated with a wetting agent only). The bunch on the right has been treated with an auxin plus wetting agent.