Dynamic of chill accumulation in Australian pistachios

The Australian pistachio (Pistacia vera) growing region stretches along the River Murray Valley, central New South Wales, Southern Victoria, and Western Australia.
Owing to climate change, there is concern of reaching the requirement of 59 dynamic chill portions during winter to ensure reproduction and yield.
We fitted bilinear models relating dynamic chill portions and date to derive three parameters: the onset of chilling accumulation, the rate of accumulation, and the day of year when 59 dynamic chill portions were achieved (DOY_59CP). For 18-23-year time series at 10 sites spanning 34.2°S to 36.3°S in eastern Australia, we found no time trends for any of the three parameters.
The DOY_59CP correlated with chill onset in 8 out of 10 locations, highlighting the importance of earlier chill onset to achieving 59 chill portions by 31^st August.
There were latitudinal and altitude gradients for: chill onset (range: 20^th April to 29^th May; rate: -2.8±0.5 days per degree latitude), rate of chill accumulation (0.48 to 0.75 d^‑1; rate: 0.064±0.01 d^‑1 per degree latitude and 0.0009±0.0002 m^-1 altitude), DOY_59CP (range: 10^th July to 30^th August; rate: -11.6±1.4 days per degree latitude and
-0.15±0.042 m^-1 altitude). Values above a threshold of 35.21°S latitude and 70 m a.m. s.l. altitude resulted in no failure years.
The higher risk of not achieving the required chilling portions in northern, inland sites can be partially managed with the current practice of oil application and has implications for the location of orchards in the future.
New technologies for chill mitigation are needed.

VIII International Symposium on Almonds and Pistachios

M. Mahadevan, C.K. Joyce, T. Ranford, V.O. Sadras

dynamic model, chill portion, chill onset, rate, chill requirement, continentality

https://doi.org/10.17660/ActaHortic.2024.1406.61