MAJOR losses in South Carolina stonefruit crops have prompted US researchers to look at breeding varieties to counter climate change.
Studies have found those producing low-chill peaches are suffering when winter doesn't cool things down as much as it once did.
One of those involved in the work is the University of Florida's Dr José Chaparro, who spoke at the TropAg 2017 conference in Brisbane in November
Dr Chapparo described the task of breeding for climate change as trying to hit a moving target.
He said climate change presented a perfect storm for stonefruit problems as it provoked inconsistent cropping through:
- reduced and protracted bloom;
- reduced fruit set;
- reduced fruit size;
- and poor fruit shape.
Added to this was developmental abnormalities, plus pest and pathogen problems.
His work has focussed on breeding subtropical peaches and cold hard citrus.
Much of the research is based around the "chilling requirement" which is the amount of cold temperature exposure endodormant flower and vegetative buds require to resume normal growth and development.
Historical climate data was gathered in 1970s and used to create a "chill map".
Dr Chaparro said the map worked well for about 30 years but in more recent times, growers experienced differing climate conditions with the lower chill varieties blooming earlier.
This might seem like a blessing to capture a seasonal gap but such varieties then have a higher potential for losing the crop.
"If you think the trend is bad, all you have to do is look at the data from the last two winters in south Florida," he said.
He said in 2015 and 2016, the area was severely under-chilled resulting in the loss of about 80 per cent of the peach crop and about 90pc in South Carolina.
Dr Chaparro said this year's crop was running at about 60pc and growers were again facing an under-chilled year.
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"If you are working in a temperate crop that has been bred to grow in the subtropics, the rules are changing," he said.
This covered peaches, pears, apples and blueberries as well.
"For all these crops, climate change is going to have a major impact," he said.
"I can tell you if we have another season like we did in 2016/17, there is a possibility the peach industry in Florida will fold."
A good cold
THE benefits of a strong chilling event include a very intense flowering which could start and finish within four days.
The flowers are then synchronised which means the fruit will be synchronised.
In under-chilled conditions there is very little synchronisation and a sporadic bud rate.
"This is a production nightmare," Dr Chaparro said.
"Instead of going into the orchard and picking three times, you are talking about going into an orchard and picking five or eight times.
"In terms of management, when do you spray? It's really a big problem."
Further problems include non-producing branches and non-budding.
Mr Chaparro said there were growers with relatively young, six-year old orchards of low-chill varieties, watching the effects of under-chilling play out.
Other problems can include poor fruit shape, less hardier fruit, defoliation, and major outbreaks for bacterial spot and peach leaf rust.
Traditionally, a cold winter would kill off the Caribbean fruit fly but with warmer traits it results in a heightened presence.
In order to combat the effects, Mr Chaparro and his team were looking to transfer genes from varieties with positive characteristics.
"We are essentially hoping to redesign the peach tree," he said.
The team hopes to select a fruit that is able to set fruit at a warm temperature.