I was honored to organize the peach session biennially for the Southeast Regional Fruit and Vegetable Conference in Savannah, GA, in January. Ahead of this year’s meeting, Jeff Cook (University of Georgia (UGA) Peach Area Extension Agent), other peach specialists, and I met with the growers in Georgia last fall to discuss topics and areas of interest. We put together a group of talks with the common threads of weather (including chill accumulation and freeze events), cultivars, and horticultural management tools for our growing conditions in the Southeast. I thought the talks were appropriate for our industry’s needs, and they fostered conversations during and after the conference between growers and researchers. Following are two of the topics discussed at the meeting.
CLIMATE TRENDS
Last year, Georgia peach production was affected by a late freeze and lack of chill accumulation. Dr. Pam Knox, Director of the UGA Weather Network and Agricultural Climatologist, explained that chill accumulation per season is trending downward through time. In Figure 1, you can observe the number of chill hours accumulated per year from 1970 to present in Fort Valley, GA. This number keeps trending downward. A similar situation can be seen in other locations throughout the Southeastern U.S. and matches what we see in different growing regions.
Another interesting point is that although chill accumulated is trending downward, the day of the last spring freeze has not really changed across the decades (Figure 2). This seems counterintuitive. However, if we think about it, our locations are being affected by warmer temperatures during the winter. This, in turn, makes our peaches’ bloom progression faster, resulting in one or two weeks of bloom ahead of what normally was seen in previous years.
This sets us up for a difficult situation. The freeze will still come at the same time, but now we have the plant bloom developmental stage more progressed and more tender to freezing temperatures as compared to what we used to have at the same time in past seasons.
BUILDING A NEW PEACH
If we had a crystal ball, what kind of peach cultivar would be needed for the future? Dr. José Chaparro, Stone Fruit and Citrus Breeder at the University of Florida, and his predecessors have been thinking about this for awhile. Florida peach production sits at the start of the U.S. peach market. The chill range of cultivars suited for this region is from 100 to 250 chill hours. Florida growing conditions always have thrown curve balls at peach production, from lack of chill to freezes and flooding, among others. These cultivars need to make a crop even when marginal chill has been accumulated. Personally, I think these requirements are needed for peaches not only in Florida but for the whole Southeastern U.S.
Dr. Ksenija Gasic, Peach Breeder at Clemson University, and Dr. Chunxian Chen, Peach Scion Breeder at USDA ARS, both agree that peaches need to be adapted to these changing conditions. Chen has released four peach cultivars in the last five years that have fared well during the challenging conditions in recent years. Similarly, Gasic is about to release two cultivars that have proven to be superior to current commercial cultivars.
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One of the goals during the peach session was to create a conversation among growers and breeders about their thoughts on peach cultivars for the future.
Chaparro said the “ideal peach” will always reach its required chill and will need large of amount of heat post-chill accumulation. The example that he gave is a peach that has a chill requirement of 400 chill hours and a heat post-chill accumulation of 2,000 to 3,000 growing degree days. The idea is that this peach will always achieve its chill requirement and will stay dormant after the risk of frost damage is past. This is a very interesting approach indeed, and it was also supported by the other breeders.
Personally, I have observed the variation for heat post-chill accumulation in cultivars blooming in different chill groups in different seasons. A few hurdles remain: the importance of nighttime temperatures during bloom for fruit set, and daily temperatures after bloom for proper fruit growth and development. It has been established in peach that high nighttime temperatures during bloom result in reduced fruit set. Similarly, high temperatures after bloom (30 days) result in smaller fruit. These are criteria every peach cultivar in Florida has to meet, so natural variation for all these traits is possible and make this “ideal peach” feasible.