Different chilling requirements for southern states

Peaches add a good percent of profit to growersand help states that grow them in large acreagesto increase their total farmgate income.One of the drawbacks to peaches is their CUrequirements. The CU is the number of hours below 45degrees Fahrenheit that a tree must receive to be able to setpeaches. In much of the lower South, many years are notcold enough for peach trees to have fruit. (However, thewinter of 2010-11 did not present that particular problemin regard to peach trees.)

Gulfcrimson peach.
PHOTO COURTESY OF DR. JOSE CHAPARRO.

The University of Florida in Gainesville has been working on developing peaches with lower CU requirements for several years, and has varieties that are in active production in many areas of Florida. A chilling hour is defined by the maximum amount of chilling that can be received by the plant in one hour.

Many of the southernmost sections of Georgia, Alabama, Mississippi and Louisiana have, traditionally, had problems getting enough chill without very late freezes to be good peach-producing areas. For example, in Georgia and South Carolina, the most commercial peach acreage is in the middle of both states. That is not to say that peaches will not produce in the southern areas, but, as mentioned above, there is sometimes a problem with too much warmth.

Originally, Florida peach breeding began with Chinese varieties that were originally imported into South Carolina, Hawaii and Okinawa. These varieties were crossed with commercial varieties from the USDA in Fort Valley, Ga. They were then backcrossed to produce melting flesh varieties.

Geographic areas and chilling units in Florida

There are several geographic areas in Florida that have different chilling units (CU) on average.

For example, the western part of the Panhandle and an area around Tallahassee down to the gulf has a 660 to 700 CU requirement on average, while the area around Jacksonville west almost to Tallahassee and part of the Panhandle registers in the 540 to 660 area. In the Gainesville area, the CU range is from 420 to 540, with north-central Florida ranging from 310 to 420. Around central Florida and Orlando, CU needed are from 110 to 210. The rest of Florida is much lower, and in the far south even goes down to 0 to 50.

Where you are located in reference to the above-mentioned areas in neighboring states might help determine the variety of peach you should be looking for. According to the University of Florida Extension Service, “Recommended cultivars should have a chilling requirement less than the average chilling calculated for a given area so that their chilling requirement is met in almost all winters. By following this recommendation, the grower would avoid the consequences of lack of chilling in winters with lower-than-normal chilling.” (Document HS1125; Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date January 2008.)

In the February 2011 issue of Growing (page A12) it was reported that on April 1, 2010, “the peach genome, its entire genetic pattern, has been isolated.” This will eliminate the scientist or breeder having to grow new varieties to maturity, because the geneticist can experiment with different characteristics and find out what the results are. This will allow the breeder to tailor the cross to specific objectives, according to the 2008 research report mentioned above.

Below is a Q&A session with Dr. Kevin Folta, Ph.D., and Jose Chaparro, Ph.D., in the department of horticultural science at the University of Florida in Gainesville. Folta works with strawberries, and Chaparro’s focus is peaches.

Varieties and Nurseries That are Licensed to Grow Them

from the Florida Foundation Seed Producers, Inc.

Flordabest – A low-chill peach variety with a winter chilling requirement estimated at 250 CU. The tree is of medium size and has a moderately vigorous and semi-upright growth habit.

Phillip Rucks Citrus Nursery, Inc.

Gulfcrimson – A variety with a winter chilling requirement estimated at 400 CU. It is medium sized and moderately vigorous with a semi-spreading growth habit.

Cumberland Valley Nurseries, Inc. and Vaughn Nursery, McMinnville, Tenn.; and Freedom Tree Farms, LLC, Pelham, Tenn.

Gulfking – A variety with a low winter chilling requirement of approximately 350 CU. It is self-fertile and regularly bears heavy annual crops, which are of moderate size for its early ripening season.

Cumberland Valley Nurseries, Inc., and Vaughn Nursery, McMinnville, Tenn.; Freedom Tree Farms, LLC, Pelham, Tenn.; and Rainbow Star Nursery, Gainesville, Fla.

Gulfprince – This variety has a winter chilling requirement of approximately 400 CU. This tree is a large size and highly vigorous with a spreading growth habit.

Cumberland Valley Nurseries, Inc. and Vaughn Nursery, McMinnville, Tenn.

To find additional varieties, visit the Florida Foundation Seed Producers’ website ,http://ffsp.net/peach.html.

Q Can you give a simple explanation of what can be expected from the discovery of the entire peach genome?

A Folta: A genome is a parts list. Once you understand what the parts are of the organism, it is easier to use them in genetics or eventually engineering. You have targets to better understand physiology or development. It is a tremendous advantage to have a genome in hand, as it defines a better starting point than we’d normally have when studying gene contributions to plant biology. We used to have to find the genes. Now they are there for us.

Chaparro: Since we now have a parts list, we can use directed breeding to mix and match parts from different peach sources to obtain a target genotype and, therefore, phenotype. This was much more difficult in the past when we did not know what genes we were working with and the magnitude of their effect.

Q Can you release any specific cultivar names that should grow and produce well in the southern areas of Georgia, Alabama, Mississippi and Louisiana?

A Chaparro: Releases from the University of Florida: UFGlo, UFSharp, Flordabest and Flordacrest. Joint releases involving the University of Georgia, USDA-ARS and the University of Florida: Gulfking, Gulfprince and Gulfcrimson.

Q Does there seem to be a movement toward peaches and away from citrus due to some of the problems the citrus industry has had in the last few years?

A Folta: I think that there are gains being made across specialty fruits, and peaches are no exception. I don’t know that this is at the expense of citrus, but the growth of fresh fruit industries is tied to changes in lifestyle and dietary preferences of consumers. The new USDA guidelines say that half of what you need to eat should be fruits and vegetables. More varieties are available at good prices throughout the year, so peaches, like any fresh fruit, are growing in popularity.

Chaparro: Growers are also trying to diversify their crops against decreases in market prices and effects of environmental (freeze damage) and biological (diseases and insects) stresses.

The other two peach breeders that make the cooperative peach breeding program possible are Dr. Patrick Conner, from the University of Georgia, and Dr. Thomas Beckman, from the USDA-ARS.

It appears that using the peach genome will be a great advantage in determining how to develop new peach varieties. There is a wide range of varieties to choose from that did not exist many years ago.

Chris E. Marsh, M.Ed., writes magazine articles and specializes in agricultural topics.