ADVANTAGES/DISADVANTAGES OF SCREENING CITRUS FOR FREEZE SURVIVAL WELL BEYOND THE NORTHERN LIMITS OF CITRUS GROWING IN FLORIDA

Authors: Yelenosky, George; Hearn, C; Barrett, Herbert

Submitted to: Citrus Industry
Publication Type: Trade Journal
Publication Acceptance Date: 5/15/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Screening citrus in Georgia, well beyond the northern limits of growing citrus in Florida, was a novel approach in 1964 by USDA/ARS to identify and secure cold hardy germplasm to develop options in addressing multi million dollar losses caused by severe freezes that have wreaked havoc on the industry since the 1800's. The effort found, and passed on to the industry, the cold hardiness of Swingle citrumelo 7 years before it was released in 1973 as a cold hardy rootstock. Over the years, Swingle has developed into one of the most favored rootstocks in the industry and is doing an exceptional job in replacing the once popular sour orange, which is rapidly declining in use because of its high susceptibility to the tristeza virus. Other germplasm, such as Citradia CPB 50097, Sacatan citradia, the Rich' selection of trifoliate orange, and pummelo and sweet orange hybrids with trifoliate orange were also challenged and successfully survived minimum temperatures as low as 3 F. These results are forerunners of constructing potential releases to the citrus industry in meeting long term goals for global advantage, and are important to other scientists addressing low temperature stress, and extension agents and the citrus industry seeking long term solutions to devastating freeze losses.

Technical Abstract: Citrus plantings were established in 1964 and maintained for several years in Georgia to find and secure germplasm that possesses superior ability to survive devastating freezes in Florida. The objective was to expand the inventory of available material to provide options for commercial use and to construct transgenic trees for greater assurance of freeze survival. Some of the more cold hardy types were identified among 37 selections of trifoliate orange, Owari satsuma, Citradia CPB 50097, Sacatan citradia, Nakon pummelo x Flying Dragon trifoliate orange, Flying Dragon x Succari sweet orange, and Swingle citrumelo. Swingle became a USDA cold hardy rootstock release in 1973 and has developed into one of the most favored rootstocks in the Florida citrus industry. The advantages of screening citrus, well beyond the northern limits of citrus growing in Florida, seemingly far outweighs the disadvantages.