The U.S. Department of Agriculture has released five citrus rootstocks that show improved tolerance to huanglongbing or citrus greening for use on the Florida flatwoods.

They include:

• US-1279—a cross between Changsha mandarin and Gotha Road #6 trifoliate orange made by Kim Bowman of USDA's Agricultural Research Service in Fort Pierce, Fla., according to a news release.

During field testing, the hybrid rootstock was identified as BS95-V3-11 or US-1279. It produced high yields and high quality fruit on sweet orange trees grown in the Florida flatwoods and infected with HLB. It proved superior to Swingle citrumelo on flatwoods but not on a Ridge site with HLB.

• US-1281—a cross between Cleopatra mandarin and Gotha Road #6 trifoliate orange made by Bowman.

It was tested as BS95-V5-1- or US-1281. It too produces high yields of quality fruit on sweet orange trees grown in the flatwoods and infected with HLB.

• US-1282—This is a cross between Cleopatra and Gotha Road #6 trifoliate orange made by Bowman.

It was tested as BS95-V5-78 or US-1282. It produces high yields and good fruit quality on sweet orange trees grown in the flatwoods and infected with HLB.

• US-1283—This is a cross between Ninkat mandarin and Gotha Road #6 trifolia orange made by Bowman.

It was tested as BS95-V6-14 or US-1283. It also produces high yields and good fruit quality on sweet orange trees grown in the flatwoods and infected with HLB.

• US-1284—This is a cross between Ninkat mandarin and Gotha Road #6 trifoliate orange made by Bowman.

It was tested as BS95-V6-24 or US-1284. It produces high yields and good fruit quality on sweet orange trees grown in the flatwoods and infected with HLB.

The Florida Bureau of Citrus Budwood Registration's clean budwood program in Winter Haven, Fla., will distribute the plant material.