Three new citrus rootstocks developed by the Agricultural Research Service have emerged as strong candidates to help the U.S. citrus industry combat key diseases and the citrus root weevil.

The new rootstocks, called US-897, US-942 and US-802, were developed at the ARS U.S. Horticultural Research Laboratory in Fort Pierce, Fla.

Geneticist Kim D. Bowman, based at the lab, has been managing the agency's effort to develop new citrus rootstock for more than 10 years.

ARS research on citrus rootstocks goes back more than a century. It's only been in recent years, however, that the industry has felt an urgency to deal with growing rootstock problems, such as those caused by citrus tristeza virus, foot rot and root rot (Phytophthora species), the Diaprepes abbreviatus root weevil and inadequate soil adaptation. The citrus industry has a total economic impact exceeding $8 billion annually in the state of Florida.

Over the past few years, ARS citrus rootstock development efforts have been expanded and accelerated because of funding from the citrus industry through grants from the Florida Citrus Production Research Advisory Council. Collaborators are an important part of Bowman's research effort, helping to test new rootstocks for resistance to diseases and pests.

A quality rootstock can defend itself against these diseases and pests, while producing a high yield of quality fruit sustained over a long period of time — up to 50 years. Rootstocks are the bottom portions of grafted trees, to which are spliced tops with branches from trees that make the best fruit. These grafted trees produce citrus fruits much quicker than seedling trees.

All three of the top rootstocks are at least three to four years away from commercialization, but they have performed well in initial tests in damp coastal soil for combating Phytophthora nicotianae, P. palmivora and the diaprepes citrus root weevil. These two phytophthora, combined with diaprepes, can form a lethal combination that could devastate Florida's citrus-producing regions.

ARS is the U.S. Department of Agriculture's primary scientific research agency.