University of Florida (UF) researchers hope to release Huanglongbing-tolerant citrus rootstocks for large-scale industry trials in March 2014, in a bid to overcome the disease that has cost the state's industry more than US$4.5 billion in losses since 2006.

A UF release said 16 citrus rootstocks had been developed, most of which showed a lower rate of infection and more tolerance to the disease, also known as citrus greening.

UF Citrus Research and Education Center horticulture professor Jude Grosser it could be another three to five years before the cultivars were available to growers.

With his colleagues Fred Gmitter and Bill Castle, Grosser has seen commercial rootstocks with 70% infection rates alongside experimental varieties that were only 10-20% infected; the latter still producing good fruit after four years of citrus greening exposure.

"What’s happening is fields are becoming living laboratories now because the greening disease is spreading so quickly," Grosser said in the release.

"Some people have estimated that 70 percent of the trees in the entire state are infected now, and it’s predicted to go up in the 90s in a very short time.

"Everything's being challenged by the disease, and we're seeing differences in the rootstock material in the field. We're seeing very genetically diverse material interact with the diseases, and some things are reacting better than others."

Whether trees grown on the less affected rootstocks will survive is yet to be seen, but hopefully they will bring new hope to an industry in need of solutions. Grosser said one of the reasons greening had hit the citrus industry so hard was that growers depended on just a few varieties to produce their crop.

"For the course of the last several 100 years, we’ve been eliminating the genetic diversity in the wild, so citrus has kind of gone to a monoculture where there are just a handful of varieties grow," he said.

"So you've limited your ability to adapt when there is a new pressure that comes along."

Grosser said he remained cautiously optimistic about the rootstocks.

"They may be part of an integrated solution to citrus greening that includes managing psyllids, the insect that spreads greening, and improved nutritional programs to keep citrus trees healthy,” he said. “All of those things together might contribute to an effective way of managing this disease and remaining profitable and keeping this industry alive."

Elsewhere in the U.S., citrus greening was also detected in California last year. The disease has been so problematic for Brazil, the world's top orange juice exporter, that a government scheme eliminated 9.7 million trees from 2004-2010.

Related story: Brazil's citrus greening lessons: 'there is no cure, just management

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