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

In some cases, the researchers have seen commercial rootstocks with 70 percent infection rates next to experimental varieties that are only 10 to 20 percent infected, but still producing fruit, after four years of exposure to the disease. Whether the trees grown on the less affected rootstocks will survive and remain productive is something the researchers will continue to monitor.

One of the reasons greening has hit the citrus industry so hard is that growers depend on just a few varieties to produce their crop, because they’re most likely to withstand Florida weather and still make fruit consumers want to buy, Grosser said.

“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 grown,” Grosser said.

“So you’ve limited your ability to adapt when there is a new pressure that comes along.”

Gmitter said it’s fortunate the researchers have maintained a diverse selection of citrus varieties for just such an occasion.

“We took that approach from the beginning to try and get as much genetic diversity into our breeding program as possible,” Gmitter said. “You don’t know what the future is going to bring or what the future problems are going to be.”

Gmitter said he is cautiously optimistic about the rootstocks and that they need to be validated on a large scale.

“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.”

To view a video that outlines the citrus breeding effort at the University of Florida, visit http://news.ifas.ufl.edu/.