Finding long-term solutions

Managing psyllids with insecticides and biological control doesn’t eliminate the entire population, and it is difficult to remove HLB-infected trees fast enough to stay ahead of the disease spread. Long-term solutions are needed to develop a citrus tree that can resist or withstand the bacterium and produce good-tasting, abundant fruit or confound the psyllid so that it cannot transmit the disease.

Gene fusion could boost citrus trees immunity to HLB

UC Davis scientists are using bioengineering to develop rootstocks that are resistant to HLB and other diseases. Abhaya Dandekar, professor in the Department of Plant Sciences at UC Davis, and his colleagues will use gene fusion, which fuses two immunosuppressive genes that attack HLB in different ways to make the plant more effective at fighting the disease. “Many disease-causing microbes can evade one defensive action of a host plant, but we believe that most microbes would have difficulty overcoming a combination of two immune-system defenses,” Dandekar said. Gene fusion is common in nature and is part of what sparks evolution. In a sense, Dandekar and his colleagues are helping citrus evolve into a plant that is immune to HLB.

Gene sequencing for developing resistant citrus

In Florida, researchers have found trifoliate orange rootstock to have some natural resistance to HLB. They have enlisted their long-time collaborators in California to help determine the mechanism of this partial resistance and, eventually, transfer it to edible citrus varieties. Mikeal Roose, professor in the Department of Botany and Plant Sciences at UC Riverside, and his colleagues are assisting in the genetic analysis of about 200 hybrid crosses between sweet orange and trifoliate orange, a species used as a rootstock. “In Florida, they are studying each plant to see how resistant it is,” Roose said. “My lab is sequencing a large number of genome fragments to find particular fragments that are associated with resistance. That will help us identify what gene is involved so we can work on transferring that gene.” In addition, the Roose lab is trying to make plants resistant to diseases like HLB by using chemical genomics. The objective is to find, in a library of hundreds of thousands of chemicals maintained at UC Riverside, one that mimics a genetic mutation, making the plant more resistant to disease.