Following the discovery of non-commercial citrus plants resistant to greening disease, Fundecitrus researchers in the field of biotechnology have been working to understand the mechanisms underlying this resistance. The Brazilian scientists also seek to identify viable pathways for transferring these traits to commercial varieties.
In 2019, hypotheses were confirmed showing that certain citrus species native to Oceania, such as Eremocitrus and Microcitrus, were capable of either avoiding infection by the disease or exhibiting greater tolerance to contamination by the bacterium. Since then, the project has advanced to a more complex stage: understanding where the genetic basis of resistance lies and how it can be harnessed by commercial citrus production.
Researcher Monica Neli Alves at Fundecitrus leads this project. Directly comparing the DNA of a resistant plant with that of a susceptible one, such as sweet orange, is no simple task. The differences between them extend far beyond resistance to greening. Leaf, flower and fruit morphology, growth habits, agronomic traits and thousands of genetic variations make comparison both complex and imprecise. As a result, the researchers adopted a different strategy.
“Instead of simply comparing the species as a whole, the project began working with controlled crosses between greening-resistant and greening-susceptible plants,” Alves said. “These crosses generate populations of offspring that, while genetically more similar to one another, exhibit different responses to the disease. Some inherit resistance, while others inherit susceptibility.”
By analyzing which regions of the DNA are frequently found in resistant offspring and are also present in the resistant parent (but absent in susceptible individuals), researchers can identify genetic regions associated with resistance traits. These regions are known as QTLs (quantitative trait loci, regions of the genome associated with a particular characteristic). QTLs do not necessarily correspond to a single gene. They may involve dozens or even thousands of genes acting together.
“Resistance to greening is a complex trait, and it may be controlled by multiple regions of the genome that interact with one another,” Alves said.
According to Nelson Wulff, manager of Fundecitrus’ Biotechnology Department, the institution’s strategy combines classical plant breeding with modern molecular genetics tools. The goal is to incorporate resistance traits from Oceanian species into plants that progressively acquire the commercial characteristics of orange varieties.
“This process requires multiple generations of crosses, generally involving species that contributed to the origin of modern oranges, such as mandarins and pomelos,” Wulff said. “With each new generation, molecular markers help select only those individuals that retain resistance, accelerating a process that would have taken decades in the past.”
Read more details about the research in an article —“Evolution of research on greening-resistant plants” — on page 8 of Fundecitrus’ latest edition of Citricultur magazine.
Source: Fundecitrus
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