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SCIENCE – Study finds that coffee varieties in Brazil have low genetic diversity

Brazil is the major producer and exporter of coffee for the international market, providing morning cups of coffee for people around the world. But a new study published in the July-August issue of Crop Science shows that the varieties of coffee produced in Brazil are quite closely related to each other, with only a few ancestral lines contributing to the current varieties. That low genetic diversity could make the crop vulnerable to pests and diseases.
 
Coffee was first introduced in Brazil in 1727, and the primary species grown there is Coffea arabica. The first coffee breeding program began in 1927, and breeding research is now done in several states throughout the country. While varieties have been released from different breeding programs, a limited number of parental lines have been used to produce those varieties.
 
Eveline Teixeira Caixeta, a researcher at the Embrapa/Universidade Federal de Viçosa, and her co-authors wanted to understand the parentage and genetic variability among coffee varieties in Brazil.
 
They looked at 121 varieties that were released from 1939 to 2009 and found that they were defined by just 13 ancestral lines of coffee. Only seven of those ancestors contributed over 97 percent of the genetic base.
 
“To our knowledge, this is the first study about the genetic base of Coffea arabica that explains the low genetic diversity among varieties released in Brazil,” says Caixeta.
 
The low genetic diversity of coffee varieties in Brazil could be harmful to the crop. Plants become vulnerable to diseases and pests when they have similar genetic backgrounds, and coffee growers in Brazil have already faced such an issue.
 
“The introduction of leaf rust in the 70s endangered the coffee crop in Brazil because all of the varieties were susceptible to the disease,” explains Caixeta. “The disease was overcome after the development of chemical controls and resistant varieties.”
 
One measure that the team used to determine ancestry in the current study was the coefficient of parentage, or COP. COP between varieties is defined
as the probability that the two lines have the same form of a gene chosen randomly for testing. The higher the COP (up to 1.0), the more closely related the varieties are.
 
In varieties released between 1960 and 1979, the average COP was 0.90, indicating that those lines were closely related. However, in varieties released after 1980, the COP dropped to 0.46 showing that those lines had greater genetic diversity.
 
The drop in COP after 1980 coincided with new parental lines being used in
the breeding program after the introduction of leaf rust in Brazil.
While there is no ideal COP, the values seen in coffee are high in comparison
to other crops, such as soybean, barley, and wheat.
 
The low genetic diversity of coffee, while improved from previous decades, still leaves the crop vulnerable to future outbreaks of pests and diseases.
 
To avoid those possible outbreaks, Caixeta and her co-authors want their study to be a starting point for the design of future breeding programs that would increase genetic variability by using new lines from around the country and
the world.
 
“We need to look for diversity in the genetic banks of different regions and incorporate those new varieties into the national breeding programs,” says Caixeta. “Introducing new parental lines into the programs will provide needed genetic variability.”