Research has shown that coffee cup quality may increase when plants produce less fruit. Other research has shown that lower fruit production is also correlated with an increased tolerance to coffee leaf rust. Ideally, plants could have all three of these traits simultaneously: disease resistance, high quality, and high yield, however the relationship between these three variables are not well understood.
To understand the interrelationship between these three key factors (yield, quality, rust resistance), WCR is comparing the performance of two varieties susceptible to rust: Catuai (a common inbred variety), and H3 (a recently developed, clonally propagated hybrid) to evaluate the effect of thinning fruit to 50% on cup quality and tolerance to coffee leaf rust.
Fruit and leaf samples from the trees will be genetically sequenced in the laboratory so researchers can determine if there are differences in gene expression when coffee plants have more or less fruit and more or less coffee leaf rust. The samples will also be analyzed using the World Coffee Research Sensory Lexicon to see if there are also significant flavor and aroma differences when trees have more or less fruit and more or less coffee leaf rust.
This research will enable coffee scientists to understand the effects of stressors (including fruit load and the presence of leaf rust) on quality at the molecular level. It is critical to do this kind of research to understand the mechanisms that influence rust to enable us to provide better tools and guidance for farmers.
In addition, if researchers can identify candidate genes involved in these interactions, it may be possible in the near future for coffee breeders to select plants with the right combination of genes to allow all three traits—quality, yield, and rust resistance—to exist simultaneously in a more efficient way.
This will be essential for creating new varieties of coffee that are tolerant to coffee leaf rust and other stressors, while maintaining high yields and having good quality—a major focus of efforts by WCR and others to support farmer profitability and reduce the economic and social losses caused by coffee leaf rust.