UNIVERSITY PARK, Pa. — Use of the powerful gene-editing tool CRISPR-Cas9 could help to breed cacao trees that exhibit desirable traits such as enhanced resistance to diseases, according to Penn State plant scientists.
The cacao tree, which grows in tropical regions, produces the cocoa beans that are the raw material of chocolate. Reliable productivity from cacao plants is essential to the multibillion-dollar chocolate industry, the economies of producing countries and the livelihoods of millions of smallholder cacao farmers.
But each year, several plant diseases severely limit global production, with 20-30 percent of cocoa pods destroyed preharvest, noted lead author Andrew Fister, postdoctoral scholar in plant science, College of Agricultural Sciences, Penn State.
"In West Africa, severe outbreaks of fungal diseases can destroy all cacao fruit on a single farm," said Fister. "Because diseases are a persistent problem for cacao, improving disease resistance has been a priority for researchers. But development of disease-resistant varieties has been slowed by the need for sources of genetic resistance and the long generation time of cacao trees."
The researchers reported recently, in Frontiers in Plant Science, the study results, which were thought to be the first to demonstrate the feasibility of using cutting-edge CRISPR technology to improve Theobroma cacao.
CRISPR stands for clustered regularly interspaced short palindromic repeats. It is a way to modify an organism's genome by precisely delivering a DNA-cutting enzyme, Cas9, to a targeted region of DNA. The resulting change can delete or replace specific DNA pieces, thereby promoting or disabling certain traits.
Previous work in cacao identified a gene, known as TcNPR3, that suppresses the plant's disease response. The researchers hypothesized that using CRISPR-Cas9 to knock out this gene would result in enhanced disease resistance.