Polyphenol oxidase genes in Hordeum chilense and implications in tritordeum breeding

Polyphenol oxidase (PPO) genes are implicated in the darkening of various wheat end-products, affecting their final color and therefore their quality and consumer acceptance. The importance of PPO1 and PPO2 genes in chromosomes 2A, 2B and 2D in wheat and the orthologous genes in barley chromosome 2H has been studied in several works. Minor quantitative trait loci affecting PPO activity have also been described in other locations. Wheat breeding programmes have selected low PPO activity varieties and great efforts have been made to design markers for assisted selection. The new cereal tritordeum (derived from the cross between the wild barley Hordeum chilense Roem. et Schult. and durum wheat) is known for the high yellow pigment and carotenoid content of its grain. Given that the final color of end-products is also influenced by the oxidation caused by PPO enzymes, the characterization of H. chilense PPO genes in tritordeum background is needed. Therefore, in this work we characterized and mapped PPO sequences including the orthologous PPO1 and PPO2 genes in H. chilense as well as other PPO-like sequences in 3H(ch)L and 4H(ch)L. The first evaluation of PPO activity in a collection of tritordeum is also reported. Finally, marker-trait associations with Diversity Arrays Technology markers revealed the importance of chromosome 2H(ch)L in tritordeum PPO activity, but associations with markers in wheat chromosomes 2A, 2B, 3B, 5B, 6A and 7A were also detected. In conclusion, all the results presented in this work provide valuable information for future challenges in tritordeum breeding.