Mapping and allelic variations of Ppo-B1 and Ppo-B2 gene-related polyphenol oxidase activity in durum wheat

Polyphenol oxidase (PPO) activity is one of the major causes of undesirable brown color of grain and flour of durum and common wheat. The Ppo-A1, Ppo-A2, Ppo-D1 and Ppo-D2 genes are known to be involved in PPO activity, while the role of Ppo-B1 and Ppo-B2 genes is not accurately established. The goals of this study were to develop homoeologspecific markers to determine the genetic map position of Ppo-B1 and Ppo-B2, detect new allelic variants and to verify their association with PPO activity. Two new functional markers, MG08 and MG33, were developed for Ppo-B1 and Ppo-B2, respectively, and mapped on chromosome bin C-2BL6-0.88, separated by 11.4 cM. Screening of a tetraploid wheat collection with MG08 and MG33 identified four and two alleles, respectively, including three novel alleles of Ppo-B1 (Ppo-B1b, PpoB1c and Ppo-B1d) and one novel allele of Ppo-B2 (Ppo-B2d). Ppo-B1 and Ppo-B2 were significantly associated with PPO activity evaluated in replicated trials carried out in 3 years. The newly developed homoeolog-specific markers can be used in wheat breeding to improve the quality of wheat-based products.