A Novel STS Marker for Polyphenol Oxidase Activity in Bread Wheat

Abstract

The enzyme activity of polyphenol oxidase (PPO) in grain has been related to undersirable brown discoloration of bread wheat (Triticum aestivum L.) based end-products, particularly for Asian noodles. Breeding wheat cultivars with low PPO activity is the best approach to reduce the undesirable darkening. Molecular markers could greatly improve selection efficiency in breeding programs. Based on the sequences of PPO genes (GenBank Accession Numbers AY596268, AY596269 and AY596270) conditioning PPO activity during kernel development, 28 pairs of primers were designed using the software ‘DNAMAN’. One of the markers from AY596268, designated as PPO18, can amplify a 685-bp and an 876-bp fragment in the cultivars with high and low PPO activity, respectively. The difference of 191-bp size was detected in the intron region of the PPO gene. The STS marker PPO18 was mapped to chromosome 2AL using a DH population derived from a cross Zhongyou 9507 · CA9632, a set of nulli-tetrasomic lines and ditelosomic line 2AS of Chinese Spring. QTL analysis indicated that the PPO gene co-segregated with the STS marker PPO18 and is closely linked to Xgwm312 and Xgwm294 on chromosome 2AL, explaining 28 – 43% of phenotypic variance for PPO activity across three environments. A total of 233 Chinese wheat cultivars and advanced lines were used to validate the correlation between the polymorphic fragments of PPO18 and grain PPO activity. The results showed that PPO18 is a co-dominant, efficient and reliable molecular marker for PPO activity and can be used in wheat breeding programs targeted for noodle quality improvement.