Distribution Of Allelic Variations Of Polyphenol Oxidase Genesin Shaanxi Wheat Cultivars (Lines)

Wheat is a leading foodstuff crop in Shaanxi province.Wheat-based products,such as noodle and steamed bread,are the most popular in this region.Colour is an important trait, exerting significant influences on the apparence of the wheat-based products,and it is of great importance to investigate the mechanisms related to colour for the wheat products. The enzyme activity of polyphenol oxidase(PPO)in grain and flour has been related to undersirable brown discoloration of common wheat based end-products.It was found that grain(flour)PPO activity was controlled by two major genes at chromosomes 2A and 2D in wheat.The PPO activity was significantly different in various PPO genotypes.In order to investigate content of polyphenol oxidase(PPO)activity and presence of allelic variations at PPO-2A and PPO-2D loci in Shaanxi wheat cultivars,a total of 138 cultivars were used to identified using functional markers PPO 18 and PPO 29.The results indicated that the frequencies of cultivars with alleles PPO-A1a(high PPO activity),PPO-A1b(low PPO activity)at PPO-2A locus were 47.1%and 52.9%, respectively,and PPO-D1a(low PPO activity)and PPO-D1b(high PPO activity)at PPO-2D locus were 30.4%and 69.6%,respectively.The frequencies of allelic combinations of PPO genes for Ppo-A1aPpo-D1a(higher PPO activity),Ppo-A1aPpo-D1b(the highest PPO activity),Ppo-A1bPpo-D1a(the lowest PPO activity)and Ppo-A1bPpo-D1b(lower PPO activity)at PPO-2A and PPO-2D loci were 10.1%,37.0%,20.3%and 32.6%, respectively.The frequencies of those genotypes were also different among wheat cultivars from Shaanxi various regions.Generally,frequency of cultivars with the lowest PPO activity in Shaanxi province was low.Therefore,a major object of wheat quality improvement in Shaanxi province in the future would be to breed cultivars with lower PPO activity. Fortunately,twenty-eight genotypes with low PPO activity have been detected,and will be been crossed with high yielding parents to improve qualities in Shaanxi wheat breeding in the future.