Exploration And Enhancement Of Low Polyphenol Oxidase Activity In Wheat Germplasm

White appearance is one of the important quality traits for wheat flour and its products. Flour whiteness is affected by environment, genetic, enzymes and many other factors. Polyphenol oxidase (PPO) is not only a major factor in browning of flour and its products, but also leading to decrease quality of the flour nutritional and appearance. Screening and characterization of low PPO activity germplasm, exploring genes governing polyphenol oxidase, and developing new cultivars with low PPO activity are of great significance for improvement of the quality of flour and enhancement of the competitiveness in China’s wheat production.A set of seed samples, including some commercial wheat varieties and core parents in China, and low PPO activity germplasm IDO580 from the United States, were used to compare the PPO activity. The results showed that PPO activity in IDO580 was only 4.56 AU, about 1/8 of Sumai 3 and Ningmai 9, the low PPO activity germplasm found in commercial wheat varieties and core parents. Testing with functional markers PPO-18 and STS 01 for PPO activity in grains, domestic varieties with low PPO activity had the same patterns of PPO 18 and STS 01 as previously reported. However, IDO580 had different STS 01 band pattern from the previously reported, indicating IDO580 might contain a new gene or allele related to low PPO activity. Therefore the introduced germplasm IDO580 is worth to be further studied and used.The RIL population with 111 lines was developed from the cross between IDO 580 and Yangmai 158 by using SSD method. The 111 RILs and their parents were planted in both field trial and greenhouse in 2012. The PPO activity showed a skewed distribution to the low PPO parent. Totally 503 pairs of SSR primers were surveyed for polymorphism between the parents.19 linkage groups were established by using Mapmaker 3.0b software, involving 119 SSR markers covering 19 chromosomes (except 5D and 6B). The total length of the linkage map was 1634.6 cM and the average interval was 13.74 cM. Four QTLs related to PPO activity were detected by using CIM function of Windows QTL Cartographer 2.5 software and resided on chromosome 2A,2D and 7A, respectively. Two QTLs were identified on the chromosome 2A. One of which, designated QPPO2A-1, was detected in filed environments and could explain 22.81% of the phenotypic variance; the other, designated QPPO2A-2, was detected in both environments and could explain 7.35% and 7.47% of the phenotypic variance. QPPO2D was detected in two environments, and could explain 31.77% and 23.33% of phenotypic variance, respectively. QPPO7A was detected only in greenhouse environments and could explain 20.46% of phenotypic variance.T1352, an advanced line with low PPO activity, was developed by crossing IDO580 with the line of (Soft wheat//Zhengmai 9023/NDW) through continuous catechol staining selection for low PPO activity and better agronomic traits. T1352 has excellent agronomic characteristics as the line of Soft wheat//Zhengmai 9023/NDW and lower PPO activity performance. Its flour-whiteness was superior to those in domestic soft red wheat, U.S. white wheat and Australian standard white. To further measure the whiteness of flour products, we made the dumpling wrappers of the T1352, domestic soft red wheat, U.S. white wheat, and Australian standard white, respectively. It showed that T1352 had the highest whiteness and the slowest discoloration rate during four hours after dumpling wrappers preparation among the four samples.Therefore T1352 has reached the goal of high whiteness with low PPO activity in wheat germplasm enhancement.