Genetics of polyphenol oxidase (PPO) activity in wheat (Triticum aestivum L.)

The enzyme activity of polyphenol oxidase (PPO) in grain is regarded as a major factor in time-dependent darkening and discoloration of wheat food products during processing or storage. The darkening phenomena of products reduce the quality of products and affect consumer acceptance. Breeding wheat cultivars with low PPO activity is the best way to reduce the undesirable darkening. The low PPO line PI 117635 was crossed to two low PPO wheats from Idaho, IDO580 and IDO377s to determine whether matings between wheats with low levels of grain PPO would result in complementation, and lines with lower or nil PPO would be generated. The F3:4 population derived from PI 117635/IDO580 showed no variation in PPO activity. The F3:5 and F3:6 populations derived from PI 117635/IDO377s grown at Yuma and Oregon fields in 2009 were analyzed for PPO activity and used to determine whether lines with nil PPO activity were generated. Of the 239 lines, 154 lines were identified to have PPO activity that was not significantly different from Ben durum wheat using t-test. STS markers, PPO18, PPO29, and STS01 were used to test lines possibly with either low or high PPO levels at Ppo-A1 and Ppo-D1 loci. All lines were fixed for the low PPO allele at Ppo-A1. However, PPO29 and STS01 showed the opposite results from the Ppo-D1 allele prediction. To examine inheritance of PPO activity in multiple wheat genetic backgrounds and to evaluate the relationship between PPO activity and alleles at two PPO loci, 5 populations (PI 117635/Antelope; Fielder/NE03681; Fielder/Antelope; NW07OR1070/Antelope; NW07OR1066/OR2050272H) were developed. STS markers were used to identify the genotypes and a putative third (null) genotype at Ppo-A1 allele was discovered in NW07OR1066 and NW07OR1070 lines. ANOVA showed all populations had significant genotypic effects on PPO activity. The generations and genotype nested within generation effects were not significant in all populations. The NW07OR1070/Antelope and NW07OR1066/OR2050272H populations had the lowest PPO activities because both populations had a null allele for Ppo-A1 on chromosome 2A. Of all 5 populations, 3 populations found the reverse results of Ppo-D1 allele from the previously reported research, indicating the markers for Ppo-D1 allele give erroneous results in some genetic backgrounds