Development and characterization of wheat yellow mosaic virus-resistant lines carrying Q.Ymym, breaking off the tightly-linked high-activity allele of the polyphenol oxidase gene in the Japanese wheat variety ‘Yumechikara’

The Japanese winter wheat variety ‘ Yumechikara ’ shows resistance to wheat yellow mosaic virus (WYMV). A single major QTL for WYMV resistance, Q.Ymym, has been identified in ‘ Yumechikara ’ . Q.Ymym is tightly linked with the high-activity allele of the polyphenol oxidase (PPO) gene, Ppo-D1b, on the long arm of chromosome 2D. The introduction of Q.Ymym into susceptible varieties results in a time-dependent discoloration of wheat end products, especially in noodles, by the cointroduction of Ppo-D1b. The objective of our current study was to break off the tight linkage between Ppo-D1b and Q.Ymym. In this study, we clarified the positional relationship between Ppo-D1 and Q.Ymym. Linkage analysis indicated that Ppo-D1 was mapped on the Q.Ymym region, whereas the reference genome sequence of chromosome 2D showed that the physical distance was 19.7 Mb between Ppo-D1 and Q.Ymym. One recombinant between Ppo-D1 and Q.Ymym could be identified from recurrent back crossed lines between ‘ Yumechikara ’ and the susceptible variety ‘ Tamaizumi ’ . We successfully developed a line carrying the low-activity Ppo-D1a allele and Q.Ymym from its progenies. The Ppo-D1a/Q.Ymym lines showed resistance to WYMV and low PPO activity. We made noodle sheets of yellow alkaline noodles from the Ppo-D1a/Q.Ymym and Ppo-D1b/Q.Ymym lines and assessed their time-dependent discoloration. The raw noodle sheet discoloration in the Ppo-D1a/Q.Ymym lines was suppressed in comparison to that in the Ppo-D1b/Q.Ymym lines. The Ppo-D1a/Q.Ymym line can solve the problem of noodle discoloration caused by the introduction of Q.Ymym. DNA markers for the selection of Ppo-D1a and Q.Ymym have been developed in previous studies. Breeding for WYMV resistance is expected to improve by combining the Ppo-D1a/Q.Ymym line and DNA markers in marker-assisted selection.