Association of Increase in Some Biochemical Components with Flax Resistance to Powdery Mildew

An outdoor pot experiment was conducted in 2014/2015 growing season at Giza Agricultural Research Station to evaluate powdery mildew (PM) severity on 18 flax lines. The tested lines were divided into two distinct groups. The first group included 12 highly resistant lines (HRLs). Disease severity on these lines ranged from 1 to 10%. The second group included 6 highly susceptible lines (HSLs) where disease severity ranged from 90–100%. Levels and activities of phenols, alkaloids, proteins, proline, polyphenol oxidase and peroxidase significantly increased in the infected leaves of the HRLs, compared with the HSLs. Of these components, phenols and peroxidase showed the highest increases in the HRLs (102.34 and 199.33%, respectively). These results indicate that the tested biochemical components have roles to play in flax defense against PM through a variety of mechanisms. The results also suggest that phenols or peroxidase in infected leaves could be used in breeding programs to select resistant lines at early stage of PM development.