Phenols as a biochemical basis of resistance in wheat against Karnal bunt

The effects of the highly aggressive isolate KB-2 of the Karnal bunt pathog en (Neovossia indica) on phenol metabolism, peroxidase (POX) and its isoenz ymes were studied in wheat. Two resistant genotypes, HD 29 of bread wheat ( Triticum aestivum) and DWL 5023 of durum wheat (T. durum), and one suscepti ble bread wheat, WL 711, were used. In the bread wheats, total phenols reac hed a maximum 2 days after inoculation (d.a.i.). In the resistant durum lin e, total phenols did not change significantly for 6 d.a.i., but declined si gnificantly at 10 d.a.i. Three phenolic compounds, caffeic acid, l-tyrosine and hydroquinone, were detected using thin-layer chromatography. The first two were detected at all times at and after inoculation, but hydroquinone was detected only in the resistant wheats at 6 d.a.i. The activity of POX w as highest at 2 d.a.i. in the two resistant wheats, but increased more slow ly to a peak at 6 d.a.i. in the susceptible wheat. The number of isoenzymes of POX detected by polyacrylamide gel electrophoresis (PAGE) changed after inoculation with KB-2. The maximum number of isoenzymes occurred at 2 d.a. i. in the two resistant wheats and at 6 d.a.i. in the susceptible wheat. Al though the isoenzymes detected in seedlings were not identical to those det ected in seeds, the PAGE banding patterns of seeds and seedlings were the s ame for the two resistant wheats. The potential use of the additional band at a relative mobility of 0.42 in seeds and 0.28 in seedlings as markers fo r Karnal bunt resistance is discussed.