USE OF FATTY ACID COMPOSITION OF SEED TO QUANTIFY RESISTANCE OF FLAX CUL TIVARS TO POWDERY MILDEW DISEASE

Abstract

A field trial was conducted in 2002/2003 and 2003/2004 growing seasons at Giza Agricultural Research Station to evaluate the reactions of ten flax cultivars to powdery mildew (PM) disease. In general, the tested cultivars could be divided into four distinct groups, i.e. highly resistant (Ottowa 770B, Dakota and Bombay), resistant (Cass, Wilden, and Clay), susceptible (Koto and Manshall), and highly susceptible (Cortland and C.1.2008). The cultivars showed considerable variation in disease severity (OS) ratings ranged from 3.69 on Bombay to 100% on C.1.2008. GLC analysis of fatty acid composition of cultivar seeds revealed the presence of the following fatty acids: Myristic, palmitic, palmitoleic, stearic, oleic, linoleic, linolenic and arachidic. However, the unsaturated fatty acids oleic, linoleic and linolenic were predominant in linseed oil. The total percentage of the three fatty acids ranged from 88 in Cortland to 92.9% in Ottowa 770B. PM severity was positively correlated with each of palmitoleic (r=0.776, p < 0.01) and stearic (r=0.704, p < 0.05). On the other hand, none of the other fatty acids was significantly correlated with PM severity. Data for PM ratings and amounts of fatty acids were entered into computerized stepwise multiple regression analysis. Using the predictors supplied by stepwise regression, a two-factor model was constructed to predict PM severity. This model showed that PM severity differences were due to largely to the fatty acids palmitoleic and myristic, which accounted for 80.16% of the total variation in PM severity. These results indicate that fatty acid composition of linseed oil may provide a supplementary assay of greenhouse and field tests to distinguish quantitatively between PM resistant and susceptible genotypes.