PHYSIOLOGICAL ALTERATIONS IN AVICENNIA MARINA (FORSKI) VIERH ASSOCIATED WITH LEAF SPOT DISEASE CAUSED BY ALTERNARIA ALTERNATA (FR.) KEISSLER

Abstract

The leaf spot disease caused by Alternaria alternata in Avicennia marina in Yanb'a city, Saudi Arabia showed significant alterations in chlorophyll a, chlorophyll b, and total pigments as compared to control plants. Glucose as well as fructose (monosaccharide hexose sugars) was increased significantly in the diseased leaves whereas sucrose (disaccharide), sorbitol (sugar alcohol) and inositol (carbocyclic polyol sugar) were decreased. The infection with A. alternata also caused a significant decrease in total lipids, triacylglycerol and sterol, however, diacylglycerol, sterol ester and non-esterified fatty acids increased significantly in diseased leaves. All phospholipid fractions decreased except phosphatidic acid, which increased as compared to healthy leaves. Gas chromatographic analysis of esterified fatty acids revealed the appearance of caprylic (C8) and a significant increase in the amount of both palmitic (C10) and palmitoleic (C16:1). A significant increase in total saturated fatty acids was observed in the infected leaves of A. marina as compared to healthy leaves. Such biochemical alterations were directly related to the destructive effect of the causal organism and its mycotoxins on the chloroplast of A. marina.