Abstract
The present study was carried out to investigate the leaf spot disease of Avicennia marina (Forski) Vierh in Saudi Arabia. The leaf spot disease is reported for the first time in mangrove plants of SA. The symptoms of leaf spot disease and the morphological characters of the causal organism are also described. The radial growth and sporulation of A. alternata were variable with obvious trend on the different growth media. The optimum pH range for maximum growth was 6.0 to 6.5 and any fluctuation in pH caused significant decrease in linear growth of the mold. The chromatographic (TLC) analysis of chloroform extract of fungal culture broth indicated clearly that the mold was able to produce both altenariol and alternariol monomethyl ether. The gas liquid chromatographic analysis of mycelial fatty acids demonstrated the presence of caproic, caprylic, lauric, myristic, palmitic, margaric, stearic, arachidic, myristoleic, palmitoleic, oleic, linoleic, alpha linolenic, Cis-11 eicosenoic, eicosatrienoic and arachidonic fatty acids in the mycelia of the causal organism. The analysis of free amino acids in the mycelia of causal organism indicated the presence of 13 amino acids namely, alanine, threonine, valine, proline, methionine, tryptophan, tyrosine, lysin, cystin, glycine, asparatic acid, tyrosine, and phenyl alanine. The PCR product amplified with A. alternata DNA indicates that the 370-bp PCR product is a useful diagnostic tool to identify the causal organism in mangrove leaves. This study demonstrated that the causal organism of leaf spot disease of A. marina was typically similar to Alternaria alternata (Fr.) Keissler via classical, biochemical and molecular characterization.