Variations in fatty acid methyl ester profiles and amplified fragment length polymorphisms among and within species of Phytophthora from ornamental plants

Fatty acid methyl ester (FAME) profile analysis and amplified fragment length polymorphism (AFLP) analysis have been proven to be efficient procedures to identify Phytophthora spp. in this study. Isolates of P. cactorum, P. citricola, P. citrophthora, P. cinnamomi, P. cryptogea, and P. nicotianae were used to test the effects of cultural conditions on FAME profiles. Fifteen fatty acids were common in all species while myristic (14:0), palmitic (16:0), linoleic (18:2o6c), oleic (18:1o9c), and eicosapentaenoic (20:5o3 c) acids comprised more than 75% of the fatty acid profiles. Medium had the greatest effect and mycelium age had the least effect on FAME profiles of Phytophthora spp. Isolates of each species then were grown under standard conditions (0.25x potato dextrose broth at 20°C in the dark for 4 days) and FAME profiles were analyzed. Isolates of the same species clustered except for P. cryptogea. Clusters revealed by FAME analyses were consistent with those generated by AFLP analysis. Fifty-one and 59 isolates of P. cinnamomi and P. nicotianae , respectively, were collected, primarily from ornamental plants, in South Carolina between 1995 and 2000. The A2 mating type of P. cinnamomi was predominant (96%) with only two A1 isolates (4%) found. All of the isolates of P. cinnamomi were sensitive to mefenoxam (EC50 < 0.2 mug/ml). AFLP analysis indicated that the two A1 isolates were in one cluster that separated from all the A2 isolates that showed little genetic variation. Comparing FAME and AFLP analyses, 35 isolates (68.6%) were clustered similarly by both FAME and AFLP analyses. For P. nicotianae, the percentages of A1 and A2 mating type isolates were approximately equal (44 and 56% respectively). The FAME profile clusters (A, B) were nearly identical to AFLP clusters (I, II). In one cluster (A, I), isolates were mating type A1, sensitive to mefenoxam (EC50 < 0.1 mug/ml), and were isolated from plants in Araliaceae. In the other cluster (B, II) isolates were mostly mating type A2, less sensitive to mefenoxam---including nine resistant isolates with EC50 values of 266 to 772 mug/ml, and were isolated mostly from herbaceous plants.