Molecular and pathogenic diversity of alternaria sp. isolated from sesamum by scar marker

A total of 164 Alternaria isolates were obtained by following standard tissue isolation method on potato dextrose agar media plates. Based on morphological features viz., growth, sporulation pattern, 45 isolates were identified as A. alternata and 28 were A. sesami and the remaining ones were non-sporulating. The colour of the isolates ranged from grey to light brown and both fluffy (37) and smooth type (30) of growth were observed with regular to irregular margin. Majority of the isolates were fast growing (119) and some were moderate (45) in growth. Twenty five percent of the isolates (40 isolates) were highly sporulating and some of them (54) were shy in sporulation. Individual isolates were studied in detail on type of growth and margin, color of the colony, radial growth, sporulation, width of the mycelium, vertical (0-3) and horizontal (2-5) septation of conidia, size of conidia (33.1-196 x 24.4-78.6 µm) and length of beak (7.1-88 µm). Out of 164 isolates, twenty one isolates were highly virulent mostly dominated by A. alternata and other species, nine of them were moderately virulent and fourteen were less virulent. Based on ITS region, Alternaria spp were identified and found 8 different species and among all A. alternata was found dominant. RAPD was also studied using different RAPD primers and found that all the species formed similar clusters with one another in their homology. Among them, A. sesami produced a single specific band with OPM-4 primer and A. sesami species specific band has been identified. A. sesami specific gene has been identified and further cloning, sequencing of the +ve cloned cells revealed that they formed 25 sets of primers. Among them, 10 were synthesized and sequence characterized amplified region (SCAR) marker of the A. sesami has been developed.