ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 95 Special Issue 2, October 2018
Morphological, pathological and molecular variability of Alternaria alternata causing leaf blight of onion in the southern region of India
Leaves of onion (Allium cepa var aggregatum G. Don.) showing leaf blight symptoms were collected from farmers? fields of different onion growing areas in Tamil Nadu, India. The pathogen was isolated from infected leaves and identified as Alternaria alternata, based on morphological and cultural characters described by Indian Type Culture Collection, New Delhi (ITCC No. 5574). All the fungal isolates were artificially inoculated on 30-day-old plants grown under glass house conditions. The disease severity at 15 days after inocultation revealed the differences in virulence among the isolates. The molecular variability among isolates of A. alternata was analysed through random amplified polymorphic DNA (RAPD) by using 10 random primers. Analysis of the genetic coefficient matrix derived from the scores of RAPD profile showed a minimum of 27.85 and a maximum of 85.71 per cent similarities among the A. alternata. Cluster analysis, using the unweighted pair-group method with arithmetic average (UPGMA) clearly separated the isolates into two clusters (A and B) confirming the genetic diversity among the isolates of A. alternata from onion. Cluster B consisted of one isolate (AA6) only, while all the other isolates belonged to cluster A. There was no relationship established between clustering in RAPD analyses and the virulence of A. alternata isolates.
Keywords: Onion, Alternaria alternata, leaf blight, virulence, molecular variability