Identification of Alternaria alternata as a Causal Agent for Leaf Blight in Syringa Species

Mmbaga, Margaret T.; Shi, Ai Nong; Kim, Mee Sook

The Plant Pathology Journal 2011;27(2):120-127.
Published online June 30, 2011.

Identification of Alternaria alternata as a Causal Agent for Leaf Blight in Syringa Species

Margaret T. Mmbaga, Ai Nong Shi, Mee Sook Kim

Abstract

While many isolates of Alternaria alternata are common saprophytes on trees and shrubs, this study clearly demonstrated that A. alternata is a primary pathogen in lilac (Syringa sp.), causing a leaf-blight that affects different Syringa species. Isolates of Alternaria sp. were collected from leaf blight samples of lilacs in the field. The internal transcribed spacer (ITS) region and morphological characterization were used to identify lilac blight pathogen. Based on 100% ITS nucleotide sequence identities to the Alternaria genus in the GenBank and morphological features, these isolates were identified as A. alternata. Disease symptoms were reproduced in lilac plants inoculated with A. alternata mycelial plugs and sprayed with a fungus-free culture filtrate, indicating that pathogenesis in lilac involves secondary metabolites or toxins. Diagnostic primers were developed to detect Alternaria sp. and A. alternata in lilac leaf blight based on ITS region and four known genes associated with pathogenesis in A. alternata: mixed-linked glucanase precursor, endopolygalacturonase, hsp70, and histone genes. The results from our study indicated A. alternata is a primary pathogen in lilac leaf blight, and these diagnostic primers can be used as a tool for the fast detection of A. alternata associated with lilac leaf blight.

Key Words: Alternaria alternata, lilac leaf blight, Syringa species, pathogen detection, toxins