FIRST REPORT OF ALTERNARIA ALTERNATA CAUSING LEAF SPOT ON FICUS BENGHALENSIS IN PAKISTAN

Abstract

In January 2014, brown, irregular, 3-10 mm necrotic spots with darker margins and yellow halos were found on about 90% of leaves of Ficus benghalensis growing in a garden at Lahore, Pakistan. The pathogen was isolated from surface sterilized infected leaf portions incubated on 2% malt extract agar (MEA) at 25±2°C. Morphological observations were made on pure culture grown on Potato Carrot Agar (PCA) for 7 days. Colonies were olive brown and 3-3.5 cm in diameter. Clear concentric growth rings of highly sporulating colony were observed. Conidia produced in short chains of upto 6 conidia on simple or branched conidiophores. Conidia were dark brown, geniculate, with or without longitudinal septa and range in size from 5-13 x 25-50 µm. Alternaria alternata (FCBP1519) was identified based on morphology (Simmons, 2007). This identification was confirmed by sequencing of ITS region of rDNA. A DNA fragment of approximately 600 bp, amplified by ITS1/ITS4 primers (White et al., 1990) was analysed by BLASTn. Results indicated that this nucleotide sequence (KT283683) was 100 % similar with many strains of A. alternata in GenBank. Pathogenicity of fungus was verified by spraying conidial suspension at the concentration of 1x106 CFU/ml on the leaves of three young plants. Three control plants were sprayed with sterilized water. All plants were covered with polythene bags, incubated at 27±2°C, watered regularly and observed daily for disease development. Re-isolation of same pathogen from the necrotic areas of artificially inoculated leaves confirmed the pathogenicity. The present study reports A. alternata leaf spot on F. benghalensis for the first time in Pakistan.