Archivio Journal of Plant Pathology

Abstract:

Dracaena marignata (family Asparagaceae) is a common ornamental plant in Pakistan on whose leaves circular brown spots were observed in March 2015 in a private garden at Lahore. For pathogen isolation, one spot per leaf from six symptomatic leaves were cut into pieces, surface-sterilized, inoculated in 2% malt extract agar (MEA) and incubated at 25±2oC. Morphological observations were made on 7-day-old cultures grown on MEA at 25±2oC. Fungal colonies were light brown, conidia were produced in short chains, had echinulate walls, were 1-4 transversely septate and ranged from 15-40 x 812 μm. The fungus was morphologically iden- tified as Alternaria arborescens (FCBP1527) (Simmons, 2007) and this identification was confirmed by sequencing of the internal transcribed spacer (ITS) of rDNA. For this purpose, a DNA fragment of approximately 650 bp was amplified us- ing the universal primers ITS1/ITS4 and total genomic DNA as template (White et al., 1990). BLASTn results indicated that the ITS nucleotide sequence of this strain (KT072732) has 100% similarly with many other isolates of A. arborescens from GenBank (JN634832, JX241641, AF397237, KC707557, KC415812). Spores from a 7-day-old culture were scratched and suspended in sterilized saline Tween 80 solution. For pathogenicity tests 105 spores were injected in stem nodes of three young plants (Farrag and Abo-Elyousr, 2011) while control plants were injected with sterilized water. Injection places were wrapped with moistened cotton. All plants were kept at 27±2oC in a greenhouse. Necrotic spots appeared on the leaves of inoculated plants only 7 days post injection. Re- isolation of the same pathogen fulfilled Koch’s postulates. To our knowledge, this is the first report of D. marginata leaf spot in A. arborescens from Pakistan.