First Report of Leaf Spot Caused by Corynespora cassiicola on Jasminum sambac in Pakistan.

Abstract

Jasminum sambac L. is a species of jasmine native to a small region in the eastern Himalayas and is cultivated worldwide as an ornamental plant (USDA-ARS 2016). In Pakistan, it is cultivated for ornamental purposes throughout the country. The flowers of this plant are traditionally used in the preparation of essential oils and for making jasmine tea. The flowers and leaves also have been used in folk medicine to treat breast cancer, epilepsy, ulcers and promote wound healing (Al-Snafi 2018). In December, 2017, almost 10 leaves of 3 plants of J. sambac growing plant nursery of Gehlan, Pattoki, Punjab a province of Pakistan were observed with leaf spot disease. Infected leaves exhibited circular to sub-circular spots with indistinct margins and grey papery centers delimited by dark brown rims. For further microscopic study, the infected leaves were examined under a stereomicroscope. For the isolation and cultural studies of infecting fungus, infected parts of leaves were surface sterilized in 1% NaOCl for about 10 seconds, washed twice in sterilized distilled water, plated on potato dextrose agar (PDA) medium and incubated at 25°C for 4 days. Pure cultures were obtained having colonies of light to dark brown color. Conidia (n=20) were light brown to pale olivaceous brown, smooth, obclavate to cylindrical in shape, 99.5-118.5 μm in length and 12.5-15.0 μm in width, with mostly 3 to 14 pseudosepta. Conidiophores (n=20) were straight to slightly curved, unbranched, and pale to light brown in color. Based on the morphological characteristics of the colonies and conidiophores and conidia, the pathogen was identified as Corynespora cassiicola (Berk and M.A. Curtis) C.T. Wei. (Berkeley & Curtis 1968; Lu et al. 2021; Wei 1950). Genomic DNA was extracted following using modified CTAB method (Gardes and Bruns 1993) and internal transcribed spacer (ITS) region was amplified with ITS1 and ITS4 primers (White et al. 1990). The ITS sequence generated of about 553 bp and deposited in GenBank (accession no. MN954556), was found more than 99% similar to previously deposited sequences of C. cassiicola (GenBank accession nos. MN339671, EU364535, FJ852574, MK139711, EU131374) as verified through BLASTn and phylogenetic tree construction. A pathogenicity test was performed for fulfilling Koch'spostulates. Conidial suspension (105 conidia/ml) of the recovered isolate was sprayed on the 5 healthy leaves of 2-month-old seedling of J. sambac. Mock inoculated plants sprayed sterile distilled water were used as a control. The seedlings were covered with plastic bags to maintain high humidity at 24 to 28°C for a week. Identical disease symptoms to those observed in nursery plants were observed on the leaves of the inoculated plants in 7 days but not mock inoculated plants and results were reconfirmed. The reoccurred fungus was isolated from the diseased spots of the inoculated leaves to complete Koch's postulates and identified microscopically. A representative sample of leaves with lesions was deposited in the LAH herbarium, Department of Botany University of the Punjab, Pakistan (LAH35691). Previously, C. cassicola has been found infecting Jasminum mesnyi in China and Jasminum sp. in Florida (Alfieri et al. 1984; Zhang et al. 2018). The best of our knowledge, this is the first report of leaf spot caused by C. cassiicola on J. sambac in Pakistan. It will establish a foundation for future studies of management strategies for this plant disease caused by C. cassiicola.