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First Report of Alternaria alternata Causing Postharvest Fruit Rot of Jujube in Pakistan

Alam, M. W., Rehman, A., Malik, A. U., Khan, S. M., Ali, S., Aslam, S., Hameed, A., Sarfraz, S.
Plant disease 2018 v.102 no.2 pp. 452
Alternaria alternata, DNA, Ziziphus mauritiana, air drying, beak, conidia, conidiophores, cultivars, culture media, disease incidence, fruits, fungi, genes, markets, pathogen identification, pathogenicity, pathogens, photoperiod, plant rots, polygalacturonase, relative humidity, sodium hypochlorite, sprayers, spraying, tissues, China, India, Korean Peninsula, Pakistan, United States
Jujube (Ziziphus mauritiana Lamk), commonly known as “ber,” is a minor fruit in Pakistan that is cultivated on an area of 5.129 ha. In January 2017, severe fruit rot disease was observed in several markets located in the Faisalabad (31°25′15.7620″N, 73°5′21.4584″E) district of Punjab-Pakistan, with disease incidence ranging from 15 to 26%. Initially, small, oval, light to dark brown lesions (1 to 3 mm) were observed on the fruit surface, which gradually enlarged in size and led to total fruit rot. To isolate the pathogen, small tissue segments were cut from rotted fruit, surface disinfected with 1% NaClO for 2 min, rinsed three times in sterilized distilled water, air dried, and then placed aseptically onto potato dextrose agar (PDA) medium. Tissue samples were cultured at 25°C under a 12-h light/dark photoperiod for 3 days. Isolates were transferred to fresh PDA medium and cultured for 7 days. The cultured isolates consistently yielded dark brown to black colonies (85% isolation rate from 40 fruit tissues). Conidiophores were short, septate, 20 to 52 μm long, and 1 to 3 μm wide. Conidia were in chains (average conidial dimension 20 to 28 × 8 to 10 μm), brown and ovoid, with a short conical beak with both transversal (two to five) and longitudinal (one to three) septa. Based on morphology, the pathogen was identified as Alternaria alternata (Simmons 2007). To confirm the identification, genomic DNA was extracted and amplified using ITS1/ITS4 primers (White et al. 1990) and endopolygalacturonase gene using primers PG3/PG2b (Andrew et al. 2009). The resulting sequences were deposited in GenBank (accession nos. KY859867 and MF371420). BLAST analysis showed 99 to 100% homology to A. alternata sequences KJ957793 and AY295025 isolated from Korea and the United States, respectively. Pathogenicity tests were conducted on 20 surface-sterilized jujube fruit (cultivar Dilbhar) by spraying them with a conidial suspension (10⁶ conidia/ml) using a handheld sprayer. Ten fruit inoculated with sterile water served as a non-treated control. Fruit samples were kept in a moist chamber at 25°C and 70 to 80% relative humidity with a 12-h photoperiod. After 2 to 3 days of inoculation, all fruit displayed small, light to dark brown lesions followed by rotting. Reisolations from symptomatic fruit consistently yielded a fungus identical to A. alternata. Control fruit remained disease-free. Fruit rot of jujube caused by A. alternata has been reported in India and China (Wadia and Manoharachary 1980; Wang et al. 2009). To our knowledge, this is the first report of A. alternata causing postharvest fruit rot of jujube in Pakistan. The disease could represent a threat to jujube cultivation.