Grape (Vitis vinifera L.) is an important commercial crop in the temperate regions of Bolivia where it has been grown for hundreds of years. In October of 2001, diseased canes of grape (cv. Muscat of Alexandria) were collected in a vineyard in Yotala, Department of Chuquisaca in southern Bolivia. In this planting of more than 1,000 plants, more than 75% were exhibiting cane dieback symptoms and many were dead or dying. No disease was observed on grape berries. Symptoms of the disease were similar to those reported for Diplodia cane dieback (1). Cankers ranging from 2 to 10 cm long and 0.5 to 3 cm wide were observed. When diseased canes were placed in a moist chamber, conidia oozed from pycnidia in black cirri. Immature conidia were hyaline and one-celled, but mature conidia were dark brown (20 to 30 × 10 to 15 μm) with one median septum and longitudinal striations. The pathogen was tentatively identified as Lasiodiplodia theobromae (Pat.) Griffon & Maubl. (synonyms Diplodia natalensis Pole-Evans and Botryodiplodia theobromae Pat.), teleomorph Botryosphaeria rhodina (Cooke) Arx) (2). Fungi were isolated from cankers on diseased canes by surface disinfestation in 0.25% NaOCl for 5 min and placing small pieces of tissue on 2% water agar or potato dextrose agar (PDA). L. theobromae was isolated from these tissues. Koch's postulates were fulfilled by inoculating grape berries and canes with the pathogen. Five grape berries were surface disinfested and inoculated by wounding with a sterile scalpel and inserting a piece of fungal mycelium on PDA in the wounded sites. The same number of control berries was similarly treated with sterile PDA. Inoculated and control berries were placed in plastic, moist chambers in the laboratory at ambient temperature (15 to 28°C) in the dark. Five canes on two potted plants were inoculated with the same isolate of the pathogen in a similar manner as the berries. The inoculated and control sites on canes were wrapped with masking tape. Plants were placed in a moist chamber for 5 days. After 8 days, inoculated berries were rotting and the inoculated sites were covered with grayish mycelium. Within 12 days, cankers as much as 3 cm long developed on the inoculated canes, and in some lesions, black pycnidia were observed. No lesions developed in the wounded control canes. The pathogen was reisolated from inoculated berries and canes, but not from control berries or canes. The teleomorph was not observed on any naturally infected canes or on those inoculated with the anamorph. The pathogen was identified as L. theobromae based on symptoms (1), cultural and morphological characteristics (2), and pathogenicity tests. The disease poses a potential threat to the cultivation of grapevine in southern Bolivia. To our knowledge, this is the first report of Diplodia cane dieback of grapevine in Bolivia.
References: R. C. Pearson and A. C. Goheen. Compendium of Grape Diseases. The American Phytopathological Society, St. Paul, MN, 1988. (2). E. Punithalingam. No. 519 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, England, 1976.
