ABSTRACT
Oilseed rape (Brassica napus L.) was recently introduced into Greece for the production of biofuels. During May of 2007, symptoms typical of stem rot were observed on oilseed rape plants in three commercial fields in the area of Galatades-Pella, Central Macedonia, Greece. Approximately 30% of the plants were affected. Symptoms began as a chlorotic wilt on the foliage and developed into necrosis of basal stems. In the advanced stages of the disease, stems and branches became bleached and eventually died. White, as well as black, mycelium and irregularly shaped sclerotia (2 to 5 mm in diameter) were produced abundantly on and inside the affected stems. To isolate the pathogen, 20 symptomatic 6-month-old plants were collected from each field. Sclerotia were dipped in 70% ethanol, surface sterilized in 1% sodium hypochlorite for 1 min, and rinsed in sterile water. Sclerotia placed on potato dextrose agar (PDA) were incubated in the dark at 25°C for 10 days. Sclerotinia sclerotiorum (Lib.) de Bary was identified on the basis of morphological characteristics (2). To conduct pathogenicity tests, 10 6-week-old oilseed rape plants (cv. Titan) were each inoculated with a 5-mm-diameter colonized PDA disk placed in wounds made in the basal stem with a sterile scalpel. Five control plants were treated similarly except that the agar disk did not contain mycelium. Plants were then covered with a plastic bag to maintain high humidity. After 72 h, the bags were removed and the plants were maintained in a growth chamber at 23 to 25°C with a 12-h photoperiod and 75% relative humidity. Pathogenicity tests were repeated three times. Symptoms identical to those observed in the field developed within 12 days after inoculation; control plants remained healthy. The fungus was reisolated from all inoculated plants, confirming Koch's postulates. S. sclerotiorum has been reported on oilseed rape in Argentina, Australia, Brazil, Canada, the United States, and New Zealand (1). To our knowledge, this is the first report of Sclerotinia stem rot of oilseed rape in Greece. References: (1) D. F. Farr et al. Fungal Databases. Systematic Botany and Mycology Laboratory. Online publication. ARS, USDA, 2008. (2) L. M. Kohn. Phytopathology 69:881, 1979.
ABSTRACT
Common bean (Phaseolus vulgaris L.) is cultivated extensively in Greece for dry and fresh bean production. During 2005 and 2006, a disease with typical blight symptoms was observed occasionally on dark red kidney, brown kidney, and black bean plants in most bean-producing areas of Greece. It rarely was destructive unless the crop had been weakened by some unfavorable environmental conditions. Infected leaves had brown-to-black lesions that developed concentric zones 10 to 30 mm in diameter and also contained small, black pycnidia. Concentric dark gray-to-black lesions also appeared on branches, stems, nodes, and pods. Infected seeds turned brown to black. Plants sometimes showed defoliation and pod drop. The fungus was consistently isolated on potato dextrose agar from diseased leaves and pods and identified as Phoma exigua var. exigua Sutton and Waterstone on the basis of morphological characteristics of conidia and pycnidia (1,2). Spores were massed in pycnidia from which they were forced in long, pink tendrils under moist weather conditions. Conidia were cylindrical to oval, allantoid, hyaline, pale yellow to brown, usually one-celled, and 2 to 3 × 5 to 10 µm. To satisfy Koch's postulates, a conidial suspension (1 × 106 conidia per ml) of the fungus was sprayed onto leaves and stems of bean seedlings (first-leaf stage) (cv. Zargana Hrisoupolis). Both inoculated and control seedlings (inoculated with sterile water) were covered with plastic bags for 72 h in a greenhouse at 23°C. Inoculated plants showed characteristic symptoms of Ascochyta leaf spot 12 to 15 days after inoculation. The fungus was reisolated from lesions that developed on the leaves and stems of all inoculated plants. The pathogen is present worldwide on bean. To our knowledge, this is the first report of P. exigua var. exigua on common bean in Greece. References: (1) D. F. Farr et al. Fungal Databases. Systematic Botany and Mycology Laboratory. Online publication. ARS, USDA, 2007. (2) B. C. Sutton and J. M. Waterstone. Ascochyta phaseolorum. No. 81 in: Descriptions of Pathogenic Fungi and Bacteria. CMI/AAB, Kew, Surrey, England, 1966.
