Gaura lindheimeri (wand flower) is a perennial plant belonging to the Onagraceae family that is used for perennial borders in xeric and mesic landscapes. It produces flowers floating above the plant like small, dancing butterflies. This plant is becoming popular in the Albenga Region (northern Italy) where white and rose varieties are grown as potted plants. In January of 2008, 5-month-old ‘Whirling Butterflies’ plants grown in plastic pots (14 cm in diameter) in the open field started showing symptoms of a previously unknown blight. When the disease developed, temperatures ranged between 3 and 17°C (average 9°C) and average relative humidity was 64%. Small, brown spots appeared on the basal portion of leaves first, eventually spreading to cover entire leaves. Subsequently, the pathogen developed abundant, soft gray mycelium on affected leaf tissue. Severely infected leaves eventually became completely rotten and desiccated. Sixty percent of plants were affected by the disease. Tissues were excised from diseased leaves, immersed in a solution containing 1% sodium hypochlorite for 10 s, and then cultured on potato dextrose agar (PDA) medium. The fungus produced abundant mycelium on PDA medium when incubated under constant fluorescent light at 22 ± 1°C. The conidia were smooth, hyaline, globoid, measuring 11.8 to 9.4 × 8.3 to 6.6 (average 10.7 × 7.4) μm, and are similar to those described for Botrytis cinerea. The identity of the pathogen was also confirmed by the production of numerous sclerotia on PDA plates incubated for 20 days at 8 ± 1°C. Sclerotia were dark, irregular, and measured 3 to 4 × 2 to 3 mm. The fungus was identified as B. cinerea on the basis of these characters (1). Pathogenicity tests were performed by spraying leaves of healthy, potted 8-month-old G. lindheimeri ‘Whirling Butterflies’ plants with a 105 conidia/ml suspension. Plants sprayed with water only served as controls. Five plants per treatment were used. Plants were covered with plastic bags for 6 days after inoculation and maintained in a growth chamber at 20 ± 1°C. The first foliar lesions developed on leaves 5 days after inoculation, whereas control plants remained healthy. B. cinerea was consistently reisolated from these lesions. The pathogenicity test was completed twice. To our knowledge, this is the first report of the presence of B. cinerea on G. lindheimeri in Italy. The economic importance of this disease will increase with the increased cultivation of this species.
Reference: (1) H. L. Barnett and B. B. Hunter. Illustrated Genera of Imperfect Fungi. Burgess Publishing Company, Minneapolis, MN, 1972.