FUSARIUM SAMBUCINUM CAUSING CANKER ON BOUGAINVILLAEA GLABRA

Bougainvillea (Bougainvillaea glabra L.) is an ornamental climbing shrub native to South America. In 2005, plants showing elongate cankers on branches and twigs were observed in La Plata city (Buenos Aires province). Cankers had brown or purple margins and were scattered or confluent. Leaves from affected branches and twigs showed minute tan spots and could dessicate and fall. Pieces (4x4 mm) of affected tissues were surface-sterilised with NaOCI and plated on potato dextrose agar (PDA). Coloured colonies of Fusarium sp. developed after 5 days at 25 degree C. Fungal structures and cultural characteristics were evaluated on PDA, carnation leaf agar, and distilled water agar (Booth, 1971; Nelson et al., 1983). Based on conidia and chlamydospore development and on colony growth rate, the fungus was identified as F. sambucinum Fuckel sensu stricto. Two inoculation methods were used for pathogenicity tests carried out on 9 potted bougainvillea plants (3 wounded with a pin, 3 non-wounded and 3 uninoculated controls). The first method consisited in depositing PDA plugs colonised by F. sambucinum on wounded and non wounded branches and twigs. With the second method plants were sprayed with a conidial suspension (3x10 super(6) spores/ml). In both cases, plants were placed in a moist chamber for 4 h at 18-24 degree C. Symptoms were observed between 15 and 20 days after inoculation. The largest cankers developed in plants inoculated with the first method, whilts with both procedures, the leaves close to infected nodes dessicated and fell. F. sambucinum was reisolated from infected tissues. F. sambucinum is known as a canker-causing organism (Booth, 1971) and was recently recorded from Phytolacca dioica in Argentina (Carranza et al., 2004). To our knowledge, this is the first world report of F. sambucinum causing cankers on B. glabra.