Recent studies on Thecaphora solani
Potato smut caused by Thecaphora solani (EPPO A1 list) is a serious disease of potato, only present in the Andean region of South America, in Panama, and Mexico. It affects various cultivated species of Solanum (S. tuberosum, S. andigenum, S. stoloniferum) and other Solanaceae (e.g. Lycopersicon, Datura stramonium). Up till now, the fungus has not been cultured or characterized in vitro. In Chile, T. solani was first reported in 1974 in region IV (region of Coquimbo) where it has established in many soils causing significant yield losses (more than 90 %) in potato crops. The disease was then reported in region VIII (region del Bío-Bío). In 1996, potato smut was discovered more than 1000 km further south from its initial finding, in region IX (region de la Araucanía) near Carahue. As this represented a very serious threat to seed-potato production areas, efforts were made to try to eradicate the disease and to study the basic biological aspects of the pathogen and the disease. Therefore, studies were done in Chile to culture T. solani in vitro, and to characterize the fungus by molecular methods. For the first time, T. solani was cultured on solid and liquid growing media. But this remained a laborious and difficult task, as only 7 of the 26 isolates studied could be cultured. This was mainly due to the low germination capacity of T. solani teliospores. The sexual cycle of the pathogen was completed under laboratory conditions. First attempts to reproduce the disease under controlled conditions were also successful. Artificial inoculation of mycelia to potato explants grown in vitro (S. tuberosum cv. ‘Désirée’) induced a gall. Molecular analysis also confirmed the initial classification of T. solani in the genus Thecaphora (it had been suggested at one point that it belonged to the genus Angiosorus).
Sources
Andrade O, Muñoz G, Galdames R, Durán P, Honorato R (2004) Characterization, in vitro culture, and molecular analysis of Thecaphora solani, the causal agent of potato smut. Phytopathology, 94(8), 875-882.