Wild tuber-bearing species of Solanum and incidence of Phytophthora infestans (Mont.) de Bary on the western slopes of the volcano Nevado de Toluca. 1. Solanum species

During the period 1982-87, wild Solanum species were surveyed in an area of 15 000 ha by observations and collections along five long (10 km) transects covering altitudes from 2900 to 3900 m, and twelve short (300 m) transects. The seven Solarium species, demissum (dms), verrucosum (ver), iopetalum, brachycarpum, x edinense, stoloniferum and an unidentified species, possibly a sterile hybrid between dins and ver, grew patchily and their many small colonies formed part of a complex plant community that changed in composition with altitude and topography. The most frequent species was dms (80 %), while other species often grew in mixed colonies with it. As the altitude increased, so did the distances between colonies, whereas species diversity decreased and above 3500 m only dms was found. Most species propagated both clonally, through tubers on long stolons, and sexually through botanical seed.