Objective  To find out the pathogen of tomato damping-off in Yinchuan area of Ningxia, and lay a foundation for disease control and disease resistance breeding.

  Methods   Possible pathogenic microbes of the disease on tomatoes were isolated by the conventional tissue isolation method and identified based on their morphology, pathogenicity, and rDNA-ITS sequence.

  Result  Of the two suspected species, Pathogen No. 1 had oval or nearly spherical sporangia with papillae and long stalks. It was preliminarily determined as Phytophthora capsici. The spherical ovipositor of Pathogen No. 2 had straight stalks with spherical, smooth oospores that did not fully fill the sacs and the wide rod- or lemon-like-shaped male organ grew laterally. It was presumed to be Pythium aphanidermatum. After inoculation on tomato cotyledons the inoculation of either of the two isolates caused the seedling stem constriction and plant collapse showing the typical symptoms of dark brown spots at infected sites. The phylogenetic trees constructed based on the ITS sequences of the two isolates confirmed No. 1 to belong in the branch of P. capsici, and No. 2 of P. aphanidermatum.

  Conclusion  The pathogens that caused damping-off on tomato plants in Yinchuan were positively identified to be strains of P. capsici and P. aphanidermatum.