Parthenium weed (Parthenium hysterophorus L., family Asteraceae), an annual herb of neotropic origin, is an invasive noxious weed with a pantropical distribution (1). It is particularly undesirable because of the serious health risks it poses to people living close to infestations (1). In January 1995, S. Neser (ARC-Plant Protection Research Institute, Pretoria, South Africa) collected a rust fungus on this plant near Brits, Northwest Province, South Africa (25°35′S, 27°46′E). Only uredinia were present. The same rust fungus was collected in the same area in January, March, and June of 2001, and again only uredinia were observed. In its native range, P. hysterophorus is infected by two rust fungus species, Puccinia abrupta Diet. & Holw. var. partheniicola (Jackson) Parmelee and Puccinia melampodii Diet. & Holw., but the latter species is microcyclic with telia only. The morphology of the urediniospores in the South African collections corresponds to Puccinia abrupta var. partheniicola (3): obovoid to almost triangular, 22 to 27 × 18 to 25 µm, echinulate, two subequatorial and one apical germ pores, spines absent around germ pores, wall 1 to 2.5 µm thick. The native range of Puccinia abrupta var. partheniicola is Mexico and northern South America (3). In addition, it has been recorded from Mauritius (3), Kenya, and India (H. C. Evans and C. A. Ellison, International Institute of Biological Control, CAB, 1987, unpublished data). It was intentionally introduced into Australia for the biological control of P. hysterophorus (2). Thirteen specimens in the Arthur Herbarium were examined, and only two had telia in addition to uredinia. The other 11 had only uredinia, indicating that nonformation of telia is common. Telia and uredinia are produced in high altitude, semiarid areas of Mexico, whereas in low altitude, more humid areas only uredinia are produced (1). The production of telia appears to depend on environmental conditions, and their absence is not unexpected at the Brits site, which is a high altitude (1,120 m) area with high summer rainfall (400 to 600 mm per year from November to February) and dry winters. Voucher specimens were deposited at the National Collection of Fungi, Plant Protection Research Institute, Pretoria (PREM 57298) and the Arthur Herbarium, West Lafayette, IN (PUR N1117). To our knowledge, this is the second report of this rust fungus in Africa and the first in southern Africa.
References: (1) H. C. Evans. Trans. Br. Mycol. Soc. 88:105, 1987. (2) A. Parker et. al. Plant Pathol. 43:1, 1994. (3) J. A. Parmelee. Can. J. Bot. 45:2267, 1967.
