The appearance of the A2 mating type (previously restricted to central Mexico) in Europe during the 1980s prompted an investigation of the genetic make‐up of European populations using allozyme loci as genetic markers. The investigation shows that major genetic changes have occurred in populations of Phytophthora infestans in the Netherlands, Poland, and the British Isles. It now appears that a new type of population has been introduced into several locations, and has displaced or is displacing the original populations in these locations. The new and old population types are characterized by unique allozyme alleles and genotypes. The mechanism for displacement of the‘old’by the‘new’population is not yet known.

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The species of Valsa and Cytospora found on hardwoods in North America are reevaluated, based on morphological studies of type specimens, herbarium specimens, and fresh collections. Three sections are accepted in Valsa: sections Valsa, Monostichae Nits., and Cypri Urban, distinguished by the number, size, and arrangement of perithecia, the distribution of ostioles in the disc, and the size of ascospores. Four sections are accepted in Cytospora: sections Cytospora, Torsellia (Fr.) Gvrit., Cytophoma (Hoehn.) Gvrit., and Cytosporopsis (Hoehn.) Gvrit., based on the number and shape of the locules. Correlations between the teleomorphic and anamorphic sections Valsa–Cytospora, Monostichae–Torsellia, and Cypri–Cytophoma are reaffirmed. Six species of Valsa on North American hardwoods are accepted, and two new subspecies are proposed: V. ambiens subsp. ambiens and V. ambiens subsp. leucostomoides (Peck) Spielman. Six species of Cytospora are accepted.

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