Untersuchungen ueber den Pflanzenparasiten Verticillium albo - atrum Reinke et Berth.

Among 70 Verticillium strains isolated from different hosts throughout the Netherlands, only 2 had the bundled dark hyphae described by Reinke and Berthold (1879) as characteristic of V.albo-atrum Reinke & Berth. This species was morphologically the same as V. dahliae Klebahn. The name V.albo-atrum had priority.

Strains with loose dark hyphae (d.m. type) were less resistant to warmth (35øC) than those with microsclerotia (mscl. type). On artificial media all strains produced toxins, specific for each strain but not correlated with type or pathogenicity. The fungus spreads through the plant's vessels as spores or mycelium. The physiological range confirmed that there was no clear distinction between the two species but demonstrated a difference between mycelial and microsclerotial types. Host range was not limited (contrast Nelson, 1950; Isaac, 1957). Culture on tomato changed the virulence.

Both types could spread in sterile soil between roots of antirrhinums only as hyphae. After 4 years in the soil only the mscl. type was slightly infective.

Microsclerotia were assumed to be merely storage organs because they did not germinate, even with root secretions.

After an infection resistant crops should be planted and possible carrier weeds eradicated. Use of resistant varieties was difficult because of differences in pathogenicity of Verticillium strains but chemical control was inadequate.