Dichotomous key for identification of Verticillium species

   It is best to use freshly isolated strains for morphological identification since production of hyphal pigments and resting structures may become attenuated and may disappear altogether after prolonged culturing. All characters used in the key can be observed from cultures on standard PDA medium left on a lab bench at room temperature for two to four weeks. For more details on morphological identification, please refer to Inderbitzin et al. (2011)
   The genus Verticillium is characterized by dark, pigmented resting structures and conidiogenous cells that are arrange in whorls along a main axis (verticilloid conidiophores). However, there are exceptions. And if the key below doesn’t work, you may have another genus.

Dichotomous key

The following key is based on morphological characters of individual species grown on PDA, and is taken from Inderbitzin et al. (2011).

1. Colonies in reverse view light or dark colored, yellow to orange pigmentation present…3
2. Yellow to orange pigmentation absent…7
3. Resting structures are predominantly resting mycelium …V. albo-atrum
4. Resting structures are predominantly microsclerotia or chlamydospores …5
5. Resting structures are predominantly microsclerotia …V. zaregamsianum
6. Resting structures are both microsclerotia, chlamydospores and resting mycelium …V. tricorpus, V. isaacii or V. klebahnii
7. Conidia on average longer than 7 µm, microsclerotia present …V. longisporum
8. Conidia shorter …10
10. Resting structures are chlamydospores …V. nubilum
11. Resting structures are resting mycelium or microsclerotia …12
12. Resting structures are microsclerotia …V. dahliae
13. Resting structures are resting mycelium …V. alfalfae or V. nonalfalfae