Studies in the Interactions Between Species of Verticillium

It is shown that five parasitic species of Verticillium, viz. V. alboatrum, V. Dahliae, V. ticorpus, V. nigrescens and V. nubilum, developed together on agar media or wheat grains as saprophytes without causing mutual antagonism but, when these were injected together, as a mixed spore suspension, into antirrhinum and tomato, suppression of V. tricorypus, V. nigescens and V. nubilum by either one or other of the remaining two invariably resulted. The two most virulent pathogens, V. alboatrum and V. Dahliae, were not recoverable from soil after the elapse of 6 months from the time of inoculation; while the other three less virulent pathogens could be isolated after about 12 months in the soil. It is concluded that V. alboatrurn and V. Dahliae may be described as ‘root inhabiting’ and V. nigrescens and V. nubilurn as ‘soil inhabiting’, while V. tricorpus may be considered as an intermediate type.