Morphological characteristics of Verticillium dahliae and V. tricorpus on semi-selective media used for the detection of V. dahliae in soil

摘要

Verticillium dahliae and V. tricorpus are common fungi in agricultural soils. Both occur world-wide and are often associated with the same crops. In a number of crops, V. dahliae can cause serious wilt disease, whereas V. tricorpus is generally harmless. There is a great need for reliable assessment of soil population densities of V. dahliae in order to predict future problems. Plating of soil samples on semi-selective media is currently the most reliable way to assess population densities of V. dahliae in soil. Microsclerotia in the soil samples are detected indirectly by their formation of new colonies with microsclerotia on a semi-selective agar medium. However, microsclerotia of V. tricorpus also can be present in soil samples and give rise tosimilar colonies with microsclerotia on the same media. Colonies and microsclerotia of V. dahliae and V. tricorpus growing on semi-selective media are sometimes difficult to distinguish. On potato dextrose agar (PDA), morphological differences between the two species are clear, as described in Isaac (1). Verticillium tricorpus forms larger and irregularly shaped microsclerotia, usually with dark hyphae growing from them. Verticillium dahliae forms smaller and oval to elongate microsclerotia on PDA which are sharply differentiated from the hyaline mycelium. Moreover, V. tricorpus forms chlamydospores and often a yellow discoloration of the PDA medium. Transferring colonies from semi-selective media to PDA for identification of species is too laboriousto employ as a standard procedure. This study was initiated to find morphological characteristics suitable to distinguish between V. dahliae and V. tricorpus on two semi-selective media commonly used for detecting V. dahliae in soil.