Mutants ofVerticillium albo-atrumspecifically affecting conidium germination

Abstract

Verticillium albo-atrum is an imperfect fungus which causes a wilt disease of many dicotyledonous crop species [1]. Wild-type strains have either dark-pigmented or hyaline mycelium, and hyaline conidia are produced typically on verticilliately branched conidiophores. Each conidiophore branch (phialide) is initially uninucleate, and generates a population of about 30 conidia which accumulate in a water droplet at the tip [2]~ Conidium germination generally occurs only after the conidia are removed from the phialide, and they do so even in distilled water after 5-6 h. These features suggest that mature conidia contain all the biochemical components required for germination and that conidia are prevented from germinating in situ, on phialides, by a germination inhibitor presumably produced by the parent colony. Most wild-type strains of V. albo-atrum are haploid, and auxotrophic mutants are easily detected after mutagen treatments [3]. We report below the results of a search for mutations affecting conidium germination and/or colonial growth. Auxotrophic mutants were also searched for in the same samples of mutagen-treated conidia so that the relative frequences of the three types of mutant could be compared. Unsuccessful attempts have been made to detect mutants of Neurospora crassa [4] and Aspergillus nidulans [5] which specifically affect conidium germination. 2.1. Wild-type strain and growth conditions