Taxonomic Importance of Microconidial Chains in Fusarium Section Liseola and Effects of Water Potential on Their Formation

Abstract

Microconidial chains in three Fusarium species of the Section Liseola that produce them (F. moniliforme, F. proliferatum and F. annulatum) increased in abundance and length as the water potential of the medium decreased. An optimal enhancing effect was obtained with water agar containing 4–8 g/l of KCl (0.053 to 0.107 M). At KCl concentrations of 32 g/l (0.427 M) and higher, growth as well as microconidial chain formation was inhibited. Isolates representing the “short-chained” type of F. moniliforme (=F.fujikuroi) were indistinguishable from F. moniliforme on water agar containing 8 g/l of KCl. The formation of microconidial chains was not induced in two species of the Section Liseola that are known not to produce them (F. subglutinans and F. anthophilum). The presence or absence of microconidial chains is, therefore, a reliable taxonomic criterion in Fusarium Section Liseola. Carnation leaf agar containing 4–8 g/l of KCl is recommended for the identification of these Fusarium species.