Clethra barbinervis, a member of the order Ericales, forms arbuscular mycorrhizae

Abstract

The mycorrhizal status of Clethra barbinervis, in the family Clethraceae of the order Ericales, was investigated. Mycorrhizal colonization of C. barbinervis roots collected from naturally occurring trees in two forests in Japan was determined monthly for 12 months. In addition, mycorrhizal colonization of C. barbinervis seedlings grown in pots of field-collected soil was evaluated. Field-collected C. barbinervis roots were extensively colonized by arbuscular mycorrhizal fungi that exhibited the Paris-type morphology. At both sites, total colonization ranged from 42–87% of root length and arbuscular colonization ranged from 6–31% of root length during the year. At one site, hyphal-coil colonization was between 37–61% year round; at the other site, it increased from between 30–56% during August-November to as high as 80% in January. Year round at both sites, vesicular colonization was 7% of root length or less. The Paris-type morphology was also seen in pot-grown C. barbinervis seedlings. Total colonization of pot-grown C. barbinervis seedlings was 34–56% of the root length over 5–20 weeks. To our knowledge, this study is the first report of the mycorrhizal status of a plant in the Clethraceae and the first report of arbuscular mycorrhizae in any member of the Ericales.Key words: Paris-type, Japan, seasonal pattern, arbuscular mycorrhiza, Ericales.