Dean A. Glawe

Characterization of three endophytic, indole-3-acetic acid-producing yeasts occurring in Populus trees

Three endophytic yeast, one isolated from stems of wild cottonwood (Populus trichocarpa), two from stems of hybrid poplar (P. trichocarpaxPopulus deltoides), were characterized by analyzing three ribosomal genes, the small subunit (18S), internal transcribed spacer (ITS), and D1/D2 region of the large subunit (26S). Phenotypic characteristics of the yeast isolates were also obtained using a commercial yeast identification kit and used for assisting the species identification. The isolate from wild cottonwood was identified to be closest to species Rhodotorula graminis. The two isolates from hybrid poplar were identified to be species Rhodotorula mucilaginosa. In addition, the three yeast isolates were observed to be able to produce indole-3-acetic acid (IAA), a phytohormone which can promote plant growth, when incubated with l-tryptophan. To our knowledge, the yeast strains presented in this study were the first endophytic yeast strains isolated from species of Populus.

First report of powdery mildew of periwinkle caused by Golovinomyces orontii in North America.

Periwinkle (Vinca major L., Apocynaceae) is a trailing, spreading evergreen plant used in landscapes as a groundcover. Beginning in 2005, a powdery mildew was observed on periwinkle in coastal (Monterey Co.) California. As reported herein, the causal agent was determined to be Golovinomyces orontii (Castagne) V.P. Heluta. This appears to be the first record of a powdery mildew species on Vinca spp. in North America. Signs of the pathogen included effuse patches of white mycelia primarily on adaxial leaf surfaces of older foliage (Fig. 1). Infected leaves developed gray lesions beneath fungal colonies. Mycelia were superficial, forming nipple-shaped appressoria (Fig. 2). Conidiophores formed foot cells (Fig. 3) that measured (38.5-) 48.5-80(-90) × 9.5-12 μm, were enlarged slightly toward apical ends, and exhibited bases that frequently were curved to strongly bent. Conidia (Fig. 4) formed in chains, measured (26-)30-37(-39.5) × (13.5-)15-18(18.5) μm, were hyaline, ovoid to shortcylindrical, and lacked fibrosin bodies. The teleomorph was not observed. A voucher specimen was deposited with the Mycology Herbarium of the Plant Pathology Department of Washington State University (herbarium designation: WSP). The fungus was determined to be Golovinomyces orontii (Castagne) V.P. Heluta on the basis of conidial ontogeny, foot cell and conidial size and morphology, shape of appressorium, and host. Braun (2) listed two species of powdery mildews on Vinca spp., G. orontii and Leveillula taurica (Lév.) G. Arnaud. Farr et al. (3) listed no Erysiphales on Vinca spp. in North America, but listed reports of species referable to G. orontii, L. taurica, or O. vincae in current systems of classification (1,2) on Vinca species in Europe, Korea, and North Africa. The present fungus was distinguished easily from L. taurica which forms dimorphic conidia and internal mycelia. Bolay (1) reported two powdery mildew species occurring on Vinca species in Switzerland, G. orontii and Oidium vincae Bolay. The latter species formed lobed appressoria and conidiophores with single conidia, suggesting it likely is the anamorph of an Erysiphe species (1). The present report appears to be the first to document G. orontii on Vinca major in North America. Fig. 1. Signs of powdery mildew on Vinca major.