R. E. Koske

A modified procedure for staining roots to detect VA mycorrhizas.

A modified technique for staining roots to detect VA mycorrhizas is described. It eliminates as many toxic compounds as possible from root fixation/staining procedures without reducing the resolution of the staining. Success has been achieved with angiosperm, fern, lycopod and psilophyte roots and bryophyte.

Seasonal variation in spore abundance and dormancy of Gigaspora gigantea and in mycorrhizal inoculum potential of a dune soil

Seasonal abundance and dormancy were examined in field-collected spores of the vesicular-arbuscular mycorrhizal fungus (VAMF) Gigaspora gigantea. Monthly collections of soil were made from a sand dune in Rhode Island from Aug, 1984, through Nov, 1985, and ca. weekly collections were made from Aug, 1985, through Jan, 1986. Spore abundance (spores/100 cc soil) increased from July onward, and reached a maximum in Dec, indicating that the majority of spores were formed in late summer and fall. A Sept increase in spore abundance was part of a highly significant cubic trend. Percent germination of spores was highest (89-98%) from Dec to July and lowest (4-9%) in Sept and Oct. Decline in spore germination in Sept, 1984, and Sept, 1985, was highly significant, and germination between Aug, 1984, and Nov, 1985, was best described by a quartic equation. Spores collected in Sept, 1986 were dormant, but were released from dormancy by incubation at 5 C for 5 wk. Dormant spores stored at 20-25 C for 5 wk did not germinate. Approximate length of the dormancy period in the field was 2-9 wk. Monthly mycorrhizal inoculum potential (MIP) values of sand dune soil varied seasonally, ranging from 13.9% to 49%, with minimal VAMF colonization in Sept and Oct, similar to the spore germination pattern of G. gigantea.

MYCORRHIZAE AND SUCCESSION IN PLANTINGS OF BEACHGRASS IN SAND DUNES

A survey of arbuscular mycorrhizal fungi (AMF), arbuscular mycorrhizae (AM), and hyphal networks of AMF was carried out in sand dune sites of different successional stages in the Province Lands Area of Cape Cod National Seashore, Massachusetts. The study focused on large-scale plantings (each of 12-20 ha) of American beachgrass (Ammophila breviligulata) aged 0-7 yr and five adjacent natural dune areas. Sample sites ranged in vegetative cover from barren to forested. Spores of 17 species of AMF were recovered from the dunes. Over the successional sequence, there were increases in the richness and spore populations of the AMF community, the extent of colonization of A. breviligulata roots, and the mycorrhizal inoculum potential of the soil. Unvegetated sites lacked propagules of AMF, but roots of planted culms of A. breviligulata (which carried propagules of AMF) became mycorrhizal in <1 yr after planting. Spores were recovered from previously AMF-free sites that had been planted with beachgrass for 47 wk, and five species of AMF sporulated in sites <6 yr old. Significant hyphal networks were not present in any of the planted areas (<6 yr old at the time of sampling), but did occur in natural areas. The rate of invasion of areas planted to A. breviligulata by later successional plant species may in part depend upon the establishment of a vigorous network of hyphae of AMF in a site.

Seasonal dynamics of selected species of V-A mycorrhizal fungi in a sand dune

Seasonal dynamics of five vesicular-arbuscular mycorrhizal fungi ( Acaulospora scrobiculata, Gigaspora gigantea, Scutellospora calospora, S. pellucida and S. persica ) occurring in a Massachusetts sand dune were examined to determine the period of maximum sporulation. Although the maximum spore population was found in October, three distinct seasonal patterns were evident. Spore abundance of A. scrobiculata and G. gigantea was highest in October samples, and that of S. calospora was greatest in the August collection. A bimodal trend of peak spore abundance in October and May, was detected for S. pellucida and S. persica . Statistically significant seasonal trends were demonstrated for A. scrobiculata and S. persica . No statistically significant linear or curvilinear relationship could be demonstrated between spore abundance and edaphic factors (pH, organic matter or chloride). High levels of spore abundance for one species in a sample were associated with significantly lower levels of sporulation by the other species in the same sample (with the exception of S. pellucida ), suggesting antagonistic interactions between species.

Endogone spores in Australian sand dunes

Five types of spores of the endomycorrhizal fungus, Endogone, were abundant in the coastal sand dunes of New South Wales. Spores of Endogone have seldom been reported from marine dunes, and at least two of the spore types recovered from Australian dunes have not previously been reported from this continent. The density of spores in sand was greater in older, more stabilized dunes than in younger foredunes and mobile dunes.

Gigaspora Gigantea: Observations on Spore Germination of a Va-Mycorrhizal Fungus

Spore germination of a vesicular-arbuscular mycorrhizal fungus in the absence of a host plant was investigated. Spores of Gigaspora gigantea were tested for the ability to germinate under laborator...

Evidence for a volatile attractant from plant roots affecting germ tubes of a VA mycorrhizal fungus

Germ-tubes from spores of Gigaspora gigantea grew vertically or horizontally through the air to contact roots of bean and corn plants situated up to 11 mm away from the spore. Up to 86% of the spores in an experiment produced aerial germ-tubes that successfully located roots, apparently in response to a volatile attractant released by the roots. Initial contact between roots and germ-tubes was made as early as 5 days after an experiment began, with maximum success occurring after 10–24 days. Bean plants in the pod-maturation stage attracted germ-tubes as well as plants in the pre-flowering stage. Mycorrhizas were not formed under the experimental conditions employed.

A preliminary study of interactions between species of vesicular-arbuscular fungi in a sand dune

Interactions between five species of VA mycorrhizal fungi sporulating in association with the dominant plants on a single barrier dune were examined. The observed frequency of simultaneous occurrence of any two species did not differ significantly from the expected value in any pairing. Spore densities of individual fungal species in the same sample were analyzed to determine if a stimulation or inhibition of sporulation resulted from high or low levels of sporulation by other VA species. The effect of host species on occurrence of VA species and spore density in the rhizosphere also was studied. Two fungi were absent or rare on three hosts, and spore production by Acaulospora scrobiculata was significantly greater in association with Ammophila breviligulata than with Lathyrus japonicus var. glaber. It was concluded that interaction between VA fungi is of less importance in determining species presence and spore density than are the species of host plant and other environmental factors.

Gigaspora gigantea: parasitism of spores by fungi and actinomycetes

Fungi and actinomycetes were isolated monthly for one year from spores of the arbuscular mycorrhizal fungus Gigaspora gigantea recovered from a maritime sand dune. Spores in four different stages of vigour (newly formed, greenish-yellow healthy; yellow, moribund, mottled with brown spots; brown; and dead, blackened and collapsed) were used for isolation. From 272 isolates cultured from crushed, surface-disinfected G. gigantea spores, 44 species of fungi and six actinomycete species were recovered. The five most frequently isolated organisms were Acremonium sp., Chrysosporium parvum, Exophiala werneckii, Trichoderma sp. and Verticillium sp. The species lists derived from the four spore types differed significantly. Thirty-one of the isolated species were tested for their ability to parasitise healthy G. gigantea spores and to invade spores killed by a hot water treatment. Twenty-two species could function as pathogens, forming internal projections (IP), fine radial canals (FRC) or both in the spore wall. IP were induced by Acremonium sp., Chrysosporium parvum, Cladosporium sp., Geomyces pannorum, Oidiodendron sp., Sporothrix sp., Verticillium sp. and by the actinomycetes Nocardia sp. and Streptomyces sp. The IP length was positively correlated with duration of exposure to the parasites. In the bioassay, both IP and FRC were formed by live spores, while heat-killed spores possessed only FRC after penetration by the test microorganisms. Pathogenicity differed among the parasites and was greatest for Verticillium and Acremonium .

The spatial dispersion of spores of vesicular-arbuscular mycorrhizal fungi in a sand dune: microscale patterns associated with the root architecture of American beachgrass

In order to develop a model of the spatial dispersion of populations of vesicular-arbuscular mycorrhizal fungal (VAMF) spores within a root zone, we hypothesized that their spatial pattern would be correlated with the below-ground architecture (growth and structure) of the root system. Detailed excavation and mapping of the roots within the vicinity of three clusters of Ammophila breviligulata ramets (culms) revealed a network of rhizomes, many of which were not connected to the original plant. The species richness of VAMF for the three plots ranged from six to nine, including five genera. A high degree of spore clumping was not significantly correlated with the location of roots, nor with any of the physical soil parameters tested, or with the abundance of spores in adjacent sampling areas. The abundance of spores at a particular location in the soil generally was not a good predictor of spore populations only 10 cm distant. Since such spores are not readily dispersed from the point of sporulation, it is likely that some spore aggregations formed previously in association with fibrous roots that have subsequently decayed and are no longer detectable in the soil profile.