Effect of drought on ericoid mycorrhizae in wild blueberry (Vaccinium angustifolium Ait.)

To evaluate the influence of water exclusion on the mycorrhizal coloni zations in wild blueberry, and to examine the spatial distribution of mycorrhizae among roots of wild blueberry plants that were in both the vegetative and cropping stages of production, a randomized complete block design was used. The mycorrhizal coloniz a tions were equally distributed throughout upper and lower soil profiles in both stages of production. Nevertheless, soil moisture levels in water exclusion treatments were as much as 50% lower than the control, drought stress had no effect on mycorrhizal colonization levels or on any other of the measured responses. Root weight and volume decreased as soil depth increased from 0-7.5 to 7.5-15 cm. Key words:

Screening Commercial Peat and Peat-based Products for the Presence of Ericoid Mycorrhizae

Pieris floribunda (Pursh) Benth. & Hook., a known host of ericoid fungi, was used as a model plant to investigate the presence of ericoid mycorrhizal fungi in select peat and peat-based products. After growing in each medium for 75 days, roots of seedlings were examined and average percent colonization was determined for each sample. Results indicate that these fungi are present in the majority of peat and peat-based media tested. Seedlings grown in some of the selected media had a greater percentage of root cells colonized by ericoid mycorrhizae than others in the study.

In Vitro Colonization of Micropropagated Pieris floribunda by Ericoid Mycorrhizae. I. Establishment of Mycorrhizae on Microshoots

Selected isolates of Hymenoscyphus ericae (Read) Korf and Kernan, Oidiodendron griseum Robak, O. maius Barron, and a second O. Robak species were evaluated as inocula for in vitro establishment of micropropagated plantlets of Pieris floribunda (Pursh ex Sims) Benth. and Hook. Severity of shoot necrosis on microshoots differed for each isolate of Oidiodendron. Inoculation of micropropagated plantlets with isolates of H. ericae benefited initial shoot and root development on agar-solidified Woody Plant Medium (WPM) supplemented with sucrose and covered by a layer of autoclaved 1 peat: 1 vermiculite (v/v). Inoculation of microshoots with H. ericae or isolates of Oidiodendron did not stimulate production of adventitious roots.

In Vitro Colonization of Micropropagated Pieris floribunda by Ericoid Mycorrhizae. II. Effects on Acclimatization and Growth

Inoculation of microshoots of Pieris floribunda (Pursh ex Sims) Benth. and Hook. (mountain andromeda) with isolates of Hymenoscyphus ericae (Read) Korf and Kernan ericoid mycorrhizal fungi stimulated growth during 1 month in vitro. However, no benefits were apparent after 3 months in a greenhouse. Acclimatization of plantlets of P. floribunda to greenhouse conditions following in vitro inoculation improved survival (42% vs. 16% for controls). The protocol reported herein is similar to procedures utilized currently for micropropagation of various ericaceous species and has potential to improve plantlet survival during acclimatization.

Host Range of a Select Isolate of the Beneficial Ericoid Mycorrhizal Fungus Hymenoscyphus ericae

Studies were conducted to examine the host range of a select isolate of the ericoid mycorrhizal fungus, Hymenoscyphus ericae (Read) Korf and Kernan [American Type Culture Collection (ATCC) #32985]. Host status was tested for 15 ericaceous species, including Calluna vulgaris, Enkianthus campanulatus, Gaultheria procumbens, Kalmia latifolia, Leucothoe fontanesiana, Oxydendrum arboreum, Pieris floribunda, Rhododendron calendulaceum, Rhododendron carolinianum, Rhododendron catawbiense, Rhododendron maximum, Rhododendron mucronulatum, Vaccinium corymbosum, and Vaccinium macrocarpon. Arbutus unedo, an ericaceous species that forms arbutoid, not ericoid, mycorrhizae was used as a negative control. All of the species were colonized by the ericoid isolate with the exception of Enkianthus campanulatus and the negative control. The benefits of the association and possible commercial applications are discussed.

Polyclonal antisera to epacrid mycorrhizae and to Hymenoscyphus ericae display specificity

Three polyclonal antisera produced in mice were used to investigate specificity and cross-reactivity between ericaceous and epacridaceous mycorrhizal fungi. One antiserum was to a culture of Hymenoscyphus ericae (Read) Korf and Kernan, the fungal endophyte of Calluna vulgaris (L.) Hull (Ericaceae). The other two were to peloton preparations from roots of Epacris impressa Labill. (Epacridaceae) from two sites (Cranbourne and Grampians) in Victoria, Australia. By immunofluorescence, all three antisera recognised H. ericae but not Oidiodendron griseum Roback, suggesting a serological relationship with the former endophyte. They also recognised 10 of the 12 fungal isolates tested, from mycorrhizal roots of E. impressa (Cranbourne), and all 4 isolates from Astroloma pinifolium (R. Br.) Benth. (Epacridaceae) (Grampians). Furthermore, none of the antisera recognised any of the nine common soil-inhabiting fungi selected for screening. Antisera recognised only unmelanized hyphae on epacrid and other plant roots taken from the wild. With plants from Cranbourne, all antisera except the Grampians antiserum recognised hyphae only on epacrid roots, demonstrating specificity. Hyphae on other plant roots were not recognised by any of the antisera. With plants from the Grampians, all antisera recognised some hyphae on both epacrid and other plant roots, except in two instances. The immunogold labelling indicates that the antisera are specific for fungi and do not recognise the plant. Since the fungal isolate forms true mycorrhizal structures, this suggests that there is a serological similarity between fungi forming epacrid mycorrhiza and those (H. ericae) forming ericoid mycorrhiza.Key words: ericoid mycorrhizae, Epacridaceae, polyclonal antibodies, immunofluorescence, immunogold.