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 (L.) Hull, Enkianthus campanulatus (Miq.) Nichols, Gaultheria procumbens L., Kalmia latifolia L., Leucothoe fontanesiana Sleum., Oxydendrum arboreum (L.) DC.,Pierisfloribunda (Pursh) Benth. & Hook.,Rhododendron calendulaceum (Michx.) Torr.,Rhododendron carolinianum Rehd., Rhododendron catawbiense Michx., Rhododendron maximum L., Rhododendron mucronulatumTurcz., Vaccinium corymbosum L., and Vaccinium macrocarpon Ait. Arbutus unedo L., 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. Inoculation with this isolate of H. ericae resulted in a significant increase in shoot growth. However, intensity of root colonization was not correlated to amount of shoot growth. In fact, an increase in growth was observed in the two species that lacked fungal colonization.

Rosebay rhododendron (Rhododendron maximum L.) seedlings were grown in controlled-environment chambers for 14 weeks under long (9-hour) days at 18, 22, 26, or 30C in factorial combination with 15-hour nights at 14, 18, 22, or 26C. Total dry-matter production was lowest for 18C days and highest for 26C days. A similar response occurred for top, leaf, root, and stem dry weights. Nights at 22C maximized total plant, top, leaf, and stem dry weights. The optimum day/night cycle for dry-matter production was 26/22C. Leaf area was optimum with 18C nights. Leaf weight ratio (leaf dry weight: total plant dry weight) increased with an increase in night temperature to a maximum at 22C. Root weight ratio (root dry weight: total plant dry weight) decreased with an increase in night temperature to a minimum at 22C. Stem weight ratio (stem dry weight: total plant dry weight) and shoot: root ratio (top dry weight: root dry weight) were not influenced significantly by day or night temperature. A day/night cycle of 26/22C seems to be optimal for producing-salable plants.

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.

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.

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