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Open access

Brenda Biermann and R.G. Linderman


The establishment and performance of vesicular–arbuscular mycorrhizae (VAM) formed by Glomus fasciculatum (Thaxter) Gerd. & Trappe were studied on geranium (Pelargonium × hortorum L.H. Bailey) and subterranean clover (Trifolium subterraneum L.) in various growth media at 2 P fertility levels. Colonization by G. fasciculatum was not extensive and shoot dry weight and P uptake consequently were not increased by VAM in soilless media such as peat, bark, perlite, and vermiculite. In media containing soil and fertilized at the low P level, roots were colonized extensively by G. fasciculatum, and host shoot growth and P concentrations were increased by VAM. Host growth enhancement by VAM was not observed at the higher P fertility level. Differences in colonization and mycorrhizal response in different fertilized growth media were correlated negatively with the logarithm of the equilibrium solution P concentration. Colonization, growth response, and P uptake by geranium inoculated with G. mosseae (Nic. & Gerd.) Gerd. & Trappe or Acaulospora spinosa Walker & Trappe were affected by growth medium and P fertilizer in the same way as plants inoculated with G. fasciculatum. Peat mosses from different sources varied considerably in their effects on mycorrhiza formation by G. fasciculatum, and on growth response of geranium when the peat was diluted with different amounts of soil. These differences appeared to be related to the equilibrium solution P concentration of the fertilized peats, and not to extractable P of the unfertilized peats. Use of rock phosphate or bonemeal instead of NaH2PO4 as a source of P did not improve the establishment of VAM and host growth response in soil, peat, or vermiculite. Addition of 5–10% Turface, bentonite, silt loam soil, or clay subsoil to peat or vermiculite resulted in increased colonization of host roots and significant mycorrhizal growth response, whereas amendment with liquid sludge inhibited formation of mycorrhizae.

Free access

James B. Shanks, Joseph J. Dymek, and Brenda J. Biermann

Growth and flowering of chrysanthemum, poinsettia, fuchsia, hydrangea, and geranium grown on rotating shelves were compared with that of plants grown in full ambient sunlight on a stationary greenhouse bench. Ambient insolation reaching plants on the rotating shelves was ca. 55% of that on the stationary greenhouse bench on a sunny day and ca. 60% of full insolation on a cloudy day. Plants grown on the rotating shelves required two to six days longer to flower and were smaller in height, weight, and number of flowers compared to plants under full light. The lasting of chrysanthemum leaves and petals was lessened by growth on rotating shelves compared to plants grown in full light while there was no effect on the lasting of poinsettia bracts or of hydrangea leaves and sepals under simulated home conditions.

Open access

Brenda J. Biermann and R.G. Linderman


Inoculation of the various potting media with the mycorrhizal fungus Glomus fasciculatum (Thaxter) Gerd. & Trappe resulted in root colonization of geranium (Pelargonium × hortorum L.H. Bailey) by the endophyte that persisted after transplanting. By flowering time, mycorrhizal transplants grown at 11 or 43 ppm P were more uniform in growth than nonmycorrhizal transplants grown at the same nutrient regimes, had greater leaf areas and leaf weights, had increased root and shoot weights, and had lower foliar Mn concentrations. Mycorrhizae were sufficiently well-established on most seedlings at a minimum of 2 weeks after emergence to persist and continue to develop after transplanting. Pretransplant inoculation with G. fasciculatum increased subsequent geranium growth over that of nonmycorrhizal controls when both were transplanted into soil heavily infested with mycorrhizal fungus inoculum, even though size of mycorrhizal and nonmycorrhizal plants did not differ at the time of transplanting. Posttransplant inoculation with G. fasciculatum did not affect the growth of plants which were already mycorrhizal at transplant, but increased the growth of previously nonmycorrhizal transplants. Pretransplant inoculation in soil, peat, or vermiculite resulted in larger plants than posttransplant inoculation in these media.