Vesicular-arbuscular Mycorrhizal Formation Research Articles

Effect of Ethylene on the Growth of Vesicular-Arbuscular Mycorrhizal Fungi and on the Mycorrhizal Formation of Trifoliate Orange Roots

The effect of ethylene on the growth of vesicular-arbuscular mycorrhizal (VAM) fungi and the VAM formation of trifoliate orange roots was investigated. Spore germination and hyphal growth of VAM fungi were stimulated at concentrations ranging from 0.01 to 0.1 ppm ethylene. At 0.2 ppm and above, however, hyphal growth was severely inhibited. The rapid hyphal growth noted at 0.07 ppm ethylene treatment was severely retarded by ethylene absorbents. VAM development in trifoliate orange trees was markedly enhanced at 0.05 ppm ethylene, but was depressed at 1 ppm. At 0.05 ppm, tree growth was vigorous and leaf P content was high. Thus we propose that very low levels of ethylene play an important role in the hyphal growth of VAM fungi and in the infection and spread of the mycorrhizae.

Effect of selected insecticides on plant growth and mycorrhizal development in sorghum

Three insecticides viz., carbofuran, endosulfan and quinalphos were assessed for their toxic effects on plant growth and vesicular-arbuscular mycorrhizal (VAM) fungi development in sorghum. Samples of a black alluvial soil, contained in earthen pots, with indigenous VAM populations were drenched with graded concentrations of the insecticides ranging from 0 to 10 kg ha −1 after 30 days (single application), or 30 and 60 days (two repeated applications), of plant growth. Single or two repeated applications of carbofuran at levels of 0.5–2.5 kg ha −1 were non-toxic to plant growth and mycorrhizal development. However, 5 and 10 kg ha −1 levels of carbofuran were phytotoxic and significantly inhibited colonization by VAM fungi. Plant growth and VAM formation were not affected by 0.5 kg ha −1 levels of both endosulfan and quinalphos. Single or two repeated applications of endosulfan, and quinalphos, at concentrations of 5 and 10 kg ha −1, exerted toxicity to the plant growth and VAM fungal colonization.

Differential Niche Response of Bouteloua gracilis and Pascopyrum smithii to VA Mycorrhizae

ALLEN, M. F., (Dept. Biology, UMC 45, Utah State Univ., Logan, UT 84322) E. B. ALLEN (Dept. Range Science, UMC 52, Utah State Univ., Logan, UT 84322), AND P. D. ST AHL (Dept. Botany, Univ. Wyoming, Laramie, WY 82071). Differential niche response of Boutelouagracilis and Pascopyrum smithii to VA mycorrhizae. Bull. Torrey Bot. Club 111: 361-365. 1984.-The seasonality of Glomus fasciculatum associated with Bouteloua gracilis and Pascopyrum smithii was contrasted in the field, as well as the effects of this vesicular-arbuscular mycorrhizal (VAM) fungus on physiological parameters of these grasses in the greenhouse. Arbuscule formation was earlier in P. smithii, which has C3 photophysiology, than in the C.4 B. gracilis. Soil spore densities were highest in fall samples of both grasses. Both grasses exhibited lower stomatal resistance and increased photosynthesis with VAM formation, but these changes were 36% greater for B. gracilis. B. gracilis has a greater percentage of VAM infection than P. smithii in the field, but % of the root length infected in the two grasses was similar in the greenhouse. We hypothesize that the greater niche response of B. gracilis than P. smithii to VAM, coupled with their differing phenologies, enable coexistence of the two grasses.

Effect of Citrus Root Exudates on Germination of Chlamydospores of the Vesicular-Arbuscular Mycorrhizal Fungus, Glomus Epigaeum

The effect of root exudates from Troyer citrange (Poncirus trifoliata x Citrus sinensis) on germination of surface-sterilized chlamydospores of the vesicular-arbuscular mycorrhizal (VAM) fungus, Glomus epigaeum, was examined on water agar. Optimum temperature for spore germination was 25 C. After 7 da exposure of spores to root exudates, germination was increased from less than 10% (distilled water control) to up to 27%. Germ tube length of exudate-treated spores was more than four times greater than that of untreated spores. Root exudates stimulated branching of germ tubes, whereas germ tubes of untreated spores branched infrequently. These results indicate that root exudates affect spore germination and germ tube growth of G. epigaeum and thereby could influence subsequent root colonization and VAM formation.

Effect of Citrus Root Exudates on Germination of Chlamydospores of the Vesicular-Arbuscular Mycorrhizal Fungus, Glomus epigaeum

The effect of root exudates from Troyer citrange (Poncirus trifoliata x Citrus sinensis) on germination of surface-sterilized chlamydospores of the vesicular-arbuscular mycorrhizal (VAM) fungus, Glomus epigaeum, was examined on water agar. Optimum temperature for spore germination was 25 C. After 7 da exposure of spores to root exudates, germination was increased from less than 10% (distilled water control) to up to 27%. Germ tube length of exudate-treated spores was more than four times greater than that of untreated spores. Root exudates stimulated branching of germ tubes, whereas germ tubes of untreated spores branched infrequently. These results indicate that root exudates affect spore germination and germ tube growth of G. epigaeum and thereby could influence subsequent root colonization and VAM formation.

EFFECT OF FLOWER BUD DEVELOPMENT IN CHRYSANTHEMUM ON VESICULAR‐ARBUSCULAR MYCORRHIZA FORMATION

SummaryRoots of single stem Chrysanthemum morifolium plants were inoculated with the vesicular‐arbuscular mycorrhizal (VAM) fungus, Glomus fasciculatus, at several stages of flower bud development. Compared to vegetative control plants, VAM formation was reduced during early stages of flower bud development, but not during later bud expansion. A decrease of reducing sugars and amino acids in root extracts during early bud development coincided with a decrease in root exudation of these compounds. These results suggest that reduction of VAM formation during early flower bud development resulted from a decrease in the availability and net leakage of metabolites necessary to sustain the mycorrhizal fungus during pre‐ and post‐infection.