Non-symbiotic Plants Research Articles

Glycine-Glomus-Rhizobium Symbiosis

Soybean (Glycine max [L.] Merr.) plants grown in pot cultures were inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe and Rhizobium japonicum strain 61A118 at planting (G(1)R(1)) or at 20 days (G(20)R(20)), or with one of the endophytes after the other has colonized the host root (G(1)R(20), G(20)R(1)). Nodulated (PR(1)) and VAM (G(1)N) dipartite associations, or nonsymbiotic plants (PN) using nutrient solutions with N, P, or N + P concentrations providing endophyte-equivalent nutrient inputs were used as controls. The delayed tripartite associations received the appropriate N, P, or N + P amendment while one or both endophytes were absent during the first 20 days of growth. Prior inoculation with one endophyte significantly inhibited development of the other. Root hexose sugar concentrations were negatively correlated with VAM colonization (r = -0.89), nodule activity (r = -0.91), and root P content (r = -0.93). Nodule (r = 0.97) and root (r = 0.96) P content correlated positively with VAM colonization. Nodule weight or VAM-fungal biomass were significantly greater in associations grown with only one endophyte. Dry weights of the PN, G(1)N, PR(1), and G(20)R(20) plants were significantly greater than those of tripartite plants inoculated at planting with either or both endophytes. Interendophyte inhibition is attributed to competition for root carbohydrates, and this effect apparently also affects overall plant productivity. The objective of the study was to determine if the timing of endophyte introduction and establishment affected the development of the other symbiotic partners.

Endomycorrhizal Synthesis by Gigaspora margarita in Poinsettia

SUMMARYThe roots of poinsettia (Euphorbia pulcherrima) cuttings became mycorrhizal when inoculated with Gigaspora margarita. Maximum endomycorrhizal formation occurred following application of azygospores to both the rooting medium in the mist bed and, subsequently, to rooted cuttings at transplant. Cuttings inoculated in the mist bed or at transplant only, however, developed fewer mycorrhizae. Application of 125 ppm N-P-K per potted plant weekly favored mycorrhizal formation but there was no associated plant growth stimulation. Increasing N-P-K fertility to 250 ppm resulted in a mycorrhiza-induced growth response, but the plants eventually became chlorotic. Application of 125 ppm or 250 ppm N-P-K twice weekly significantly improved plant growth and appearance. At the lower rate, mycorrhizal synthesis was repressed, occurring only as scattered hyphae in the roots, and at the higher rate mycorrhizal synthesis was completely inhibited. Gigaspora margarita, in conjunction with Rootone, stimulated rooting of cuttings in the mist bed by markedly increasing the number and weight of roots over cuttings treated with Rootone alone. The mycorrhizal cuttings withstood transplant shock under high temperatures and low moisture conditions better than nonmycorrhizal cuttings. Thus, endomycorrhizal plants grew better than nonsymbiotic plants under conditions of low fertility and moisture stress, but the relationship appeared to be of minimal importance under cultural conditions favorable for the plant