Localized Increase in Nodule Activity but No Competitive Interaction of Cowpea Rhizobia Due to Pre‐establishment of Vesicular‐arbuscular Mycorrhiza

Abstract

SUMMARYCowpea [Vigna unguiculata (L.) Walp.] plants were grown in a split-root system using a calcined montmoriUonite clay (Turface) as the growth medium. At transplantmg, either the vesiculararbuscular mycorrhizal (VAM) fungus Glomus macrocarpum Tul. & Tul. and 100 mg hydroxyapatite (HAP) or 100, 200 or 400 mg HAP kg-^ without the VAM fungus were mixed into side 1 of the split-root system. Side 2 received only lOOmgHAPkg-^ After 30 d, a combined inoculum of four Rhizobium isolates (TAL169, TAL173, TAL658 and IRC256) was applied to the surface of all pots. At harvest (60 d), root systems were separated from shoots and nodule activity (acetylene reduction), plant dry weight, nitrogen (N) and phosphate (P) content and the percentage of VAM colonization were determined. There was no signihcant efTect of treatment on either the N or P content of leaves or roots. The VAM fungus, however, significantly (P < 0-01) increased shoot dry weight. Root dry weight and nodule activity were significantly increased only on the VAM side of the split-root system. Rhizobia from 30 nodules per half-root system were identified using fluorescent antibody techniques. Strain TAL173 was detected from 95 % of the nodules and neither the VAM fungus nor P application affected competitive interaction by rhizobia for nodulation sites. Our work suggests the existence of a localized, non-systemic, non-P-mediated infiuence of a VAM fungus on root dry weight and nodule activity in cowpea.

Influence of growth stage on the association between some tropical legumes and two variant species ofGlomusin an andosol

“…Growth, nodulation as well as nitrogen-fixing activities of nodules were better correlated with VAM fungi colonization than with shoot P concentrations. These findings agree with those of Ames and Bethlenfalvay (1987) who reported that improved P nutrition is not the sole mechanism by which VAM contribute to the enhanced N2 fixation in a VAM-plantrhizobium tripartite association. Other mechanisms may include photosynthesis, trace element nutrition or plant hormone production (Bagyaraj 1983).…”

“…These authors also observed that regardless of the type of inoculum employed, the shoot P concentration ranged between 0.57-0.65 mg g-1 in the two types of soil used. Ames and Bethlenfalvay (1987) also obtained a relatively high level of P (2.85 mg P g-l) in leaves of cowpea plants inoculated with Glomus macrocarpum and treated with an additional 100mgkg -1 of hydroxyapatite (Ca~0(OH)~(PO4)8). Increased stem P concentration of G. et.-inoculated pigeonpea plants at earlier stages of growth (Table 5) might have been due to an early establishment of VAM (Fig.…”

Interactions between plant‐growth‐promoting rhizobacteria (PGPR), arbuscular mycorrhizal fungi and Rhizobium spp. in the rhizosphere of Anthyllis cytisoides, a model legume for revegetation in mediterranean semi‐arid ecosystems

“…Because mycorrhizal status benefits the uptake of immobile ions, the symbiotic N., fixation results were favoured by the increased P content in plant tissues (Barea & Azcon-Aguilar, 1983;Barea, Azcon-AgLiilar & Azcon, 1987;Azcon, Rubio & Barea, 1991). Some other non-P-mediated effects might also be involved (Ames & Bethlenfalvay, 1987;Johansen et al, 1993). Thus, increases in P content of plants inoculated with several specific associations of micro-organisms (i.e.…”

Effect of the VAM fungus Glomus sp. on the growth and yield of soybean inoculated with Bradyrhizobium japonicum

“…Both rhizobia and VAM fungi are active in root cortical cells and, hence, it can be assumed that the presence of one microsymbiont will affect the activity of the other. Most studies have concentrated on indirect relationships between VAM fungi and rhizobia, in which a successful symbiosis has been measured as an increased uptake of nutrient elements, P in particular, by the plant (Ames and Bethlenfalvay, 1987) and an increased N 2 fixation and nodule mass (Fredeen and Terry, 1988), but more direct non-nutritional effects of VAM fungus-rhizobia interactions have also been reported (Bethlenfalvay et al, 1985;Ross and Harper, 1970). However, studies concerning the effect of rhizobial strains on the development of a VAM fungus (Bayne and Bethlenfalvay, 1987;Kucey and Paul, 1982) and, inversely of VAM fungal species on nodulation (Bethlenfalvay et al, 1982) are relatively scarce.…”