‘Fine’ and ‘coarse’ mycorrhizal fungi on red clover plants in acid soils: Root colonization and plant responses

Three sterilized acid soils were inoculated with inocula of vesicular-arbuscular mycorrhizal fungi. Soils were limed and/or P fertilized to produce different fertility levels. Most inocula consisted of mixtures of fine + coarse type endophytes. Red clover (Trifolium pratense L.) was seeded in pots and grown in a glasshouse for 4 months. Root colonization by VAM fungi, the relative infection byGlomus tenue compared to that by coarse VAM fungi and the effect of inoculation on red clover growth and mineral nutrition (P, K, Ca and Mg) were studied. Spores were also checked and tentatively identified.Results showed that root colonization by VAM fungi was higher than 50% in most cases, the lower values being found in the soil with the highest P content. Inocula containingG. mosseae + G. tenue infected plant roots only in limed (pH>5.7) soils. A study of the relative colonization by fine and coarse endophytes showed that the competitive ability againstG. tenue followed the orderG. fasiculatum > G. mosseae > G. epigaeum > G. macrocarpum, although soil properties and fertility were crucial factors.Glomus lacteum was tentatively identified in two of the three experimental soils. The inoculum in whichGlommus tenue was most infective was also the most efficient in improving plant growth and nutrient uptake. The effect of inoculation on P and Mg uptake followed a similar pattern.     

Contribution of an arbuscular mycorrhizal fungus to the uptake of cadmium and nickel in bean and maize plants

Two experiments were carried out in pots with three compartments, a central one for root and hyphal growth and two outer ones which were accessible only for hyphae of the arbuscular mycorrhizal fungus, Glomus mosseae ([Nicol. and Gerd.] Gerdemann and Trappe). In the first experiment, mycorrhizal and nonmycorrhizal bean (Phaseolus vulgaris L.) plants were grown in two soils with high geogenic cadmium (Cd) or nickel (Ni) contents. In the second experiment, mycorrhizal and nonmycorrhizal maize (Zea mays L.) or bean plants were grown in a non-contaminated soil in the central compartment, and either the Cd- or Ni-rich soil in the outer compartments. In additional pots, mycorrhizal plants were grown without hyphal access to the outer compartments. Root and shoot dry weight was not influenced by mycorrhizal inoculation, but plant uptake of metals was significantly different between mycorrhizal and nonmycorrhizal plants. In the first experiment, the contribution of mycorrhizal fungi to plant uptake accounted for up to 37% of the total Cd uptake by bean plants, for up to 33% of the total copper (Cu) uptake and up to 44% of the total zinc (Zn) uptake. In contrast, Ni uptake in shoots and roots was not increased by mycorrhizal inoculation. In the second experiment, up to 24% of the total Cd uptake and also up to 24% of the total Cu uptake by bean could be attributed to mycorrhizal colonisation and delivery by hyphae from the outer compartments. In maize, the mycorrhizal colonisation and delivery by hyphae accounted for up to 41% of the total Cd uptake and 19% of the total Cu uptake. Again, mycorrhizal colonisation did not contribute to Ni uptake by bean or maize. The results demonstrate that the arbuscular mycorrhizal fungus contributed substantially not only to Cu and Zn uptake, but also to uptake of Cd (but not Ni) by plants from soils rich in these metal cations. Deceased 21 September 1996 Deceased 21 September 1996     

Nitrogen and phosphorus requirements for raising mycorrhizal seedlings of Leucaena leucocephala in containers

A greenhouse study was undertaken to determine the nitrogen and phosphorus fertilization requirements for raising mycorrhizal seedlings in soil in containers. Seedlings of Leucaena leucocephala were grown for 40 days in dibble tubes containing fumigated or nonfumigated soil uninoculated or inoculated with Glomus aggregatum. The soil was fertilized with NH₄NO₃ solution to obtain 25–200 mg N kg^-1 soil, and with a KH₂PO₄ solution to establish target soil solution P concentrations of 0.015–0.08 mg P l^-1. At the end of 40 days, seedlings were transplanted into pots containing 5-kg portions of fumigated soil. Posttransplant vesicular arbuscular mycorrhizal fungal (VAMF) effectiveness, measured as pinnule P content, plant height, shoot dry weight and tissue N and P concentrations, was significantly increased by pretransplant VAMF colonization in both soils. The best posttransplant mycorrhizal colonization and mycorrhizal growth responses were observed if the nonfumigated pretransplant soil was amended with 50 mg N kg^-1 soil and 0.04 mg P l^-1 or if the fumigated pretransplant soil was amended with 100 mg N kg^-1 soil and 0.04 mg P 1^-1. There was no relationship between NP ratios of nutrients added to the pretransplant soil medium and shoot NP ratios observed after transplanting. Shoot NP ratio was also not correlated with root colonization level.Contribution from the Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No. 4025     

Mycorrhizal inoculation effect on nodulation and N accumulation in Cajanus cajan at soil P concentrations sufficient or inadequate for mycorrhiza-free growth

The interaction of Cajanus cajan with Rhizobium and vesicular-arbuscular mycorrhizal fungi (VAMF) was investigated in a greenhouse experiment. C. cajan was planted in soil that had been inoculated with Glomus aggregatum or treated with benlate to suppress VAMF activity. Initial soil solution P concentrations of 0.06, 0.2, 0.4, and 0.8 mg l^-1 were established to test the interaction at external P levels that ranged from inadequate to nonlimiting for the host plant. At 0.06 and 0.2 mg P l^-1, mycorrhizal inoculation significantly increased plant P concentrations as well as nodule numbers and shoot dry weight. Mycorrhizal inoculation also significantly increased nodule dry weight at a soil P concentration of 0.4 mg l^-1 but did not significantly influence any of the other variables. The mycorrhizal inoculation effect observed at this soil solution P concentration could not be explained by any of the measures of plant P status. At 0.8 mg P l^-1, none of the measured variables were affected significantly by mycorrhizal inoculation. The results indicate that the enhanced nodulation associated with mycorrhizal inoculation at soil P concentrations lower than 0.4 mg l^-1 was explainable by mycorrhizal-mediated P uptake. The small but significant increase in nodule mass due to VAMF inoculation at 0.4 mg P l^-1 suggests that factors not related to plant P nutrition may be involved. On the other hand, the lack of a VAMF inoculation effect at 0.8 mg P l^-1 despite VAMF colonization at a level comparable to that observed at the former P concentration appear to discount this hypothesis. This observation is also supported by the lack of response of plant N status and nodule number to VAMF inoculation at this soil P concentration.Contribution from the Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No.4066     

Limitation of vesicular-arbuscular mycorrhizal activity in Leucaena leucocephala by Ca insufficiency in an acid Mn-rich oxisol

Glomus aggregatum and Leucaena leucocephala were interacted in an acid Mn-rich oxisol unamended or amended with lime [Ca(OH)₂] or gypsum (CaSO₄) at soil P concentrations considered optimal for mycorrhizal host growth and sufficient for mycorrhiza-free growth. At 0.02 mg P 1^-1, both vesicular-arbuscular mycorrhizal fungal (VAMF) colonization and function were significantly curtailed if soil was not amended with gypsum or lime. The highest mycorrhizal effect was observed in the limed soil, followed by the soil treated with gypsum at the rate of 32 g Ca kg^-1 soil. Higher concentrations of gypsum deleteriously affected VAMF infectivity and effectivity. The first increment of gypsum compensated completely for the VAMF colonization and for part of the mycorrhizal effect that was lost due to low pH. The superiority of the limed soil to that amended with gypsum apparently lies in the fact that Ca supply was assured in the former and also that the adverse effects of toxic constituents such as H⁺ and Mn²⁺ were eliminated. We were unable to separate the effect of Ca on VAMF from its effect on the host because a P concentration sufficient for mycorrhiza-free growth was not attained due to interaction of some of the P with Ca to form insoluble phosphate.Contribution from the Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No. 4045     

Interactions between the root-knot nematode Meloidogyne incognita and Glomus mosseae in banana

The effects of the interaction between the arbuscular mycorrhizal fungus Glomus mosseae and the root-knot nematode Meloidogyne incognita on growth and nutrition of micropropagated ;Grand Naine banana (Musa AAA) cultivar was studied under greenhouse conditions. Inoculation with two G. mosseae isolates significantly increased growth of plants in relation to non-mycorrhizal plants. Response to mycorrhizae was as effective as with an optimum P fertilization in promoting plant development for most growth parameters. Meloidogyne incognita had no apparent effect on the percentage of root colonization in mycorrhizal plants. In contrast, G. mosseae suppressed root galling and nematode buildup in the roots. The percentage of mycorrhizal colonization was high (over 80%) in low P fertilized plants, but optimum P rates for bananas (four times higher than low P) significantly reduced mycorrhizal colonization. Most elements were within sufficiency levels for banana with exception of N which was low for all treatments. Mycorrhizal plants fertilized with a low P rate showed higher N, P, K, Ca, and Mg contents as compared to non-mycorrhizal plants low in P with or without the nematode. Inoculation with G. mosseae favours growth of banana plants by enhancing plant nutrition and by suppressing nematode reproduction and galling during the early stages of plant development.     

Accumulation of sesquiterpenoid cyclohexenone derivatives induced by an arbuscular mycorrhizal fungus in members of the Poaceae

Sixty one members of the Poaceae, including various cereals, were grown in defined nutrient media with and without the arbuscular mycorrhizal (AM) fungus, Glomus intraradices Schenk & Smith. The roots of all species investigated were colonized by the AM fungus, however, to different degrees and independent of their systematic position. High-performance liquid chromatographic analyses of methanolic extracts from the roots of mycorrhizal and nonmycorrhizal species revealed dramatic changes in the patterns of UV-detectable products along with a widespread occurrence of AM-fungus-induced accumulation of sesquiterpenoid cyclohexenone derivatives. The latter occur most often in the tribes Poeae, Triticeae and Aveneae. Some additional control experiments on plant infection with pathogens (Gaeumannomyces graminis) and Drechslera sp.) or an endophyte (Fusarium sp.), as well as application of abiotic stress, proved that the metabolism of these terpenoids is part of a response pattern of many gramineous roots in their specific reaction to AM fungal colonization. Received: 23 October 1996 / Accepted 11 December 1996     

Dual colonization of Eucalyptus urophylla S.T. Blake by arbuscular and ectomycorrhizal fungi affects levels of insect herbivore attack

Abstract 1 Eucalypts are an important part of plantation forestry in Asia but, in south China, productivity is very low. This is due to infertile soils and lack of indigenous symbiotic mycorrhizal fungi. The genus Eucalyptus is unusual because it forms both arbuscular (AM) and ectomycorrhizal (ECM) associations. 2 Eucalyptus urophylla saplings were grown with and without AM (Glomus caledonium) and ECM (Laccaria laccata) fungi in a factorial design. Two experiments were performed: one to simulate nursery conditions and the other to simulate the early stages of plantation establishment. Plant growth was measured over 18 weeks and levels of insect attack were recorded. 3 The AM fungus reduced tree growth in the early stages, but the effect appeared to be transient. No effects of ECM were detected on tree growth, but the ectomycorrhiza reduced colonization by the arbuscular mycorrhiza. AM fungi appear to be rapid invaders of the root system, gradually being replaced by ECM. 4 Both fungal types affected levels of damage by insect herbivores. Most importantly, herbivory by the pest insects Anomala cupripes (Coleoptera) and Strepsicrates spp. (Lepidoptera) was decreased by ECM. 5 It is suggested that mycorrhizal effects on eucalypt insects may be determined by carbon allocation within the plant. Future studies of eucalypt mycorrhizas need to take into account the effects of the fungi on foliar‐feeding insects and also the effects of insect herbivory on mycorrhizal establishment.     

Synergistic effects of Arbuscular mycorrhizal fungi and plant growth promoting rhizobacteria in bioremediation of iron contaminated soils

Three Arbuscular mycorrhizal fungi (AMF) from Glomus, Acaulospora and Scutellospora, and four plant growth promoting rhizobacteria (PGPR) isolates related to genera Streptomyces, Azotobacter, Pseudomonas and Paenibacillus were found to be effective in phytoremediation of Fe³⁺ contaminated soil where Pennisetum glaucum and Sorghum bicolor were growing as host plants. Co-inoculation of AMF and PGPR showed better results in comparison to either, AMF and PGPR under pot conditions. Both AMF and PGPR were able to produce siderophores. AMF and PGPR associated to P. glaucum and S. bicolor plants increased the extent of iron absorption. AMF and PGPR combination exhibited superior (p < 0.01) phytoremediation efficiency with P. glaucum compared to S. bicolor. These findings warrant further investigations of these synergistic interactions and large-scale in situ studies for bioremediation of iron-contaminated soils.