Effects of the root-lesion nematode Pratylenchus vulnus and the mycorrhizal fungus Glomus mosseae on the growth of EMLA-26 apple rootstock

The interaction between Pratylenchus vulnus and the endomycorrhizal fungus Glomus mosseae on the growth of EMLA 26 apple rootstock was studied under shadehouse conditions in the field during the first 6 months of growth. Fresh top weights, fresh root weights, and shoot lengths of mycorrhizal plants with and without P. vulnus were significantly higher than those of nonmycorrhizal plants. Addition of P to non-mycorrhizal controls had little overall effect. Mycorrhizal treatments with the nematode showed a significantly lower amount of nematodes per gram of root than nonmycorrhizal treatments with P. vulnus. Root colonization by G. mosseae was not affected by the presence of the nematode. No nutrient deficiencies were detected in foliar analyses, although low levels of K, A1, and Fe were detected in nematode treatments. The highest levels of S, Mg, Mn and Zn were detected in P. vulnus inoculated plants. Mycorrhizal plants had the highest levels of N, Na, P, K, and Fe. The importance of early mycorrhizal infection of EMLA 26 apple root-stock in the presence of the nematode is discussed.     

Increased tolerance to the root-lesion nematode Pratylenchus vulnus in mycorrhizal micropropagated BA-29 quince rootstock

The interaction between Glomus intraradices and the root-lesion nematode Pratylenchus vulnus was studied on micropropagated BA-29 quince rootstock during one growing season. Inoculation with G. intraradices significantly increased growth of plants in low P soil and was more effective than P fertilization at increasing top-plant development. In the presence of the nematode, mycorrhizal plants achieved higher values in all growth parameters measured. P. vulnus caused a significant decrease in the percentage of root length colonized by G. intraradices and fewer internal vesicles were formed within the host roots. Enhanced root mass production accounted for the twofold increase in final nematode population recovered from plants with combined inoculations of pathogen and symbiont. Low levels were found of Al, Fe, Mn and Zn in nonmycorrhizal nematode-infected plants in low P soil. G. intraradices-inoculated plants reached the highest foliar levels of N, Ca, Mg, Mn, Cu and Zn. Mycorrhizal plants infected with P. vulnus maintained normal to high levels of Mn, Cu, and Zn. Inoculation with G. intraradices favours quince growth and confers protection against P. vulnus by improving plant nutrition.     

Effects of the root-lesion nematode Pratylenchus vulnus and the vesicular-arbuscular mycorrhizal fungus Glomus mosseae on the growth of three plum rootstocks

The effects of Pratylenchus vulnus and the endomycorrhizal fungus Glomus mosseae on growth of Myrobalan 605, Marianna 2624 and San Julian 655-2 plum rootstocks were measured under shadehouse conditions in the field for two growing seasons (1990–91). Shoot dry weights were higher in the majority of the vesicular-arbuscular mycorrhizal (VAM) alone inoculated plants after both growing seasons. Root weights of mycorrhizal Myrobalan and Marianna were higher than root weights of the same rootstocks lacking mycorrhizae, inoculated with P. vulnus, and VAM in combination with the nematode. Mycorrhizal Marianna inoculated with the nematode showed a considerably higher final nematode population in relation to non-inoculated VAM treatments. No correlation was found in the number of nematodes per gram of root between mycorrhizal and non-mycorrhizal treatments. P. vulnus adversely affected the mycorrhizal colonization in Marianna, but not in Myrobalan and San Julian. Marianna appears to be more mycorrhizal dependent than the two other rootstocks.     

Effects of the mycorrhizal fungus Glomus intraradices on uranium uptake and accumulation by Medicago truncatula L. from uranium-contaminated soil

Phytostabilization strategies may be suitable to reduce the dispersion of uranium (U) and the overall environmental risks of U-contaminated soils. The role of Glomus intraradices, an arbuscular mycorrhizal (AM) fungus, in such phytostabilization of U was investigated with a compartmented plant cultivation system facilitating the specific measurement of U uptake by roots, AM roots and extraradical hyphae of AM fungi and the measurement of U partitioning between root and shoot. A soil-filled plastic pot constituted the main root compartment (C_A) which contained a plastic vial filled with U-contaminated soil amended with 0, 50 or 200 mg KH₂PO₄−P kg^–1soil (C_B). The vial was sealed by coarse or fine nylon mesh, permitting the penetration of both roots and hyphae or of just hyphae. Medicago truncatula plants grown in C_A were inoculated with G. intraradices or remained uninoculated. Dry weight of shoots and roots in C_A was significantly increased by G. intraradices, but was unaffected by mesh size or by P application in C_B. The P amendments decreased root colonization in C_B, and increased P content and dry weight of those roots. Glomus intraradices increased root U concentration and content in C_A, but decreased shoot U concentrations. Root U concentrations and contents were significantly higher when only hyphae could access U inside C_B than when roots could also directly access this U pool. The proportion of plant U content partitioned to shoots was decreased by root exclusion from C_B and by mycorrhizas (M) in the order: no M, roots in C_B > no M, no roots in C_B > M, roots in C_B > M, no roots in C_B. Such mycorrhiza-induced retention of U in plant roots may contribute to the phytostabilization of U contaminated environments.     

Identification of heavy metal-induced genes encoding glutathione S-transferases in the arbuscular mycorrhizal fungus Glomus intraradices

Arbuscular mycorrhizal fungi are able to alleviate the stress for plants caused by heavy metal contamination of soil. To analyze the molecular response of arbuscular mycorrhizal fungi to these pollutants, a subtractive cDNA library was constructed using RNA from Glomus intraradices extraradical hyphae of a root organ culture treated with a mixture of Cd, Zn, and Cu. Screening by reverse Northern blot analysis indicated that, among 308 clones, 17% correspond to genes up-regulated by heavy metals. Sequence analysis of part of the clones resulted, amongst others, in the identification of six genes putatively coding for glutathione S-transferases belonging to two different classes of these enzymes. Expression analyses indicated that the genes are differentially expressed during fungal development and that their RNA accumulation dramatically increases in extraradical hyphae grown in a heavy metal-containing solution.     

Glomus intraradices dominates arbuscular mycorrhizal communities in a heavy textured agricultural soil

Arbuscular mycorrhizal fungal (AMF) spore communities were surveyed in a long-term field fertilization experiment in Switzerland, where different amounts of phosphorus (P) were applied to soil. Plots receiving no P as well as plots systematically fertilized in excess to plant needs for 31 years were used to test the hypothesis that application of P fertilizer changes the composition and diversity of AMF communities. AMF spores were isolated from the field soil, identified, and counted so as to quantify the effect of P fertilization on AMF spore density, composition, and diversity. Trap cultures were established from field soil with four host plants (sunflower, leek, maize, and Crotalaria grahamiana), and the spore communities were then analyzed in substrate samples from the pots. Altogether, nine AMF species were detected in the soil. No evidence has been acquired for effect of P fertilization on spore density, composition, and diversity of AMF in both the field soil and in trap cultures. On the other hand, we observed strong effect of crop plant species on spore densities in the soil, the values being lowest under rapeseed and highest under Phacelia tanacetifolia covercrop. The identity of plant species in trap pots also significantly affected composition and diversity of associated AMF communities, probably due to preferential establishment of symbiosis between certain plant and AMF species. AMF spore communities under mycorrhizal host plants (wheat and Phacelia in the fields and four host plant species in trap pots) were dominated by a single AMF species, Glomus intraradices. This resulted in exceptionally low AMF spore diversity that seems to be linked to high clay content of the soil.Electronic supplementary material Supplementary material is available for this article at and accessible for authorised users.     

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.     

Interactions between the arbuscular mycorrhizal (AM) fungus Glomus intraradices and nontransformed tomato roots of either wild-type or AM-defective phenotypes in monoxenic cultures

Monoxenic symbioses between the arbuscular mycorrhizal (AM) fungus Glomus intraradices and two nontransformed tomato root organ cultures (ROCs) were established. Wild-type tomato ROC from cultivar “RioGrande 76R” was employed as a control for mycorrhizal colonization and compared with its mutant line (rmc), which exhibits a highly reduced mycorrhizal colonization (rmc) phenotype. Structural features of the two root lines were similar when grown either in soil or under in vitro conditions, indicating that neither monoxenic culturing nor the rmc mutation affected root development or behavior. Colonization by G. intraradices in monoxenic culture of the wild-type line was low (<10%) but supported extensive development of extraradical mycelium, branched absorbing structures, and spores. The reduced colonization of rmc under monoxenic conditions (0.6%) was similar to that observed previously in soil. Extraradical development of runner hyphae was low and proportional to internal colonization. Few spores were produced. These results might suggest that carbon transfer may be modified in the rmc mutant. Our results support the usefulness of monoxenically obtained mycorrhizas for investigation of AM colonization and intraradical symbiotic functioning.     

Alleviation of salt stress in Lotus glaber by Glomus intraradices

Lotus glaber is a glycophytic, perennial legume from Europe that occurs widely in saline habitats. We evaluated the effect of mycorrhizal fungus colonization on the response to salt stress of two genotypes of L. glaber differing in their tolerance to salinity. The experiment consisted of a randomized block design with two factors: (1) mycorrhizal fungus treatments (with or without AM fungus) and (2) two salinity levels of 0 and 200 mM NaCl. Our results indicated that Glomus intraradices established a more efficient symbiosis with the tolerant than with the sensitive genotype. G. intraradices improved growth of L. glaber plants under saline conditions. They showed higher values of net growth, shoot/root and K⁺/Na⁺ ratios, and protein concentrations than controls. Tolerant AM plants also showed higher chlorophyll levels than non-AM ones. Prevention of Na⁺ accumulation in the plant and enhancement of K⁺ concentrations in roots observed in this work could be part of the general mechanism of salt stress alleviation of L. glaber by G. intraradices.     

Aquaporin genes GintAQPF1 and GintAQPF2 from Glomus intraradices contribute to plant drought tolerance

Arbuscular mycorrhizal (AM) symbiosis, established between AM fungi (AMF) and roots of higher plants, occurs in most terrestrial ecosystems. It has been well demonstrated that AM symbiosis can improve plant performance under various environmental stresses, including drought stress. However, the molecular basis for the direct involvement of AMF in plant drought tolerance has not yet been established. Most recently, we cloned two functional aquaporin genes, GintAQPF1 and GintAQPF2, from AM fungus Glomus intraradices. By heterologous gene expression in yeast, aquaporin localization, activities and water permeability were examined. Gene expressions during symbiosis in expose to drought stress were also analyzed. Our data strongly supported potential water transport via AMF to host plants. As a complement, here we adopted the monoxenic culture system for AMF, in which carrot roots transformed by Ri-T DNA were cultured with Glomus intraradices in two-compartment Petri dishes, to verify the aquaporin gene functions in assisting AMF survival under polyethylene glycol (PEG) treatment. Our results showed that 25% PEG significantly upregulated the expression of two aquaporin genes, which was in line with the gene functions examined in yeast. We therefore concluded that the aquaporins function similarly in AMF as in yeast subjected to osmotic stress. The study provided further evidence to the direct involvement of AMF in improving plant water relations under drought stresses.     

Relative mycorrhizal dependency and mycorrhiza-nematode interaction in banana cultivars (Musa spp.) differing in nematode susceptibility

Four Musa cultivars, differing in nematode susceptibility, were selected to study their relative mycorrhizal dependency and to study the interaction between the arbuscular mycorrhizal fungus (AMF), Glomus mosseae, and two migratory endoparasitic nematodes, Radopholus similis and Pratylenchus coffeae. Mycorrhization with G. mosseae resulted in significantly better plant growth, even in the presence of R. similis and P. coffeae. No differences in relative mycorrhizal dependency (RMD) were observed among the four cultivars. G. mosseae suppressed nematode population build-up in Grande Naine and Pisang Jari Buaya. Only in the case of R. similis (Indonesian population) in Pisang Jari Buaya, no significant suppression was observed. In the case of P. coffeae, the AMF reduced the damage in the roots, caused by the nematodes. For R. similis, no reduction of damage was observed. In all, except one experiment, the frequency of the mycorrhizal colonisation was negatively affected by the nematodes.     

Root colonization of different hosts by the vesicular-arbuscular mycorrhizal fungus Glomus dimorphicum

Colonization of the roots of beans, alfalfa, onions, red clover, corn, and four barley cultivars (Bonanza, Klondike, Gateway 63, and Olli) by Glomus dimorphicum Boyetchko and Tewari, a vesicular-arbuscular mycorrhizal fungus isolated from a barley field in Alberta, Canada, was studied under greenhouse conditions. Infection levels were low in all four barley cultivars but were higher in beans, alfalfa, and onions and were highest in red clover and corn roots. The infection patterns of G. dimorphicum varied among all the hosts. Coiling of intracellular hyphae occurred in corn, alfalfa, and red clover roots. Appreciable numbers of intraradical vesicles were found only in red clover and bean roots, while arbuscules formed in all hosts except barley. It was concluded that the pattern of root colonization by G. dimorphicum is influenced by the host genome and that the fungal morphology in the roots is variable and, thus, not diagnostic for the mycorrhizal species.     

Influence of Glomus intraradices and Soil Phosphorus on Meloidogyne incognita Infecting Cucumis melo

The interaction among Glomus intraradices, Meloidogyne incognita, and cantaloupe was studied at three soil phosphorus (P) levels in a greenhouse. All plants grew poorly in soil not amended with P, regardless of mycorrhizal or nematode status. In soil amended with 50 μg P /g soil, M. incognita suppressed the growth of nonmycorrhizal plants by 84%. In contrast, growth of mycorrhizal plants inoculated with M. incognita was retarded by only 21%. A similar trend occurred in plants grown in soil with 100 μg P /g soil. Mycorrhizal infection had no effect on the degree of root-knot gall formation and did not affect the number of nematode eggs per egg mass. Mineral levels in plant shoots generally declined as soil P levels increased and were not significantly influenced by G. intraradices or M. incognita.     

Soil receptiveness to VA mycorrhizal association: Concept and method

The concept of soil receptiveness widely used for soil borne pathogens, is applied to the fungi forming vesicular-arbuscular endomycorrhizae. The authors propose a method for determining the mycorrhizal soil receptiveness (MSR) using leek, a highly mycotrophic plant, as a host for a bioassay. Under controlled conditions, populations of leek plants are grown in a soil inoculated with a range of inoculum levels. The inoculum consists of standardized root pieces infected with G. intraradices which are considered as propagules. The relationship between the percentage of plants forming mycorrhizae and the level of inoculum is used as a basis for determining the quantity of inoculum required to obtain mycorrhizae formation on 50% of the host plant population. The results are defined in terms of MSR unit, and are expressed as number of propagules corresponding to a MSR₅₀ unit, or as MSR₅₀ unit per propagule. This method is illustrated in a comparative study of four agricultural soils from France.     

Reproductive Fitness and Random Amplified Polymorphic DNA Variation among Isolates of Pratylenchus vulnus

The reproductive fitness of seven isolates of Pratylenchus vulnus from different geographical areas and hosts was assessed in monoxenic cultures (carrot), and greenhouse cultures (plum, sour orange, and quince). The genetic makeup of the different isolates was compared by Random Amplified Polymorphic DNA (RAPD-PCR). The apple (PvAP-S) and apricot (PvAT-F) isolates reproduced less in monoxenic cultures than the rose (PvRO-S) and walnut (PvWA-A and PvWA-U) isolates. On plum, the rose isolate (PvRO-S) reproduced better than the apple (PvAP-S) and walnut isolate from the United States (PvWA-U). On sour orange, the apple (PvAP-S), unknown origin (PvU-UK), and walnut isolate from Argentina (PvWA-A) multiplied well, whereas the walnut isolate from the United States (PvWA-U), apricot (PvAT-F), and rose (PvRO-S) did not. On quince, the apple (PvAP-S) and walnut (PvWA-U) isolates showed a higher reproduction than the one from unknown origin (PvU-UK). RAPD-PCR patterns among the seven P. vulnus isolates were similar, although high intraspecific varibility was detected. Very few bands of P. neglectus were shared by any population of P. vulnus. A high degree of similarity was found among the patterns corresponding to the rose (PvRO-S), apple (PvAP-S), walnut from the United States (PvWA-U), and unknown origin (PvUK-U) isolates. The apricot isolate (PvAT-F) was the most dissimilar among the seven isolates. No correlation could be established between the genetic variation of P. vulnus detected by RAPD-PCR and reproductive fitness. Results demonstrate high genetic varibility between geographically separated populations of P. vulnus.     

Cold-storage of mixed inoculum of Glomus intraradices enhances root colonization,phosphorus status and growth of hot pepper

Growth response of hot pepper (Capsicum annuum L.) inoculated with the arbuscular mycorrhizal (AM) fungus, Glomus intraradices Schenck and Smith was evaluated in a greenhouse study. Three treatments in a soil-based medium amended with rock phosphate were: (1) control (CON), (2) inoculation of G. intraradices as a freshly prepared soil mixture of spores, hyphae and colonized roots of Sorghum vulgare (FM), and (3) inoculation of the fungus as cold-stored mixed inoculum (CM). Colonization at 14 weeks after inoculation with CM was 42.5%, but was significantly lower with FM (14.5%). Inoculation with G. intraradices as FM and CM increased growth of pepper, and total phosphorus and nitrogen uptake in shoots and roots compared with the CON treatment. Inoculation with CM resulted in significant increases in plant dry weight and chlorophyll concentration compared to the FM and CON treatments. Acid phosphatase activity in the rhizosphere was generally increased by AM fungal treatments. Highest acid phosphatase activity occurred at 14 weeks after inoculation with CM. Alkaline phosphatase activity in the CM treatment was significantly higher compared to that in CON and FM treatments throughout the growth period. Thus, cold storage of mixed inoculum enhanced colonization and growth-promoting activity of G. intraradices compared to freshly prepared inoculum.     

Response of the grapevine rootstock Richter 110 to inoculation with native and selected arbuscular mycorrhizal fungi and growth performance in a replant vineyard

Two indigenous arbuscular mycorrhizal (AM) fungi from the Mediterranean wine growing area in the Northeast of Spain were isolated and classified as Glomus intraradices Schenck & Smith. Both native fungi were found to increase the growth of the vine rootstock 110 Richter under greenhouse conditions compared with G. intraradices (BEG 72) and a phosphorus (P) fertilization treatment. The effectivity of field inoculation of Cabernet Sauvignon plants grafted on Richter 110 with the former native fungi and with G. intraradices BEG 72 in a replant vineyard severely infested by the root-rot fungus Armillaria mellea (Vahl ex Fr.) Kummer was assessed. The native fungi were not effective at enhancing plant development, and only G. intraradices BEG 72, resulted in a positive response. Field inoculation with this selected fungus increased plant shoot dry weight at the end of the first growing season.     

Differential host plant performance as a function of soil arbuscular mycorrhizal fungal communities: experimentally manipulating co-occurring Glomus species

In order to evaluate host plant performance relative to different soil arbuscular mycorrhizal fungal (AMF) communities, Andropogon gerardii seedlings were grown with nine different AMF communities. The communities consisted of 0, 10, or 20 spores of Glomus etunicatum and 0, 10, or 20 spores of Glomus intraradices in all possible combinations. Spores were produced by fungal cultures originating on A. gerardii in a serpentine plant community; seeds of A. gerardii were collected at the same site. The experiment was performed in the greenhouse using a mixture of sterilized serpentine soil and sand to which naturally occurring non-mycorrhizal microbes were added. There was no difference in root AMF colonization rates between single species communities of either G. etunicatum or G. intraradices, but G. intraradices enhanced plant growth and G. etunicatum did not. However, plants grew larger with some combinations of G.␣intraradices plus G. etunicatum than with the same quantity of G. intraradices alone. These results suggest the potential for niche complementarity in the mycorrhizal fungi. That G. etunicatum only increased plant growth in the presence of G. intraradices could be illustrative of why AMF that appear to be parasitic or benign when examined in isolation are maintained within multi-species mycorrhizal communities in nature.     

Production of vesicular-arbuscular mycorrhizal sporocarps,Glomus aggregatum,on fiberglass screens

Glomus aggregatum was culture onZea mays in sand. Fiberglass screen layers wrapped around the sand medium effectively provided a framework for sporocarp formation, and facilitated the subsequent harvest of the sporocarps.