Interactions between wild oat and a weed-competitive and non-competitive wheat cultivar as influenced by arbuscular mycorrhizal fungi

Non-Peer ReviewedThe response of a weed-competitive (Columbus) and non-competitive (Oslo) wheat (Triticum aestivum L.) cultivar, alone and in competition with wild oat (Avena fatua L.) to arbuscular mycorrhizal fungi (AMF) was assessed in a greenhouse study using four AMF species. Plants were inoculated with 300 spores of Glomus clarum, G. etunicatum, G. intraradices or G. mosseae and grown for 77 d in field soil containing low levels of indigenous AMF populations. The AMF species had no significant (P<0.05) effect on the shoot fresh or dry weight of single stands of Oslo or Columbus compared to the uninoculated controls. However, G. etunicatum significantly (P<0.05) enhanced the shoot fresh weight of single stands of wild oat, and G. intraradices significantly (P<0.05) increased the shoot fresh and dry weight of wild oat compared to the uninoculated control. The competitiveness of wild oat in competition with Oslo was significantly (P<0.05) enhanced by inoculation with G. mosseae, whereas the other AMF species had no effect. In contrast, inoculation of Oslo with G. clarum significantly (P<0.05) increased the ability of Oslo to withstand wild oat competition. On the other hand, there were no differences in the ability of any of the AMF species to impact on wild oat growth in competition with Columbus. However, G. intraradices significantly (P<0.05) increased the shoot dry weight of Columbus in competition with wild oat. These preliminary results indicate that different AMF species interact differently with various hosts, and that these interactions may be specific. In addition, it is apparent that these specific interactions may enhance the competitiveness of a non-competitive host against weeds

Can Arbuscular Mycorrhizal Fungi Reduce the Growth of Agricultural Weeds?

BACKGROUND: Arbuscular mycorrhizal fungi (AMF) are known for their beneficial effects on plants. However, there is increasing evidence that some ruderal plants, including several agricultural weeds, respond negatively to AMF colonization. Here, we investigated the effect of AMF on the growth of individual weed species and on weed-crop interactions. METHODOLOGY/PRINCIPAL FINDINGS: First, under controlled glasshouse conditions, we screened growth responses of nine weed species and three crops to a widespread AMF, Glomus intraradices. None of the weeds screened showed a significant positive mycorrhizal growth response and four weed species were significantly reduced by the AMF (growth responses between -22 and -35%). In a subsequent experiment, we selected three of the negatively responding weed species--Echinochloa crus-galli, Setaria viridis and Solanum nigrum--and analyzed their responses to a combination of three AMF (Glomus intraradices, Glomus mosseae and Glomus claroideum). Finally, we tested whether the presence of a crop (maize) enhanced the suppressive effect of AMF on weeds. We found that the growth of the three selected weed species was also reduced by a combination of AMF and that the presence of maize amplified the negative effect of AMF on the growth of E. crus-galli. CONCLUSIONS/SIGNIFICANCE: Our results show that AMF can negatively influence the growth of some weed species indicating that AMF have the potential to act as determinants of weed community structure. Furthermore, mycorrhizal weed growth reductions can be amplified in the presence of a crop. Previous studies have shown that AMF provide a number of beneficial ecosystem services. Taken together with our current results, the maintenance and promotion of AMF activity may thereby contribute to sustainable management of agroecosystems. However, in order to further the practical and ecological relevance of our findings, additional experiments should be performed under field conditions

Susceptibility of barley cultivars to vesicular-arbuscular mycorrhizal fungi

The relative susceptibility of selected barley cultivars produced in western Canada to vesicular-arbuscular mycorrhizal (VAM) fungi under field and greenhouse conditions was evaluated in this study. Cultivars tested under field conditions at the University of Alberta and Lacombe research stations showed no significant differences in VAM colonization of barley roots; colonization was light. Greenhouse trials at the University of Alberta with eight cultivars inoculated with individual mycorrhizal species illustrated significant differences among the barley cultivars in their reactions to Glomus dimorphicum, G. intraradices, and G. mosseae. Distinct differences were observed in the ability of each Glomus species to colonize the barley cultivars. The VAM fungi increased growth and yield in some cultivars, depending on the Glomus species. This study indicates that a degree of host-specificity exists in VAM fungi and that the host-mycorrhizal fungus genotypes may influence the effectiveness of the symbiosis. Key words: Barley, cultivars, susceptibility, VA mycorrhizal fungi </jats:p

A new species of <i>Glomus</i> (Endogonaceae, Zygomycotina) mycorrhizal with barley in Alberta

A new species of endogonaceous fungus mycorrhizal with barley in Alberta is described. Glomus dimorphicum sp. nov. has two types of spores formed singly and in loose, often radiately arranged clusters. This new species produces very few vesicles, and arbuscule formation has so far not been observed. </jats:p

Sustainability, conservation tillage and weeds in Canada

The sustainability of conservation tillage is dependent on the extent of changes in weed community composition, the usage of herbicides, and the development of integrated weed management (IWM) strategies, including biological weed control. The objective of this paper is to review research on conservation tillage and weed management in light of these factors. Recent Canadian research has found that changes in weed communities due to the adoption of conservation tillage are not necessarily those expected and were not consistant by species, location, or year. Changes reflected the use of different selection pressures, such as different crop rotations and herbicides, within the studies to a greater extent than weed life cycle groupings. Therefore, research that determines the reasons for change or the lack of change in weed communities is required to provide the scientific basis for the development of IWM strategies. Documented herbicide usage in conservation tillage varies from less than to more than conventional-tillage systems. Potential to reduce herbicide usage in conservation-tillage systems exists. Furthermore, the herbicides used in western Canada are different from those causing ground water contamination in the United States, are less volatile, and are used at lower rates. The presence of surface crop residues in conservation tillage may provide a unique environment for classical and inundative biological control agents. Some insects, fungi, and bacteria have the potential to survive to a greater extent in undisturbed plant residues. Residue management and conservation tillage systems are evolving in Canada. Research must keep pace by providing weed management strategies that enchance the sustainability of these systems. Key words: Biological control, zero tillage, integrated weed management, residues, herbicides, rhizobacteria. </jats:p