Vesicular-Arbuscular Mycorrhizae and their potential use in Cucurbita maxima growth Rachael Picard

Introduction Main types of mycorrhizae Glomus spp. which is most often associated with Cucurbit species Why is mycorrhizae important How it can be used in agriculture Results seen in Cucurbita maxima

Mycorrhizae There are two main forms of mycorrhizae Endomycorrhizae Ectomycorrhizae http://ag.arizona.edu/yavapai/anr/hort/byg/archive/mycorrhizaeinthelandscape.html

Ectomycorrhizae Colonize the short feeder roots of plants which form after germination Penetrate of hyphae occurs between cortical cells of the roots forming a Hartig net The Hartig net is a interlocking hyphal structure that surrounds root cells. Eventually each cell is surrounded by the Hartig net causing them to be separated by a single fungal layer. This seems to prolong the life of the cells The formation of root hairs is suppressed since they are rendered redundant by the fungal mantle that surrounds each root. Ectomycorrhizae are mostly basidiomycetes and therefore form mushrooms. http://web.utk.edu/~htoler/448_assignments/ystudymyc/ystudymyc_introduction.htm

Vesicular-Arbuscular Mycorrhizae (VAM) The most common and widespread form of endomycorrhizal fungi. Forms a hyphal, tree-like structure called an arbuscule which serves as the main site of nutrient exchange. Arbuscules typically cause an enlarged nucleus and increased cytoplasm where active transport of phosphorus to the host plant occurs. After several days the arbuscule breaks down and the root cell returns to its normal state. Can also form thin-walled structures called vesicles which are often filled with lipids. Like arbuscules, the vesicles do not hinder the growth of the root or its ability to transfer nutrients from the root tips . http://www.apsnet.org/edcenter/illglossary/Article%20Images/Forms/DispForm.aspx?ID=367

Glomus The most common genus of VAM fungus with 90 identified species. Most species in this group produce globose or irregular spores that have a thick outer membrane to help them overwinter when there are no host plants available for colonization. The spores have pigmentation that is often yellow, red, brown or black. Spores are produced on a single hypha either singularly or in large groups called sporocarps. Glomus intraradices http://www.agr.gc.ca/eng/science-and-innovation/research-centres/ontario/eastern-cereal-and-oilseed-research-centre/the-glomeromycetes-in-vitro-collection/images-catalogue-of-am-fungi-strains-available-in-the-glomeromycota-in-vitro-collection/?id=1236886304350

The importance of mycorrhizae Provides the host plant with several times its normal root surface area. Allows plants to reach nutrients and water that would be normally out of reach. Helps plants to withstand many different soil conditions. Includes heavy metal abundance and acid rain pollution, a wide pH range, different salinity levels, and soil temperature. Carbon that is transferred from the plant to the fungus eventually makes its way into the soil becoming a carbon sink. The extra carbon stimulates the growth of soil biota including microbes that are antagonistic against soil-borne pathogens

The importance of mycorrhizae cont. VAM fungi are able to generate water-stable soil particles that stick together improving soil density and quality. It can reduce the effects of nematodes on roots: suppressing nematode growth and migration due to higher phosphorus levels. Increased competition between the pathogen and VAM can cause tolerance and resistance in plants. If VAM fungi have colonized the host tissue before exposure to a pathogen, it is less likely that the pathogen will be able to obtain the nutrients that it needs as well as have significant access to the plant past the extracellular matrix of the fungus VAM fungi partially digest their arbuscules with chitinolytic enzymes which may be able to digest other invading fungi. https://www.southlandorganics.com/article/microorganisms-enrich-your-soil-part-iii

Mycorrhizae in agriculture VAM increases the uptake and size of the nutrient pools around crops farmers do not need to add as many chemicals to the soil reducing the negative impact that overly fertilized fields have on the environment and the local crop systems. The natural mycorrhiza found in the soil is killed off by the addition of fungicides used to control disease and therefore needs to be reintroduced to the soil.

Mycorrhizae in agriculture cont. VAM spores taken from soil samples can be placed into individual pots with a host of choice where the mycorrhizae can grow without competition in a method called pot culturing. Plants can be inoculated with a specific fungus in a greenhouse and transplanted to the field where the mycorrhizae can establish a network where there previously was none. A mixture of VAM spores and mycelium collected from pot cultures or natural sources that is mixed with water which can be poured directly onto crops already planted in the field. http://mycorrhizas.info/vam.html

Effects of mycorrhizae on Cucurbits The presence of VAM can cause male flowers to produce more pollen and therefore can spread their genes. Female flowers produce larger healthier seeds. VAM increases the amount of phosphorus and nitrogen which increases the reproductive success of cucurbits. http://www.omafra.gov.on.ca/english/crops/facts/00-031.htm

Effects of mycorrhizae on Cucurbits cont. Provides nutrients such as phosphorus for large growth and calcium for pumpkin rind stability keeping it from cracking and being disqualified from competition. Current pumpkin record holder is 2,009 lbs. http://www.bigpumpkins.com/ViewArticle.asp?id=175&gid=57

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