VA Mycorrhizae & Pumpkins

and their potential use in
Cucurbita maxima growth
Rachael Picard
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
 There are two main forms of mycorrhizae
 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.
Vesicular-Arbuscular Mycorrhizae
 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
 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.
 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
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
 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.
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
 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
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.
Effects of mycorrhizae on Cucurbits
 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.
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