Forage Crops

HCS612 Forage Crops
Endophyte

Mycology
The association
Effects on plants
Effects on animals
So what? - practical implications

Mycology

	Fungus found in the intercellular spaces of grasses
	Over 50 grass species (including corn) Over 20 fungus species (diverse effects on plants) Includes ergot fungi that infect seed-heads of many grasses and small grains	ergot on quackgrass (left) and ryegrass (right) (click to enlarge)
	Classic seed-borne "disease"
	Fungus is only present in plants as mycelium, sexual phase only found in culture
	Species specific: Tall fescue (Festuca arundinacea) = Neotyphodium coenophialum (formerly Acremonium) Ryegrass (Lolium perenne) = Neotyphodium lolli
	Variation in fungal races – variation in the amount and expression of alkaloids
	Endophyte-free plants beside infected planted can not become infected
	Endophyte viability in seed decreases with storage at room temperature and humidity. Total loss of endophyte from seed can occur after 2 years (in seed storage or for seed buried in soil)

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The Association

	Symbiotic relationship the fungus only draws nutrition and a protected environment the host derives insect resistance, environmental tolerance, reduced grazing
	together the association is more productive and persistent
	Plant variety – fungal race specific. Not all fungal races infect all varieties with equal vigor
	The fungus originates in meristematic areas as hyphae. It is most concentrated in the base of the plant. It can also spread up the pseudo-stem and into leaves During flowering the infected seed head is particularly toxic (and readily grazed)
	The symbiosis produces 20-30 alkaloids – neither plant nor fungus can produce these alone The most important alkaloid in tall fescue is ergovaline Lolitrem and peramine are produced in ryegrass
	Ergovaline has low solubility and its distribution is closely related to the presence of mycelium (crown and pseudo-stem). It can be found in leaves Some alkaloids are highly water soluble and spread through the leaves and roots

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Effects on Plants

No visual symptoms

Production – up to 20% more production (usually 5-10%)

Persistence – insect resistance

Seasonal variation in alkaloid concentration, high in summer, low in spring & fall

Variable drought effects - osmotic adjustment, earlier leaf curling and altered stomatal conductance have been observed

Absent in bluegrass, orchardgrass, timothy and legumes

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Effects on Animals

In ryegrass lolitrem is a nervous trematogen – causing animals to loose muscular control and have a staggering walk hence “staggers”

Ergovaline is a vasoconstrictor, and cuts blood supply to animal extremities – in severe cases can result in loss of ears and feet “fescue-foot”

Horses extremely sensitive, sheep intermediate sensitivity, cattle least sensitive, young stock very sensitive

Clinical effects – rough coat, staggers, fescue-foot, abortion, elevated temperature (seeking shade/stand in water), reduced blood prolactin
Sub-clinical effects – reduced intake, reduced growth rate, reduced milk production

Cattle on E+ pasture seek shade
16 Aug 2004, Coshocton OH
(click to enlarge 382 kb)

Close grazing increases exposure (especially in sheep and horses)

Altered grazing behavior – stock avoid grazing fields of endophyte-infected pasture.

The mechanism is unclear – do they respond to the endophyte or the alkaloids?

Plant avoidance at the plant-scale is a mechanism for fields with intermediate levels of infection to become dominated by endophyte-infected plants with time.

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Practical applications

Dilemma
Use endophyte-infected ryegrass or tall fescue because it is productive and persistent, or
Use endophyte-free seed because it has better animal performance?

The seed industry has adopted a standard of selling low-endophyte seed (<5% of seed being infected)

Overwhelming evidence shows this has better animal production than when endophyte is present

But, it has poor persistence, and fields become infected after several years (~20% point per year)

Establish into ‘clean’ fields – 2-year fescue exclusion period (practical?)

Factors contributing to breakdown of endophyte-free status:

Buried seed – infected seed from previous stands (can last in the soil 2 years)

Incomplete plant kill from cultivation – suggest 2 years out of ryegrass/fescue (cropping) to ensure fields are clean

Contaminated seed

Contaminated seed in fed hay (see photo)

Contaminated seed passing animal digestion

Tall fescue seedlings growing in hay debris, in an E- ryegrass pasture,
Apr. 2001, Caldwell OH
(click to enlarge, 188 kb)

Avoid any turf grass for livestock:

x future turf varieties will be infected with increasingly toxic endophytes

x Do not graze stock on turf or sport fields
x Never include any turf seed in pasture sowings
x Never make or buy hay from turf

x future turf varieties may have novel endophytes with super-high ergovaline expression

A new option is non-toxic endophyte (friendly endophyte):

ü A naturally occurring fungal isolate of the same endophyte species – but has low or no ergovaline

ü MaxQ is the only nontoxic-endophyte tall fescue available at present (AMPAC, Barenbrug and FFR have near-market lines

ü The same establishment criteria as endophyte-free seed (two years free of fescue, clean seed, clean seedbed, no hay feeding, pre-grazing on orchardgrass, bluegrass or alfalfa)

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	No visual symptoms
	Production – up to 20% more production (usually 5-10%)
	Persistence – insect resistance
	Seasonal variation in alkaloid concentration, high in summer, low in spring & fall
	Variable drought effects - osmotic adjustment, earlier leaf curling and altered stomatal conductance have been observed
	Absent in bluegrass, orchardgrass, timothy and legumes

	In ryegrass lolitrem is a nervous trematogen – causing animals to loose muscular control and have a staggering walk hence “staggers”
	Ergovaline is a vasoconstrictor, and cuts blood supply to animal extremities – in severe cases can result in loss of ears and feet “fescue-foot”
	Horses extremely sensitive, sheep intermediate sensitivity, cattle least sensitive, young stock very sensitive
	Clinical effects – rough coat, staggers, fescue-foot, abortion, elevated temperature (seeking shade/stand in water), reduced blood prolactin Sub-clinical effects – reduced intake, reduced growth rate, reduced milk production	Cattle on E+ pasture seek shade 16 Aug 2004, Coshocton OH (click to enlarge 382 kb)
	Close grazing increases exposure (especially in sheep and horses)
	Altered grazing behavior – stock avoid grazing fields of endophyte-infected pasture. The mechanism is unclear – do they respond to the endophyte or the alkaloids? Plant avoidance at the plant-scale is a mechanism for fields with intermediate levels of infection to become dominated by endophyte-infected plants with time.

Dilemma Use endophyte-infected ryegrass or tall fescue because it is productive and persistent, or Use endophyte-free seed because it has better animal performance?
The seed industry has adopted a standard of selling low-endophyte seed (<5% of seed being infected) Overwhelming evidence shows this has better animal production than when endophyte is present But, it has poor persistence, and fields become infected after several years (~20% point per year) Establish into ‘clean’ fields – 2-year fescue exclusion period (practical?)
Factors contributing to breakdown of endophyte-free status: Buried seed – infected seed from previous stands (can last in the soil 2 years) Incomplete plant kill from cultivation – suggest 2 years out of ryegrass/fescue (cropping) to ensure fields are clean Contaminated seed Contaminated seed in fed hay (see photo) Contaminated seed passing animal digestion		Tall fescue seedlings growing in hay debris, in an E- ryegrass pasture, Apr. 2001, Caldwell OH (click to enlarge, 188 kb)
Avoid any turf grass for livestock:
x	future turf varieties will be infected with increasingly toxic endophytes
x	Do not graze stock on turf or sport fields
x	Never include any turf seed in pasture sowings
x	Never make or buy hay from turf
x	future turf varieties may have novel endophytes with super-high ergovaline expression
A new option is non-toxic endophyte (friendly endophyte):
ü	A naturally occurring fungal isolate of the same endophyte species – but has low or no ergovaline
ü	MaxQ is the only nontoxic-endophyte tall fescue available at present (AMPAC, Barenbrug and FFR have near-market lines
ü	The same establishment criteria as endophyte-free seed (two years free of fescue, clean seed, clean seedbed, no hay feeding, pre-grazing on orchardgrass, bluegrass or alfalfa)