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evaluation of their possible use as functional food in-

gredients. In order for a food ingredient of a food

substance to be classified as a prebiotic, it must:

0016 be neither hydrolyzed nor absorbed in the upper

part of the gastrointestinal tract;

0017 be a selective substrate for one or a limited number

of beneficial bacteria commensal to the colon,

which are stimulated to grow and/or are metabol-

ically stimulated;

0018 consequently be able to alter colonic microflora in

favor of a healthier composition; and

0019 induce luminal or systemic effects that are

benefical to the health of the host.

Oligosaccharides are generally defined as carbohy-

drates from two to 20 monomeric units long. Re-

cently, interest in oligosaccharides has increased not

only because of properties that include sweetening

ability and fat replacement, but also because of resist-

ance to digestion in the upper gastrointestinal tract

and fermentation in the large bowel. These oligo-

saccharides are the nondigestible oligosaccharides

(NDOs). As regards NDOs, there is a general consen-

sus that:

0020 there is strong evidence to indicate the prebiotic

effect of NDOs in humans; a prebiotic effect may

be defined as a food-induced increase in numbers

and/or activity predominantly of bifidobacteria

and lactic acid bacteria in the large intestine of

humans;

0021 there is strong evidence to indicate the impact of

NDOs on bowel habit;

0022 there is promising evidence to indicate that con-

sumption of inulin-type fructans may result in

increased Ca absorption in man;

0023 there are preliminary indications that inulin-type

fructans interact with the functioning of lipid

metabolism;

0024 there is preliminary evidence in experimental animals

of their preventive effect against colon cancer.

0025 For instance, fructooligosaccharides (FOSs) are

fructose polymers and may be classified into two

main groups depending on the linkage type of the

fructose units, such as inulin with b (2–1) linkages

and levans with b (2–6) linkages. They occur natur-

ally in foods such as onions, bananas, garlic, and

tomatoes. FOSs, like other fermentable dietary fibers,

serve as a substrate for colonic bacteria to produce

short-chain fatty acids (SCFAs). FOSs help to main-

tain and restore the balance of healthy gut flora

by creating an environment that supports beneficial

bifidobacteria but does not support the growth of

some pathogenic bacteria. An example is inulin,

which is a linear polymer of lined fructose molecules

with a glucose moiety at the end, and in crop foods

consists of a mixture of various oligo- and polyfructo-

sides with different chain lengths; its functional prop-

erties depend partly on its length distribution. Inulin

is widely distributed among plants such as many

grasses, onions, asparagus, artichoke, chicory, dahlia,

and Jerusalem artichoke.

Sugar Alcohols and Other Alcohols

0026Sugar alcohols are ‘polyols.’ This term refers to chem-

ical compounds containing three or more hydroxyl

groups. Polyols can be divided into acyclic polyols

(alditols or glycitols, which are true sugar alcohols),

and cyclic polyols. An example of the first group is

xylitol, and an example of the second is myo-inositol.

In general, different functional properties have been

attributed to these groups of substances, such as low

caloric intake by incomplete absorption, sweeteners

in diabetic diet and caries-reducing agents.

0027The most ubiquitous sugar alcohols are sorbitol and

d-manitol, and their concentrations in some plants

and plant exudates may be very high. Fruits belonging

to the family Rosaceae, such as pears, apples, cherries,

plums, peaches, apricots, etc., contain appreciable

amounts of sorbitol. Xylitol is a naturally occurring

five-carbon sugar alcohol that can be found in many

fruits and berries, being most abundant in yellow

plums and greengages. Some research papers have

documented the noncariogenic and anticariogenic

effects in addition to sweetener properties, and recent

studies have indicated that xylitol may have prebiotic

properties and other effects on health.

Amino Acids, Peptides, and Proteins

0028The bioactivities of peptides encrypted in major milk

proteins are latent until released and activated by

enzymatic proteolysis, e.g., during gastrointestinal

digestion or food processing. The proteolytic system

of lactic acid bacteria may contribute to the release of

bioactive peptides, and the further degradation of

these peptides by endopeptidases and exopeptidases

of lactic acid bacteria may induce the release of

bioactive peptides in fermented milk products, these

activated peptides being potential modulators of

various regulatory processes in the body.

0029Several studies have shown that cows’ milk proteins

may stimulate the growth of Bifidobacterium species.

For instance, it has been shown that a-lactalbumin

and lactoferrin are potent growth promoters for sev-

eral Bifidobacterium species, or that trypsin-digested

k-casein presents bifidogenic activity.

Glycosides

0030Broccoli and other cruciferous vegetables are a good

source of one type of glycosides: glucosinolates.

2828 FUNCTIONAL FOODS

These are hydrolyzed by myrosinase, an enzyme

found in plant cells, resulting in a variety of hydroly-

sis products, including isothiocyanates and indoles.

Indole-3 carbinol (I3C) is currently being studied

for its cancer-chemopreventive properties, particu-

larly of the mammary gland. In addition to the induc-

tion of phase I and II detoxification reactions, I3C

may reduce the risk of cancer by modulating estrogen

metabolism.

Vitamins

0031 Because there is a substantial loss of folic acid during

cooking, supplementation with folic acid, especially

during pregnancy and in the elderly, helps to prevent

anemia. So folic acid has been added to some foods,

such as enriched breads, pastas, rice and cereals.

0032 l-Ascorbic acid (vitamin C), which is synthesized

by most animals but not by man, is one of the

most important water-soluble antioxidants. Several

molecular and biochemical mechanisms of ascor-

bate-mediated immunostimulation have also been

proposed.

0033 Supplementation with vitamin E may help to pre-

vent CHD, due to at least two mechanisms: one

mechanism is by protecting blood lipoproteins

against oxidation; the other is by inhibiting blood

clotting, a process that is involved in the initiation

of a heart attack. So both vitamin C and vitamin E

are used to prevent CHD. It has been suggested that

mortality resulting from to CHD is inversely related

to a cumulative antioxidant index, defined in terms of

concentrations in plasma, as

½vitamin E½vitamin C½b  carotene

½selenium=½cholesterol,

because a-tocopherol (vitamin E), l-ascorbic acid

(vitamin C), and b-carotene (which have vitamin A

activity) are excellent antioxidants.

0034 Vitamin D (1,25-dihydroxyvitamin D

) has re-

cently been identified as an immunoregulatory hor-

mone, serving as an immunostimulatory agent of

nonspecific immunity and exerting both stimulatory

and inhibitory effects on specific immune responses.

Cholines

0035 Lecithin (phosphatidylcholine) is a major component

of crude soybean oil. However, raw lecithins are com-

plex mixtures of lipids, namely, phosphatidylcholine,

phosphatidylethanolamine, and phosphatidylinositol

as main components. Lecithin plays an important

role in normal metabolism, for example, forming

part of membrane phospholipids; some metabolites

are messengers in cells; choline derived from lecithin

plays a role in brain cells in the resynthesis of new

phosphatidylcholine molecules needed for cells that

envelop the axons of neurones; and choline appar-

ently has a protective role, allowing cells to die rather

than to turn into malignant cells (cancers) when they

undergo mutations.

Lactic Acid Bacteria

0036In contrast to prebiotics, which represent a new con-

cept, probiotic activities have been the object of nu-

merous hypotheses and have been known since the

turn of the century, when it was postulated that lactic

acid bacteria provided health and longevity benefits.

It is estimated that over 400 species of bacteria, clas-

sified in two broad categories, inhabit the human

gastrointestinal tract. The categories are: those con-

sidered to be benefical (e.g., Bifidobacterium and

Lactobacillus) and those considered to be detrimental

(e.g., Enteobacteriaceae and Clostridium spp.). The

bacteria in the first category are used traditionally in

food fermentation and are often referred to as pro-

biotics. Probiotics are viable microbial dietary supple-

ments that beneficially affect the host through their

effects in the intestinal tract. They are widely used to

prepare fermented dairy products such as yogurt or

freeze-dried cultures, and may help to improve

human health.

0037Beneficial effects on human health by specific pro-

biotic microorganisms such as prevention of gastro-

intestinal tract infections, immune stimulation, and

balancing of the intestinal microflora have been

established in numerous clinical trials.

0038The hypocholesterolemic effect of fermented milk

products was discovered more than 30 years ago

during studies conducted in Masai tribesmen in

Africa. The Masai have low levels of serum choles-

terol and clinical CHD despite a high-meat diet, but

they consume daily 4–5 l of fermented whole milk.

More evidence supports the role of probiotics in

cancer-risk reduction, particularly colon cancer. This

observation may be due to the fact that lactic

acid cultures can alter the activity of fecal enzymes

(e.g., b-glucuronidase, azoreductase, nitroreductase)

that are thought to play a role in the development

of colon cancer. Some evidence also suggests that

probiotics play a role in reducing the risk of rota-

virus-induced diarrhea. The increase in the growth

of Bifidobacterium sp. is also accompanied by the

production of nitrogen derivatives, such as ammonia,

indole, phenol, and skatole, and by the elimination of

carcinogenic substances during fermentation.

0039Prebiotics and probiotics must be seen as comple-

mentary in many aspects, because often a combin-

ation of both may prove to be an important clinical

method of treating intestinal disorders. A mixture of

probiotics and prebiotics may improve the survival

FUNCTIONAL FOODS 2829

and implantation of live microbial dietary supple-

ments in the gastrointestinal tract. It has been

suggested that such an approach may produce the

following nutritional benefits:

0040 improved survival of live bacteria in supplementary

or food products and consequently prolonged

shelf-life;

0041 an increased number of ingested bacteria reaching

the colon in viable form;

0042 stimulation in the colon of the growth and implant-

ation of both exogenous and endogenous bacteria;

and

0043 activation of the metabolism of these bacteria (only

metabolically active bacteria can promote health).

A new symbiotic concept, or combination of both

pre- and probiotics, has been proposed to obtain the

healthy benefits of both pre- and probiotic and in

addition other new benefits, but this is an attractive

concept that needs to be tested in clinical conditions.

Minerals

0044 Minerals play an important role in maintaining

muscle and nerve function, regulating water balance

and metabolism, mineralization of the skeleton, and

transformation of energy. Selenium functions as an

antioxidant and is a component of another antioxi-

dant, glutathione peroxidase. It also helps to main-

tain adequate levels of coenzyme Q in heart muscle.

Similar to selenium, several other metalloenzymes are

directly involved in immunity and antioxidant

defenses, including copper/zinc superoxide dismutase

and iron-catalase. Zinc is essential for normal

growth, appetite, and immune function. Recommen-

dations for an increased daily dietary intake of cal-

cium have been made in many countries, so the dairy

industry has developed different milk products en-

riched in calcium, up to about 25% on a product

basis. It has recently been shown that food products

enriched with a milk calcium extract may increase the

rate of bone-mass accumulation in prepubertal girls

by 1.5% per year.

Polyunsatured Fatty Acids

0045 Dietary polyunsaturated fatty acids (PUFAs) are clas-

sified into two families: o-6, or n-6, and o-3, or n-3.

Each has different functions in the regulation of

physiological processes in the human body. n-6

PUFA, but not arachidonic acid, is found primarily in

plants; n-3 family linolenic acid (18:3n-3) is similarly

converted into eicosapentaenoic acid (EPA) (20:5n-3)

and docosahexaenoic acid (DHA) (22:6n-3); linolenic

acid is found in plant sources, whereas EPA and DHA

occur in marine oils.

0046Research has shown that polyunsaturated fatty

acids can play a key role in reducing the risk of

cardiovascular diseases by lowering serum triglycer-

ides, and reducing the development of thrombosis

and arteriosclerosis.

0047There is good scientific evidence to indicate that

the composition of dietary fatty acid is involved in the

etiology of many diseases. Increasing the supply of

n-3 PUFA may reduce the risk of CHD. In terms of

disease status, epidemiological studies have demon-

strated that the incidence of CHD is inversely associ-

ated with consumption of n-3 PUFA. However the

cardioprotective effect of fish consumption has been

observed in some prospective investigations but not in

others. Negative results could be explained by the fact

that although n-3 fatty acids have been shown to

lower triglycerides by 25–30%, they do not reduce

low-density lipoprotein (LDL) cholesterol. In fact, a

recent review of 72 placebo-controlled human trials

showed than n-3 fatty acids increased LDL choles-

terol. PUFA are derived primarily from fish oils.

Therefore, increasing fish intake is the most obvious

way of increasing n-3 PUFA intake. However, a large

percentage (up to 65%) of the population do not eat

fish. Thus, there is a need for alternative sources of

n-3 PUFA, such as functional foods, whose unique

fatty acid composition could fortify staple foods,

thereby promoting optimal levels of n-3 PUFA intake.

0048Furthermore, an anticarcinogenic fatty acid known

as conjugated linoleic acid (CLA) was first isolated

from grilled beef in 1987. CLA is a mixture of pos-

itional and geometric isomers of linoleic (18:2 n-6) in

which the double bonds are conjugated instead of

existing in the typical methylene interrupted configur-

ation. Nine different isomers of CLA have been

reported as occurring naturally in food. Over the

past two decades, CLA has been shown to be effective

in suppressing forestomach tumors in mice, aberrant

colonic crypt foci in rats, and mammary carcinogen-

esis in rats. More recently, CLA has been investigated

for its ability to change body composition, suggesting

its role as a weight-reduction agent.

Other (e.g., Phytochemicals and Antioxidants)

0049Recent epidemiological studies have indicated that a

high intake of fruit and vegetables is associated with

a reduced risk of a number of chronic diseases. This is

attributed to the fact that these foods may provide an

optimal mix of phytochemicals, such as natural anti-

oxidants, fibers and other bioactive compounds.

0050Experts from the US Food Administration have

defined phytochemicals as substances found in edible

fruits and vegetables that may be ingested by humans

daily in gram quantities and that exhibit a potential

for modulating human metabolism in a manner

2830 FUNCTIONAL FOODS

favorable for cancer prevention. Most recently, other

beneficial properties, such as cardiovascular-protect-

ive properties, have been considered.

0051 Phytochemicals could provide health benefits, such

as: (1) substrates for biochemical reactions; (2) cofac-

tors of enzymatic reactions; (3) inhibitors of enzym-

atic reactions; (4) absorbents/sequestrants that bind to

and eliminate undesirable constituents in the intestine;

(5) ligands that agonize or antagonize cell surface

or intracellular receptors; (6) scavengers of reactive

or toxic chemicals; (7) compounds that enhance the

absorption and or stability of essential nutrients; (8)

selective growth factors for beneficial gastrointestinal

bacteria; (9) fermentation substrates for beneficial

oral, gastric or intestinal bacteria; and (10) selective

inhibitors of deleterious intestinal bacteria. Nutraceu-

ticals have been defined as bioactive phytochemical

compounds that have disease-preventing, health-

promoting and/or medicinal properties.

0052 Free radicals are unstable molecules that have an

unpaired electron, which makes them highly ener-

gized and reactive, and which can damage DNA and

induce cancer. Food ingredients capable of quenching

or stabilizing free radicals are referred to as antioxi-

dant ingredients. There are many antioxidants in

foods, but the primary antioxidants that play this

very important role in the human body are vitamin

C, vitamin E, and carotenoids such as b-carotene,

lycopene, lutein, or zeaxanthin. In addition to pre-

venting cancer, some antioxidants such as vitamin E

may help to prevent heart disease by preventing

oxygen in the blood from combining with LDL

cholesterol (oxidized LDL cholesterol is one of the

contributors to plaque in the coronary arteries).

0053 Several crops, including grains, oilseeds and horti-

cultural crops, are rich sources of phytochemicals.

Cereals such as wheat, barley, and oats, oilseeds such

as canola, flaxseed, and mustard, and horticultural

crops such as grapes are good sources of phytochem-

icals. Anthocyanins are flavonoids (pigments) present

in fruits such as blueberries and also have antioxidant

properties. Isoflavones are a group of phytochemicals

that can reduce the risk of heart disease and several

cancers, including breast, lung, and prostate cancer.

Polyphenols, which are said to be present in large

quantities in tea, coffee, red grapes, kidney beans,

prunes and red wine, display anticarcinogenic, antioxi-

dant, antibacterial, and antiviral action. Most clinical

studies have been carried out on tea; catechins are the

predominant and most significant of all tea polyphe-

nols, and the four major green tea catechins are epigal-

locatechin-3-gallate, epigallocatechin, epicatechin-3-

gallate, and epicatechin. Recent studies suggest that

benefits from tea consumption are restricted to high

intakes in high-risk populations. This hypothesis

supports the recent finding that the consumption of

five or more cups of green tea per day was associated

with a reduced recurrence of stages I and II of breast

cancer in Japanese women. Saponins, also known as

triterpenoids, are classified as polyphenols, and are

abundant in soyabeans more than in any other legume,

including various beans and chickpeas. Saponins have a

modest hypocholesterolemic effect. Citrus fruits con-

tain particularly high contents of one class of phyto-

chemical known as limonoids, and over the last decade,

evidence has been gathered to support the cancer-pre-

ventive effect of limonene. Based on these observations,

and because it has little or no toxicity in humans,

limonene has been suggested as a good candidate for

human clinical chemoprevention trial evaluation. Phy-

tosterols (plant sterols), structurally related to choles-

terol, reduce blood cholesterol and lower LDL

cholesterol levels, possibly by either inhibiting choles-

terol absorption by displacing cholesterol from intes-

tinal micelles or altering the activity of enzymes

involved in cholesterol metabolism and excretion.

The most abundant plant sterol is b-sitosterol (sitos-

terol), whereas sitostanol, the saturated derivative of

sitosterol, occurs at negligible levels in plant lipids.

See also: Amino Acids: Properties and Occurrence;

Ascorbic Acid: Properties and Determination;

Bifidobacteria in Foods; Cancer: Diet in Cancer

Prevention; Carbohydrates: Digestion, Absorption, and

Metabolism; Cholecalciferol: Properties and

Determination; Choline: Properties and Determination;

Coronary Heart Disease: Prevention; Dietary Fiber:

Properties and Sources; Fatty Acids: Tr a n s -fatty Acids:

Health Effects; Lactic Acid Bacteria; Probiotics;

Tocopherols: Properties and Determination

Further Reading

Brassart D and Schiffrin E (2000) Pre- and probiotics. In:

Schmidl MK and Labuza TP (eds) Essentials of Func-

tional Foods, pp. 205–216. Guithersburg, MD: Aspen.

Duthie GG and Brown KM (1994) Reducing the risk of

cardiovascular disease. In: Goldberg I (ed.) Functional

Foods. Designer Foods, Pharmafoods, Nutraceuticals,

pp. 19–38. New York: Chapman & Hall.

Hardy G (2000) Nutraceuticals and functional foods –

Introduction and meaning. Nutrition 16: 688–689.

Hasler CM (1998) Functional foods: their role in disease

prevention and health promotion. Food Technology

52: 63–70.

Kwak NS and Jukes DJ (2001a) Functional foods – part 1 –

The development of a regulatory concept. Food Control

12: 99–107.

Kwak NS and Jukes DJ (2001b) Functional foods – part 2 –

The impact on current regulatory terminology. Food

Control 12: 109–117.

Pszczola DE (1998) ABCs of nutraceutical ingredients.

Food Technology 52: 30–37.

FUNCTIONAL FOODS 2831

Salminen S, Ouwehand A, Benno Y and Lee YK (1999)

Probiotics: how should they be defined. Trends in Food

Science & Technology 10: 107–110.

Sawicki J and Slusarki B (1997) Lipids. In: Sikorski ZE (ed.)

Chemical and Functional Properties of Food Compon-

ents, pp. 99–118. Lancaster, PA: Technomic.

Sloan AE (1999) The new market: food for the not-

so-healthy. Food Technology 53: 54–60.

Zubillaga M, Weill R, Postaire E et al. (2001) Effect of

probiotics and functional foods and their use in different

diseases. Nutrition Research 21: 569–579.

Fungi See Mushrooms and Truffles: Classification and Morphology; Use of Wild Mushrooms; Spoilage:

Chemical and Enzymatic Spoilage; Bacterial Spoilage; Fungi in Food – An Overview; Molds in Spoilage; Yeasts in

Spoilage

FUNGICIDES

N A Smart, Harpenden, Hertfordshire, UK

Introduction

0001 A fungicide is any substance, preparation, or organ-

ism intended for destroying or controlling any fungal

species during production, storage, or distribution of

an agricultural commodity or food, in ornamental

plants, or in situations endangering the health of

animals or humans. Numerous organic chemicals, as

well as some inorganic ones, are formulated for use as

fungicides in agriculture and food storage. Fungicides

help to increase efficiency of production, by prevent-

ing or reducing damage to the growing crop or stored

commodity, and to improve the quality of the prod-

uct, by preventing rotting and a damaged appearance.

These chemicals are closely scrutinized for any toxic

hazard before they are marketed. Plant breeders can

produce cultivars of plants, fruits, and vegetables that

are resistant to attack by specific diseases so that a

fungicide may not be required. The damage done by

fungi (pathogens) depends on the host plant–patho-

gen–fungicide interaction. Different mechanisms of

fungitoxicity can operate in different hosts and envir-

onments so that standard measures may not work in

every situation. More information on mechanisms

that influence host–pathogen interactions, predictive

tools for use in the field, and wider options of

treatment are desirable to obviate development of

resistance to fungicides.

Types of Compound

0002 Fungicides used for preharvest control of fungal

and bacterial infections of commercial crops at the

beginning of the 20th century were simple inorganic

compounds. Organic chemicals began to be de-

veloped for use as general agricultural fungicides

during the 1950s and many organic compounds,

which often have a specific biological action, have

been marketed since then. The structural types of

chemicals used as fungicides have changed as newer

molecules have been found to give more effective

control than the earlier ones, and better technologies

have been developed for manufacture, making them

more cost-effective. However, a significant propor-

tion of inorganic (probably over a third of the total)

and older organic compounds (probably about a

quarter of the total) are used worldwide.

0003Fungicides used in agriculture and food storage

may be systemic or nonsystemic, eradicant, curative,

or protectant, or a combination of these effects. Era-

dicant fungicides are only active against the later,

visible stages of the fungal life cycle. Curative fungi-

cides are active against the early but postpenetrative

effects of fungal action. Protectant fungicides prevent

infection and are active against spore germination,

germination development, and growth.

0004Although about one-third of organic fungicides can

exist in more than one stereochemical form, i.e., can

be chiral, only about 1–2% of the products marketed

are sold as single isomers. Most of such formulations

are mixtures of isomers.

0005This entry outlines the subject at the end of 1999

and some more recent material has also been

included. International common names are used.

Fungicides are grouped mainly in terms of their bio-

chemical mechanism of fungicidal action (in as far as

this is known):

0006General cell toxicants

0007Inhibition of biosynthesis of microtubules

2832 FUNGICIDES

3.0008 Inhibition of methionine biosynthesis

0009 Inhibition of ribosomal RNA synthesis

0010 Inhibition of sterol biosynthesis

0011 Inhibition of melanin biosynthesis

0012 Glutathione system targeting

0013 Uncoupling oxidative phosphorylation

0014 Inhibition of respiratory chain in the mitochon-

dria

10.

0015 Inhibition of mitochondrial electron transport

11.

0016 Inhibition of fungal biosynthesis of nucleic acids

12.

0017 Inhibition of glycerophospholipid biosynthesis

13.

0018 Inhibition of protein synthesis

14.

0019 Acquired systemic resistance

15.

0020 Biological control

16.

0021 Unknown or very uncertain mechanisms of action

This list is not exhaustive and it should be realized

that a fungicide may exhibit control by more than one

mechanism. Grouping in terms of chemical structure

so as to cover most known agricultural fungicides can

be arranged within this framework. The chemical

structures of some representative organic fungicides

within each type are given in Table 1; again, the lists

are not exhaustive. Only a few of the many possible

compounds of a chemical structural group listed will

show sufficient fungicidal activity and be of practical

use in the field.

0022 A significant number of fungicides are now

generic and off-patent. Such chemicals can be manu-

factured by any company provided that the manu-

facturing process satisfies the legal requirements of

the country in which it is situated. Health and safety

regulations of any country in which the fungicide is

then used will, of course, still need to be complied with

(see below).

Use

Pathogens Controlled

0023 Fungicides of various types have been successful in

controlling most major diseases in growing crops

intended for market. The commercially important dis-

eases are (in an order of relative importance): leaf spot

diseases, late blight/downy mildew, rice diseases, fruit

rots, cereal seed-borne diseases, powdery mildews,

cereal stem diseases, rusts, and smuts. Diseases in

particular crops which it is commercially essential to

control with fungicides are given in Table 2.

0024 Fungicides are also used to control many posthar-

vest diseases that cause rapid and extensive break-

down of high-moisture commodities and pose serious

problems. Some infections, such as Monilinia fructi-

colis in stone fruits, will have started in the field.

Storage rots in potatoes may be controlled with suit-

able fungicide treatment in store, e.g., 2-butylamine.

0025Some crop diseases caused by fungi are still difficult

to control with chemicals, e.g., eyespot of cereals can

only be partially controlled and a fungicide has only

very recently been developed that is effective against

take-all of wheat.

Mode of Action

0026Fungicidal action is not simply interaction between

fungicide and fungus; it involves the host (plant) and

its environment. Hence plant variety, temperature,

humidity, cultivation regime, and several other

factors play a part in the control of fungal attack.

For effective action, careful timing of fungicide appli-

cations in relation to the stages of development of

infection is essential. The persistence of a fungicide

on the surface or within the plant is an important

factor in deciding whether to use that chemical.

0027Many older-type fungicides, e.g., copper and

dithiocarbamates, are surface-acting and protectant

in action; they are fungistatic and do not prevent

infection. They are also multisite in action.

0028The highly effective, modern, systemic fungicides

are often curative and protectant as well as eradicant,

i.e., they are fungitoxic. Systemic fungicides are often

selective in the range of pathogens they effectively

control: they act on a specific receptor or process,

e.g., are sterol C14-demethylation inhibitors. How-

ever, there are some uncertainties about the mechanism

of action of some fungicides and different mechanisms

can operate in different hosts/environments, e.g.,

carpropamid has two different modes of action.

0029The build-up of resistance to some groups of

fungicides, further discussed in the next section, is

considered to be related to single-site attack on the

mechanism of fungal cells. Detailed discussion of the

biochemistry of the mechanism of action of individ-

ual fungicides and of resistance of diseases to control

by fungicides is beyond the scope of this article and

may be followed up elsewhere (see Further Reading).

0030The systemic activity of fungicides takes place

almost entirely through the xylem. Fungicides are

usually applied to the foliage/leaves of plants, al-

though some are effective through root uptake. At-

tempts have been made to design fungicides that will

translocate through the phloem but without success.

Systemic fungicides are generally longer-lasting than

the older surface-acting chemicals.

0031The mode of action of the groups of fungicides

listed above is now discussed in outline:

0032General cell toxicants. Numerous multiple-site,

nonselective older chemicals are widely used. This

is particularly the case in some less well-developed

countries as these chemicals cost less than more

recent selective and systemic fungicides. Their

FUNGICIDES 2833

tbl0001 Table 1 Grouping of fungicides in terms of their biochemical mechanism of fungicidal action and chemical structure

Mechanism of action Chemical structural group Example(s) with chemical formula

Multisite nonselective Diverse Copper (Cu

2þ

)

Sulfur (S)

Dichlofluanid

Alkylenebisdithiocarbamates

NHCH

−−−−

where x is large and = y þ z

(polymeric)

Mancozeb

Inhibition of biosynthesis of microtubules Benzimidazoles

NHCOOCH

Carbendazim

N-arylcarbamates

(CH

)

CHO.CONH

Diethofencarb

Inhibition of methionine biosynthesis Anilinopyrimidines

Pyrimethanil

Inhibition of ribosomal RNA synthesis Acylalanines

CH(CH

)COOCH

COCH

Metalaxyl

Sterol biosynthesis inhibition

14a-demethylation inhibitors

Triazoles

Propiconazole (4 stereoisomers)

Imidazoles

OCH

CH CH

Imazalil

Continued

2834 FUNGICIDES

Mechanism of action Chemical structural group Example(s) with chemical formula

Some 6-membered heterocyclics

C(OH)

Fenarimol

-reductase and D

isomerase inhibitors

Morpholines

2n+1

Where n = 11,12,13,

or 14 (60−70%)

Tridemorph

Piperidines

(CH

)

Fenpropidin

Melanin biosynthesis inhibition

Dithianon

Targeting the glutathione system Dicarboximides

NCONHCH(CH

)

Iprodione

Uncoupling oxidative phosphorylation

Fluazinam

Inhibition of respiratory

chain in mitochondria

E-b-methoxyacrylates

COOCH

Azoxystrobin

Continued

Table 1 Continued

FUNGICIDES 2835

Mechanism of action Chemical structural group Example(s) with chemical formula

Inhibition of mitochondrial electron transport Hydroxypyrimidines

NHC

Ethirimol

Inhibition of fungal biosynthesis

of nucleic acids

Carboxanilides

(oxazolidinones)

Famoxadone

Inhibition of glycerophospholipid bisynthesis Diverse

Edifenphos

Inhibition of protein synthesis Microbiological origin

NN NH

HOOC

Blasticidin S

Acquired systemic resistance

OCH

Probenazole

Biological control

Unknown or very

uncertain mechanisms of

action

Organophosphorus compounds

COOC

Pyrazophos

Aromatic hydrocarbons

Quintozene

Table 1 Continued

2836 FUNGICIDES

preventive action is mainly due to inhibition of

spore germination related to the blocking of several

thiol-containing enzymes involved in spore respir-

ation. Copper (Cu

2þ

) fungicides are among the

oldest known fungicides (e.g., as Bordeaux mixture,

with lime) and are simply protectant. Sulfur and

lime sulfur are also protectant. The alkylenebisi-

dithiocarbamates (EBDCs), e.g., mancozeb, became

commercially viable in the 1960s and are essentially

surface-acting protectant fungicides. However, in

recent years they have been closely scrutinized on

toxicological grounds and their use is now restricted

in some countries. Dichlofluanid, tolylfluanid, and

captan are likewise contact multiple-site fungicides

and have protectant and curative action. Orthophe-

nylphenol is used as a dip and on wrapping paper to

control storage diseases in citrus fruit.

0033 Inhibition of biosynthesis of microtubules. Several

benzimidazoles, e.g., carbendazim, benomyl,

inhibit biosynthesis through forming complexes

with b-tubulin leading to increased acid pro-

duction and polymerization of tubulin. Some

N-arylcarbamates, e.g., diethofencarb, are also

multiplication inhibitors. These are systemic fun-

gicides having a wide range of action and are both

protectant and curative.

0034 Inhibition of methionine biosynthesis. Anilino-

pyrimidines, e.g., pyrimethanil, cyprodinil, can

inhibit methionine synthesis. These chemicals are

systemic and both protectant and eradicant. They

act primarily on the process of penetration of fungi

into their host so that the excretion of hydrolytic

enzymes is blocked.

0035Inhibition of ribosomal RNA synthesis. Several

acylanilines, e.g. metalaxyl, oxadixyl, and related

compounds, are systemic, eradicant, and protec-

tant fungicides which are selective and good for

controlling Oomycetes and Phytophthora spp.

diseases. (Carboxanilides, although of an acylala-

nine structure, have a different mode of action from

the above and are considered separately below.)

0036Sterol biosynthesis inhibitors (SBIs). There are two

groups:

0037C14a-demethylation inhibitors (DMIs) which

interfere with cytochrome P-450

. The chem-

ical structural types present in these compounds

are: triazoles, e.g., bitertanol, propiconazole;

imidazoles, e.g., imazalil, prochloraz; and

some 6-membered heterocyclics, e.g., fenari-

mol, triforine. They are systemic, being trans-

located in the xylem, and have protectant and

curative action; some have an eradicant action.

They are effective against Ascomycetes, Basi-

diomycetes, and Fungi imperfecti spp., but are

not effective against Oomycetes spp.

0038D

-reductase and D

! D

isomerase inhibi-

tors. Several morpholines, e.g., tridemorph,

and piperidines, e.g., fenpropidin, are systemic

fungicides of this type and have eradicant

action while affording some protection. The

use of tridemorph has been revoked in the UK.

0039Melanin biosynthesis inhibitors (MBIs). These

fungicides, e.g., carpropanid or dithianon, are

protectant and partly eradicant in action.

0040Glutathione system targeting. Some dicarboxi-

mides, such as iprodione, which is a contact fungi-

cide with preventive and eradicant action, and

vinclozolin, which is again nonsystemic with pro-

tectant action, are effective in controlling Botrytis

spp. and Sclerotonia spp.

0041Uncoupling of oxidative phosphorylation. Fluazi-

nam, which is protectant with good residual effect

but little eradicant and systemic activity, acts as a

potent uncoupler of oxidative phosphorylation

leading to disorder of the mitochondrial

membrane (other factors may also be involved).

Fenpiclonil, a phenylpyrrole, and fentin fungicides

also inhibit oxidative phosphorylation.

0042Inhibition of respiratory chain in the mitochon-

dria. A number of E-b-methoxyacrylates are

specific inhibitors of the cytochrome bc

complex

(complex III) in the mitochondrial respiratory

chain. Azoxystrobin has protectant, eradicant,

translaminar, and systemic properties. It is broad-

spectrum in action against the major groups

of pathogenic diseases that attack crops and is a

tbl0002 Table 2 Important diseases controlled by fungicides in the field

Crop Important diseases against which fungicides are used

Barley Loose smut (Ustilago nuda), stripe

(Puccinia striiformis)

Rice Rice blast (Magnaporthe grisea, anam.

Piricularia oryzae), sheath blast (Rhizoctonia solani,

anam. Thanatephorus cucumeris)

Wheat Rusts (Puccinia spp.), bunts (Tilletia spp.), loose

smut (Ustilago spp.)

Potato Late blight (Phytophthora infestans)

Cocoa Black pod (Phytophthora palmivora)

Coffee Leaf rust (Hemileia vastatrix), berry disease

(Colletotrichum coffeanum)

Banana Black and brown (yellow) Sigatoka (Mycosphaerella

spp.), Panama disease (Fusarium oxysporum)

Grapes Powdery mildew (Uncinula necator), downy mildew

(Plasmopora viticola), Botrytis cinerea

Top fruit Apple scab (Ventura inaequalis), pear scab (V. p i r i n a ),

powdery mildew (Podesphaera leucotricha)

Cotton Macrosporiosis (Alternaria macrospora), seedling

disease complex

Vegetables Powdery mildew (Sphaerotheca fuliginea), early

blight (Verticillium spp.),damping off (Pythium

spp.)

Sugar beet Leaf spot (Cerospora spp.)

FUNGICIDES 2837