Artigo (Fito) Traduzindo

8/12/2019 Artigo (Fito) Traduzindo

1/10


2/10

University of WyomingCooperative Extension ServiceCollege of Agriculture

Trade or brand names used in this publication are used only for the purpose of educational information. The information given

herein is supplied with the understanding that no discrimination is intended, and no endorsement information of products by the

Agricultural Research Service, Federal Extension Service, or State Cooperative Extension Service is implied. Nor does it imply

approval of products to the exclusion of others which may also be suitable.

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30,1914, in cooperation with the U.S. Department

of Agriculture, Glen Whipple, Director, Cooperative Extension Service, University of Wyoming Laramie, WY. 82071.

Persons seeking admission, employment or access to programs of the University of Wyoming shall be considered without regard

to race, color, national origin, sex, age, religion, political belief, handicap, or veteran status.


3/10

AN INTRODUCTION TO PLANT PATHOLOGY AND PLANT DISEASE

MANAGEMENT

Gary D. Franc, Associate Professor

Department of Plant Sciences

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

THE DISEASE TRIANGLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

The Pathogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Fungi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Bacteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Nematodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Viruses and Viroids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

The Host . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

The Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Moisture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Wind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Other Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

DISEASE DIAGNOS IS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

DISEASE DEVELOPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

PLANT DISEASE CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Exclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Evasion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Eradication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Environmental Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Chemical Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Fumigants a nd Sterilants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Nematicides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Seed T reatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Protectan ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Systemics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Integrated Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

ADDITIONAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

PLANT PATHOLOGY TERMINOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

ADDITIONAL READING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7


4/10

1

INTRODUCTION

Anyone working as a p lant professio nal will need to

determine why plants appear abnormal and what

control measures, if any, are appropriate. This manual

introduces the reader to the subject of plant pathology

and the information it contains w ill aid in

understanding how plant diseases develop as well as

the various methods used for control. Terminology

importan t to the study of plant dise ases is ident ified

for the reader by printing in bold/italicsand isdefined either in t he text or in the section on 'Plan t

Pathology Terminology.'

THE DISEASE TRIANGLE

Plant disease results when a specific agent, such as

pe rs is tent un favo rabl e envi ronm ental cond itio ns or

the acti vity of a pat hogen, disrupts physiolo gical

function s causing p lants to deviate from normal

development. The word 'persisten t' is used to

distinguish between a disease which develops over

time and an injury which occurs, more or less,

instantaneously.

Noninfec tious diseases , perhaps m ore app ropria tely

called disorders , do not spread from plant to plant.

These disorders result from the pla nt's exposure to

such factors as unfavorable weather, mechanical

damage, nutrient deficiencies, excess salts or toxic

chemicals. Although disorders canpredispose plants

to infection by pathogens, d isorders are not directly

treated using pesticides. The remainder of this manual

emphasizes the discussion of infectious plant diseases

caused by pathogens.

An infectious disease results when apathogen lives

in close association with the host plant. The pathogenis functioning as a parasite since this relationship

usually benefits the pathogen at the host's expe nse.

Although r elationships resulting in disease are often

complex, three critical factors must be p resent in

order for a particular disease to result. The three

factors necessary for disease development are (1) the

pathogen must be p resen t, (2) a susceptible host must

be presen t and (3 ) the proper en vironm ent must be

present, permit ting infecti on of the host . These factors

give us the concept of the disease triangle (Figure 1).

Production practices followed by large growers andhome ga rdene rs serve to modif y the int eract ion of

these thr ee factors t o reduce (o r unwittingly increase)

the overall impact and severity of plant diseases.

Plant professionals use the disease triang le concept to

simplify remembering and understanding how a

part ic ular di seas e deve lops an d why vari ous cont ro l

strategies are used. The pathogen, host and

environment are discussed in more detail below.

The Pathogen

Fungi, bacteria, viruses, viroids, nemato des, parasitic

plants (dodder and mistle toe) , phytoplasmas, and

protozoa are examples of var ious pathogens tha t

cause plant diseases. General descriptions of the most

common and economically important classes of

pathogen s are lis ted belo w. I t is importan t to

remember that man y beneficial microorganisms exist

in nature, and that only a small frac tion infects plants.

Fungi. Bread molds and mushrooms are examples offungi familiar to all of us. Most of the 100,000 fungus

species identified by scientists are only saproph ytes

and not capable of infecting plants. However, more

than 8,000 plant pathogenic species have been

identified making f ungi the most numerous and

economically impor tant class of plant pat hogens. The

great diversity o f fungi and the co mplex and intricate

life cycles of some pla nt pathogenic species make

generalizations difficult.

Plant infection by fun gi occu rs via a g reat variety of

mechanisms. Some species directly penetrate plant

surfaces or enter through n atural openings, whileothers require wounds or i njury for infection. During

disease development, many species of fungi produce

spores which are dispersed by wind, water or by other

means. Each spore may cause a new infection

resulting in a rapid increase in disease incidence and

severity. Some fungi form special re sting spore s

whic h perm it surv ival for lon g peri ods of time

(several months or years) in soil or plant d ebris.

Fungi are identified primarily from their mo rphology,

with emphasis placed on their reproductive structures.

Laboratory techniques can be used to induce

sporulat ion in many fung i if reproduc tive structuresare not vi sible on pla nt tissue.

Bacteria. Bacteria are perhap s the second most

economically important class of plant pathogens.

Bacteria are considered more primitive than fungi and

general ly have simpl er life cycles. With few

exceptions, bacteria exist as single cells and increase

in numbers by dividing in to two cells during a


5/10

2

process c alled binary fissio n. Their ab ili ty to rap idly

reproduce when environmental conditions are

favorabl e give bacteria their potential for causing an

explosive increase in disease.

Some species are ab le to survive o n healthy-

appearing plant surfaces as epiphytes, and only cause

disease when environmental conditions are favorable

or when injuries, such as those c aused by hail, occur.

Overwintering weed hosts, infected seedstocks orcontami nated cr op debris may serve as the initial

source of bacterial inoculum. The p resence of certain

bacterial species on p lant surfaces increa ses frost

sensitivity while other species are able to move lon g

distances in aerosols or i rrigation water.

Bacterial ooze on plant surfaces or bacterial

streamin g can aid in the identification of bacterial

diseases when working in the field. However,

laboratory methods are usually required for

identification.

Nematodes. Nemat odes ar e microscopic round wo rmsthat reside in the soil. Disease induced by nematodes

usual ly resu lts in po or plant growth a nd may be

overlooked when there are no healthy plants av ailable

for comparison. Roots of poorly growing plants

should be examined carefully for evidence of

nematode feeding. Sym ptoms ma y be deform ed roots

or galls.

Feeding by plant-pathogenic species can cause

disease by direct interference with normal plant

developmen t, by interacting with other disease

causi ng organisms or by acting as a vector for

pathogens. Al though most plant pa thogen ic spec iesaffect only roots, some species infect stem, foliar and

bud tissues.

Viruses and Viroids. Viruses and viroids are

extremely tiny particles consisting of protein and

genetic materia l (viruses) or genetic materi al with no

associated protein (viroids). Biologists disagree on

whether viruses and viroids should be classified as

'living' since they are true obligate para sites incapable

of carrying out any physiol ogical processes in the

absence of a host.

In order for disease to spread, these particles must bephys ical ly inserted into a l iv ing h ost c el l by vectors

includi ng insects or ma n, or they ma y be transmitted

through s eeds, tubers, grafts or merel y by physica l

contact between healthy and infected plants. The

metho d(s) of transmission for a specific virus or

viroid is a charact eristic of that pathogen a nd the

disease it causes. Once in serted into a host, the

physiologic al processe s of the cel l are re directed into

the manufacture of more particles. Chemical controls

usually target insec t vectors and some disinfe ctants

inactivate viruse s, rendering the m noninfectious.

Most virus diseases are identified by characteristic

symptoms coupled with electron microscopy and/or

serological tests. Viroid identification requires even

more specialized detection methods.

The HostLevels of resistanceor susceptibility of the host plant

will affect disease development. Plants with high

level s of res istanc e are essentially immun e or not

susceptible and do not allow the pathogen to become

established, e ven if present. Plants with lower levels

of resistance may become i nfected but only al low the

pathogen to develop slowly, limiting the ec onomic

impact of the disease to accep table levels. Stress,

such as that bro ught on by an unfavorable

environment, poor fe rtility or irrigation will affect a

host pla nt's ability to resi st infec tion and , therefore,

also effects dise ase development.

In some cases, resistan ce in th e host i s overc ome by

the pathogen, resulting in rapid and devastating

disease development . This risk is increased if large

produc ti on are as are plan ted to a monocu ltur e of

identical hosts. Therefore, genetic diversity of host

plants will decre ase the r isk of catastroph ic losses.

The Environment

Environmental conditions play a large role in disease

development and disease severity. However, broad

generalizations about environmental effects have

many exceptions. The disease triangle shows that the

environment influences disease development byinteracting with b oth the host and pathogen.

Furthermore, environmental stress can predispose

plants to infect ious disease. Several important

environmental factors are given below.

Temperature. Temperature greatly influences disease

development. Temperatures that are not ideal for the

host plant induce stress and predispose plants to

disease by lowering host r esistance. This may occur

for hosts de termined t o be resistant under normal

growing conditions.

Temperature also affects the amount of inoculumavail able. Cold winters interr upt the disease c ycle by

killing pathogens or vectors that otherwise may

persist unti l the next growing s eason. During the

growing se ason, temperature will directly influence

the pathogens abi lity to reproduce and infe ct the

host. This will directly affect the rate of disease

development, disease severity or even if diseased

plan ts wi ll ap pear in the firs t place.


6/10

3

Moisture. Abundant, prolonged or repeated moisture

is the predominant factor in the development of most

epidemics caused by fungi, bacteria and nematodes.

Although relationships can be complex, rain, greater

relative humidity or prolonged dew periods will

increase the likelihood of many, but not all, diseases.

Moisture affects the host by inducing new growth that

may be more susceptible, or re sistant, to infection.

Moisture also induces sporulation of fungi,replication of bacteria and m obility of nematodes,

thus, increasing th e amount and disper sal of available

inoculum. For other p athogens, rain may suppress

movement of insects acting as vectors of pathogens,

thus reducing disease spread.

Wind. Fungal spores, vectors, and, to a lessor e xtent,

bacter ia and n ematodes , can be dispersed b y the

action of wind. This will en able pathogens to move

from infected plants to healthy plants. Wind can also

injur e hosts, thus providing an a venue f or infect ion

and/or increasing susceptibility to some p athogens.

Other Factors. There are many factors including light

inten sity, light quality, soil pH, fertility an d soil type

that influence disease development. Relationships can

be complex with environmental influences being

exerted on the host and the pathogen. Each disease

must be studied carefully to determine what

interactions ar e important for its development.

DISEA SE DIA GNOSIS

Diagn osis requires knowledge of what i s normal for

the host p lant as well as knowledge of p roblems that

occur red in the past. Accurate diagn osis is critical for

deci ding if a disease is present and if effective cont rolmeasures are available or justified. An accurate

diagnosis is based upon rec ognition of specific signs

of the pathogen on the host as well as the presence of

symptoms on the host.

Signsare defined as the vi sible presence of the

pathogen or pro ducts of the pathogen on the host

plan t. Fungal sp ores , f ruiting st ructures that bear

spores and bacterial ooze are all examples of signs. In

contrast, symp tom sare the e xternal and internal

react ions or a lterat ions of a plant as a result of

disease. For example, dead spots in leaves or bark,

rotte n spots i n fruits or tube rs, swel lings on roots orbranch es , clus tere d b ranc hes, unnatu ra l colo r or

shape and vascular discoloration in stems are all

symptoms that may aid in diagnosis of a plant

disease.

Because most diseases encountered have previously

been described, it is usually p ossible to di agnose a

specimen by comparison with the symptoms and signs

of pathoge ns already described for diseases of that

part icular host . Books, manuals and p ictures a re very

useful aids in diagnosis of many plant diseases.

Experienced diagnosticians recognize many diseases

on sight or are able to quickly narrow down

poss ib il ities t o s everal choices. Although experience

is the best teacher, the general guidelines listed below

will help focus attention on information needed for

accurate diagnosis.

1. Carefully describe the

characteristics that make the plant

appear abnormal (symptoms).

2. Determine the distribution of

symptoms in the host by looking at

the entireplant.

3. Determine if evidence of the

pathogen (signs) exist.

4. Determine the distribution of

affected plants in the field.

If dia gnosis is still not p ossible , contac t fieldm en or

your local Cooperative Extension Educator for

assistance. Specimens can be mailed by your

Extension Educator to the University of Wyoming,

when additional assistance is required.

DISEASE DEVELOPMENT

Every i nfecti ous disea se requi res a series of

sequential ev ents in order for disease to develop. This

series of e vents is ca lled the disease cycle. Although

the specific characteristics are unique for each

disease, the general events in the disease cycl e are;

(1) dispersal of the pathogen to the host, (2)

penetrat ion a nd infect ion of the host, (3) i nvasion a nd

colonization o f the host, (4) reproduction o f the

pa thogen , (5) pathogen di spersa l (6) pa thogen

survival between growing seasons and/or in the

absence of a host.

Completion of events #1-5 is onegenerationof the

pa th ogen and, depe nd ing on th e pa thogen , can be

repeated before the growing season ends at event #6.

The generation time and the number of generations a

pathogen completes dur ing one season determines the

dynamics of disease development and the potential

for plant or crop loss. Graphic representations of


7/10

4

disea se severity over time are called disease progress

curvesand are discussed below for Fi gures 2, 3 and

4.

Mon ocyclic pathogens have a maximum of one

generation per growing season and possess a

characteristic disease progress curve (Figure 2).

Pathogens are monocyclic because environmental

conditions or other physical factors prevent repeating

events #1-5 until the next growing season; examples

are Verticilliumwilt and some other soil-borne

diseases. Other pathogens are monocyclic because

their life cycle requ ires at least one season to

complete; examples are cedar-apple rust and corn

smut.

Polycyc lic pathogens complete more than one

generation per growing season and, therefore, areable to reproduce and infect additional healthy plants

during the current gr owing season (Figure 3). As the

potent ial for the number o f generat ions in creases (i.e .,

the generation time decreases), so does the potential

for devastating losses. Some fung i have such short

gener ation times that steps i n the cy cle of

pathogenesis completely over lap r esulting in a

continuous series of new i nfections giving the

appearance of explosive disease development.

Examples of polycyclic pathogens can be found in

virtually all classes of p athogens including fungi,

bacter ia , nematodes and viruses. Several examples

are early and late bl ight of potatoes, and wheat a ndbean rust .

The time over which disease develops in a production

area or region for both monocyclic and polycyclic

diseases can vary from days to yea rs and is a

characteristic of the specific disease involved. Severe

losses ca n occur regardless of the speed at wh ich

disease develops and can result from both monocyclicand polycyclic pathogens.

PLANT DISEASE CONTROL

Control measures are used to interrupt or weaken at

least one of the six sequential events in the disease

cycle (see above). In ge neral, monocyclic dise ases are

most efficiently suppressed by reducing the amount of

the initial inoculum at events #1 and/or 6. P olycyclic

diseases are most effici ently suppressed by reducing

the in itial inoculum a nd/or by re ducing the rate of

disease increase that occurs when events #1-5 are

repeated. Various control methods commonly used to

reduce or eliminate disease are categorized below;much overlap exists between categories.

Exclusion. The disease tri angle illustrates that if the

pathogen and hos t rem ain separate d, no disea se wil l

develop. Disease co ntrol metho ds that maintain

separation can be very effective. However, this

approach to disease control is largely regulatory in

natu re and includes quara ntines, inspections, use of

pa thogen-f ree plan t mate rials, ce rtif icat ion o f s eed

stocks, and b y other means.

Evasion. The use of healthy seed, planting and

growing plants under environmental conditionsunfavorable for disease development, selecting early

(or late) planting and harvest dates and maintaining

the proper distance be tween rows and fields are all

examples of methods for evading disease. The se

practices inc rease the cha nce that the ho st wil l remain

healthy or go through it s susceptible stage be fore the

pathogen reaches the h ost .


8/10

5

Eradication. Eradication is the elimination or

destruction of the pathogen. Methods of eradication

include temporary removal and destruction of host

plants, chemical treatment of soil or seeds to k il l the

pathogen, and sanitation of eq uipment and s torages.

Growers routinely practice crop rotation to reduce the

amount of inoculum present to acceptable levels, by

growing a no n-host plant.

Resistance. Resistance is the growing of plants n otsusceptible to the di sease. Resistant cultivars are

usually developed through special breeding and

selection programs. Immunity or total resistance is

often unobtainable and many varieties have partial

resistance th at allo ws the pla nt to grow in spite of

contact with a pathogen.

Environmental Modification. Creating conditions

unfavorable for the pathogen is a practical disease

control method used by some growers. Proper

spacing of the plants in the field o r greenhouse will

aid in reducing humidity that favors development of

some diseases. Good soil drainage and properirrigation pr actic es are al so impor tant. Flooding fields

during the fallow period may also reduce the

incidence of some disease caused by soil borne

organisms. Environmental modification by drying

and/or refrigeration of harvested products is one of

the most common methods used to slow growth of

pa thogens a nd reduce disease.

Protection. Infection of plants may be reduced

throughprophy laxisor protection. Although

biolog ical control agen ts are used in some instances

to pro tect plants from infecti on, the mos t common

metho d to directly or indirectly protect p lants frompathogens is through the careful use o f chemicals.

Chemical Controls

Chemicals orpes ticidesare often used to help control

plant di seases . T he correc t timing of chemical

applications as well as choosing the proper chemical

is essential for good control. Labels provide

application information and the directions must be

followed.

Fumigants and Sterilants.These chemicals generally

have a broad range o f activity but are not applied to

growing plants. Soil fumigation is commo nly used toreduce nematode populations as well as other soil-

bo rne pa thogen s a nd pests. To ta l erad ic atio n o f

pa thogens and pest s is genera lly not poss ible.

Fumigants are typically expensive, difficult to apply,

highly toxic and nonselective in their activity.

Therefore, beneficial microorganisms and insects are

affected, as well.

Proper soil prepa ration, soil mo isture (appr oximately

70% field capacity) and soil temperature (55-85 F) is

critical for achieving uniform chemical distribution

and effective disease control. Methyl bromide and

chloropicrin are highly vo latile fumigants, and plastic

sheeting is require d to seal the soil surface during

their application. In contrast, metham sod ium is less

volatile and water can be used to seal the soil surface.

Label directions will give precise directions on the

soil conditions required and suitable applicationmethods.

Nemat icides. Fumigants are considered nematicides.

However, other liquid and granular chemical

formulations are available for nematode control, in

addition to fumigants. These products have low

volatility and can be applied before and after planting

many, particu larly non-food , crops. N ematicides k ill

nematodes that come in contact with the chemical and

may kill some insects, as well. Nematicides are

generally highly toxic and may contaminate ground

water when not used properly.

Seed Treatments.Seed treatments are typically

fungicides that protect the seed and germinating

seedling from infection and/or decay. Pathogens can

be seed-borne or soil-borne. S ome advantages of seed

treatments are that smal l amounts of chemical are

requi red and that seedlings are able to get o ff to a

strong start. Because treated seed is not to be used for

feed, food or processing, dyes are used to color

treated seed and treated seed should be properly

labeled. An excepti on is the treatment of high

moisture grains with acetic or propionic acid. Acid-

treated grain is commo nly used for livesto ck feed.

Protectants.These chemicals are usually applied to

the seed or foliage of the gro wing crop so that a

protec tive chemical barr ie r o ver the host surface

prev en ts the in itia l infect ion. These products must no t

be toxic to the hos t.

Systemics.These are applied to the seed or growing

crop and are often absorbed and transmitted

systemica lly within the plant. These substance s may

kill or suppress the pathogen growing within host

tissue and, therefore , may hav e a curative or

therapeutic effe ct. Some systemics have very

selective activity and, through repeated use, becomeineffec tive due to selection for insensitive funga l

isolates.

Integrated Methods

Frequently, a number of control methods are

integratedor used simultaneously to reduce the

economic loss of plant d iseases. Relying on a single

method for disease co ntrol frequently results in


9/10

6

failure. Integrated methods c an reduce costs

associated with more expensive control methods and

decrease the risk associated with dependence on a

single method of control. Added benefits of

integrated methods are that disease co ntrol is

generally greater than for each method used

individually (Figure 4).

ADDITIONAL INFORMATION

Numerous reference books and publ icat ions are

available that p rovide summaries of specific plant

diseases, their c ontrol, and photogra phs to aid

diagnosis. The professional society of plant

patholog ist s, The American Phytopathological

Society , offers many of these publications for sale at

reasonable prices (approximately $35.00). ContactAP Sat (800) 328-7560, or

write; 3340 Pilot Knob Road, St. Paul, MN 551 21-

2097. Some of the publications listed in the section

ADDITION AL READING are readily available

through AP S.

PLANT PATHOLOGY TERMINOLOGY

Atrophy- A lack of development of certain plant

parts or t issues .

Bactericide - A compound toxic to bacteria.

Canker - A diseased or dead area in the bark and

wood of trees or shrubs characterized by a drying out

of the tissues.Cell- The smallest unit that makes up a plant and

cons ists of the cellular contents (proto plasm)

surrounded by a cell wall.

Damping-off - A type of seedling di sease in which the

stem deca ys in the vicinity of or bel ow the soil line.

Disease Cycle - The chain of events involved in

disease development, including the stages of

developmen t of the pathogen and the effect of disease

on the host.

Ecology - The study which deals with the effect of

environmental fac tors, such as soil, climate, and

culture on the occurrence, severity, and distribution

of plant diseases.

Environment- The external conditions and influences

that surround living organisms.

Epidermis- The superficial layer o f cells occurring

on all plant parts.

Exudate - Material that has been fo rced out.Fungal - Relating to fung i.

Fungi cide - A compound tox ic to fungi.

Gall - An unusual en largement o n some portion of a

plant.

Host - The plant upon which a parasite lives.

Hyperplasia- A symptom due to an abnormal

increase in the number of individual cells.

Hypertrophy- An symptom due to an abnormal

increase in the size of individual cells.

Hyphae - Fungal filaments which collectively form

the mycelium of a fungus.

Immune- Cannot be infected by a given pathogen.

Incubation period - The period between the time theinoc ulum is introd uced o nto the host and the time

when the diseased condition becomes evident.

Infection - The process of the pathogen gaining

entrance to the host and becoming established as a

pa rasi te .

Infection court - Speci fic area on a plant whe re a

pathogen gains entranc e to the hos t.

Infest - To overrun or contaminate.

Inoculum - The pathogen, or its parts, that can cause

infection.

Inoculation- The process of transferr ing inoculum to

host.

Lesion - A diseased region of the host.Local invasion - That involving only a portion of the

plant.

Mummy- A dried, dise ased fruit.

Mycelium - The group of hyphae that form the fungal

body.

Necros is - A symptom marked by r apid death o f the

host or parts of the host.

Nemati ci de - A compound toxic to nematode s.

Obligate - Necessar y or essential.

Obligate parasite- Organisms that live on ly as

parasit es.

Pathogen- A disease-p roducing agent.

Pathogenicity- Ability of an organism to producedisease.

Pathology - The study of disease.

Pesticide - A compound toxic to a specific pest(s).

Physiology - The study of metabolic processes,

activities and phenomena related to life.

Predispose - Make favorable for.

Primar y infection - The first infection of a host by the

overwintering or over summering inoculum.


10/10

Artigo (Fito) Traduzindo

Documents

Transcript of Artigo (Fito) Traduzindo