Development of disease

Overwinter: ascospore, thick walled Conidia 1st inoculum : ascospore Penetration : directly through cuticle or through stoma Habit: intercellular between cuticle and epidermis Habitat : biotrophs Dissemination : by wind Interest : complicated (by budding of ascospore and conidia) More susceptible period : low temp, high humidity; Older plant is more resistance than young one

Control

Fungicide spray late fall or early springs Bordeaux mixture.

Chlorothalonil applied twice (Late fall and early spring).

Diseases caused by chytridiomycota

Chytrids lack true mycelium round or irrigular shaped thallus cell wall: chitin, maturation

thick-walled resting spore or sporangia.

Local spread of disease depends on moisture. Synchytrium &physoderma do not kill host but

stimulate it to divide. Overwinter as resting spore in soil or

spherical,irrigular shaped thallus in host tissue. Resting spore gives zoospore –cyst-2ry zoospore.

Soil- water inhabiting

Olpidium: root disease of many kinds.

Synchytrium: Black wart of potato.

Physoderma.

P. alfalfae : crown wart of alfalfa.

P. maydis: brown spot disease of corn.

Olpidium is a vector for six plant virus : TNV (Tobacco necrtrotic virus), lettuce big

vein virus

Disease caused by zygomycota

Mycelium without cross walls- non motile spore- sporangia.

resting spore=(2 similar morphological units).

Terrestrial fungi-spore floating around in air Saprophytic, weak parasite cause soft rot or molds.

Rhizopus are opportunistic pathogen human.

Three genera cause disease to plants

1. Choanephora: soft rot of floral part ,fruit squash, pumkin, peper, okra.

2. Rhizopus common bread mold fungi.3. Mucor soft root corms ,bulbs, veg flower ,seed It colonizes the tissues which it killed by growing and enzyme

secreting. Endomycorrhizae Glomus, Endogone, associated with root

benificial plant.

Rhizopus causes

Soft root of fruit and fleshly organ Hull rot of maturing almond

Head rot of some flowerDuring harvesting, storage, transit, marketing

e.g. sweet potato, strawberry, peaches, flowers…..

http://www.davidlnelson.md/Cazadero/CazImages/Common_mold_Rhizopus.jpg

Symptoms

Water soaked area ,very soft. If skin of organ intact loss water mummy. Exuding liquid- bushy growth on surface. Give off a mildly pleasant smell. yeast & bacteria sour odor. Loss of moisture dry mummify. Loss of moisture slow break down &

disintegrate in a leaky water rot.

Development of disease

Growth pectinolytic enzymes.

dissolves pectin in middle lamella Loss cohesion soft rot.

cellulytic enzumes degredation of cellulose.

Rhizopus lives more like a saprophyte than a parasite.

Factors help to develop disease are humidity, temp and insufficient maturity.

When food supply diminsh, fungus form zygospores (resting spore).

Plant form cork layer to inhibit more fungal growth.

Control

Avoid wounding.

clean containers CuSO4, formaldehyde, S-fume, chlorpicrin.

Storage: Temp. below 10 c for strawberry, 25-30C & 90% hum. 10-14 days(to form cork layer.

Biocontrol: Candida, Pichia.

FOLIAR DISEASES CAUSED BY ASCOMYCETES AND DEUTEROMYCETES (MITOSPORIC FUNGI)

Ascomycota Some of the most common Ascomycetes causing primarily

foliar diseases include the following:

-Cochliobolus, several species of which cause leaf spots, blights and root rots on most cereals and grasses.

-Blumeriella (Higginsia), causing leaf spot or shot hole of cherries and plums. Magnaporthe, M. grisea causing the rice blast disease and gray leaf spot of other cereals and of turf grasses.

Microcyclus, M. ulei causing South American leaf blight of rubber.

- Dothistroma, D. pini causing needle blight of pines Elytroderma deformans, causing a leaf spot and witches'-broom of pines

- Lirula, causing needle blight of spruce Lophodermium seditiosum,

Deuteromycota

Some of the most common mitosporic fungi causing primarily foliar but also other symptoms on a large variety of host plants are Alternaria, Ascochyta, Cercospora, Cladosporium, Phyllosticta, Pyricularia, Septoria, and Stemphylium. Many others are less common

Similarity

The foliar spots and blights caused by imperfect fungi on numerous hosts and are quite diverse.

The disease cycles and controls of these diseases are quite similar, however. Nevertheless, considerable variability may exist among diseases on different hosts, or when the diseases develop under different environmental conditions

Dissemination

It spread to other plants by wind, wind-blown rain, water, and insects and cause more infections .

Overwinter In most cases, these fungi overwinter primarily as conidia or

mycelium in fallen leaves or other plant debris. Some, however, can overwinter as conidia or mycelium in or on seed of infected plants or as conidia in the soil.

When perennial plants are infected, the pathogens may overwinter as mycelium in infected tissues of the plant.

When these fungi are carried with the seed of annual plants,

damping-off of seedlings may develop.

Control

Control of such diseases is accomplished primarily by using resistant varieties and employing fungicidal sprays or seed treatments.

In some diseases, however, use of disease-free seed, removal and destruction of contaminated debris, or both may be most important.

ALTERNARIA DISEASES Alternaria diseases : as leaf spots and blights.

damping-off of seedlings, stem rots, and tuber and fruit rots

early blight of potato and tomato, leaf spot and fruit spot on cucurbits and onions and on apple and citrus,

fruit rot on cherry and sour cherry, core rot of apple, and rot of lemons and oranges.

Symptoms

The leaf spots are generally dark brown to black, often numerous and enlarging, and usually developing in concentric rings, which give the spots a target-like appearance.

Lower, senescent leaves are usually attacked first, but the disease progresses upward and makes affected leaves turn yellowish, become senescent, and either dry up and droop or fall off.

Symptoms of stem Dark sunken spots develop on branches and stems

of plants such as tomato.

Stem lesions developing on seedlings may form cankers, which may enlarge, girdle the stem, and kill the plant.

In belowground parts, such as potato tubers, dark, slightly sunken lesions develop that may be up to 2 centimeters in diameter and 5 to 6 millimeters in depth.

Symtoms of fruits

Alternaria may attack fruits when they approach maturity in some hosts at the blossom end .

The spots may be small and sunken or may enlarge to cover most of the fruit, and they may be leathery and have a black, velvety surface layer of fungus growth and spores.

Development of Disease

Overwinter

Overwinter :as mycelium or spores in infected plant debris and in or on seeds.

If the fungus is carried with the seed, it may attack the seedling, usually after emergence, and cause damping-off or stem lesions and collar rot.

The PathogenAlternaria spp

Penetration & dissemination The germinating spores penetrate susceptible tissue

directly or through wounds

and soon produce new conidia that are further spread by wind, splashing rain, etc.

With few exceptions, Alternaria diseases are more prevalent in older, senescing tissues, particularly on plants growing poorly because of some kind of stress.

Habit

infect Actually, many species of Alternaria are mostly saprophytic, i.e., they cannot living plant tissues but grow only on dead or decaying plant tissues and, almost, on senescent or old tissues such as old petals, old leaves, and ripe fruit.

Therefore, it is often difficult to decide whether an Alternaria fungus found on diseased tissue is the cause of the disease or a secondary contaminant.

Control

Adequate nitrogen fertilizer generally reduces the rate of infection by Alternaria.

Alternaria diseases are controlled primarily through the use of resistant varieties, disease-free or treated seed, and chemical sprays with appropriate fungicides.

Crop rotation, removal and burning of plant debris, if infected, and eradication of weed hosts help reduce the inoculum for subsequent plantings of susceptible crops.

Biocontrol&UV

Several mycoparasitic fungi are known to parasitize various species of Alternaria, but so far none has been developed into an effective biological control of the pathogen.

In the greenhouse, infections by UV at least some Alternaria species can be reduced drastically by covering the greenhouse with special UV light-absorbing film, as filtering out light inhibits spore formation by these fungi.

VASCULAR WILTS CAUSED

BY ASCOMYCETES AND

DEUTEROMYCETES (MITOSPORIC FUNGI)

Vascular Wilt Vascular wilts are widespread, very destructive, spectacular,

and frightening plant diseases.

They appear as more or less rapid wilting, browning, and dying leaves and succulent shoots of plants followed by death of the whole plant.

Wilts occur as a result of the presence and activities of the pathogen in the xylem vessels of the plant.

Entire plants may die within a matter of weeks, although in perennials, death may not occur until several months or years after infection.

Common Genera

There are four genera of fungi that cause vascular wilts: Ceratocystis, Ophiostoma, Fusarium, and Verticillium. Each of them causes disease on several important crop, forest, and ornamental plants.

Ceratocystis causes the vascular wilt of oak Ophiostoma causes the vascular wilt of elm trees,

known as Dutch elm disease (O. novo-ulmi).

Fusarium spp

Fusarium causes vascular wilts of vegetables and flowers, herbaceous perennial ornamentals, plantation crops, and the mimosa tree (silk tree).

Most of the wilt-causing Fusarium fungi belong to the species Fusarium oxysporum.

Specificity Different host plants are attacked by special forms or

races of the fungus. The fungus that attacks tomato is designated F.oxysporum f. sp. Lycopersic; cucurbits, F. oxysporum f. sp. conglutinans; banana; F. oxysporum f. sp. cubense; cotton, F. oxysporum f. sp. vasinfectum; carnation, F. oxysporum f. sp. dianthii; and so on.

http://www.icrisat.org/vasat/learning_resources/pigeonpea/disease/disesae_fig/fusarium_wilt3.jpg

Verticillium spp

Verticillium causes vascular wilts of vegetables, flowers, field crops, perennial ornamentals, and fruit and forest trees. Two species, Verticillium albo-atrum, and V. dahliae, attack hundreds of kinds of plants, causing wilts and losses of varying severity.

Fusarium Wilts

Fusarial wilts are most severe under warm soil conditions and in greenhouses.

Most fusarial wilts have disease cycles and develop similar to those of the Fusarium wilt of tomato.

FUSARIUM WILT OF TOMATO

The disease causes great losses, especially on susceptible varieties and when soil and air temperatures are high .

Infected plants become stunted and soon wilt and

finally die. Occasionally, entire fields of tomatoes are killed or

damaged severely before a crop can be harvested.

Symptoms

The first symptoms appear as slight vein clearing on the outer, younger leaflets

. Subsequently, the older leaves show epinasty caused by drooping of the petioles.

.

. It followed by stunting of the plants, yellowing of the lower leaves, occasional formation of adventitious roots, wilting of leaves and young stems, defoliation, marginal necrosis of the remaining leaves, and finally death of the plant.

Internal symptoms A combination of the processes of vessel clogging by

mycelium, spores, gels, gums, and tyloses and crushing of the vessels by proliferating adjacent parenchyma cells, is responsible for the breakdown of the water economy of the infected plant.

When the leaves transpire more water than the roots and stem can transport to them, the stomata close and the leaves wilt and finally die, followed by death of the rest of the plant.

The fungus then invades all tissues of the plant extensively, reaches the surface of the dead plant, and there sporulates profusely.

The PathogenFusarium oxysporum f. sp.

lycopersici.

Development of Disease

Dormant Stage &Dissemination

The pathogen is a soil inhabitant. it survives in infected plant debris in the soil as mycelium and in all its spore forms but, most commonly, especially in the cooler temperate regions, as chlamydospores

It spreads over short distances by means of water and contaminated farm equipment and over long distances in infected transplants or in the soil carried with them.

Penetration&Habit The germ tube of spores or the mycelium penetrates root tips

directly or enters the roots through wounds or at the point of formation of lateral roots.

through the root cortex intercellularly, and when it reaches the xylem vessels it enters them through the pits.

and travels through them, mostly upward, toward the stem and crown of the plant.

The mycelium also advances laterally into the adjacent vessels, penetrating them through the pits.

Control Use of tomato varieties resistant to the fungus Seedbed sterilization and crop rotation,

Use of healthy seed and transplants

hot-water treatment of seed .

Biological control Control may involve prior inoculation of plants with

nonpathogenic strains of F. oxysporum or

The use of antagonistic fungi, such asTrichoderma and Gliocladium, Pseudomonas fluorescens

Solar heating (solarization) of field soil by covering with transparent plastic film during the summer also reduces disease incidence.

systemic acquired resistance More recently, it was shown that spraying tomato

plants with a suspension of zoospores of the oomycete Phytophthora cryptogea induces the development of systemic acquired resistance in the tomato plants, which remained free of wilt following inoculation with F. oxysporum f. sp. lycopersici.

Although promising, none of these methods have been used for control of Fusarium wilt in practice so far.

FRUIT AND GENERAL DISEASES CAUSED BY ASCOMYCETES AND DEUTEROMYCETES (MITOSPORIC FUNGI)

Most common ascomycete Claviceps, C. purpurea, causing ergot of cereals and grasses

Diaporthe, D. citri, causing melanose of citrus fruits, D, phaseolorum causing stem canker of soybeans

Botryosphaeria (Physalospora), causing black rot, frogeye leaf spot, and canker of apple (P. obtusa),

Didymella, D. bryoniae causing the gummy stem blight of cucurbits

Guignardia, G. bidwellii causing the black rot of grape

Venturia inaequalis, causing apple scab

Monilinia, three species causing brown rot of stone fruits Moniliophthora, causing the Monilia pod rot of cacao

The most common mitosporic fungus

The most common mitosporic fungus causing fruit and general diseases on plants is Botrytis, causing blossom blights and fruit rots but also damping-off, stem cankers or rots, leaf spots, and tuber, corm, bulb, and root rots of many vegetables, flowers, small fruits, and other fruit trees.

Another mitosporic fungus causing a variety of diseases is Phomopsis.

BOTRYTIS DISEASES Botrytis diseases are probably the most common and most widely distributed

diseases of vegetables, ornamentals, fruits, and even some field crops throughout the world.

They are the most common diseases of greenhouse-grown crops. Botrytis diseases appear primarily as blossom blights and fruit rots, but also as, damping-off, stem cankers or rots, leaf spots, and tuber, corm, and bulb rots.

Under humid conditions, the fungus produces a noticeable gray-mold fruiting layer on the affected tissues that is characteristic of Botrytis diseases.

Some of the most serious diseases caused by Botrytis include gray mold of strawberry, grapes and of many vegetables, calyx end rot of apples, onion blast and neck rot, blight or gray mold of many ornamentals, bulb rot of amaryllis, corm rot of gladiolus, and others.

Botrytis also causes secondary soft rots of fruits and vegetables in storage, transit, and market.

Symptoms In the field, blossom blights often precede and lead to fruit rots and stem

rots. The fungus becomes established in flower petals, particularly when they begin to age, and there it produces abundant mycelium. In cool, humid weather the mycelium produces large numbers of conidia, which may cause further infections. The mycelium grows and invades the inflorescence, which becomes covered with a whitish-gray or light brown cobweb-like mold. The fungus then heads to the pedicel, which rots and lets the buds and lowers lop over. The fungus later moves from the petals into the fruit and causes a blossom end rot of the fruit, which advances and may destroy part or all of the fruit. Infected fruit and succulent stems become soft, watery, and light brown. As the tissue rots, the epidermis cracks open and the fungus fruits abundantly. Flat black sclerotia may appear on the surface or are sunken within the wrinkled, dry tissue (Fig. 32).

Damping-off of seedlings due to Botrytis occurs primarily in cold frames, where the humidity is high. It also occurs in the field if the seed is contaminated with sclerotia of the fungus or if fungus mycelium or sclerotia are present in the soil.

Some species of Botrytis cause leaf spots on their hosts, e.g., on gladiolus, onion, and tulip. The spots are small and yellowish at first but later become larger, whitish gray or tan, and sunken, coalesce, and frequently involve the entire leaf.

Stem lesions usually appear on succulent stems or stalks. They may spread through the stalk and cause it to weaken and break over at the point of infection. In wet weather the diseased parts become covered with a grayish-brown coat of fungus spores. Sclerotia may also be produced on infected stems.

Infection of belowground parts, such as bulbs, corms, tubers, and roots, may begin while these organs are still in the ground or at harvest. Infected tissues usually appear soft and watery at first, but later they turn brown and become spongy or corky and light in weight. Black sclerotia are often found on the surface or intermingled with the rotted tissues and mycelium (Fig. 33).

The pathogen, Botrytis cinerea The pathogen, Botrytis cinerea and a few other species,

produces abundant gray mycelium and long, branched conidiophores that have rounded apical cells hearing clusters of colorless or gray, one-celled, ovoid conidia. The conidiophores and clusters of conidia resemble a grape-like cluster. Conidia are released readily in humid weather and are carried by air currents. The fungus frequently produces black, hard, flat, irregular sclerotia. Some species of Botrytis occasionally produce a Botryotinia perfect stage in which ascospores are produced in an apothecium.

Development of Disease Development of Disease Botrytis overwinters in the soil as mycelium in decaying plant debris and

as sclerotia. The fungus does not seem to infect seeds, but it can be spread with seed contaminated with sclerotia the size of the seed or with bits of plant debris infected with the fungus. The fungus requires cool (18-23°C), damp weather for best growth, sporulation, spore release and germination, and establishment of infection. The pathogen is active at low temperatures and causes considerable losses on crops kept for long periods in storage, even if the temperatures are between 0 and 10oC. Germinating spores penetrate tissues through wounds and produce mycelium on old flower petals, dying foliage, dead bulb scales, and so on. Botrytis sclerotia usually germinate by producing mycelia threads that can infect directly, but in a few cases sclerotia germinate by producing apothecia and ascospores (Fig. 34).

Control The control of Botrytis diseases is aided by the removal of infected and infested debris from the field and storage rooms and

by providing conditions for proper aeration and quick drying of plants and plant products. I In greenhouses, humidity should be reduced by ventilation and heating. Storage organs such as onion bulbs can be protected

by keeping them at 32 to 50oC for 2 to 4 days to remove excess moisture and then keeping them at 3oC in as dry an environment as possible.

Biological control of Botrytis gray mold was obtained by spraying the flowers or fruits with spore suspensions of certain antagonistic fungi and with mixtures of several biocontrol fungi and bacteria, but this is not used in practice yet.

Control of Botrytis in the field through chemical sprays has been only partially successful, especially in cool, damp weather. Sprays with a number of broad-spectrum of systemic fungicides give excellent control of Botrytis on a wide variety of crops.

Botrytis strains resistant to several systemic and even to some broad-spectrum fungicides have been found in various crops sprayed with these chemicals.

Therefore, the use of different fungicides and fungicide combinations is recommended to reduce the appearance and establishment of resistant strains