FARMERS’ TRAININGDiseases and Insect Pests

ARUN KUMARFormer Principal Scientist, CAZRI, Jodhpur, India

Diseases 14.1% Insects 10.2% Weeds 12.2% Total av. looses 36.5%

ESTIMATED ANNUAL LOSSES WORLDWIDE DUE TO DISEASES

Losses are more in developing world and less in developed world

PART I- (A) IMPORTANCE OF PLANT PATHOLOGY

• The disease triangle: plant, pathogen and the environment

Disease

Susceptible Host

Favo

rable

envir

onmen

t

Virulent

Pathogen

HEALTHY AND DISEASED PLANT• A plant is considered healthy if it

functions to the best of its genetic ability

• When a plant function is interfered by a microorganism or environmental factor the plant becomes diseased

• The visible changes are expressed in the form of symptoms or signs in a diseased plant

SYMPTOMS OF PLANT DISEASES CAUSED BY FUNGI

Alternaria leaf spot Cercospora leaf spot Powdery mildew

Downy mildew Leaf Blast Ergot Stem rust

SYMPTOMS OF BACTERIAL DISEASES

Citrus canker by Xanthomonas citri Angular leaf spot of cotton

Lima bean spot

NUTRITIONAL DEFICIENCY IN PLANTS

Iron deficiency in maize Zinc deficiency in tomato

Types of malformations with a healthy ear head (extreme left)

Infected plant showing asexual sporulation as half-leaf symptom. 

DOWNY MILDEW DISEASE OF PEARL MILLET

SPHACELOTHECA- COVERED KERNEL SMUT

Teliospores of S. sorghi are seed-borne and germinate within the seed.

Seedling plants are infected, but symptoms generally are not apparent until heading.

Smutted ovaries are covered by a thick membrane

Seedling infection by sporidia produced by teleutospores present on seed or in the soil

USTILAGO-THE SMUTS Plant is systemically

infected, looks normal till ears appear

Seeds covered with thin layer, which ruptures to disperse black sooty mass of teleutospores

In case of corn the fungus forms galls on all above-ground parts

wheat

Corn

ALTERNARIA LEAF SPOT Most characteristic symptom is brown or dark spots

on older leaves. The circular to angular spots enlarge and soon

develop dark, concentric rings or ridges, giving a target-like appearance.

Spotted leaves soon turn yellow, wither, and drop. Leaf spots are usually covered with dark, velvety

spores (conidia).

Guar

Sesame

DISEASE CAUSING AGENTS

Non Infectious diseases

• Diseases caused by low or high temperature

• Diseases caused by lack or excess soil water

• Diseases caused by lack or excess light• Diseases caused by lack of oxygen• Diseases caused by air pollution• Diseases caused by nutrient deficiencies• Diseases caused by mineral toxicities

Bacterial Diseases

• Bacterial galls: In some cases, toxic materials are produced that cause plant tissues of roots, stems or leaves to grow abnormally as in crown gall.

• Bacterial leaf spot disease: The bacteria usually enter through leaf stomata.

• Symptoms include water-soaking, slimy texture, fishy or rotten odor, confined initially between leaf veins resulting in discrete spots that have straight sides and appear angular.

Disease Development• Infections occur through leaf scars and wounds. These

give rise to small cankers in which the bacteria survive the winter.

• Rain or water splash, and pruning tools spread the bacterium.

• Bacteria overwinter in active cankers, in infected buds, and on the surface of infected and healthy trees and weeds.

• The bacterium reproduces best between 21ºC and 25ºC.

• Generally disease seems to be more severe after cold winters and prolonged spring rains.

Viruses

• Viruses are "submicroscopic" entities that infect individual host plant cells.

• Viruses are obligate parasites: They can only replicate themselves within a host's cell.

• In the virus infected plant, production of chlorophyll may cease (chlorosis, necrosis)

• Cells may either grow and divide rapidly or may grow very slowly and be unable to divide

Viral Diseases• > 400 viruses infect plants; few are

economically important pathogens• The infection remains forever• Viruses are transmitted from plant to

plant by living factors: insects, mites, fungi and nematodes

• Or non-living factors: rubbing, abrasion or other mechanical means (including grafting or other forms of vegetative propagation)

• Occasionally transmitted in seed.

Virus Disease SymptomsFour types of major

symptoms :1. Lack of chlorophyll formation

in normally green organs

2. Stunting or other growth inhibition

3. Distortions

4. Necrotic areas or lesions

Plant Pathology: The Practice

• Some plant disease makes the plant poisonous to humans and animals such as ergot of rye, pearl millet and wheat

• Several fungi will make hay poisonous• May contain nematodes which carry virus• Plant disease causes great financial loss

from a few % to total crop• The cost of disease control must be less

than cost of crop loss

FUNGI AS RESOURCEFUNGI AS RESOURCE Fungi constitute largely

unexploited resource Strains of fungi maintained in

culture collections In over 200 collections number

exceeds 1 lack 70 thousand Around 7 thousand species are

represented

Economic Importance of Fungi

FERMENTED FOODSTUFFS / DRINKSFERMENTED FOODSTUFFS / DRINKS In Asia many

fermented foodstuffs and drinks are based on fungi

This include species of Aspergillus, Monascus, Mucor and Rhizopus

Role of certain Penicillium spp.

(P. camembertii and P. roquefortii) is important in cheese production

BIOTECHNOLOGICAL APPLICATIONSBIOTECHNOLOGICAL APPLICATIONS

FOOD FOR MANFOOD FOR MAN Mushrooms grown in pastures and

forests of different geographical regions

No. of species are more than 500 Around 20 spp. are currently

exploited commercially (Agaricus, Lentinula, Tricholoma, Volvariella, Pleurotus etc. )

EDIBLE MUSHROOMS

Podaxis pistillaris

Phellorinia inquinansMorchella sp.

Pleurotus sajor-caju

ANTIBIOTIC INDUSTRYANTIBIOTIC INDUSTRY

Antibiotic is a chemical, effective at very low concentration, produced by or derived from certain fungi, bacteria, and other organisms, that can destroy or inhibit the growth of other micro-organisms. Antibiotics are widely used in the prevention and treatment of infectious diseases.

INDUSTRIAL CHEMICALSCHEMICAL

Aspergillus niger Citric and gluconic acid

Eremothecium ashbyii Vitamins - riboflavin Aureobasidium pullulans

Polysaccharides- pullulan

Rhizomucor pusillusPenicillium roquefortiiAspergillus oryzae

Enzymes - Rennin LipaseProtease

Trichoderma viride Cellulase

FUNGUS

                                                                                 

a). Beauveria bassiana produces creamish-white conidia alternately on an extending tip of a conidiophore

b). Metarhizium anisopliae produces greenish- conidia in chains from phialides

Beauveria bassiana

Metarhizium anisopliae

                                                                                                         

Sporulation of Beauveria on green cockchafer beetle

Metarhizium spores on locust               

Beauveria bassiana on leaf hopper h

Metarhizium anisopliae on bug and beetle beetles

INSECT BIOCONTROLINSECT BIOCONTROL

BIOCONTROL OF PLANT DISEASESBIOCONTROL OF PLANT DISEASES

FUNGUS PLANT DISEASETrichoderma harzianum

Leaf blights, wilts, root rot

T. koningii T. pseudokoningii

Foot rot, Collar rotRoot and Butt rot in tree

T. viride Die-back or anthracnose, LCD of Chilli

Gliocladium virens Downy Mildew of pearl millet

Trichoderma Colonizing Fungal Mycelium

BIOFERTILIZER FOR FORESTRY AND ORCHID INDUSTRYBIOFERTILIZER FOR FORESTRY AND ORCHID INDUSTRY

Sclerocystis microcarpa Gigaspora margaritaGlomus macrocarpum

VESICULAR ARBUSCULAR MYCORRHIZA (VAM Fungi)150 species in Zygomycotina

Obligate symbiotic association with agricultural,medicinal,shrubs and treesImprove plant growth and nutrient uptake(phosphorus), reduce water stressProduce growth promoters and induce resistance to plants against pathogens

Role in organic farming and hardening in plant tissue culture

ECONOMICALLY IMPORTANT PHYTOPATHOGENIC BACTERIA

Bacterial wilt of egg plant Bacterial canker & gumming in Prunus sp.

R

S

R

R

Exposed cambium necrotic, discolored area

USEFUL BACTERIAL PATHOGENSTaxon Function

Agrobacterium radiobacter

Biological control, Biodegradation of Atrazine

A. tumefaciens Plasmid vector for plant transformation

Erwinia amylovora Source of harpin, an elicitor of disease resistance in plants

Xanthomonas campestris pv. Campestris

Xanthan gum, a polysaccharide used in food production, agriculture, cosmetics and pharmaceuticals.

Several plant associated bacteria

Restriction endonucleases, enzymes used for specific cutting of DNA in scientific research

PLANT PATHOGENSPLANT PATHOGENS

VIRUSESVIRUSES

TULIPOTULIPOMANIAMANIA

SYMPTOMS OF VIRAL DISEASES

MAJOR DISEASE SYMPTOMS ARE

• Leaf yellowing (either of the whole leaf or in a pattern of stripes or blotches)

• Leaf distortion (e.g. curling) and/or

• Other growth distortions (e.g. stunting of the whole plant, abnormalities in flower or fruit formation)

LEAF CURL OF CHILLI (LCD)

Disease is caused by Begomovirus (ChiLCuV)

The disease is transmitted by insect vectors such as

whitefly and thrips

• Curling of upper leaves with shortened internodes

• Severely infected plants produce clusters of reduced sized leaves with fewer flowers and fruits

• Small sized fruits are produced with deformed seeds Small sized fruits

GOLDEN YELLOW BEAN MOSAIC OF MOTHBEAN (Vigna aconitifolia )

There are two types of infections: localized and systemic. In localized infections (as shown here), the upper leaves are affected; in systemic infections, the

whole plant becomes chlorotic and stunted. The virus is transmitted by whiteflies

3. Transmission Through Vectors

(i). Insects: Some insect species are the vector of plant viruses which can carry/ transmit viruses from infected plants to the healthy plants e.g.

• aphid (potato virus Y) • white flies (tobacco/chilli leaf curl) • beetles (cowpea mosaic virus) • mealy bugs (cacao mottle leaf) • thrips (tomato spotted wilt) • lace bugs (sugar beet viruses) • mites (sterility mosaic of arhar)• leaf hoppers (beet curly top, rice tungro) • plant-hoppers (maize mosaic)• tree hopper (tomato pseudo curly top)

(ii) NematodesFive genera of nematodes viz., Xiphinema, Longidorus, Paralongidorus, Trichodorus and Paratrichodorus can transmit plant viruses (iii) Fungi Some species of fungi can also transmit viruses e.g. Olpiduim brassicae (tobacco necrosis), O. cucurbitacearum (cucumber necrosis), Polymyxa graminis (oat mosaic, wheat mosaic), P. betae (beet necrotic yellow vein) and Spongospora subterranea (potato mop top) etc.

4. Dodder transmission

Many viruses can be transmitted through dodder (Cuscuta spp.). Dodder transmission is used in the laboratory to transfer viruses from the hosts

5. Transmission through seeds and pollens

Seed coat (testa), embryo, and also pollens of some plants can transmit viruses. e.g. alfalfa mosaic, barley stripe mosaic, bean common mosaic and lettuce mosaic are transmitted by both seeds and pollens of Medicago sativa, Hordeum vulgare, Phaseolus vulgaris and Lactuca sativa, respectively.

• The multicolor effects of intricate lines and flame-like streaks on the petals were vivid and spectacular and made them even more exotic-looking, highly sought-after plants

• Tulip breaking virus is a member of the potato virus Y group

Variegated tulips was a complete mystery till 1927 when it was known that this is due to the infection of a VIRUS (Tulip break virus, Tulip mosaic virus or TBV )

PLANT PATHOGENSPLANT PATHOGENS MYCOPLASMA (MLO)MYCOPLASMA (MLO)

SUBJECT EXPERTDr. ARUN KUMARDr. ARUN KUMAR

PART-IVPART-IV

• Several hundred important food, vegetable, and fruit crops; ornamental plants; and timber and shade trees are affected

• Aster yellows phytoplasma causes major economic losses of vegetable crops (lettuce, carrot, and celery), ornamental plants (gladiolus, hydrangea, China aster, and purple coneflower)

• Peanut and Sweet potato witches’ broom, sesame and soybean phyllody cause considerable losses of these crops in Asia

MYCOPLASMA DISEASES

• Proliferation of axillary buds/shoots changing in “witches’ broom” symptoms

• Sterility of flowers• Abnormal internode elongation• Generalized stunting with yellowing or

reddening of leaves, decline and death of plant• Phytoplasmas are transmitted by insects

belonging to the families- Cicadellidae, Cixidae, Psyllidae, Delphacidae and Derbidae

SYMPTOMS AND TRANSMISSIONProfound disturbance in the normal balance of growth

regulators, leading to virescence or phyllody (green leaf-like structures instead of flowers) results in:

Empoasca fabae

INSECT VECTORS OF MLOs

Nephotettix cincticeps

SESAMUM PHYLLODY

2nd & 4th from left healthy

Sesamum Phyllody in severity

Little leaf disease of Eggplant or BrinjalFirst reported from India by Thomas and Krishnaswami in 1939

MYCOPLASMA LIKE ORGANISMS

Electron micrographs of cross sections of sieve tubes showing variations in the size and shape of

phytoplasmas infecting plants

PLANT PATHOGENSPLANT PATHOGENS Phanerogamic Parasites

SUBJECT EXPERTDr. ARUN KUMARDr. ARUN KUMAR

PART- IVPART- IV

LORANTHUS

It is non chlorophyllous, leaf less parasitic seed plant

It is yellow, pink or orange in colour and attached to the host

They do not bear leaves but have minute functionless scale leaves

                                                                                                                     

CUSCUTA or DODDER (Amarbel)

CUSCUTA / DODDER

CUCUTA FLOWERS

FRUITS OF CUSCUTA

SEVERE INFESTATION OF DODDER

OROBANCHE

Lauki-Mula

Striga hermonthica parasitising sorghum crop

THANKS