Diseases of Onion and garlic and their management

WEL-COME

Assignment on

DISEASES OF ONION AND GARLIC AND

THEIR MANAGEMENT

Submitted By: - Vakaliya Mustufa

M. Sc. (Agri.)Agril. Entomology,

BACA, AAU, ANAND

Sub. PL. Path.- 509 (Diseases of Vegetables and Spices Crops)

DISEASES OF ONION AND GARLIC AND THEIR MANAGEMENT

IntroductionOnion (Allium cepa L.) and garlic (Allium sativum L.) are two most important bulbous vegetables crops cultivated in many countries of the world. In India, it is grown in an area of 0.29 Mha With annual production of 3.14 million tones production of bulbs for local consumption as well as for export. The main onion growing states are Maharashtra, Uttar Pradesh, Haryana, Punjab, Gujarat, TamilNadu, Andhra Pradesh. Among these Maharashtra is leading with about 26 percent of country production (Pathak, 1994).The onion and garlic crops are susceptible to several diseases of fungal, bacterial and viral diseases which cause substantial production losses. A detailed review of various diseases affecting these crops along with management strategies is given below.

FUNGAL DISEASES

1. DOWNEY MILDEWC.O. Peronospora destructor (Berk)Geographical distributionThe diseases was first time reported from England in 1841 by Berkeley (Yarwood, 1943) subsequently , it was reported from Bermuda , USA, Canada, brazil , Iraq, Holland, Australia etc. in India, these diseases was first time reported from Kashmir valley during 1974-75 seasons(Mirakhur et. al.,1978).LossesIn India, the losses from these diseases ranges from 12-75 per cent in crop yield depending on the time of diseases outbreak and disease severity (Sugha and Singh, 1991).

Symptoms • Symptoms differ with the type of infection. Infection develops from

three different sources like systemically infected perennating leaves, plants grown from infected onion bulbs or from local lesion resulting from air borne inoculum.

• Systematic infection occurs when the plants are raised from diseased bulbs or infected seedlings used for planting.

• Plants raised from such bulbs remain stunted, become distorted and light green in colour.

• In humid weather condition, sporulation develop on the leaves and cover them with felty whitish to grayish fungal growth.

• In secondary and local infections, spots with greenish and chlorotic zones appear and at times at the points of infection , the plants fall off.

• In humid weather the fungus develops as white to purplish downy growth on these spots. In such cases undersized bulbs are produced.

Favorable condition• Cool, moist nights and moderate warm days

for development of disease• Heavy dews atmosphere• Cloudy days• Humid atmosphere with 4 to 250C temp. with

optimum 130C• Germination of pathogen occur at temp. 7 to

160C and the optimum lies between 10 to 130C

Disease cycleThe carry-over of the fungus from the one season to another may occur as mycelium in the bulbs, sees or soil , as oospore on or in the seeds or in plant debris (yarwood, 1943) and systemically infected onion bulbs are another important source of primary infection ,. Bur role of oospores has not been established in induction of disease even under controlled conditions(Virayni, 1981). The onion seedlings from disease prone play important role in introduction of disease in new localities. Secondary infection is caused by wind borne sporangia disseminated from the plants with primary infection.

Management• cultural practices like use of healthy bulbs for planting.• collection and destruction of infected crop debris• crop rotation with non-host crops • Application of balanced doses of fertilizers along with

potassium as the increases in level of potassium decreases diseases severity (Devlash and Sugha, 1997).

• use of resistant varieties like as IC-48045, IC-32149, DOP-11(sharma, 1997)

• Spray crop with various systematic and non-systematic fungicides like as Mancozeb or Zineb , Copper oxychloride, propineb, metalaxyl+ Mancozeb etc. have been reported to check downy mildew effectively (Mir et.al.,1987, Khalid et. al.,2002)

2. PURPLE BLOTCHC.O.: Alternaria porri(Ellis) Cif. Geographical distribution The disease was first time reported from Bombay (Ajrekar, 1921). Since then has been reported from many states of the country like Maharashtra, Gujarat,Tamilnadu, Rajasthan, Haryana and Punjab (Pandotra, 1964).LossesThe disease causes 20-25 per cent losses to the onion seed crop (Pandotra, 1981)

Symptoms• The characteristic symptoms of the diseaseappear as a

small, light coloured, sunken lesions, which become zonated with purplish center.

• These lesions rapidly enlarge and eventually girdle the leaf or inflorescence stalk.

• In moist weather the surface of the spot is covered with the brown or almost black sporulation of the fungus.

• Usually the affected leaf or stem falls down and dies within 3 or 4 weeks under favorable environmental conditions.

• In garlic these disease appears on leaves with the similar symptoms.

Disease cycleThe fungus survives from one season to other in infected plants debris as dormant mycelium. the fungus can also survive in diseased onion leaves and seed stalk debris for 12 month buried at 5 to7.5 cm depth (Gupta and Pathak, 1988).wherever the chlamydospores of the fungus are formed they can also serve as source of perrenation, invasion takes place either through stomata or directly through the cuticle , to form an intercellular mycelium, which in turn forms conidiospores and conidia. Conidia produced on the primary infection lesions serve as the source of secondary inoculum.

Favorable condition: • The fungus requires rain or persistent dews for reproduction and

penetration.• The optimum temperature for disease development is 21 – 300C and

relative humidity above 90%. Management• various cultural practices like use of healthy seed/planting materials ,

crop rotation with non-related crops, collection and destruction of infected debris , good drainage , summer ploughing (Srivashtva et. al. 1996)

• use of recommended doses of fertilizers• Hot water (500C for 20 min. )soak was found to be highly effective in

reducing seed borne inoculum (Aveling et. al.,1993)• Use of disease resistance varieties viz. Pusa red, IIHR-56-1, hybrid PVM-7

etc.• Spraying crop with Copper oxychloride , mancozeb, Metalaxyl+

mancozeb , Fosetyl-as, Difenconazole etc with recommended doses.(Sastrahidayat, 1994).

3. STEMPHYLIUM BLIGHTC.O :Stemphylium vesicarium (Wallr.)Geographical distributionThe disease has been reported from united states , south Africa , Venezuela(Millar et. al. 1978) in India the occurrence of this disease on onion was first reported from Uttar Pradesh during 1973 while on garlic it was reported on Kullu ,Himachal Pradesh during 1973 (Singh and Sharma, 1977).

Symptoms• The main symptoms of the disease appear in the

middle of the leaf as small, yellow to pale orange flecks or streaks which later develop into elongated spindle shaped diffused spots surrounded by characteristic pinkish margin.

• The spots turn grey at the center and later become brown to dark brown with the appearance of conidiospores and conidia of the fungus.

• Gradually the entire foliage is blighted. Similar symptoms also develops on inflorescence stalks.

Disease cycle• The pathogen survives in infected plant debris. In

favorable weather spores from the debris are splashed to the lower leaves and cause infection. Spores produced on the primary infections cause secondary infections.Management

• use of healthy planting materials • two to three years crop rotation with non host crops• Collection and destruction of infected plant debris to

reduce inoculum load.• Spraying crop with Carbendezim 0.2 % or

Propineb ,chlorothalonil, difenconazole etc. for effective management of this diseases.

4. BASAL ROT/BULB ROT C.O.: Fusarium oxysporum f.sp.cepaeGeographical distribution

• This disease is prevalent in almost all parts of the world where onion are grown ( Evertset al.,1985). In India the occurrences of this disease was first reported from Rajasthan (Mathur and Sankhala, 1963).

Symptoms• The main symptoms appear as wilting and rapid

dying back of leaves from the tips of the plant near maturity.

• Watery decay on open the soft bulbs are evident. • Infected garlic show reddish or reddish purple

discoloration on stem and bulbs early in the season with some discoloration on bulb sheath at harvest.

• Infected stem plates may show of brown discoloration.

• Infected bulbs may rot during storage.

Disease cycle• The fungus over winter in the infected onion sets, garlic cloves and in

soil, in soil the fungus perennates as chlamydospores. The pathogen may be disseminated widely through infected onion sets and garlic cloves.Management

• The diseases can be kept under check by following cultural practices like long crop Rotation, mixed cropping with tobacco and jowar , green manuring to increases antagonistic microbial population in soil.

• Resistance varieties. Viz. hf-555, IIHR Yellow, Hybrid-1.• Spraying crop with Mancozeb, carbendazim have been found good

efficacy against basal rot (Naik and Burden , 1981, Gupta et. al.,2000).

• Pre-harvest sprays of Carbendezim(0.1%) reduced decay of stored onion even after 5 month of storage (Shrivastva and Tiwari , 1997).

5. RUSTC.O. Puccinia porri (Sow.)Geographical distribution The diseases is widely distributed in temperate regions of the world. The occurrences of the diseases has been reported from different parts of Europe, USA, and Asia (Walker, 1951). In India, the prevalence of this disease on garlic has been reported from Ludhiana in 1987 (Sadhu and Kang, 1988).

Symptoms• Early symptoms appear as of small yellow to white flecks,

streaks and spots on leaves.• As these small areas expand, the leaf tissue covering them

breaks and the orange spores (urediniospores) of the fungus become visible as pustules.

• Resulting in complete yellowing,wilting and drying of the leaves. • As the disease progresses, teliospores may occur on the same

leaves, resulting in black pustules on infected onions and chives, symptoms consist of small, white to tan spots.

• The orange pustules often from concentric group on the spot periphery.

• Disease severity on onion and chives is significantly less severe than on garlic.

Disease cycle• The fungus probably overwinters in plant debris and also in

the soil as teliospores. Urediniospores are repeative spores and spread and cause secondary infection.Favorable condition

• Cool temperature, high humidity, no heavy rainfall, frequently dews formation and moderate day temperatureManagement

• Crop rotation and sanitation help in reducing the initial inoculum level in the soil.

• Eradication of alternative hosts from nearby area to avoid contamination is useful.

• Spraying crop with Copper oxychloride, or Triadimefon ,Propiconazole etc. at recommended doses.

6. ONION SMUDGEC.O.: Colletotrichum circinans (Berk)Geographical distribution The disease is wide spread in temperate regions of the world and was first described in England. Since than it has been reported from many countries of the world like USA, japan , Argentina and European countries. The disease is of common occurrence in India also.

Symptoms• The disease is characterized as small dark green to black

dots that appear on the outer scales. • These small dotes are scattered over the surface of the

bulbs or grouped together in concentric rings giving a smudge appearance to the white onions.

• During moist conditions, acervuli of the fungus develop on the infected areas and spore masses and the setae can be easily recognized fleshy scales resulting in yellow depressions on the bulb.Favorable condition

• Temperature ranges from 10 to 320 C• Excessive rainfall.• Moist condition are essential for production of conidia.

Management

• Cultural practices like as crop rotation , good drainage, use of healthy seed materials, (Walker, 1952)

• Protection of the harvested crop from rains, rapid and through curing and provision of well- ventilated storage also reduce the incidence of the disease.

• Pre-harvest sprays either of Carbendezim or Mancozeb reduce the infection of this disease under storage conditions.

VIRAL DISEASES7. GARLIC MOSAICC.O.: Garlic Mosaic Virus (GMV)

Geographical distribution This viral disease prevalent in different garlic growing areas. (Ahlawat, 1997). Reported the disease from Laimpong town of Darjeeling (West Bengal) India for the first time.Symptoms

• The infected plants show typical mosaic symptoms and yield is also recorded comparatively less than in healthy plants.

• Foliar symptoms can vary greatly, but most consists of mild to severe mosaic, streaking , striping and chlorotic mottling.

• Symptoms are often most evident in the youngest leaves.• The overall effect is generally bulb size and yield reductions of up to

50%.

Transmission • The virus is easily transmissible by two species

of aphids viz. Myzus persicae Suzl. And Aphis gosypii Grover to garlic only and not to any other crop.Management

• Crop rotation and field sanitation help in reducing the diseases.

• spraying crop with Dimethoate (roger) or Monocrotophos 36 SL for control of vector.

STORAGE DISEASESNeck rotC.O.: Botrytis alliiSymptoms:

• This is a wide spread and most destructive storage disease of onion

• Mildly pungent varieties are more affected• It has latent infection, thus infection takes place in the field• Pathogen causes softening of scales giving a water soaked

appearance• Under moist condition a greyish sporulatingmycelial mat

develops on the surface of the scales, causing secondary spread of the diseases.

Disease cycle:• The fungus persists saprophytically on dead onion tissue, on

humus in soil and as sclerotia near the surface of previous onion crop soils. Sclerotia germinate in moist weather and produced conidia that are disseminated by air currents.Management:

• Dusting the seed with benomyl 1g/kg as soon as after harvest

• Rapid and thorough drying of bulbs after harvest• Apply recommended doses of nitrogenous fertilizers• Presence of downy mildew, weeds and wind barriers should

be avoided• Onions should be stored in slatted crates or wooden tubs so

that air can circulate thorough and around them.