Diseases of Citrus
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This document provides information on several diseases that affect citrus plants: 1. Citrus gumosis is caused by the oomycete Phytophthora citrophthora and leads to gummosis, bark cracking, and tree death. Prolonged water contact and wet soils promote spread. 2. Citrus scab, caused by Elsinoe fawcetti, forms wart-like lesions on leaves, twigs, and fruit, reducing fruit quality. It spreads via airborne conidia and prefers humid conditions. 3. Citrus canker, caused by Xanthomonas axonopodis pv. citri, forms small yellow spots on leaves, twigs, and
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Diseases of Citrus
- 1. DISEASES OF CITRUS Anurag Kerketta CHRS, Jagdalpur
- 2. Introduction • Citrus fruits have a prominent place among popular and extensively grown tropical and sub- tropical fruits. • After grapes and olives they are cultivated on larger area than any other fruits of these zones in the world. • Their wholesome nature, multifold nutritional and medicinal values have made them so important. • Citrus fruits possess greater adoptability to different climatic conditions, so are grown with equal success in tropical and subtropical regions.
- 3. DISEASES OF CITRUS 1. CITRUS GUMMOSIS: Phytophthora citrophthora 2. CITRUS SCAB: Elsinoe fawcetti 3. CITRUS CANKER: Xanthomanas campestris pv. Citri 4. DIPLODIA GUMMOSIS: Diplodia natalensis 5. CITRUS TRISTEZA/ QUICK DECLINE- Virus disease 6. CITRUS EXOCARTIS- Viroid disease 7. CITRUS GREENING- Phytoplasma disease
- 4. CITRUS GUMMOSIS/ LEAF FALL/ FOOT ROT Economic importance: • Gummosis is widespread in Punjab and Assam. • Lemons are highly susceptible compared to grapefruit, rough lemons and sweet orange. • In South India, it is common in the sweet orange.
- 5. Symptoms • Disease starts as water soaked large patches on the basal portions of the stem near the ground level. • First symptoms are dark staining of bark which progresses into the wood. • Bark in such parts dries, shrinks and cracks and shreds in lengthwise vertical strips. • Bark at the base is destroyed resulting in girdling and finally death of the tree.
- 6. • Later profuse exudation of gum from the bark of the trunk occurs. There may be a considerable amount of gum formation in sweet oranges, but relatively little in grapefruit. • Infection extends to crown roots. • Prior to death, the plant usually blossoms heavily and dies before the fruits mature.
- 7. Etiology C. O. Phytophthora citrophthora. Classification Phylum: Mastigomycotina Class: Oomycotaetes Order: Peronosporales Family: Peronosporaceae Genus: Phytophthora Species: P. citrophthora • Aseptate mycelia, zoospore are asexual spores produced in the sporangium, oospore are • sexual spores or resting/dormant spores borne in oogonium.
- 8. Epidemiology/Favourable conditions • Prolonged contact of trunk with water as in flood irrigation. • water logged areas and heavy soils predispose the disease. • Incidence is more in black soils than in light soils; high water table leads to high incidence. • The disease is severe in high rainfall areas.
- 9. Mode of spread and survival • PI: Dormant mycelia and oospore present in effected debris and infested soil. • SI: Zoospore spread through soil, irrigation water.
- 10. Management Preventive measures: • Selection of proper site with adequate drainage and high budding (30 to 46 cm or above). • Provision of an inner ring about 45 cm around the tree trunk to prevent moist soil. (Double ring method of irrigation) • Avoid irrigation water from coming in direct contact with the trunk. • Avoid injuries to crown roots or base of stem during cultural operations. • Use resistant sour orange rootstocks for propagating economic varieties • Painting Bordeaux paste or with ZnSO4, CuSO4, lime (5:1:4) to a height of about 60 cm above the ground level at least once a year.
- 11. Curative measures: • Scrape the diseased portion with a sharp knife. • Protect the cut surface with Bordeaux paste followed by spraying of 0.3% fosetyl- AL reduces the spread. • Soil drenching with 0.2% metalaxyl and 0.5% Trichoderma viride commercial formulation is also effective
- 12. Scab / Verucosis Economic Importance: • In India this disease is reported from Bengal, Punjab, Assam, Karnataka, Uttar Pradesh and Andhra Pradesh. • It is one of the common diseases of sour oranges, rough lemon, tangelos and Pummelo. • In Andhra Pradesh it is severe on Rangapur lime. The sweet oranges are mostly resistant to the disease.
- 13. Symptoms: • The disease attacks leaves, twigs and fruits. • The lesions on leaves in early stages consist of small, semi-translucent dots which become sharply defined pustular elevations usually on the underside, flat or somewhat depressed at the center. The opposite surface corresponding to the warty growth shows a circular depression with a pink to red centre. In later stages, leaves often become distorted, wrinkled, stunted and mis-shapened. • The twigs also develop similar lesions and the affected twigs are ultimately killed.
- 14. • On the fruit, lesions consist of corky projections which often break into scab affecting larger areas on the fruits. The surface becomes rough and distorted. • The market value of the fruits is considerably reduced, though the fungus rarely affects the fruit flesh below the skin.
- 15. Favourable conditions • Young leaves are highly susceptible. • The fungus infects tissues only when the surface is wet and prefers temperature of 16 to 23ºC. • The disease is a problem under low temperature and high humidity conditions.
- 16. Mode of survival and spread • The fungus survives the off-season as ascospores • The secondary spread is through air borne conidia
- 17. Management • Collect the infected leaves and burn it. • The disease can be controlled by spraying with 1% Bordeaux mixture, difolatan and benomyl. • Chemical:Carbendazin-1.25gm/lit. • Avoid excess N application. • Provide recommended K application.
- 18. Citrus canker Economic Importance: • In India, citrus canker is endemic and occurs in all the citrus growing areas. It is reported from Punjab, Tamil Nadu, Andhra Pradesh, Karnataka, Rajasthan, Madhya Pradesh, Assam, and Uttar Pradesh. • Acid lime is highly susceptible to canker. C. O.- Xanthomonas axonopodis pv. citri
- 19. Symptoms • Canker appears on leaves, twigs, petioles, branches, fruit stalks, fruits and thorns. • When it is severe, trunk and roots are also affected. But the symptoms are most conspicuous on leaves, twigs and fruits. • The lesions appear as minute water soaked round, yellow spots which enlarge slightly and turn brown, eruptive and corky. • On acid lime and sweet orange they are about 2 to 3 mm in diameter. These pustules are surrounded by a characteristic yellow halo. • Canker lesions on the fruit do not possess the yellow halo as on leaves.
- 20. • Several lesions on fruit may coalesce to form a patch. The crater-like appearance is more marked on fruits than on leaves. • The market value of the fruits is considerably reduced by the canker spots, though such infections are mostly confined to the fruit skin. • Due to severe infections of the leaves there may be defoliation, and severe infections of the twig and stem may cause die-back symptoms. • The plants also remain stunted and fruit yields are reduced considerably.
- 21. Mode of survival and spread • Survives in infected leaves for 6 months. • Bacteria overwinters in leaf, twig and fruit canker lesions. • Citrus leaf miners (Phyllocnistis citrella) helps in the dissemination of thepathogen • Spread by rain splashes.
- 22. Management • Prune out and burn all canker infected twigs before monsoon. • Periodical spraying of bactericides along with an insecticide. • Use canker tolerant varieties like “Tenali selection” and “Balaji” • Select seedlings free from canker for planting in main field. • Spray Streptocycline (1g) + Copper oxy chloride (30g) in 10 litres of water at fortnightly intervals for effective management of canker in citrus nurseries. • Three sprayings of Streptocycline (1g) + Copper oxy chloride (30g) in 10 litres of water at an interval of 20 days during rainy season is effective for leaf canker. • Fruit infection can be prevented by two sprays of Streptocycline (1g) + Copper oxy chloride (30g) in 10 litres of water at marble stage followed by another spray 30 days later. • Control leaf miner when young flush is produced.
- 23. Diplodia gummosis C. O. - Diplodia natalensis (Perfect stage: Physalospora rhodina) Economic Importance: • Occurs commonly in Andhra Pradesh, Tamil Nadu and Uttar Pradesh. • It is common on Sathgudi and Batavian oranges, mandarins and lemons in A.P. and Tamil Nadu.
- 24. Symptoms • Profuse gumming on the upper portions of the trunk, branches and twigs. • Infection starts at growth cracks or ridges at crotches. • Gum oozes out from the cracks developed on the diseased portion. • From bark, the infection spreads to wood which dries and becomes discoloured. • Large limbs are killed and if left unchecked the whole tree may be killed in course of time. • Sometimes branches break at the infected portion.
- 25. Mode of spread and survival • Black pycnidial bodies appear on the diseased bark which gets removed in flakes. • The disease spreads through dissemination of pycnidiospores or conidia by air, rain and insects. Favourable conditions • Reduced tree vigour, insect damage, malnutrition and old age predispose the disease.
- 26. Management • The tress should be kept in a vigorous growing condition. • Wound in the bark especially on limbs and forks should be scraped and protected with Bordeaux paste.
- 27. Tristeza or quick decline C. O. – Citrus Tristeza Virus (CTV). Economic Importance: • This disease was first reported in Citrus aurantifolia and C. sinensis from Italy and Florida in the U.S.A. In India, tristeza is present in Andhra Pradesh, Tamil Nadu, Karnataka, Madhya Pradesh, Maharashtra, Punjab, Bihar, West Bengal and Sikkim. • It affects all kinds of citrus plants but primarily orange, grapefruit and lime. Tristeza symptoms consisting of a quick or chronic tree decline are particularly common and severe on trees propagated on sour orange root stocks. The name “Tristeza” was suggested to describe the sad appearance of the diseased citrus trees. • Kagzi lime and Nasnaran are indicator plants for CTV detection.
- 28. Symptoms • Tristeza affected trees look chlorotic and sickly in the early stages. Gradually the leaves drop and the defoliated twigs show die-back. The declining trees die gradually but sometimes apparently healthy trees die suddenly. • Vein clearing or vein flecks (elongated translucent area) in young leaves of acid lime is seen intermittently when viewed against light (characteristic symptom).
- 29. • In sweet orange, the specific symptom of tristeza is honeycombing, a fine pitting of inner face of bark in the portion of trunk below the bud union. In acid lime which is highly susceptible to the disease, vermiform or linear pits appear in the woody cylinder. • Tristeza infected citrus trees on sour orange rootstocks cause phloem necrosis at the graft union • Diseased trees usually blossom heavily. Trees with stem pitting are stunted and set less fruits. The fruits are of smaller size and of poor quality (insipid fruits). As the fruits develop, the tree wilts partly or completely. • Grapefruit and acid lime are susceptible irrespective of root stock.
- 30. Pathogen • Tristeza is a highly flexuous filamentous virus 2000nm long and 10-12nm in width. The virus is restricted to only phloem tissue and is a member of Closterovirus group. CTV has ss +ve sense RNA of 20 K nucleotides as its genome. Mode of survival and spread • The disease primarily spreads through grafting and budding. Under field conditions, it is transmitted by the black citrus aphid, Toxoptera citricida. The virus is not seed borne.
- 31. Management • Strict quarantine measures to be enforced. • Use certified budwood free of CTV. • Remove all diseased trees as and when the disease is noticed. Fresh plantings to be taken with virus free materials on tolerant rootstocks. For sweet orange and mandarin avoid susceptible root stocks. • For Andhra Pradesh, Maharashtra and Karnataka, Rangapur lime is recommended as a root stock resistant to Tristeza. For the Punjab region, Jattikhatti, Cleopatra mandarin and sweet orange are recommended as resistant root stocks. • For acid lime, use seedling preimmunised with mild strain of tristeza virus (Cross protection). • Periodic sprays of insecticides like Monochrotophos 0.05 % reduce s the secondary spread of the disease in the orchard.