Banana ; BUNCHY TOP;PANAMA DISEASE; SIGATOKA LEAF SPOT

Banana: Musa paradisica var. sapientum Family: Musaceae     1. BUNCHY TOP The disease was recorded first time in 1879 from Fiji. The disease has also been reported from Egypt, Sri Lanka, Australia, Pacific islands, Malaysia and India. It is believed that the disease has been introduced in India from Sri Lanka through infected suckers. The disease is reported from Kerala in1940 and spread in banana growing neighbouring states like Tamilnadu, Karnataka, Andhra Pradesh, Maharashtra, Bihar, Orissa and Assam. Symptoms: - The disease is transmitted to the plant by the aphid vector Pentalonia nigronervosa and dwarf varieties of banana are very susceptible to the disease. The primary symptoms of the disease are seen when infected banana suckers are planted. The suckers put forth narrow leaves, which are chlorotic and mosaic. The affected leaves are brittle, with dark green patches and margins rolled upwards. The characteristic symptom of bunchy top virus is the presence of dark green streaks along the secondary veins or midrib of petiole. The diseased plants remain stunted and do not produce fruits. The infected plant leaves shows characteristic rosette or bunchy top symptoms. The disease does not kill the plant but once the plant gets infected it does not recover from the disease. Causal Organism: - The disease is caused by Banana virus I or Musa virus I or Banana bunchy top virus transmitted by the aphid vector Pentalonia nigronervosa. Disease Cycle: - The virus is found systemically in all parts of the plant including rhizomes and suckers. The first symptom of the disease is appeared after 5-6 weeks of inoculation from insect vector. The vector usually feed at basal portion of pseudostem of host plant but may be found on upper portion of the host plant. The aphids may migrate at long distances. The aphid retains the infective potential for a period of 13 days and transmits the virus to healthy host in a period of 90 minutes. Disease Management: Removal of clumps, suckers and diseased plants is very important to stop dissemination of disease. Planting material should be disease free and not collected from disease prone areas. The vector (aphid) should be controlled to check spread of the disease by spraying with 0.1-0.5% Metasystox. The disease affected banana plants should be killed with herbicide (2,4- D or 2, 4, 5 – T). The infected rhizomes dug out and cut into small pieces with further spray of herbicide to check germination, which may harbour the virus.   2. PANAMA DISEASE Fusarium wilt of banana (panama disease) is one of the most devastating diseases of banana in the world. The disease is prevalent in Australia, Coasta Rica, Hawaii, India, Jamaica, Panama, South America, Surinam and West Africa. The disease affects many economically important varieties. The disease has been reported in India from Andhra Pradesh, Assam, Bihar, Karnataka, Kerala, Maharashtra, Tamilnadu, and West Bengal states. Symptoms: - The pathogen attacks banana plants of all ages and spreads mainly through the soil. The pathogen gets entry in the plant body through roots damage caused by the nematodes. The fungus blocks the vascular system and causes wilting. It is most damaging in poorly drained soil. Banana plants affected by fusarium will show yellowing of leaves starting with the oldest leaves. The newly emerged leaf remain green and erect for a long period but later it also shows blotchy and yellowing symptom with wrinkling lamina. Other petioles may remain erect but will soon become yellow then brown and dry. In some cases the outer leaf sheaths of the pseudostem may split longitudinally near soil level. If the pseudostem cut longitudinally, many black or brown coloured streaks can be seen which run upward to leaf bases and all other directions. The cut stem smells like rotten fish. Plants affected by panama will generally not develop sufficiently for a mature bunch to be produced and the disease can cause total crop loss. The disease spread is favoured by warm soil temperature, poor drainage, light soils and high soil moisture. Red or brown dots or streaks are also seen. Causal Organism: - The pathogen causing wilt or panama disease of banana is Fusarium oxysporum f. sp. cubense (E. F. S.) Snyder and Hansen. The fungal hyphae are present inter and intra cellularly in the host tissues. The pathogen fills the cavities of vascular tissues and spread systemically. The fungus produces numerous micro-conidia, macro-conidia and chlamydospores. The sporodochium bears many conidiophores, is arises from pseudo-parenchymatous tissues. The macro-conidia are sickle shaped, hyaline, thin walled, 2-5 septate and measures 24-36 x 4-5 µm and micro-conidia are ovate, single to non septate, hyaline and thin walled which measures 5-7 x 2-3 µm. The chlamydospores are oval or spherical, thick walled, may be paired, measuring 7-12 x 7-8 µm. The pathogen has several races which are reported from many countries. Disease Cycle: - Light textured loam and sandy loam soils which are acidic favours the disease development. The pathogen is soil borne and invades the plant through injured roots and rhizomes. The mycelium of the pathogen colonized the vascular bundles of host plant and produces micro-conidia, macro-conidia and chlamydospores. The chlamydopores survive in the soil for a long time. The pathogen can also survive in disease rhizomes and other plant parts saprophytically and become active when conditions are favourable and infection takes place. The pathogen spreads through suckers from disease infested area to other areas. The pathogen can survive in the soil more than twenty years. Disease Management: Highly infected soil should not be replanted with banana at least for 4-5 years. Flooding of wilt affected areas for six months has been reported to give satisfactory results. Use the healthy planting material, removal of infected plants at first sight and avoidance of root injury through intercultural operations helps in reducing the disease incidence. Use of disease resistant cultivars is recommended. Growing of paddy followed by banana for 3-5 years once or twice, use of quick lime near the base of the plant and soaking with water and avoiding sunflower or sugarcane in crop rotation helps to reduce the disease incidence. Application of bioagents, such as, Trichoderma viride or Pseudomonas fluorescence in the soil is effective. Application of the capsule filled with P. fluorescence at 60 mg/capsule is recommended at 2, 4 and 6 months after planting. The modified Panchagavya mixture at 101 dilution should be applied (soil drenching) at 2-3 liters/plant. Soil drenching with 0.01% vapam or 0.15% thiram helps in managing the disease. Dipping of banana suckers in 0.1% carbendazim before plantation gives good control. Banana cultivars Giant Cavendish, Lacatan, Rajavazhai, Peyladen, Moongil, Poovan and Vamanakeli are reported to be resistant to wilt.   3. SIGATOKA LEAF SPOT The disease mostly attacks leaves and has been reported to cause economic losses to the banana crop. It has been reported to cause severe losses to banana crop in Coasta Rica, Colombia, Fizi, Guatemala, Guyana, Haiti, Honduras, India, Jamaica, Java, Mexico, Panama, Surinam, Tanzania, Uganda and Venezuela. In India, the disease is found in Andhra Pradesh, Assam, Bihar, Gujarat, Karnataka, Kerala, Maharashtra, Tamilnadu, and West Bengal. Symptoms: The initial symptoms seen in the field are small lesions on leaves which are pale yellow or greenish yellow streaks that appear on both sides of leaves parallel to the leaf veins. The leaf spots on leaves are increases in size to form dark brown to black linear oblong areas. Center of the spots eventually dry out, becoming light gray, but a narrow, dark brown to black border persists giving a spindle shaped appearance. Rapid drying and defoliation is the characteristic feature of this disease. In severe cases, the petiole collapses and the leaf hangs down from the pseudo stem. The infection may cause complete failure of maturity of the bunch. In some cases, premature ripening of fruits is also reported. In a growing plant, the leaf spots are seen mostly on the older leaves, the young leaves can be free from the spots. Epidemiology and Disease Cycle: During rainy season, spread of the disease is very rapid. Both conidia and ascospores can cause infection but conidia predominate for most of the period. Conidia are produced in wet weather or in dew on the surface of lesions. The conidia are dispersed by water droplets to other leaves, particularly to the leaves of suckers. Ascospores are borne on older leaves in perithecia sunken into the leaves tissue. The disease is favoured by warm temperature (23-25 °C), rainy or humid weather, close planting, heavy weed or grass cover and failure to remove the suckers. Disease Management: Removal and destruction of infected leaves is necessary. Spraying 1 % Bordeaux mixture mixed with 2 % linseed oil, providing improved drainage, good weed control, removal of suckers and correct spacing helps in reducing the disease incidence. Spraying 0.1% Topsin M or prochloraz or 0.1 % carbendazim or 0.2 % chlorothalonil or 0.15% kitazin 3-4 times at fortnightly intervals was quite effective in field trials.