Banana is one of the most important staple food and fruit crop in the globe. It plays major role for millions of poor resource less people for their livelihood and food security. In India, the fruit crops stands first in production and has importance in the socio, economic point and religious festivals. This important fruits crop succumbs for many pest and diseases and lead to unbearable damage to the growers. In this lecture note major sucker borne diseases caused by virus, fungus and bacteria are described along with management aspects.
Banana Bunchy Top Virus :
In India Bunchy top was first reported occur in Kerala in 1943. Later it has been reported from many banana-growing states. Now the disease has been found
even in the deep forest of North eastern hill regions. The hill banana of lower Palani hills has been wiped out due to this disease. One of the reasons for the severity in hill regions is the disease inoculam and the vector is present all round the year. The crop is grown as perennially for 10 to 15 years as large clumps. The virus is transmitted primarily by infected suckers and through tissue propagated material. Secondary transmission is by banana aphid Pentalonia nigronervosa in a semi persistent manner.
BBTV is a DNA virus belonging to Nanoviridae family and babuvirs genus. The BBTV is the type species of the genus. The virus is an isometric particle measure 20nm diameter. The coat protein molecular weight found to be 20 K Dalton. The virus has multicomponant genome. There are six circular single stranded genomes have been known to be associated. The virus concentration is more present in phloem.
Visual symptoms:
Intermittent dark green dots and streaks of variable length is visible in leaf sheath, midrib, leaf veins and petioles. Sometimes the typical streaks may not appear in some cultivars. The leaves produced are progressively shorter, brittle in texture, narrow and give the appearance of bunchy ness. The affected plant fails to produce any flowers. If late infection occurs the plant can throw bunch but the fingers never develop to maturity. Marginal chlorosis in leaf lamina is also noticed. Vein flecking symptoms are noticed in some varieties. When infection occurs very late in the season, the plant would show dark green streaks on the tip of the bracts. Sometimes the bracts tip of male bud is green and leafy. Symptom less infection or latency is reported to present for two seasons. Mild vein clearing and also blisters with dark green colour on mid rib and leaf sheath have also been recorded.
Banana Streak Disease :
Banana Streak Virus, a plant para retrovirus, causes banana streak disease. Non-enveloped bacilliform
particles, having the size of 130 x 30nm with double stranded DNA as the genome are the characteristic of the virus. In India, the virus severely infects Mysore group of banana namely Poovan, Red banana, Robusta, Nendran, Cheni champa, Alpan, Chamba and also in Cavendish group (Basrai, Grand Nain) in Maharashtra region. The tissue-cultured plants supplied by some of the firms have infection with BSV. This virus is not transmitted mechanically by sap or by tools used for inter-cultivation operations. The primary mode of transmission of BSV is through suckers and TC plants.
Visual Symptoms :
Initially small dots, with golden yellow colour develops later it extend to form long streaks. The chlorotic streaks become necrotic giving a blackish appearance on lamina. Necrotic streaks on midrib, pseudo stem petiole is also observed. The symptoms are erratically distributed over individual leaves as well as in leaves of same plant. The midrib mosaic symptom, one of the symptoms of CMV, is not found with banana streak disease. Bunch choking, abortion of bunch and seediness in fingers are seen in infected plants. Symptoms appear on young emerging leaves, all leaves would not bear symptoms and also within the leaf intermitant symptoms are seen. Fruits get distorted, plant vigour/growth get reduced. Dieback and internal pseudostem necrosis have been associated with the disease. Plants/part of the leaves with pronounced symptom should be used for serological indexing. Virus particles are more in symptomatic portions than asymptomatic areas. Various changes in symptom have been noticed in different varieties. Leaf stripping symptoms are commonly noticed in cultivars Poovan, Grand Nain and Robusta. Typical symptoms of the virus can be noticed in cultivars Poovan, Cavendish, Nendran, and Red banana
Mild to severe mosaic pattern also been observed. The temperature plays a major role in symptom expression. At ambient conditions the expression of symptoms by the virus is very minimal, but Dahal et al has proved that the plants kept at 22° C express more typical symptoms and the virus titre also been increases considerably or sufficient enough to detect the virus by different serological assays. In tissue cultured Grand Nain, different types of symptoms have been noticed in Maharastra and Madhya Pradesh.
Banana Bract Mosaic Virus :
Bract mosaic was first noticed in 1966 in India but in the name of a malady caused by unknown etiology. They have described the malady in the name of Kokkan, but failed to prove the association of a virus in Kokkan disease. The attempt to
prove its etiology in past has taken a long time, which was sufficient enough for unexpected level of spread, not only in plantain Nendran, but also to many commercial cultivars such as Poovan, Robusta, Karpooravalli, Neypoovan and Monthan. Presently the virus is a major constraint in southern states of India, it requires quarantine restriction to avoid further spread to other major banana growing states. Cooking bananas and Pisang Awak are also affected but the yield loss is minimal.
Banana bract mosaic virus is belongs to the family Potyviridae, genus potyvirus. It is distinct member of the genus. Cytopathological observations revealed the presence of pinwheel inclusions and flexuous rod shaped particles measuring 750x15nm in size, which are the typical feature of potyvirus genus. The genome of the virus is positive sense single stranded RNA having approximately 7.5 kb. The virus titre is more in bracts, mid rib than leaf sheath. This virus is transmitted through Rhopalosihum maidi, Aphis gossypii and Pentalonia nigronervosa in a nonpersistent manner.
Visual symptoms :
Banana bract mosaic disease is characterized by the presence of spindle shaped pinkish to reddish streaks on pseudostem, midrib and peduncle. Typical mosaic and spindle shaped mild mosaic streaks on bracts, peduncle and fingers also observed. In Nendran, the leaf orientation changes in such a way giving the appearance of 'Travelers palm' plant. The lower side of the leaf spindle shaped waxy coating, appears corresponding to these, on upper surface of the leaf spindle shaped mosaic pattern is seen. In Nendran, unusual long peduncle and very short peduncle, abort of bunches, raised corky growth on peduncle is also observed to be the symptoms of BBMV. Necrotic streaks on fingers, leaf, pseudostem and mid rib are found in some varieties. Extended female phase after a short male phase has also been observed in Nendran and Neypoovan cultivars. In Red Banana and Robusta the leaf stripping symptoms is common in some seasons in Tamil Nadu. In Robusta, fingers of infected plants stop to develop and give the appearance of 'pencil', explaining the local name 'pencil kai' (pencil-sized fruit). Though Thomas and Magnaye reported that this disease could only be diagnosed when symptom appears on bract, in Trivandrum district of Kerala farmers have named the disease Pola roga, means 'disease of pseudostem' in cultivar Nendran. Necrotic symptoms on pseudo stem, midrib and petiole of infected plants of cv Neypoovan has been observed. When the pseudostem was cut horizontally, the necrosis was found to be deep seated.
Banana Mosaic or Infectious Chlorosis (CMV) :
Banana mosaic or infectious cholorosis caused by cucumber mosaic virus, has been known to occur in+.jpg)
early 1940's in Maharashtra states. Later the disease has been reported from many parts of the country. This disease was reported from Poovan and Cavendish clones widely grown in the country. In Tamilnadu, an outbreak of this disease was reported by Mohan and Lakshmanan in Poovan and Robusta in 1988. Actually CMV is known to occur in wide range of hosts in crop plants, many weed hosts and cucurbitaceous crops grown as winter crop in banana are the actual source of the virus, and transmitted through aphid vectors.
Visual symptoms
CMV induces mild mosaic symptoms which appear in whole leaf or all the leaves of an infected plant, where as BSV induced symptoms are present only parts of leaf and irregularly distributed. CMV has also been related to heart rot symptoms in banana. Rotting of cigar leaf, internal necrosis of pseudo stem and death of the whole plant are associated with CMV. Cholortic banding, rosette appearance of leaf arrangement are also the symptoms of CMV. In Poovan, it is often confused with BSV symptoms.
Management of banana viral diseases :
· Farmers must be aware of external symptoms of disease and must take necessary action to contain the virus spread through destruction of such plants as and when noticed.
· Use virus free planting material for multiplication for TC plants such plants should have been maintained in glass house at 22°C for the expression of episomal BSV.
· Maintain a virus free mother block for routine use for extracting suckers for mass multiplication. Use vector proof net house in mother block nurseries. Keep mother block nurseries in isolation.
· Visual diagnosis along with either serological or PCR based detection would prove useful in eliminating the infected material. Detection or indexing the mother plants becomes important for tissue culture companies to assure their plantlets free of virus infection. For this, it is necessary to use appropriate techniques like ELISA or DIBA using highly reliable antiserum. Immuno-capture RT-PCR can also be used to detect the viruses like BSV where the integrated sequences need to be distinguished from episomal infection.
· Avoid banana cultivation in sugarcane area as the ScBV known to be transmitted to Banana and BSV can infect Sugarcane. Cucurbitaceous plants should not be cultivated along with banana as CMV can easily spread to Banana. Weeds such as Commelina spp need to be removed which is an alternate host for CMV and found in banana gardens.
· Effective quarantine measures to be followed to avoid entry of the viral pathogens to in new disease free area with in India. Banana bract mosaic is widespread in southern districts especially Kerala, Tamil Nadu, Karnataka and Andhra Pradesh, hence quarantining of this disease will play a major role in stopping the spread. Farmers and tissue culture companies located in central and north India should not carry the suckers and mother plants from south India without indexing them for BBrMV.
· Banana aphid, Pentalonia nigronervosa and cotton, cowpea aphids transmits banana viruses which should be, brought under control using systemic insecticide. If the viral inoculum were not present, presence of these vectors pest may not cause economic damage to the crop.
Fusarium Wilt :
Fusarium wilt of banana is a major constraint in banana production world wide and is one of the most notorious of all plant disease. As a result of epidemics in
export plantations, Fusarium wilt to be one of the six most destructive plant diseases in recorded history. This was first reported from South East Queensland, Australia in 1874 In India, the disease was recorded for the first time in the year 1911 by Basu. Smith (1910) recovered the pathogen from the host tissue received from Cuba and named it Fusarium cubense as the fungus was recognized in the genus Fusarium. Fusarium oxysporum f sp. cubense is a highly variable soil-borne fungus Fusarium species are not only pathogens of agricultural and forestry crops, but is also important in the medical field. Some species produce mycotoxins and when ingested by humans and animals can cause certain cancer as well as other disease symptoms. Resource poor farmers are particularly badly affected as their grain is usually stored under less than optimum conditions. There have been many documented reports of mycotoxins-associated esophageal and other cancers from people living in rural areas of South Africa.
Distinctive Symptoms :
The first internal symptoms develop in feeder roots, the initial site of infection. They progress to the rhizome and are most prominent where the stele joins the cortex. As the pseudostem is colonized, faint brown streaks or flecks become evident on and within older leaf sheaths. Eventually, large portions of the xylem turn a brick red to brown color. First obvious external symptQm is the yellowing of leaf margins that eventually encompasses the entire leaf or a longitudinal splitting of the lower portion of the outer leaf sheaths on the pseudostem. Yellowing begins with the oldest and progresses to the youngest leaves of a plant over a period of one to three weeks until only the center leaf remains erect and green. Often the yellow leaves remain erect for one to two weeks, or the petiole may collapse and leaves hang down. These symptoms have been designated as the "Leaf-yellowing syndrome". In other cases, affected leaves remain green except for a streak or patch in the petiole and collapse as a result of the weakening and breaking of the petiole. The leaves fall, the oldest first, until they hang ground the plant like a green shroud. These symptoms have been designated as the ''Non yellowing syndrome". As the disease progresses, younger and younger leaves collapse until the entire canopy consists of dead or dying leaves. However fruits are not infected by the pathogen and are not discolored
Causal Agent :
Panama disease is caused by the soil-borne hyphomycete, Fusarium oxysporum Schlect. f sp. cubense. It is one of more than 100 formae speciales (special forms) of Fusarium oxysporum that cause vascular wilt of flowering plants. It contains pathogenic and saprophytic strains that cannot be distinguished morphologically. Colonies grow 4-7 mm/day on PDA at 24°C, with slight to significant aerial mycelium, and white to purple pigmentation. Sporodochia are tan to orange and sclerotia are blue and submerged. Micro and macroconidia are produced on branched and unbranched monophialides. Microconidia are 5 - 16 x 2.4 - 3.5 µm, one- or twocelled, oval- to kidney-shaped, and are borne in false heads. Macroconidia are 27 - 55 x 3.3 - 5.5 μm, four- to eight-celled and sickle-shaped with foot-shaped basal cells. Terminal and intercalary chlamydospores are 7 - 11 flm in diameter, usually globose and are formed singly or in pairs in hyphae or conidia.
Distribution of Fusarium in Soil :
The wilt pathogen, F. oxysporum f sp. cubense was found distributed in soil at various levels according to the depth of the soil. The population densities of F. oxysporum, F. solani, and F. roseum significantly decreased with the increasing soil depth. Fusarium wilt was observed mostly in the sandy loam soil and lea~t in the heavy clay soil.
Survival of the Pathogen :
The pathogen Foc is a facultative parasite capable of saprophytic growth and it would be classified as a root inhabiting fungus. Soil population is unevenly distributed and declining rapidly in the absence of the host. The fungus could survive and remains viable in the field for up to 30 years as chlamydospores in infested plant debris or in the roots of alternative hosts. The short distance spread between the plants in plantation is affected by the roots. The long distance spread of the pathogen is mainly through the infected rhizomes and adhered soil. The pathogen can also be effectively spread in soil attached to implements or vehicle. It also spreads through the irrigation water very rapidly.
Management of wilt disease :
· In India, the race-I, which attacks the Rasthali (silk), Karpuravalli (Pisang Awak) and Pachanadan, Ney Poovan, Virupakshi (Pome) and race-2 affects Monthan, Sakkia (Bluggoe) varieties are widely spread. If soil has plenty of inoculum, it is better to avoid growing of susceptible varieties in same filed. Grow resistant varieties such as Robusta, Grand Nain, Dwarf Cavendish, Poovan and Nendran in soils known for wilt susceptibility.
· Use tissue culture plants which are devoid of fungal, bacterial and nematodes.
Tissue culture material are more susceptible for wilt pathogen, hence choose the fields which are pathogens free. Susceptible varieties should be pathogen free and should be planted only in pathogen free fields.
· Paring and pralinage helps in controlling the wilt incidence. The suckers should be trimmed; the dead roots should be removed and dipped in 1% carbendazim for half an hour and shade dry before planting. This treatment is necessary especially for susceptible cultivars.
· As nematodes also helps in wilt pathogen entry into rhizome, application of carbofuran granules and neem cake is necessary for control of nematodes population.
· Soil drenching of 0.1 % Bavistin once at 5th\ 6th and 7th month after planting can minimize the disease incidence.
· Gelatin capsule filled with 50 mg of carbendazim has to be inserted into the rhizomes at 450 angle using capsule applicator gives better control. This application has to be done at 5th, 7th and 9th month of after planting or instead of capsule, 3ml of 2% carbendazim can also be injected into rhizome.
· Biocontrol agent's viz., Trichoderma viride and Pseudomonas fluorescens can also be applied. But fungicide and biocontrol agents should not be applied together. It is better to apply biocontrol agents combined with FYM at the time of planting or 10 to 15 days prior to fertilizer application.
Erwinia Head Rot or Tip Over :
Of late the Erwinia head rot is most commonly observed in banana plantations during hot summer
months and also during monsoon seasons in some parts. This disease prominently observed in tissue culture plants at third to fifth month after planting and becoming economically very important. In Rajamundry district of AP, and Theni district of TN the disease manifestation is seen even in later stage of plant growth. The pathogen is soil borne and enters the corm through wounds and also through decaying leaf sheath of suckers. In affected plants, the bunch fails to develop and fall apart leaving the rotten corm inside the soil. The affected plant shows severe splitting in pseudostem and being locally called vedivazhai (Split banana). The pathogen does not spread into the plant systemically through vascular bundles, rather it confine within the affected corm and can spread to corm of developing daughter suckers.
Symptoms :
· Rotting of collar region is a commonest symptom this disease followed by epinasty of leaves, which dry out suddenly.
· If affected plants are pulled out it comes out from the collar region leaving the corm with their roots in the soil.
· Splitting of pseudo stem is common in late stage of infection in cultivars Robusta, Grande Naine and ThelIa Chakkerakeli.
· When affected plants are cut open at collar region yellowish to reddish ooze is seen.
· In early stage of infection dark brown or yellow, water soaked areas are more in the cortex area.
· In advance stage the interior lesions may decay to such an extent that cavities surrounded by dark spongy tissues are formed.
· This soft rotting may spread radially towards growing point through the cortical tissues. The rotten corm emits foul smell.
Management of Erwinia head rot :
· Select infection free suckers for planting and should be trimmed to remove dead tissues.
· Drench suckers 2% bleaching powder to control the disease in field at planting followed by another drenching the soil after 3rd month of planting to control the pathogen.
· Avoid planting during rainy season and in soils, which do not have good drainage.
· Use of bigger suckers (more than 500 g) for planting. A void very small suckers.
· Banana should not be grown along with onion and other vegetables. The soft rot pathogen load increases in such cropping system.
Banana Bunchy Top Virus :
In India Bunchy top was first reported occur in Kerala in 1943. Later it has been reported from many banana-growing states. Now the disease has been found
even in the deep forest of North eastern hill regions. The hill banana of lower Palani hills has been wiped out due to this disease. One of the reasons for the severity in hill regions is the disease inoculam and the vector is present all round the year. The crop is grown as perennially for 10 to 15 years as large clumps. The virus is transmitted primarily by infected suckers and through tissue propagated material. Secondary transmission is by banana aphid Pentalonia nigronervosa in a semi persistent manner.BBTV is a DNA virus belonging to Nanoviridae family and babuvirs genus. The BBTV is the type species of the genus. The virus is an isometric particle measure 20nm diameter. The coat protein molecular weight found to be 20 K Dalton. The virus has multicomponant genome. There are six circular single stranded genomes have been known to be associated. The virus concentration is more present in phloem.
Visual symptoms:
Intermittent dark green dots and streaks of variable length is visible in leaf sheath, midrib, leaf veins and petioles. Sometimes the typical streaks may not appear in some cultivars. The leaves produced are progressively shorter, brittle in texture, narrow and give the appearance of bunchy ness. The affected plant fails to produce any flowers. If late infection occurs the plant can throw bunch but the fingers never develop to maturity. Marginal chlorosis in leaf lamina is also noticed. Vein flecking symptoms are noticed in some varieties. When infection occurs very late in the season, the plant would show dark green streaks on the tip of the bracts. Sometimes the bracts tip of male bud is green and leafy. Symptom less infection or latency is reported to present for two seasons. Mild vein clearing and also blisters with dark green colour on mid rib and leaf sheath have also been recorded.
Banana Streak Disease :
Banana Streak Virus, a plant para retrovirus, causes banana streak disease. Non-enveloped bacilliform
particles, having the size of 130 x 30nm with double stranded DNA as the genome are the characteristic of the virus. In India, the virus severely infects Mysore group of banana namely Poovan, Red banana, Robusta, Nendran, Cheni champa, Alpan, Chamba and also in Cavendish group (Basrai, Grand Nain) in Maharashtra region. The tissue-cultured plants supplied by some of the firms have infection with BSV. This virus is not transmitted mechanically by sap or by tools used for inter-cultivation operations. The primary mode of transmission of BSV is through suckers and TC plants.Visual Symptoms :
Initially small dots, with golden yellow colour develops later it extend to form long streaks. The chlorotic streaks become necrotic giving a blackish appearance on lamina. Necrotic streaks on midrib, pseudo stem petiole is also observed. The symptoms are erratically distributed over individual leaves as well as in leaves of same plant. The midrib mosaic symptom, one of the symptoms of CMV, is not found with banana streak disease. Bunch choking, abortion of bunch and seediness in fingers are seen in infected plants. Symptoms appear on young emerging leaves, all leaves would not bear symptoms and also within the leaf intermitant symptoms are seen. Fruits get distorted, plant vigour/growth get reduced. Dieback and internal pseudostem necrosis have been associated with the disease. Plants/part of the leaves with pronounced symptom should be used for serological indexing. Virus particles are more in symptomatic portions than asymptomatic areas. Various changes in symptom have been noticed in different varieties. Leaf stripping symptoms are commonly noticed in cultivars Poovan, Grand Nain and Robusta. Typical symptoms of the virus can be noticed in cultivars Poovan, Cavendish, Nendran, and Red banana
Mild to severe mosaic pattern also been observed. The temperature plays a major role in symptom expression. At ambient conditions the expression of symptoms by the virus is very minimal, but Dahal et al has proved that the plants kept at 22° C express more typical symptoms and the virus titre also been increases considerably or sufficient enough to detect the virus by different serological assays. In tissue cultured Grand Nain, different types of symptoms have been noticed in Maharastra and Madhya Pradesh.
Banana Bract Mosaic Virus :
Bract mosaic was first noticed in 1966 in India but in the name of a malady caused by unknown etiology. They have described the malady in the name of Kokkan, but failed to prove the association of a virus in Kokkan disease. The attempt to
prove its etiology in past has taken a long time, which was sufficient enough for unexpected level of spread, not only in plantain Nendran, but also to many commercial cultivars such as Poovan, Robusta, Karpooravalli, Neypoovan and Monthan. Presently the virus is a major constraint in southern states of India, it requires quarantine restriction to avoid further spread to other major banana growing states. Cooking bananas and Pisang Awak are also affected but the yield loss is minimal.Banana bract mosaic virus is belongs to the family Potyviridae, genus potyvirus. It is distinct member of the genus. Cytopathological observations revealed the presence of pinwheel inclusions and flexuous rod shaped particles measuring 750x15nm in size, which are the typical feature of potyvirus genus. The genome of the virus is positive sense single stranded RNA having approximately 7.5 kb. The virus titre is more in bracts, mid rib than leaf sheath. This virus is transmitted through Rhopalosihum maidi, Aphis gossypii and Pentalonia nigronervosa in a nonpersistent manner.
Visual symptoms :
Banana bract mosaic disease is characterized by the presence of spindle shaped pinkish to reddish streaks on pseudostem, midrib and peduncle. Typical mosaic and spindle shaped mild mosaic streaks on bracts, peduncle and fingers also observed. In Nendran, the leaf orientation changes in such a way giving the appearance of 'Travelers palm' plant. The lower side of the leaf spindle shaped waxy coating, appears corresponding to these, on upper surface of the leaf spindle shaped mosaic pattern is seen. In Nendran, unusual long peduncle and very short peduncle, abort of bunches, raised corky growth on peduncle is also observed to be the symptoms of BBMV. Necrotic streaks on fingers, leaf, pseudostem and mid rib are found in some varieties. Extended female phase after a short male phase has also been observed in Nendran and Neypoovan cultivars. In Red Banana and Robusta the leaf stripping symptoms is common in some seasons in Tamil Nadu. In Robusta, fingers of infected plants stop to develop and give the appearance of 'pencil', explaining the local name 'pencil kai' (pencil-sized fruit). Though Thomas and Magnaye reported that this disease could only be diagnosed when symptom appears on bract, in Trivandrum district of Kerala farmers have named the disease Pola roga, means 'disease of pseudostem' in cultivar Nendran. Necrotic symptoms on pseudo stem, midrib and petiole of infected plants of cv Neypoovan has been observed. When the pseudostem was cut horizontally, the necrosis was found to be deep seated.
Banana Mosaic or Infectious Chlorosis (CMV) :
Banana mosaic or infectious cholorosis caused by cucumber mosaic virus, has been known to occur in
+.jpg)
early 1940's in Maharashtra states. Later the disease has been reported from many parts of the country. This disease was reported from Poovan and Cavendish clones widely grown in the country. In Tamilnadu, an outbreak of this disease was reported by Mohan and Lakshmanan in Poovan and Robusta in 1988. Actually CMV is known to occur in wide range of hosts in crop plants, many weed hosts and cucurbitaceous crops grown as winter crop in banana are the actual source of the virus, and transmitted through aphid vectors.Visual symptoms
CMV induces mild mosaic symptoms which appear in whole leaf or all the leaves of an infected plant, where as BSV induced symptoms are present only parts of leaf and irregularly distributed. CMV has also been related to heart rot symptoms in banana. Rotting of cigar leaf, internal necrosis of pseudo stem and death of the whole plant are associated with CMV. Cholortic banding, rosette appearance of leaf arrangement are also the symptoms of CMV. In Poovan, it is often confused with BSV symptoms.
Management of banana viral diseases :
· Farmers must be aware of external symptoms of disease and must take necessary action to contain the virus spread through destruction of such plants as and when noticed.
· Use virus free planting material for multiplication for TC plants such plants should have been maintained in glass house at 22°C for the expression of episomal BSV.
· Maintain a virus free mother block for routine use for extracting suckers for mass multiplication. Use vector proof net house in mother block nurseries. Keep mother block nurseries in isolation.
· Visual diagnosis along with either serological or PCR based detection would prove useful in eliminating the infected material. Detection or indexing the mother plants becomes important for tissue culture companies to assure their plantlets free of virus infection. For this, it is necessary to use appropriate techniques like ELISA or DIBA using highly reliable antiserum. Immuno-capture RT-PCR can also be used to detect the viruses like BSV where the integrated sequences need to be distinguished from episomal infection.
· Avoid banana cultivation in sugarcane area as the ScBV known to be transmitted to Banana and BSV can infect Sugarcane. Cucurbitaceous plants should not be cultivated along with banana as CMV can easily spread to Banana. Weeds such as Commelina spp need to be removed which is an alternate host for CMV and found in banana gardens.
· Effective quarantine measures to be followed to avoid entry of the viral pathogens to in new disease free area with in India. Banana bract mosaic is widespread in southern districts especially Kerala, Tamil Nadu, Karnataka and Andhra Pradesh, hence quarantining of this disease will play a major role in stopping the spread. Farmers and tissue culture companies located in central and north India should not carry the suckers and mother plants from south India without indexing them for BBrMV.
· Banana aphid, Pentalonia nigronervosa and cotton, cowpea aphids transmits banana viruses which should be, brought under control using systemic insecticide. If the viral inoculum were not present, presence of these vectors pest may not cause economic damage to the crop.
Fusarium Wilt :
Fusarium wilt of banana is a major constraint in banana production world wide and is one of the most notorious of all plant disease. As a result of epidemics in
export plantations, Fusarium wilt to be one of the six most destructive plant diseases in recorded history. This was first reported from South East Queensland, Australia in 1874 In India, the disease was recorded for the first time in the year 1911 by Basu. Smith (1910) recovered the pathogen from the host tissue received from Cuba and named it Fusarium cubense as the fungus was recognized in the genus Fusarium. Fusarium oxysporum f sp. cubense is a highly variable soil-borne fungus Fusarium species are not only pathogens of agricultural and forestry crops, but is also important in the medical field. Some species produce mycotoxins and when ingested by humans and animals can cause certain cancer as well as other disease symptoms. Resource poor farmers are particularly badly affected as their grain is usually stored under less than optimum conditions. There have been many documented reports of mycotoxins-associated esophageal and other cancers from people living in rural areas of South Africa.Distinctive Symptoms :
The first internal symptoms develop in feeder roots, the initial site of infection. They progress to the rhizome and are most prominent where the stele joins the cortex. As the pseudostem is colonized, faint brown streaks or flecks become evident on and within older leaf sheaths. Eventually, large portions of the xylem turn a brick red to brown color. First obvious external symptQm is the yellowing of leaf margins that eventually encompasses the entire leaf or a longitudinal splitting of the lower portion of the outer leaf sheaths on the pseudostem. Yellowing begins with the oldest and progresses to the youngest leaves of a plant over a period of one to three weeks until only the center leaf remains erect and green. Often the yellow leaves remain erect for one to two weeks, or the petiole may collapse and leaves hang down. These symptoms have been designated as the "Leaf-yellowing syndrome". In other cases, affected leaves remain green except for a streak or patch in the petiole and collapse as a result of the weakening and breaking of the petiole. The leaves fall, the oldest first, until they hang ground the plant like a green shroud. These symptoms have been designated as the ''Non yellowing syndrome". As the disease progresses, younger and younger leaves collapse until the entire canopy consists of dead or dying leaves. However fruits are not infected by the pathogen and are not discolored
Causal Agent :
Panama disease is caused by the soil-borne hyphomycete, Fusarium oxysporum Schlect. f sp. cubense. It is one of more than 100 formae speciales (special forms) of Fusarium oxysporum that cause vascular wilt of flowering plants. It contains pathogenic and saprophytic strains that cannot be distinguished morphologically. Colonies grow 4-7 mm/day on PDA at 24°C, with slight to significant aerial mycelium, and white to purple pigmentation. Sporodochia are tan to orange and sclerotia are blue and submerged. Micro and macroconidia are produced on branched and unbranched monophialides. Microconidia are 5 - 16 x 2.4 - 3.5 µm, one- or twocelled, oval- to kidney-shaped, and are borne in false heads. Macroconidia are 27 - 55 x 3.3 - 5.5 μm, four- to eight-celled and sickle-shaped with foot-shaped basal cells. Terminal and intercalary chlamydospores are 7 - 11 flm in diameter, usually globose and are formed singly or in pairs in hyphae or conidia.
Distribution of Fusarium in Soil :
The wilt pathogen, F. oxysporum f sp. cubense was found distributed in soil at various levels according to the depth of the soil. The population densities of F. oxysporum, F. solani, and F. roseum significantly decreased with the increasing soil depth. Fusarium wilt was observed mostly in the sandy loam soil and lea~t in the heavy clay soil.
Survival of the Pathogen :
The pathogen Foc is a facultative parasite capable of saprophytic growth and it would be classified as a root inhabiting fungus. Soil population is unevenly distributed and declining rapidly in the absence of the host. The fungus could survive and remains viable in the field for up to 30 years as chlamydospores in infested plant debris or in the roots of alternative hosts. The short distance spread between the plants in plantation is affected by the roots. The long distance spread of the pathogen is mainly through the infected rhizomes and adhered soil. The pathogen can also be effectively spread in soil attached to implements or vehicle. It also spreads through the irrigation water very rapidly.
Management of wilt disease :
· In India, the race-I, which attacks the Rasthali (silk), Karpuravalli (Pisang Awak) and Pachanadan, Ney Poovan, Virupakshi (Pome) and race-2 affects Monthan, Sakkia (Bluggoe) varieties are widely spread. If soil has plenty of inoculum, it is better to avoid growing of susceptible varieties in same filed. Grow resistant varieties such as Robusta, Grand Nain, Dwarf Cavendish, Poovan and Nendran in soils known for wilt susceptibility.
· Use tissue culture plants which are devoid of fungal, bacterial and nematodes.
Tissue culture material are more susceptible for wilt pathogen, hence choose the fields which are pathogens free. Susceptible varieties should be pathogen free and should be planted only in pathogen free fields.
· Paring and pralinage helps in controlling the wilt incidence. The suckers should be trimmed; the dead roots should be removed and dipped in 1% carbendazim for half an hour and shade dry before planting. This treatment is necessary especially for susceptible cultivars.
· As nematodes also helps in wilt pathogen entry into rhizome, application of carbofuran granules and neem cake is necessary for control of nematodes population.
· Soil drenching of 0.1 % Bavistin once at 5th\ 6th and 7th month after planting can minimize the disease incidence.
· Gelatin capsule filled with 50 mg of carbendazim has to be inserted into the rhizomes at 450 angle using capsule applicator gives better control. This application has to be done at 5th, 7th and 9th month of after planting or instead of capsule, 3ml of 2% carbendazim can also be injected into rhizome.
· Biocontrol agent's viz., Trichoderma viride and Pseudomonas fluorescens can also be applied. But fungicide and biocontrol agents should not be applied together. It is better to apply biocontrol agents combined with FYM at the time of planting or 10 to 15 days prior to fertilizer application.
Erwinia Head Rot or Tip Over :
Of late the Erwinia head rot is most commonly observed in banana plantations during hot summer
months and also during monsoon seasons in some parts. This disease prominently observed in tissue culture plants at third to fifth month after planting and becoming economically very important. In Rajamundry district of AP, and Theni district of TN the disease manifestation is seen even in later stage of plant growth. The pathogen is soil borne and enters the corm through wounds and also through decaying leaf sheath of suckers. In affected plants, the bunch fails to develop and fall apart leaving the rotten corm inside the soil. The affected plant shows severe splitting in pseudostem and being locally called vedivazhai (Split banana). The pathogen does not spread into the plant systemically through vascular bundles, rather it confine within the affected corm and can spread to corm of developing daughter suckers.Symptoms :
· Rotting of collar region is a commonest symptom this disease followed by epinasty of leaves, which dry out suddenly.
· If affected plants are pulled out it comes out from the collar region leaving the corm with their roots in the soil.
· Splitting of pseudo stem is common in late stage of infection in cultivars Robusta, Grande Naine and ThelIa Chakkerakeli.
· When affected plants are cut open at collar region yellowish to reddish ooze is seen.
· In early stage of infection dark brown or yellow, water soaked areas are more in the cortex area.
· In advance stage the interior lesions may decay to such an extent that cavities surrounded by dark spongy tissues are formed.
· This soft rotting may spread radially towards growing point through the cortical tissues. The rotten corm emits foul smell.
Management of Erwinia head rot :
· Select infection free suckers for planting and should be trimmed to remove dead tissues.
· Drench suckers 2% bleaching powder to control the disease in field at planting followed by another drenching the soil after 3rd month of planting to control the pathogen.
· Avoid planting during rainy season and in soils, which do not have good drainage.
· Use of bigger suckers (more than 500 g) for planting. A void very small suckers.
· Banana should not be grown along with onion and other vegetables. The soft rot pathogen load increases in such cropping system.
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