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Fusarium leaf blight (Fusarium pallidoroseum)
Introduction
            The disease is a minor disease first reported from Mysore (Govindaiah et al., 1990). Though the disease occurs all over India, the incident is found more in south India. The disease is also known as twig blight. However, the twig blight was reported as a serious disease of mulberry in the Kashmir valley.
Symptoms
            Appearance of dark brown spot on infected twigs, shrinkage of cortex, bark bursting, yellowing and pre-mature leaf fall are the main characteristic symptoms of the disease. Marginal browning of leaves and forming of irregular black lesion at the at the initial stage of infection. In the later stage, the lesions coalesce and spread longitudinally resulting in splitting and drying of branches. The branches become feeble and fragile. Bursting of bark, yellowing and pre-mature leaf fall are observed in the later stages.
Causal agent
Fusarium pallidoroseum (Cooke) Sacc
Systematic position
Division: Eumycota
Sub Division: Deuteromycotina
Class: Hyphomycetes
Order: Moniliales
Class: Deuteromycetes
Family: Moniliaceae
Genus: Fusarium
Species: pallidoroseum
Description of pathogen
       Fusarium pallidoroseum grow on Potato Dextrose agar medium at 25-28°C and produce rose pink coloured woolly to cottony, flat, spreading colonies when mature. Hyaline septate hyphae with slightly bulged compartments, conidiophores, phialides, macro conidia ad micro conidia are found. The fungus also produces chlamydospores. Phialides are cylindrical with a small collaret, solitary or produced as complex branching system. monophialides and polyphialides are observed. Macroconidia (3-8 x 11-70 µm) are produced from phialides on unbranched or branched conidiophores. They are two or more celled, thick walled, smooth, cylindrical or sickle shaped. Macroconidia are of two types. Those born in the aerial mycelium are mostly straight, 3-5 septate, and measure 7.5-35 x 2.5-4 µm. Macro conidia born in sporodochia are curved, possess a foot cell, 3-5 septate measure 20-46 x 3-5.5 µm. Micro conidia (2-4 x 4.8 µm), on the other hand , are formed on long or short simple conidiophores. They are one celled (occasionally 2 or 3celled), smooth, hyaline, ovoid to cylindrical, and arranged in balls (occasionally occur in chains). Chlamydospores are sparse, present in pairs, clumps or chains. They are thick walled, hyaline intercalary or terminal, (5-8 x 8-10   µm). 
Disease cycle
           The disease prevails throughout the year with peak in summer and rainy season and cause 5-8% yield loss. Pathogen was present throughout the year on un-pruned blighted twigs with maximum conidial density from June to August and that of chlamydospores from December to March. There was positive and significant correlation of air temperature with conidial density and disease development. Dispersal of spores occurs by water splash, blow off and wash off mechanisms and also through insects. The pathogen perpetuated on diseased twigs in the form of mycelium, conidia and chlamydospores. The proportion of conidia decreased with increase in depth of placement of blighted twigs in soil.       
 Pre disposing factors
            The disease is air borne and spread through conidia. High humidity is the key factor for spread of the disease. The pathogen perpetuated on diseased twigs in the form of mycelium, conidia and chlamydospores. There is positive and significant correlation of air temperature with conidial density and disease development.
Control
            The application of Bavistin @ 0.2% or Foltaf @ 0.2 % concentration is recommended for control of the disease. A safe period of 7 days is to be kept in case of bavistin and 10 days in case of Foltaf after which the leaves can be used for silkworm rearing. 
 Related literature 
Govindaiah, Sharma DD, Singhal BK, Sengupta K (1990) Fusarium pallidoroseum Cooke Sacc. - a new pathogen causing leaf blight in mulberry Morus alba L.. Indian Journal of Sericulture 29(2): 291-292
Gulzar P, Tanki TN, sahaf KA, Munshi NA, Shahzad AZMA, Raja TA, (2009) In vitroevaluation of various botanical extracts againstFusarium pallidoroseum (Cooke) Sacc. - the causal pathogen of twig blight of mulberry. Ind. J. Seric. 48 (2): 133-137.
Gupta  VP, Raju HV, Vineet Kumar, Govindaiah (1998)Surface ultrastructure of infection process of Alternaria alternata and Fusarium pallidoroseum on mulberry.Archives of Phytopathology and Plant Protection 31(5): 429-434
 
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