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Stem canker/ soft rot (Botryodiplodia theobromae Pat.)

Introduction

It was reported by Luke and Sathiya (1982) from the mulberry fields in and around Bangalore. Shree and Boraiah (1983) reported 10 to 15 % disease incidence in mulberry stem cuttings. Sukumar et al. (1991) reported an average mortality of 30 % in mulberry nurseries due to the disease. The disease develops as a greenish black lesion on the stem  and plenty of dark structure producing pycnidial bodies in groups in latter stages. The disease inhibits sprouting of mulberry cuttings (Shree, 1984; Sukumar et al., 1991). Studies on leaf quality revealed that the fungus utilizes D-glucose carbon source best and likes pectin least (Sullia and Padma, 1986). It grows fast on PDA and slowest on mulberry leaf decoction agar. The fungus sporulates heavily in both mulberry leaf decoction agar and PDA.

Causal agent

Botryodiplodia theobromaePat.(syn: Lasiodiplodia theobromae)

Systematic position

Kingdom: Fungi 
Division: Ascomycota 
Family: Diaporthaceae
Species:  theobromae

Description of pathogen

  Colonies are grayish sepia to mouse grey to black, fluffy with abundant aerial mycelium; reverse fuscous black to black. Conidiophores are hyaline, simple, sometimes septate, rarely branched cylindrical, arising from the inner layers of cells lining the pycnidial cavity. Conidiogenous cells are hyaline, simple, and cylindrical to subobpyriform, holoblastic, annellidic. Conidia are initially unicellular, hyaline, granulose, subovoid to ellipsoide-oblong, thick-walled, base truncate,  mature conidia one-septate, cinnamon to fawn, often longitudinally striate, 20-30 x 10-15 µm. Paraphyses when present are hyaline, cylindrical, and sometimes septate, up to 50 µm long.

Predisposing factors

The physical and mechanical injuries are the major predisposing factors of the disease. In case of newly planted mulberry cuttings the cut edges act as portal of entry for the pathogen.

Disease cycle

          B. theobromae Pat. forms chlamydospores and specialized hyphae to overcome unfavorable periods. With favorable conditions, the chlamydospores germinate and the specialized hyphae formed serve as sources of infection to new plants; they infect through wounds or cut edges of the cuttings. Germination tubes infect by means of terminal approsoria      

 Control 

Cultural control 

Deep plough and exposure of soil to sunlight for about a month kills the soil borne pathogens, keep the land leveled to avoid water logging.   Keep the land free from weeds during establishment of the saplings/ plants. 

Chemical control 

Prepare 0.1% solution of Indofil M-45 by mixing 1 g in 1 litre of water. Keep the cuttings immersed in Indofil M-45 solution for 30 minutes.  Plant these soaked cuttings in nursery beds followed by irrigation after 3-4 hours.

 Integrated management 

This method involves the dipping of cuttings in Indofil M-45 (0.1%) solution and application of bio-fungicide (like ‘Nursery-Guard’ containing Trichoderma pseudokoningii). The method of application is as follows. 

Mix 1 kg Nursery-Guard (Trichoderma pseudokoningii) with 60 kg Farm Yard Manure  (sufficient for 2000 cuttings). Store the mixture under shade and keep it moistened by adding 10 - 12 litres of water for one week. After one week, broadcast the mixture in to nursery beds @ 2 kg/m2 and mix well in the soil.  Soak the mulberry cuttings in Indofil M-45 (0.1 %) solution for 30 minutes and plant the cuttings in to treated beds followed by irrigation.  

         For direct plantation of cuttings in to main field, apply ‘Nursery Guard’ mixture in pits @ 50 g/ pit before plantation. 

Related literature 

Gupta VP, Sharma DD, Govindaiah, Chandrashekar DS, (1999) Soil solarization for the control of nursrery diseases in mulberry. Indian J. Seric. 38(1): 44-47. 

Gupta VP, Sharma DD, Rekha M, Chandrashekar DS, (1999) Integration of Trichoderma pseudokoningii with agrochemicals for disease management and plant development in mulberry. Arch.  Phytopath. Pflanz. 32: 521-529.

Sharma DDNishitha Naik VChowdary NBMala VR, (2003) Soilborne diseases of mulberry and their management - a review.  Int. J. Indust. Entomol., 7(4): 93-106.

Siddaramaiah A L, (1987) A new root rot, bud and leaf blight of mulberry seedlings from India. Ind. J. Seric., 27(2): 161.

Teotia RS, Sen SK (1994) Mulberry diseases in India and their control. Sericologia, 34(1)1-8.

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