Print

Sclerotium wilt/ Collar rot (Sclerotium rolfsii Sacc.)

Introduction 

Wilt of sprouted mulberry cuttings caused by Sclerotium rolfisii was reported first by Siddaramaiah and Patil (1984) from Dharwar, Kamataka (India). The disease is very common in the rainy season and cause wilting sprouted cuttings in mulberry nursery. The disease is common in the established mulberry plantations also. 

Causal organism 

Sclerotium rolfsii Sacc. 

Systematic position 

Kingdom: Fungi 
Division: Basidiomycota 
Class: Basidiomycetes 
Order: Agaricales 
Family: Typhulaceae 
Genus: Sclerotium 
Species: rolfsii 

Symptoms 

 The disease is characterized by presence of dark brown to black water soaked spots on the collar region of the stem which rapidly encircle the stem and eventually more upward and downward regions. White mycelial mat with a large number of chocolate brown sclerotial bodies will develop over the infected tissues.  Sclerotia are ellipsoidal in shape and vary from 0.5 to 1.5 mm in size. Once the stem base is affected, the entire shoot drops down. 

Causal organism 

Sclerotium rolfsii Sacc. 

Description of the pathogen

            The mycelia are white in early stages of development become tan as they mature and finally form strands of brown pigmented hyphae. They measure 6-9 µm wide have clamp connections and numerous dikaryotic nuclei. The sclerotia resemble mustard seeds, are round to irregular in shape, generally tan outside and have a white medulla . 

 

Disease cycle

 Sclerotia of S. rolfsii are easily spread in soil attached to hand tools, machinery or in splashing water. Long-distance movement occurs by means of sclerotia in plant material or soil. During favorable weather conditions, sclerotia resume activity either by eruptive or hyphal germination. Eruptive germination means that aggregates of white mycelium burst out of the sclerotial rind. An external food source is not required for this type of germination. Sclerotia can germinate eruptively only after being induced by dry conditions or volatile compounds Sclerotia can germinate hyphally more than once. Growth of individual hyphae from sclerotia is in response to availability of exogenous nutrients.

Predisposing factors

 The disease is favoured by basal pruning, building of mounds around the stem for irrigation and spreads to the whole plantation through irrigation water (Dayakar Yadav and Kasturi Bai, 1988) apparently because mycelial fragments and sclerotial structures of the fungus remain uniformly distributed in the top soil. S. rolfsiiis able to survive (and thrive) within a wide range of environmental conditions. Growth is possible within a broad pH range, though best on acidic soils. The optimum pH range for mycelial growth is 3.0 to 5.0, and sclerotialgermination occurs between 2.0 and 5.0. Germination is inhibited at a pH above 7.0. Maximum mycelial growth occurs between 25 and 35°C with little or none at 10 or 40 °C.Sclerotialformation is also greatest at or near the optimum temperature for mycelial growth. Mycelium is killed at 0°C, butsclerotiacan survive at temperatures as low as -10 °C. High moisture is required for optimal growth of the fungus.Sclerotia fail to germinate when the relative humidity is much below saturation.

Control

Deep plowing (at least 20 cm) with a moldboard extention inverts soil so that organic matter, sclerotia, and plant debris are buried at least 10 cm beneath the surface. It is controlled effectively by pruning the stumps at 30 cm and above the ground level because hard cortical tissues around the developed stem prevent entry of the pathogen (Dayakar Yadav and Kasturi Bai, 1988).

The compost amendment may increase populations of antagonistic soil microorganisms. Further integrated control of S. rolfisii with nitrogen fertilizers and Trichoderma hazarianum reduces the disease incidence. Further, soil drenching with bavistin (0.05 %), brassicol (0.2 %) or captan (0.2 %) was found effective to control the disease (Siddaramaiah and Pati!, 1984)

 

Related literature

Dayakar Yadav BR, Sukumar J, (1987) Occurrence of a new stem- blight and collor- rot disease of                    mulberry from India.  Sericologia, 27(2): 205-206.

Hong SK, Kim WG, Sung GB, Nam SH, (2007) Identification and distribution of two fungal species causing sclerotial disease on mulberry fruits in orea. Mycobiology, 35(2): 87-90

Pratheesh Kumar PM, Setua GC, (2004) Bacillus lentimorbus a potential biocontrol agent  of collar rot pathogen (Sclerotium rolsfii) of mulberry. Bull. Acad. Seric., 7(1): 108-111.

Sharma DD, Mala VR, Das PK, Dandin SB, (2008) Effect of composts enriched with useful/ antagonistic microbes on suppression of nursery diseases in mulberry. Sericologia, 48 (1): 101-108.

Sharma DD, Nishitha Naik V, Chowdary NB Mala VR, Kamble CK, (2009) management of mulberry diseases through eco-friendly approaches- a review. Sericologia, 49(2): 123-138.

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

Teotia RS, Sen SK, (1994) Mulberry diseases in India and their control. Sericologia, 34(1)1-18.

Friday the 28th. This is the official Website of CSRTI, Mysore - The R & D Organisation of Central Silk Board