Madras Agric. J., 97 (7-9): 281-284, September 2010

Survey for Determining Predisposing Factors of Major Diseases of Mulberry Silkworm, Bombyx mori L. S. Manimegalai1, T. Rajeswari and R. Shanmugam Department of Sericulture Tamil Nadu Agricultural University, Coimbatore-641 003

Extensive surveys were conducted in major silkworm growing regions of Tamil Nadu to assess the disease incidence level, losses due to major diseases and prioritize the factors that predispose the larvae to diseases. The results of the survey revealed that the incidence of grasserie, flacherie, muscardine diseases and cocoon melting was the highest in Salem district (4.5 %, 7.5 %, 1.0 % and 4.0 %) followed by Erode (3.2 %, 6.0 %, 1.0 % and 2.4 %) and Coimbatore district (2.4 %, 3.0 %, 1.2 % and 2.0 %). Garrett’s ranking of etiological agents responsible for diseases showed that leaf quality was the most important factor with mean score of 71.60 (rank 1) followed by rearing condition (69.46, rank 2) and disinfection practice (54.90, rank 3). Key words: Bombyx mori L., survey, grasserie, flacherie, muscardine, cocoon melting, disease incidence, etiological agents, Garrett’s ranking.

Mulberry silkworm, Bombyx mori L. is affected by viral, bacterial, fungal and protozoan pathogens due to various biological, chemical, physical, nutritional and environmental causes. Survey in Coimbatore revealed a loss of 3.5 to 4.0 kg of cocoon for every 100 disease free layings (dfls) and considering the total utilization of 30 lakhs dfls, the annual loss in Tamil Nadu alone was estimated to be Rs.0.9 crores (Anonymous,1989). A survey in Tamil Nadu revealed that the loss due to nuclear polyhedrosis virus disease ranged from 0.5 to 22.5 per cent in the districts of Coimbatore, Salem, Erode and Dharmapuri (Sivaprakasam, 1994). Results of survey conducted in traditional districts of Tamil Nadu, showed that flacherie incidence ranged from 0-25,0-22,0-28 and 0-35 per cent in Coimbatore, Erode, Salem and Dharmapuri districts with an average of 5.56, 4.64, 7.12 and 11.08 per cent respectively. (Manimegalai and Chandramohan, 2005). Selvakumar et al. (2000) reported that muscardine disease was common during winter and rainy seasons. The maximum yield reduction due to muscardine was 6.86 kg, 29 kg and 26.14 kg/100dfls during winter, summer and rainy seasons. Fluctuations in temperature, leaf quality, poor disinfection practices, improper rearing conditions predispose the larvae to disease and hence identification of the etiological agents and its importance with relevance to disease occurrence will be helpful to design appropriate disease management approaches. Though different *Corresponding author email: [email protected]

methods are available for disease management, designing an appropriate integrated strategy taking into consideration the etiological agents will be highly economical and will be appropriate to the current situation. Rather than a single method, an integrated approach will always prove highly successful. In this study an attempt was made to gather information on incidence of diseases and relate the disease incidence to etiological agents. Materials and Methods A detailed survey was carried out to assess the level of disease incidence and to study the etiological agents responsible for disease occurrence in various Technical Service Centres (TSC) of Coimbatore, Erode and Salem districts of Tamil Nadu. The villages covered in each district are listed in Table 1. A structured questionnaire was prepared for the collection of information on disease occurrence and etiological factors by personal interview with farmers and through visual observation. The loss due to the diseases was also estimated from the data collected. Etiological agents / Predisposing factors

Garrett’s ranking technique was adopted to analyze the reasons for disease occurrence (William, 1984). The farmers were asked to rank the factors responsible for disease occurrence. The order thus given by them was converted into ranks using the formula 100 (Rij-0.5) Per cent position = Nj

282 Table 1. Villages covered under survey in Technical Service Centres of three districts of Tamil Nadu District

Coimbatore Annur Avinashi

Erode

Villages

TSC

Allapalayam, Allikulam, Kunnathur, Manikkampalayam, Masakkan chettipalayam, Narayanapuram,Ponnaikoundan puthur, Pothanayakkanur, Ponnai goundanpalayam, Oraikkalpalayam. Cheyur, Pallikkattuputhur, Pulippar, Kootapalli.

Coimbatore

Kolumam, Kovilpalayam, Kovilpatti, Mylavaram, Ruthriampalayam, Thudiyalur.

Udumalpet

Aranmanaithottam, Bodipatti, Jothipuram, Kulathupalayam, Kuttaithottam, Madathukulam, Manupatti, Pappankulam, Sundakkampalayam, Valavadi, West Neelampur.

Bhavani

Odathurai, Othaikkalpalayam

Gobichettipalayam

Aallampalayam, Allankuttuvalam, Bommanaikanpalayam, Chinnakosanam, Dhasampalayam, Goundaputhur, Kallankattuvalasu, Kalramani,Kosanam, Nanjan Goundampalayam, Muruganputhur, Palayur, Polavakkalipalayam, Pommanayakkampalayam, Oralpatti, Othakkuthirai,Thasampalayam,Vadugampalayam,Vellalampalayam, Vellaiyampadi, Vellankovil, Velmaninager.

Kundadam

Eragampatti, Maruthur, Parappallayam, Sadaiyampalayam, Sengattupalayam, Vannapatti.

Nambiyur

Karaukkampalayam, Kunnathur, Nallangoundanpalayam, Oothupalayam.

D.Perumalpalayam

D. Perumalpalayam, Valaiyakkaranur, Vellalakundam, Vellampalayam.

Salem

Salem

D. Pommapalayam,Katchupal,Kombaikkadu,Koranampatti,Panakkarapalayam, R.Puthupatti.

Salem bivoltine

Katchipalli, Mannarpalayam, Pallipatti, Panjampatti, Seeragampadi, Vedappatti.

Edapadi

Iyyampalayam, Konganapuram, Manivizhunthan colony, Nallampatti.

Aranoothumalai

C.N.Palayam, Puthupatti, Poosaripatti, Kuruchi, Nammadipatti, Nodappatti, Ranganoor, Sukkampatti.

Attur

Hemmampatti, Jagathish Samuthiram, Kondaiyampatti, Krishnapuram, Othaikkadu, Thammampatti.

Meicherry

Adhagampatti, D. Pommapalayam, Ramnagar.

Where,

Results and Discussion

Rij = Rank given for ith factor by jth individual, Nj = Number of factors ranked by jth individual

Among the three districts surveyed for the incidence of grasserie and yield loss due to the disease, Salem recorded the highest disease incidence and yield loss (4.50 %, 3.80 kg / 100 dfls) followed by Erode (3.20 %, 3.10 kg/100 dfls) (Table 2). Incidence of flacherie and cocoon melting was also the highest in Salem (7.5 %, 4.0 %) followed by Erode (6.0 %, 2.4 %). Among the districts, Coimbatore recorded the lowest disease incidence (2.40 %, 3.0 % and 1.2 %) and cocoon melting (2.0 %).

The per cent position of each rank thus obtained was converted into scores by referring to table given by Garrett’s. The seven predisposing factors considered were rearing house, disinfection practice, silkworm race, leaf quality, spacing, temperature fluctuation and rearing condition.

Table 2. Incidence of Grasserie, Flacherie, Muscardine and Cocoon melting in three districts of Tamil Nadu Grasserie District

Coimbatore Erode Salem Average

Per cent incidence 2.40 3.20 4.50 3.37

DM Sa2 2.0 3.10 3.80 2.93

Flacherie Per cent incidence 3.0 6.0 7.5 5.50

In the present study, it was found that crop failure occured due to diseases. According to Samson (1985), in tropical countries, two to three crop failures or poor yield due to silkworm diseases was experienced out of five to six crops. He also concluded that diseases are known to occur in almost all silkworm rearing areas of the world (Samson, 1987).The present results on the highest grasserie incidence are supported by the works of Manimegalai and Chandramohan (2005) who reported that the flacherie

DM Sa2 2.50 5.50 6.0 4.67

Muscardine Per cent incidence 1.2 1.0 1.0 1.1

DM Sa2 1.0 1.0 0.2 1.0

Cocoon Melting Per cent incidence 2.0 2.4 4.0 2.8

DM Sa2 1.2 2.0 3.0 2.0

incidence was high in Salem (7.12 %) followed by Coimbatore (5.50 %) and Erode (4.64 %).In a survey conducted by Sivaprakasam (1994) in four districts of Tamil Nadu, it was concluded that the grasserie disease incidence was maximum (25 %) at Dharmapuri followed by Erode (15.5 %), Coimbatore (11.8 %) and Salem (9.13 %) during summer months. The present result also revealed that the disease incidence showed a declining trend over years. The reduction in disease incidence may be due to rearing

283 of season specific breeds apart from following adequate disease prevention methods and producing mulberry leaves of good quality. Ranking of predisposing factors in all four TSCs of Coimbatore district showed that the leaf quality was the major factor (rank 1) followed by rearing conditions (rank 2). Similar results were observed in Erode district. No significant difference in ranking was observed between TSCs in Coimbatore. The same trend was observed in Erode excepting the silkworm race and spacing. However in Salem, irrespective of TSCs, rearing condition was identified as the major factor followed by leaf quality (Table 3)

Garrett’s ranking of etiological agents responsible for disease occurrence revealed that the leaf quality with mean score of 71.60 was the major predisposing factor followed by rearing conditions (69.46) and disinfection practice (54.90) (Table 3). The present result corroborates with the findings of Venkatesh and Patil (2001) who reported that farmers lose considerable quantity of cocoon crop due to bacterial and viral diseases mainly due to poor quality leaf coupled with inadequate hygiene and disinfection practices. Krishnaswami et al. (1973) identified feeding of unsuitable leaves as a major causative factor for flacherie and grasserie. According to Boraiah (1994),

Table 3. Garrett's ranking of factors responsible for disease occurrence in Bombyx mori in various Technical Service Centres of Coimbatore, Erode and Salem districts of Tamil Nadu Predisposing factors District / TSCs

Coimbatore Coimbatore Avinashi Annur Udumalpet Erode Gopichettipalayam Nambiyur Kundadam Bhavani Salem Salem Salem bivoltine D.Perumalpalayam Edappadi Aranoothumalai Attur Meicherry Overall Mean Coimbatore Erode Salem

Rearing shed

Disinfection practice

Silkworm race

Leaf quality

Spacing

Temperature fluctuation

Rearing condition

50.7 (4) 52.2 (4) 50.0 (4) 51.0 (4)

55.5 (3) 54.4 (3) 58.9 (3) 58.3 (3)

23.7 (7) 22.0 (7) 22.0 (7) 23.3 (7)

Mean score 75.0 (1) 76.9 (1) 72.3 (1) 75.0 (1)

34.3 (6) 35.0 (6) 35.7 (6) 33.7 (6)

43.7 (5) 45.1 (5) 42.9 (5) 44.0 (5)

67.9 (2) 65.3 (2) 69.0 (2) 65.1 (2)

54.3 (4) 51.6 (4) 52.1 (4) 50.7 (4)

55.6 (3) 53.9 (3) 54.4 (3) 55.5 (3)

34.4 (6) 33.5 (6) 22.0 (7) 22.0 (7)

73.0 (1) 76.0 (1) 74.4 (1) 74.7 (1)

23.3 (7) 24.1 (7) 35.0 (6) 35.0 (6)

46.5 (5) 44.6 (5) 44.8 (5) 44.4 (5)

63.7 (2) 66.1 (2) 68.2 (2) 68.4 (2)

57.0 (3) 52.8 (3) 52.1 (4) 55.6 (3) 52.3 (4) 54.4 (3) 52.8 (3)

49.0 (5) 51.4 (4) 56.7 (3) 53.2 (4) 57.2 (3) 53.0 (4) 52.3 (4)

22.0 (7) 22.0 (7) 22.0 (7) 22.0 (7) 22.0 (7) 22.0 (7) 22.0 (7)

63.8 (2) 69.6 (2) 65.2 (2) 61.9 (2) 65.0 (2) 65.2 (2) 68.7 (2)

35.0 (6) 35.0 (6) 35.0 (6) 35.0 (6) 35.0 (6) 35.0 (6) 35.0 (6)

49.5 (4) 45.8 (5) 44.4 (5) 48.1 (5) 45.1 (5) 45.8 (5) 45.8 (5)

74.7 (1) 74.4 (1) 75.6 (1) 75.2 (1) 74.4 (1) 75.6 (1) 74.4 (1)

50.9 (4) 52.1 (4) 53.8 (3)

56.8 (3) 54.8 (3) 53.2 (4)

22.7 (7) 28.0 (7) 22.0 (7)

74.8 (1) 74.5 (1) 65.6 (2)

34.7 (6) 29.3 (6) 35.0 (6)

43.9 (5) 45.1 (5) 46.3 (5)

66.8 (2) 66.6 (2) 74.9 (1)

Figures in parentheses indicate the rank

leaf quality and climatic condition contribute 38.2 and 37.0 per cent respectively for successful cocoon production. Manimegalai (2003) on studying the etiological agents responsible for flacherie disease

of silkworm concluded that leaf quality was the major factor with rank 1 followed by rearing conditions. The rearing conditions including improper disposal of cadavers, maintenance of proper

284 spacing and starvation are considered important predisposing factors. Larval starvation as an important predisposing factor for grasserie was earlier identified by Satish and Govindan (1987). The role of poor hygiene in disease occurrence was stressed by Samson (1999).

Samson, M.V. 1987. Bacterial diseases of silkworm, Bombyx mori L. Ph.D. Thesis, University of Mysore. 137 p.

Acknowledgement: The authors are grateful to Department of Science and Technology, New Delhi, Government of India for financial assistance.

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Received: July 23, 2010; Accepted: September 15, 2010