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ASIAN JOURNAL OF SCIENCE AND TECHNOLOGY

Asian Journal of Science and Technology Vol. 3, Issue 04, pp.90-94, March, 2012

RESEARCH ARTICLE SURVEY ON THE INCIDENCE OF GROUNDNUT ROOT ROT DISEASE IN CUDDALORE DISTRICT OF TAMIL NADU AND ASSESSING THE CULTURAL CHARACTERS AND PATHOGENICITY OF Macrophomina phaseolina (Tassi.) Goid. *Raja Mohan, K. and Balabaskar, P. Department of Plant Pathology, Faculty of Agriculture, Annamalai University, Annamalainagar-608002 Received 25th January, 2012; Received in Revised from; 17th February, 2012; Accepted 15h March, 2012; Published online 10th April, 2012

ABSTRACT Groundnut (Arachis hypogaea L.), the ‘king’ of oilseeds is an important leguminous oilseed crop and is one of the most important food and cash crops of our country. During the recent years root rot caused by Macrophomina phaseolina causes significant losses in groundnut growing areas of Cuddalore district of Tamil Nadu. Hence, the present study was conducted with an objective to assess the prevalence and incidence of dry root rot of groundnut in Cuddalore district of TamilNadu, India during 2008-09 and assess the cultural characters and pathogenic variability among the isolates of M. phaseolina. The survey in different locations of Cuddalore district revealed the endemic nature of the root rot disease incidence with the maximum incidence of the disease (31.68%) registered in Vengatakuppam (MP 18) location. The disease incidence was more in improved cultivars like, VRI2, JL24; more in sandy loam soils and rainfed conditions. Also the isolates of M.phaseolina exhibited cultural and pathogenic variability among them. The isolate (MP18) with faster mycelial growth, maximum sclerotial production and maximum sclerotial size recorded the maximum incidence of root rot disease under pot culture conditions. Key words: Macrophomina phaseolina, Groundnut, Disease incidence, Pathogenic variability

INTRODUCTION Groundnut (Arachis hypogaea L.), is an important leguminous oilseed crop, belonging to the family Fabaceae (Nordern et al., 1982). Groundnut is called as the ‘king’ of oilseeds. It is one of the most important food and cash crops of our country. Groundnut is grown under rainfed and as well as irrigated condition. It is grown in 21.33 million hectares worldwide contributing 34.43 million metric tones of seeds to world oil seed production. China leads in production of peanuts, having a share of about 41.5% of overall world production, followed by India (18.2%) and the United States of America (6.8%) (USDA, 2009). Being a leguminous crop, groundnut increases soil fertility by fixing nitrogen without disturbing the agro ecological balance (Reddy and Kaul, 1986). In India, groundnut occupies an important place in oil seed production and is being grown in an area of 6 million hectares contributing 6.25 million metric tonnes of seeds to the country’s oil seed production. The crop is subjected to various diseases caused by fungi, bacteria and viruses. Of these diseases, root rot caused by Macrophomina phaseolina (Tassi.) Goid. is an important pathogen of groundnut, distributed worldwide and causes considerable losses (Raguchander et al., 1995). The fungus causes complex disease syndromes like charcoal rot of stem, root rot, seedling blight, foliage blight, dry rot, pod and seed rot. *Corresponding author: [email protected]

During the recent years this disease causes significant losses in groundnut growing areas of Cuddalore district of Tamil Nadu. Hence, the present study was conducted with an objective to assess the prevalence and incidence of dry root rot of groundnut in Cuddalore district of TamilNadu, India during 2008-09 and assess the cultural characters and pathogenic variability among the isolates of M. phaseolina.

MATERIALS AND METHODS Survey on the root rot incidence of groundnut in Cuddalore district A field survey was conducted to assess the extent of root rot occurrence of groundnut in Cuddalore district of Tamil Nadu State. The villages where groundnut is traditionally grown are selected for assessing the prevalence of root rot disease caused by M. phaseolina. Twenty locations representing both rainfed and irrigated situations were selected for the survey. The per cent disease incidence was worked out as per phytopathometry (Mayee and Datar, 1986). Also, the infected plants showing the typical symptoms of root rot due to infection with M. phaseolina were collected along with rhizosphere soil for isolation of the pathogen. The other information’s regarding the soil type in which the crop is grown and the variety of groundnut cultivated were also recorded in the respective survey fields.

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Isolation of the pathogen

Sclerotial size

The pathogen M. phaseolina was isolated from the diseased roots of groundnut plants showing the typical root rot symptoms by tissue segment method (Rangaswami, 1972) on potato dextrose agar (PDA) medium. The axenic cultures of the different isolates of the pathogen were obtained by single hyphal tip method (Rangaswami, 1972) and these were maintained on PDA slants.

For each isolate 100 sclerotia were collected at random. These were dried under shade for two h. and their size was measured using an ocular micrometer in a calibrated microscope.

Mass multiplication of M.phaseolina inoculum for soil application

The data presented in table 1 on the survey in different locations of Cuddalore district revealed the endemic nature of the root rot disease incidence. Among the different locations of Cuddalore district surveyed for groundnut root rot incidence, Vengatakuppam (MP18) registered the maximum incidence of the disease (31.68%) followed by Keelpuvanikuppam (MP13) with 29.00 per cent, Aduragaram (MP1) with 26.33 per cent and Nellikuppam (MP11) with 24.87 per cent. The other locations viz., Rajakuppam (23.54), Kammapuram (24.76), Chinnakannadi (21.73) and Meensurtti (23.12) had moderate disease incidence while the minimum root rot incidence of 14.00 per cent was recorded in Ellappanpettai. In general, the crop grown under rainfed conditions showed more root rot incidence when compared with the crops grown under irrigated conditions. In respect of soil type, sandy loam had more root rot incidence (14.00 to 31.68%) than red sandy (16.60 to 19.65%) and clay loam (15.87 to 24.76%) soil. The local cultivars of groundnut recorded comparatively lesser (14.00 to 20.00) root rot incidence than the improved cultivars viz., VRI2 and JL24 (15.87to 31.68 % and 18.45 to 26.75% of disease incidence respectively). The variation in the extent of the disease incidence might be due to the prevalence of the isolates of the pathogen differing in their virulence as observed in the present study. Similar such endemic nature of root rot disease of groundnut in Gujarat was reported by Moradia and Khandar (2011). The results of the present survey revealed higher levels of disease incidence in rainfed crop than that of irrigated crop. The dry condition prevalent in the rainfed conditions might have favoured the pathogen which could be attributed for the higher level of disease incidence. It has been reported that dry rainfed conditions favoured higher root rot disease in crops (Bremer, 1944; Maiti et al., 1985). The disease incidence was more in sandy loam as compared to clay or clayey loam (Table 1). Taya et al. (1988) found that root rot disease caused by R. bataticola in cowpea was the maximum in sandy soil while it was the minimum in clay soil. Similar observations with M. phaseolina in mungbean (Hooda and Grover, 1990) and sesame (Karunanithi, 1996) have been reported. Higher incidence of the disease in sandy soils might be attributed to the less competitive saprophytic ability (CSA) of the pathogen at high moisture holding capacity (MHC) associated with heavy soils like clay (Umamaheswari, 1991) and reduction in the germination of sclerotia of M. phaseolina at high MHC (Ali and Ghaffar, 1991).

The isolates of the pathogen were multiplied in sand maize medium (Riker and Riker, 1936). Sand and ground maize seeds were mixed in the ratio of 19:1, moistened to 50 per cent level, filled in 500ml conical flask and autoclaved at 20 psi for two h. Four actively growing mycelial discs (9 mm) of the M.phaseolina collected from different locations were inoculated into each flask under aseptic condition and the flasks were incubated at room temp.(28+2°C) for 15 days. The inoculum thus obtained was used for the experiments. Assessing the virulence of M.phaseolina isolates The potting mixture was prepared thoroughly mixing clay loam soil, sand and farm yard manure at 1:1:1 ratio. The inoculum of each isolate of M.phaseolina collected from different locations were separately mixed at five per cent level (w/w) with the sterilized soil filled in 30cm earthen pots ten days before sowing (Sanker, 1994). Surface sterilized (using 0.1% HgC12 solution for 30 sec. followed by two washings in sterile water) groundnut seeds were sown @ 03 seeds pot-1. Three replications were maintained in a completely randomized design and the groundnut cultivar VRI-2 was used in this study. The pots were maintained in glass house with regular, judicious and uniform watering. The root rot incidence was recorded at 45, 60 and 75DAS and the per cent disease incidence was calculated. Cultural characteristics of the isolates Mycelial growth Fifteen ml of the sterile PDA medium was poured into sterile Petri dishes and allowed to solidify. A nine mm culture disc of M.phaseolina obtained from actively growing region was aseptically placed at the centre of the dish and incubated. The radial growth and colour of the isolates (in mm) measured three days after inoculation. Sclerotial number From seven day old culture of the isolates, four culture discs (9 mm) were cut and placed into 50 ml beakers containing 10 ml of sterile water. These beakers were kept on a mechanical shaker at 1000 rpm for 30 min. to separate the sclerotia from the medium; then squeezed through cheese cloth; washed several times with dist. Water and the sclerotia were transferred to a glass vial containing 2.5 ml of 2.5 per cent ammonium sulphate. After 10 min. the floating sclerotia were filtered through a Whatman No. 1 filter paper; rinsed with dist. water and the number of sclerotia was counted using stereo zoom microscope (Dhingra and Sinclair, 1978).

RESULTS AND DISCUSSION Survey on the root rot incidence of groundnut in Cuddalore district

Cultural characteristics Mycelial growth All the thirteen isolates of the root rot pathogen M. phaseolina produced cottony white or dull white mycelial growth on PDA medium. The isolates MP1, MP11, MP13 and MP18 significantly recorded the maximum (90 mm) mycelial growth, while it was the minimum (75.00 mm) in the case of MP5 (Table 2). Similar

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Table 1. Survey on the incidence of groundnut root rot disease Sl.No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Village Aduragaram Chathiram Pattampakkam Parangipatti Thannur Srimusnam Meensuruti Kammapuram Mandharakuppam Vengadampatai Nellikuppam Periyapettu Keelpuvanikuppam Chinnakannadi Sedapalayam Sivapuri Ellappanpatti Vengatakuppam Rajakuppam Meenachipatti

Soil type Sandy loam Red sandy Clay loam Sandy loam Sandy loam Red sandy Sandy loam Clay loam Clay loam Red sandy Clay loam Sandy loam Sandy loam Sandy loam Clay loam Clay loam Sandy loam Sandy loam Sandy loam Red sandy

Variety VRI-2 JL-24 VRI-2 Local JL-24 Local VRI-2 JL-24 Local VRI-2 JL-24 VRI-2 TMV-7 VRI-2 JL-24 VRI-2 Local VRI-2 JL-24 Local

Situation Rain fed Irrigation Irrigation Rain fed Rain fed Rain fed Rain fed Irrigation Irrigation Irrigation Irrigation Rain fed Irrigation Rain fed Irrigation Irrigation Rain fed Rain fed Rain fed Irrigation

Root rot incidence (%) 26.33c 18.45j 21.47i 20.00g 21.64i 14.60l 23.12e 24.76d 16.88h 17.22i 24.87c 28.00f 29.00b 21.73c 26.75g 15.87k 18.00j 31.68a 23.54c 19.65j

Table .2 Cultural characters of M. phaseolina isolates Sl.No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Isolate number MP1 MP2 MP3 MP4 MP5 MP6 MP7 MP8 MP9 MP10 MP11 MP12 MP13 MP14 MP15 MP16 MP17 MP18 MP19 MP20

Mycelial Growth (mm) 90.00a 81.33c 82.33c 80.00d 75.00g 85.66b 78.00e 84.33c 83.66c 82.00c 90.00a 85.66b 76.33f 80.00d 90.00a 83.50c 80.50d 90.00a 78.47f 81.62c

Mycelium characters Grey profusely aerial growth Grey profusely aerial growth White Grey profusely aerial growth White scanty aerial growth Grey profusely aerial growth Light grey scanty aerial growth Black grey profusely aerial growth Black grey profusely aerial growth Black profusely aerial growth Grey profusely aerial growth Light grey profusely aerial growth Black profusely aerial growth Light grey scanty aerial growth Light grey scanty aerial growth Black scanty aerial growth Light grey scanty aerial growth Black profusely aerial growth Grey profusely aerial growth Light grey profusely aerial growth Black grey profusely aerial growth

Number of Sclerotia (9mm disc) 182.75a 175.80d 176.40c 175.10d 170.80f 180.70b 173.90c 185.00a 178.90b 177.80c 185.30a 179.90b 171.70f 174.50d 184.40a 176.50c 178.20b 185.40a 178.40b 176.45c

Sclerotial Size µ 104.70a 93.70c 91.99d 90.90d 85.70e 99.80b 92.80d 102.40a 97.70b 95.80c 105.10a 98.70b 87.60e 90.70d 103.30a 98.60b 92.80d 96.49c 90.30d 94.60c

Table 3. Pathogenicity of M. phaseolina native isolates Isolates Sl.No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

MP1 MP2 MP3 MP4 MP5 MP6 MP7 MP8 MP9 MP10 MP11 MP12 MP13 MP14 MP15 MP16 MP17 MP18 MP19 MP20

45 DAS 24.20b 18.80f 20.40d 19.30e 12.55j 14.75i 15.86g 14.40i 18.47f 17.50g 23.10c 19.40e 15.60h 18.40f 17.30g 20.10d 19.30e 25.90a 22.40c 15.80a

Root rot incidence (%) 60 DAS 75 DAS 36.95b 50.69a e 27.30 36.70d 31.50d 40.40b e 26.80 38.30c 18.25h 22.90i 20.30g 26.80h 23.50f 29.70f 26.30e 35.10d 27.37e 37.10c 26.87e 35.80d 36.70b 49.10b 27.13e 34.70e 23.19f 30.17f 26.59e 35.20d 25.70f 34.45e 30.40d 39.49b 27.10e 36.30d 38.63a 51.70a 34.90c 47.90b 23.00f 28.60g

variations in the mycelial growth among the isolates of M. phaseolina were observed by earlier workers (Bansal et al., 1990; Sobti and Sharma, 1992; Singh and Malhotra, 1994;

Mean At harvest 65.70b 53.40c 58.35d 55.30e 35.60k 38.90j 40.70i 47.70g 55.70e 49.40g 64.30b 50.14f 44.50h 48.80g 49.70g 57.80d 52.30f 67.34a 62.60c 40.50i

44.38 34.05 37.66 34.92 22.32 25.18 27.44 30.87 34.66 32.39 43.30 32.84 28.36 32.24 31.78 36.94 33.75 45.89 41.95 26.97

Ebenezar, 1996). The results of the present experiment also revealed that the isolates of M. phaseolina with faster mycelial growth were more pathogenic and produced higher incidence

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of the disease. The virulence of the isolates of M. phaseolina was positively correlated with their growth rate (Ghosh and Sen, 1973). Isolates of M. phaseolina with faster mycelial growth were found more pathogenic to cluster beans (Sharmishha Purkayastha et al., 2004). These reports corroborates with that of the present findings. Sclerotial number All the isolates of M. phaseolina varied in their ability to produce sclerotia on PDA medium. The maximum sclerotial number of 185.30 per nine mm culture disc was obtained from the most virulent isolate MP18. The minimum number of sclerotial production of 171.70 was recorded by the least virulent isolate MP13 (Table 2). It is evident from the observations that sufficient build up of the growth is absolutely necessary for the aggressiveness of the pathogen. Hooda and Gover (1982) observed a positive correlation between the disease intensity and the inoculum density. Similarly, the correlation between inoculum density and disease development was worked out for carrot, tomato and pepper (Punja et al., 1984), sesame (Sankar, 1994) and in other crops (Umamaheswari, 1991; Rettinasababady, 1996; Ebenezar, 1996) in respect of M. phaseolina. Generally isolates producing more sclerotia are more pathogenic and caused higher seedling mortality as reported by Sharmishha Purkayastha et al. (2004). Sclerotial size In the present study the biggest (105.10µ) and the smallest (85.70) sclerotia were produced by MP11 and MP5, respectively (Table 2). Similar variation in the sclerotial size was observed by several workers (Raut and Ingle, 1989; Sobti and Sharma, 1992; Singh and Kaiser, 1994). Manici et al. (1992) observed the sclerotia of 64 isolates of M. phaseolina and found that the size varied from 72.8 to 127.8. Monga and Sheo Raj (1994) found that the isolates producing bigger sclerotia caused more root rot incidence in cotton even at low inoculum level. In the present study also the isolate (MP6), which produced the biggest sclerotia caused the maximum root rot incidence. All these above reports corroborated with the present investigations. The possibility of containing more food materials and subsequent production of more pathogenic germ tubes by bigger sclerotia might have resulted in more aggressiveness of the isolate. Virulence of different isolates of M. phaseolina on groundnut The results of the pot culture experiment conducted by artificial inoculation of the pathogen revealed varied levels of pathogenicity with different isolates. Among the twenty isolates of M. phaseolina collected from different conventionally groundnut growing areas of Cuddalore district, the isolate from Vengatakuppam (MP18) was found to be the most virulent, recording the highest incidence of 67.34 per cent at harvest and the isolate MP5 collected from Pattampakkam was the least virulent which recorded the lowest incidence of 35.60 per cent (Table 3). The variations in root rot incidence in different locations could be well attributed to the difference in virulence of the M. phaseolina isolates prevalent in the respective areas.

The variability in the pathogenecity among the isolates of M. phaseolina was reported by several workers (Byadgi and Hegde, 1985; Karunanithi, 1996) with different crops. Mungan and Yildiz (1990) observed variation in pathogenecity among M. phaseolina isolates of tobacco which ranged from 0 to 100 per cent. Sobti and Sharma (1992) recorded 13 to 63 per cent root rot incidence of groundnut with different isolates of R. bataticola. The pathogenic variation in the isolates of M. phaseolina from different cowpea growing areas of Udaipur was reported by Ratnoo et al. (1997). Similarly, the occurrence of 26 M. phaseolina isolates from 11 different localities of green gram growing areas in India was reported by Devi and Singh (1998). The above reports are in agreement with the present investigation. In the present study it was observed that incidence of root rot was the maximum in 75 day old plants when compared to younger crop (Table 3). Similar observations were made by Shanmugasundaram (1992) in sunflower, Sankar (1994) in sesame and Rettinasababady and Ramadoss (2000) in rice fallow blackgram. Thus, the observations of the present survey indicated the endemic nature of groundnut root rot disease in cuddalore district of Tamilnadu, India.

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