Sclerotinia sclerotiorum (Lib.) de Bary [Syn. S. libertiana Fuckel: Whetzelinia sclerotiorum (Lib.) Korf and Dunont], commonly called the white mold, is among the most non-specific, omnivorous and successful plant pathogens. Plants susceptible to this pathogen belong to 64 families, 225 genera and 361 species (Purdy, 1979) and the pathogen has an ability to survive in soil for long periods as sclerotia (Purdy, 1979; Willetts and Wong, 1980). The pathogen attacks nearly all kinds of succulent plants including flowers, shrubs weeds and almost all vegetables (Chupp and Sherf, 1960). Phaseolous lunatus (lima bean) is one of the important vegetable crops. Its fresh seeds can be used as vegetable and dry seed as pulse for human consumption and as fodder in general, especially for mulch cattle. The crop suffers due to infection of Sclerotinia sclerotiorum (Lib.) de Bary which causes white mold. The pods can become infected while on the plant and at post-harvest. To combat the disease, soil solarization (Ferraz, 2001), crop rotation and chemical control (Kurozawa and Pavan, 1997) are employed. Due to lack of adequate levels of host resistance, many fungicides have been employed to control sclerotinia disease (Steadman, 1979; Bardin and Huang, 2001). Use of fungicides to control S. sclerotiorum has been evaluated in snap bean (Phaseolus vulgaris L.). Efficacy of fungicides for control of white mold (Sclerotinia sclerotiorum Lib.) de Bary in lima bean Ashutosh Pandey, Amita J. Mathew, Madhu Kamle, Rupesh Kumar Mishra and Pradeep Kumar Plant Pathology Laboratory Central Institute for Subtropical Horticulture Rahmankhera, Lucknow- 227 107, India E-mail : ashutosh.pandeybt@gmail.com ABSTRACT White mold of lima bean (Phaseolous lunatus) caused by Sclerotinia sclerotiorum is a major disease in India. Isolates of the pathogen from different region of Uttar Pradesh were assayed both in vitro and in the greenhouse (in vivo) for their sensitivity to eight commercially available fungicides, viz., dithiocarbamic acid, carbendazim, ziram, phenylthiourea, carboxin + dithiocarbamic acid, difenoconazole, hydrogen sulphide, and mancozeb. Phenylthiourea and difenoconazole were found to be most effective and these inhibited radial growth of the test organism a level of to 71.5% and 70.5%, respectively. These two fungicides were also found as most promising in controlling the disease under greenhouse conditions, reducing disease severity to 0.14% and 0.22%, respectively compared to the control where it was 18.9%. Keywords: Sclerotinia sclerotiorum, white mold, Phaseolous lunatus, lima bean, fungicides However, control has been inconsistent (Hunter et al, 1978; Steadman, 1979) primarily due to difficulty in achieving good coverage with the fungicide and timing of application in relation to ascospore release. Fungicides have been used successfully on a commercial scale for controlling the disease on soybean, dry bean, oilseed rape and several vegetables (Bailey et al, 2001; Budge and Whipps, 2001; Del Rio et al, 2004), but, adequate information on the efficacy of various fungicides and their judicious usage is lacking in controlling white mold on P. lunatus (Gossen et al, 2001). Therefore, the present investigation describes the efficacy of eight commercially available fungicides [which were tested both in vitro and under greenhouse (in vivo) condition] against the pathogen causing white mold in P. lunatus. Maintenance of Sclerotinia sclerotiorum isolates Five isolates of S. sclerotiorum used in the present study were collected from infected P. lunatus plants growing in five different districts of Uttar Pradesh namely Faizabad, Akbarpur, Gonda, Basti and Lucknow (Table 1). The pathogen was isolated on PDA plates and the isolates were further purified by growing sclerotia singly from each colony on Potato Dextrose Agar (PDA) slants. Short communication J. Hortl. Sci. Vol. 7(1):114-117, 2012 115 Colony characteristics Radial growth (mm), morphology and number of sclerotia per plate were evaluated in Petri dishes on PDA. At least three PDA plates were inoculated with 5mm dia. mycelial discs taken from the margin of actively growing five day old colonies in each plate. Inoculated plates were then incubated at 25±2oC. Colony diameter was measured every day until fifth day. Number of sclerotia per plate was estimated at 20-25 days of incubation. Data from replicated plates were averaged. Colony morphology was also observed at 10 days of incubation. In vitro experiment Eight fungicides, viz., dithiocarbamic acid, carbendazim, ziram, phenylthiourea, carboxin + dithiocarbamic acid, difenoconazole, hydrogen sulphide and mancozeb (Table 2) were evaluated for control of white mold fungus on PDA and on seedlings of P. lunatus as per Bhaktavatsalam et al (1978). Greenhouse experiment Eight commercially available fungicides were evaluated for control of S. sclerotiorum on P. lunatus as per Mueller et al (2002). Colony characteristics: Data on colony characteristics, growth rate, number of sclerotia per plate and period taken for sclerotia formation in five isolates of S. sclerotiorum collected from different location is presented in Table 1. Of the five, three isolates collected from Faizabad, Akbarpur and Gonda formed fluffy colonies whereas, isolates from Basti and Lucknow had compact colonies. The isolate collected from Basti showed maximum growth rate, i.e., 48mm per day, and the isolate collected from Lucknow showed minimum growth of 35mm per day. A maximum of 42 sclerotia per plate were formed in the isolate collected from Akbarpur, whereas only 19 sclerotia per plate were formed in the Lucknow isolate. All the isolates took uniformly seven days for sclerotia formation. Fungicides in control of white mold in lima bean Table 1. Colony characteristics of various isolates of Sclerotinia sclerotiorum collected during 2007 on host Phaseolus lunatus Isolate(s) Place of Colony Growth rate No. of sclerotia Period (days) of Pattern of sclerotium collection morphology (mm per day) per plate sclerotium formation formation Ss 1 Faizabad Fluffy 40 31 Days Scattered Ss 2 Akbarpur Fluffy 42 19 Days Near rim Ss 3 Gonda Fluffy 39 25 Days Near rim Ss 4 Basti Compact 48 25 Days Scattered Ss 5 Faizabad Compact 35 12 Days Scattered Table 2. Nature of fungicides used and their active chemical S. No. Common name IUPAC name Active chemical Nature 1 Thiram Tetramethyl thiuram disulphides Dithiocarbamic acid Contact 2 Bavistin Methyl benzimidazol-2-ylcarbamate Carbendazim Systemic 3 Cuman Zinc dimethyl dithiocarbamate Ziram Contact 4 Topsin-M Methyl-ethyl-thiophanate Phenylthiourea Systemic 5 Vitavax 5,6-Dihydro-2-methyl-1,4-oxathi-ine-3-carboxanilide Carboxin + Dithiocarbamic acid Systemic + Contact 6 Score 1-(2-[4-(4-chlorophenoxy)-2-chlorphenyl]-4-methyl-1, Difenoconazole Systemic 3-dioxolan-2-yl methyl]-1 H-1,2,4-triazole 7 Sulfex Elemental sulfur Hydrogen sulphide Contact 8 Indofil- M 45 Manganese ethylene (dithiocarbamate) (polymeric) Mancozeb Contact complex with zinc salt Table 3. Effect of fungicides on percentage inhibition of radial growth of S. sclerotiorum (in vitro) S. sclerotiorumisolates Inhibition of radial growth (%) by fungicides Dithiocarbamic Carbendazim Ziram Phenylthiourea Carboxin + Difenoconazole Hydrogen sulphide Mancozeb acid Dithiocarbamic acid Ss 1 27.8 34.5 24.6 70.2 34.8 67.9 31.5 42.0 Ss 2 34.7 32.5 26.5 71.5 36.5 66.0 30.6 41.4 Ss 3 23.4 32.5 22.8 69.6 33.6 68.4 28.6 38.9 Ss 4 27.9 33.4 22.8 69.9 34.0 70.5 28.4 39.9 Ss 5 32.8 29.8 22.6 69.5 35.3 69.8 32.4 38.9 CD (P>0.05) 0.55 1.02 0.28 1.18 0.88 1.25 0.64 1.04 J. Hortl. Sci. Vol. 7(1):114-117, 2012 116 In vitro experiments: It is clear from data presented in Table 3 that all the chemical pesticides tested were effective against the test organism in comparison to control. Extent of mycelial growth in S. sclerotiorum in response to each fungicide varied considerably. Phenylthiourea was found most effective in reducing mycelial growth by 69.5% to 71.5%, followed by difenoconazole where inhibition was recorded 66% to 71.5%. Mancozeb, carboxin + dithiocarbamic acid and carbendazim exhibited intermediate level of inhibition, whereas hydrogen sulphide, ziram and dithiocarbamic acid showed lowest effectiveness in inhibiting mycelial growth. In vitro studies have earlier been used to identify specific fungicide and rate of fungicidal activity against S. sclerotiorum (Hawthorne and Jarvis, 1973). Phenylthiourea has been proved to be effective against Fusarium oxysporum and Rhizoctonia solani (Iqbal et al, 1996) and aganist Ascochyta. lentis (Rauf et al, 1996). Greenhouse experiments: A significant (P<0.05) effect among the eight fungicides tested was observed on disease severity. Plants not sprayed with fungicide had expanded foliar lesions that caused defoliation. Fungal colonized stems and some plants were dead. Phenylthiourea and difenoconazole were most effective in controlling the disease under greenhouse, exhibiting 0.14% and 0.22% disease severity, respectively (Table 4). These results are in accordance with earlier findings showing that spraying the whole plant with effective fungicides provides excellent control of S. sclerotiorum (Hunter et al, 1978). Thus the present study revealed that topsin–M was found to be most effective, both in in vitro and greenhouse conditions, against Sclerotinia rot in lima bary. In Brinjal (Iqbal et al, 2003). Muller et al, (2002) reported that plants treated with benomyl, thiophanate methyl and vinclozolin expressed no symptoms or signs of Sclerotinia stem rot in soybean. REFERENCES Bailey, K.L., Johnson, A.M., Kutcher, H.R., Gossen, B.D. and Morrall, R.A.A. 2001. Managing crops losses from foliar diseases with fungicides, rotation and tillage in the Saskatchewan Parkland spring sown oilseed rape. Crop Prot., 17:405-411 Bardin, S.D. and Huang, H.C. 2001. Research on biology and control of Sclerotinia disease in Canada. Can. J. Pl. Pathol., 23:88-98 Bhaktavatsalam, G., Satyanarayana, K., Reddy, A.P.K. and Johri, V.T. 1978. Evaluation of sheath blight resistance in rice. Int’l. Rice Res. Notes., 3:910 Budge, S.P. and Whipps, J.M. 2001. Potential for integrated control of Sclerotinia sclerotiorum in glasshouse lettuce using Coniothyrium minitans and reduced fungicide application. Phytopath, 91:221-227 Chupp, C. and Sherf, A.F. 1960. Sclerotinia diseases In: Vegetable Diseases and their Control. The Ronald Press Company, New York, pp 43-46 Del Rio, L.E., Venette, J.R. and Lamey, H.A. 2004. Impact of white mold incidence on dry bean yield under non- irrigated conditions. Pl. Dis., 88:1352-1356 Ferraz, L.C.L. 2001. Praticas culturais para o manejo de mofo-branco (Sclerotinia sclerotiorum) em feijoeiro. Piracicaba: USP/ESALQ, (Tese - Doutorado) Gossen, B.D., Rimmer, S.R. and Holley, J.D. 2001. First report of resistance to Benomyl fungicide in Sclerotinia sclerotiorum. Pl. Dis., 85:1206 Hawthorne, B.T. and Jarvis, W.R. 1973. Differential activity of fungicides on various stages in the life cycle of Sclerotinia spp. New Zealand J. Agril. Res., 16: 551-557 Hunter, J.E., Abawi, G.S. and Crosier, D.C. 1978. Effects of timing, coverage and spray oil on control of white mold of snap bean with Benomyl. Pl. Dis. Rep., 62:633-637 Hunter, T., Hutchinson, M.A. and Eckhart, W. 1978. Translation of polyoma virus T antigens in vitro. Proc. Nat’l. Acad. Sci., USA, 75:5917–5921 Iqbal, S.M., Bashir, M., Rauf, C.A. and Mali, B.A. 1996. Efficacy of fungicides against soil-borne pathogens of chickpea. Pakistan J. Phytopathol., 8:65- 67 Ashutosh Pandey et al Table 4. Evaluation of fungicide against S. sclerotiorum under green house condition (in vivo) Fungicidesname Rate Disease severity (kg a.i./ha) in Seedlings Control (Untreated) - 18.90 Dithiocarbamic acid 0.52 2.60 Carbendazim 0.65 1.90 Ziram 0.66 2.20 Phenylthiourea 0.72 0.14 Carboxin + Dithiocarbamic acid 0.72 1.30 Difenoconazole 1.16 0.22 Hydrogen sulphide 0.86 1.10 Mancozeb 1.22 0.88 CD (P>0.05) 0.58 0.84 J. Hortl. Sci. Vol. 7(1):114-117, 2012 117 Iqbal, S.M., Ghafoor, A., Ahmad, Z. and Haqqani, A.M. 2003. Pathogenicity and fungicidal efficacy for Sclerotinia rot of brinjal. Int’l. J. Agril. Biol., 5: 618-620 Kurozawa, C. and Pavan, M.A. 1997. Doencas do tomateiro. In: Kimti, H., Amorim, L., Bergamin Filho, A., Camargo, L.E.A. and Rezende, J.A.M. (ed.). Manual de fitopatologia: doencas das plantas cultivadas. 3. ed. Sao Paulo Agronomica Ceres. pp. 690-719 Mueller, D.S., Dorrance, A.E., Derksen, R.C., Ozkan, E., Kurle, J.E., Grau, C.R., Gaska, J.M., Hartman, G.L., Bradley, C.A. and Pedersen, W.L. 2002. Efficacy of fungicides on Sclerotinia sclerotiorum and their potential for control of Sclerotinia stem rot on soybean. Pl. Dis, 86:26–31 Purdy, L.H. 1979. Sclerotinia sclerotiorum history, diseases and symptomlogy, host range, geographic distribution and impact. Phytopathol., 69:875-80 Rauf, C.A., Iqbal, S.M. and Rahat, S. 1996. Fungicidal efficacy against Ascochyta lentis. Pakistan J. Phytopathol., 8:49–51 Steadman, J.R. 1979. Control of plant diseases caused by Sclerotinia species. Phytopath., 69:904-907 Steadman, R.G. 1979: The Assessment of Sultriness. Part II: Effects of wind, extra radiation and barometric pressure on apparent temperature. J. Appl. Meteor., 18:874-885 Willetts, H.J. and Wong, A.L. 1980. The biology of Sclerotinia sclerotiorum, S. trifoliorum and S. minor with emphasis on specific nomenclature. Bot. Rev., 46:101-65 (MS Received 8 April 2010, Revised 4 March, 2012) Fungicides in control of white mold in lima bean J. Hortl. Sci. Vol. 7(1):114-117, 2012