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International Journal of Enviornmental Science and Technology, Vol. 2, No. 2, Summer, 2005, pp. 129-132 Comparative efficacy of brown, green and red seaweeds in the control of root infecting fungi and okra 1V. Sultana, 2S. Ehteshamul-Haque, 3J. Ara and 4M. Athar 1Department of Biochemistry, University of Karachi, Karachi, Pakistan Code Number: st05017 Abstract The effect of soil amendment by brown, green and red seaweeds was studied in controlling the root rot infecting fungi of okra seedlings in the greenhouse. The soil amendment with seaweeds Stokeyia indica, Padina pavonia (brown), Solieria robusta (red), at 1% w/w reduced Macrophomina phaseolina, Rhizoctonia solani and Fusarium solani infection on okra roots. Codium iyengarii (green) at 0.5 % w/w was effective against F. solani, while at 1% w/w was found phytotoxic. S.robusta showed better control of F. solani infection when used with Pseudomonas aeruginosa than either used alone. S. robusta produced better plant height and fresh weight of shoot than P. aeruginosa. Results of the present study suggest that the use of brown seaweeds S. indica and P. pavonia alone and S. robusta alone or in combination with P. aeruginosa have great potential to control root-infecting fungi of okra with enhancement of plant growth. These seaweeds alone or in combination with P. aeruginosa may be utilized as biological control of root infecting fungi of okra. Key words: Seaweeds, Pseudomonas aeruginosa, root infecting fungi, okra, biocontrol Introduction Seaweeds are rich and varied source of bioactive natural products and have been studied as potential biocidal and pharmaceutical agents (Ara, et al., 1998, 1999, 2002a and 2002b). Seaweeds are also known to aid and stimulate growth of vegetables, fruits and other crops (Blunden, 1991; Crouch, et al., 1994 and Washinton, et al., 1999). They contain all major and minor plant nutrients as well as biocontrol properties and contain many organic compounds such as auxins, gibberellins and precursor of ethylene and betaine which affect plant growth (Wu, et al., 1997). Liquid concentration of brown algae Ecklonia maxima significantly reduced the root knot infestation and increased growth of tomato plant. Antimicrobial activity of Canary species of Phaeophyta and Chlorophyta has been reported (Febles, et al., 1995). Seaweeds occurring at Karachi, Pakistan coast have also shown cytotoxic (Ara, et al., 1999), nematicidal and fungicidal (Ara, et al., 1998) hypoglyceamic (Ara, et al., 2002a) and antibacterial (Ara, et al., 2002b) activities. Soil amendment with brown seaweeds Stoechospermum marginatum and Sargassum tenerrimum with or without rhizobia significantly reduced root knot nematode (Meloidogyne javanica) and root infecting fungi infections (Ehteshamul-Haque, et al., 1996). The present Study describes the efficacy difference among the brown, red and green seaweeds in the control of root infecting fungi and growth of okra seedlings used alone or in combination with a plant growth promoting rhizobacterium Pseudomonas aeruginosa. The resaerch was conducted at Karachi University, Karachi, Pakistan during 2003. Materials and Methods Seaweeds Stokeyia indica, Padina pavonia (brown), Codium iyengarii (green) and Solieria robusta (red) collected from Buleji, Karachi under low tide. Seaweeds exposed on sands and rocks were collected in polyethylene bags and brought to the laboratory. Seaweeds were washed under tap water and air dried under shade and powdered in an electric blender. Powdered seaweeds were mixed in sandy loam soil, pH 8.05 at 0.5% and 1% w/w. The soil mixture (350 g.) was transferred in 8 cm diam. plastic pots and kept at 50% water holding capacity by watering daily. The soil had a natural infestation of 4-13 sclerotia of Macrophomina phaseolina g-1 of soil as determined by wet sieving and dilution techniques, 5-12 % colonization of Rhizoctonia solani on sorghum seeds used as baits and 3,500 cfu of mixed population of Fusarium solani and F. oxysporum as assessed by soil dilution technique. After two weeks, an aqueous suspension of Pseudomonas aeruginosa (108 cfu m/l) multiplied on nutrient agar was drenched in each pot at 25 ml/pot. Five seeds of okra (Abelmoschus esculentus (L.) Moench.) were sown in each pot. Each treatment was replicated four times and the pots were randomized on a screen house bench. Pots without seaweed or P. aeruginosa served as control. After germination four seedlings were left in each pot. C. iyengarii at 1% w/w was found phytotoxic and was excluded from the experiment. Plants were uprooted after six weeks growth and data on height and fresh weight of shoot were recorded. Incidence of fungi on roots was examined, using method of Short, et al. (1980). Roots were washed under tap water and five one cm long root pieces were cut from tap root of each plant. Root pieces were surface sterilized with 1% Ca (OCl)2 for 3 minutes and transferred onto potato dextrose agar plates containing penicillin (100,000 units/l) and streptomycin (0.2 gm/l). After incubation for 5 days at 28oC incidence of root infecting fungi M. phaseolina, R. solani and Fusarium spp., were recorded. Data was analyzed statistically to least significant differences. The experiment was repeated to confirm the results. Results A significant ((p<0.05) control of M. phaseolina infection was observed where P. pavonia, S. robusta at 1% w/w and C. iyengarii at 0.5% were used alone or where seaweeds were used in combination with P. aeruginosa. Infection of R. solani was completely controlled where P. aeruginosa and S. robusta were used alone or where P. pavonia at 0.5% and 1% w/w, S. indica and C. iyengarii at 0.5% w/w and S. robusta at 1% w/w were used in combination with P. aeruginosa. A significant (p<0.05) control of F. solani infection was found where seaweeds were used alone or with P. aeruginosa (Table 1). S. indica, P. pavonia and S. robusta significantly (p<0.05) enhanced plant height. Plant height was increased where P. pavonia was used with P. aeruginosa. Use of C. iyengarii at 0.5% w/w showed maximum fresh weight of shoot when used in combination with P. aeruginosa as compared to untreated control (Table 2). C. iyengarii at 1% w/ w showed phytotoxicity during this study. Incidence of fungi on roots and plant growth data recorded after 6 weeks showed that S. indica, P. pavonia and S. robusta significantly (p<0.05) reduced M. phaseolina infection (at 0.5 and 1% w/w). C. iyengarii was also found effective against M. phaseolina at 0.5% w/w. Infection of R. solani was significantly (p<0.05) reduced by S. indica, P. pavonia and S. robusta at 1% w/w. Use of seaweeds with P. aeruginosa also significantly (p<0.05) controlled R. solani infection. A significant control of F. solani infection was observed where seaweeds were used alone or with P. aeruginosa (Table 1). Plant height was increased where P. pavonia and S. robusta were used at 1% w/w. Maximum fresh weight of shoot was observed where S. robusta was used at 1% w/w followed by S. indica at 1% w/w used with P. aeruginosa (Table 2). Discussion and Conclusion The marine environment has great potential for the discovery of lead compounds that could be used against infectious diseases and parasites. In the present study soil amendment with S. indica, P. pavonia, C. iyengarii and S. robusta significantly reduced infection of M. phaseolina, R. solani and F. solani infection on okra. In the present study use of S. robusta with P. aeruginosa showed better control of F. solani infection than either used alone. Plant growth promoting rhizobacteria that colonize roots have been reported to improve plant growth either through direct stimulation of the plant by producing growth regulators or by suppression of pathogens (Raaijmaker, et al., 2002; Weller, et al., 2002). Of the various rhizosphere bacteria, the one belonging to the fluorescent Pseudomonas which colonizes roots of a wide range of crop plants are reported to induced resistance in carnation against Fusarium wilt by a strain of Pseudomonas sp. Species of Pseudomonas are also reported to be antagonistic to soil-borne plant pathogens (Siddiqui et al., 2000; Siddiqui and Ehteshamul-Haque, 2001). The production of certain antibiotics (Leavy, et al., 1992) and siderophores (Buysens, et al., 1996) by P. aeruginosa has been regarded as one of the mechanism involved in antagonism. Raajimaker and Weller, (1998) reported role of 2, 4diacetylphloroglucinol an antifungal metabolite from species of fluorescent Pseudomonas in plant root disease suppression. Van Peer, et al. (1991) reported induced resistance in carnation against Fusarium wilt by a strain of Pseudomonas sp. Species of Pseudomonas are also reported to induce systemic resistance in cucumber against Pythium aphanidermatum (Zhou and Paulitz, 1994). These characteristics make these species good candidates to use as biocontrol against soil-borne plant pathogens. Results of the present study suggest that the use of brown seaweeds S. indica and P. pavonia alone and S. robusta alone or in combination with P. aeruginosa have great potential to control root-infecting fungi of okra with enhancement of plant growth. Acknowledgements This work was funded by a research grant from the Office of Naval Research (ONR), USA, which is sincerely acknowledged. References
© 2005 Center for Environment and Energy Research and Studies (CEERS) The following images related to this document are available:Photo images[st05017t2.jpg] [st05017t1.jpg] |
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