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Effects of bacterial strains and isolates on in situ germination, subsequent developmental stage of striga hermonthica onto sorghum roots.

Introduction

Parasitic plant species of the genus Striga are obligate root parasites that constitute a major constraint to cereal and legume production in the savannas of Africa [13]. It causes severe damage to infested crops, some times leading to total grain yield and Stover loss on farmers. Typical yield losses range from 5 to 70% depending on the degree of infestation and susceptibility of the cultivar [12]. Germination of conditioned Striga seeds is known to be triggered by several synthetic and natural compounds which are structurally unrelated [14]. Biological control as a component of integrated S. hermonthic a management holds promise in Africa only if it gives a demonstrable crop yield benefit within the season of use. The use of fungi (biological control agent) as a component of integrated Striga management had been highlighted [1]. [5] concluded from their study that the use of the strain F. oxysporum M12-4A integrated with other control measures may provide an effective means of controlling Striga. Rhizobacteria, capable of destroying or suppressing germination of S. hermonthica seeds-appear particularly promising since they can easily be formulated as seed inoculants, there by avoiding the need for application equipment and labor that would be otherwise cost prohibitive.

The use of microorganisms for the control of Striga is limited. This present study focuses on the effects of soil borne bacteria on the control of S. hermonthica in the Sudan.

Materials and Methods

This experiment was undertaken to investigate the effects of bacterial strains and isolates on in situ germination, haustorium initiation and penetration of intact sorghum roots.

Striga hermonthica seeds were collected from parasitic plants growing under sorghum at the Gezira Research Station Farm in Wad Medani. The seeds were surface sterilized by soaking in 1% sodium hypoclorite (NaOCl) solution for 3 min with continuous agitation. Subsequently the seeds, thoroughly washed with sterilized distilled water and plotted dry on Whatman No. 1 filter paper, were allowed to dry under a laminar flow hood. The seeds were stored in sterile glass vials and kept at room temperature until used.

Bacterial isolates and isolation procedure:

Bacteria were isolated from soil samples from four location (Shambat, Gadarf, Wad madni and Abuharaz) in Sudan soil samples were collected from a high root density zone (upper 5cm soil layer) where there was potentially high microbial activity. Isolates were designated by initial refereeing place of connection viz: S: for Shambat, G: for Gadarf, M: for Wad madni and D: for Abuharaz. The spread- plate method was used for isolation of the bacteria. Ten gram soil samples suspended, each, in 90 ml sterile distilled water, were shaken for 10 min till completely dispersed. The Petri dishes, inverted, were incubated in the dark at 30 [degrees]C for 48 h. Representative microbial colonies were purified by sub-culturing and were subsequently characterized. The isolated bacteria were preserved in nutrient agar slants and kept at 30 [degrees]C for further studies. Two hundred and two bacterial isolates were obtained from the soil samples. In addition eight bacteria strains were included, Azotobacter vienlandi was obtained from Faculty of Agriculture, University of Khartoum, while Pseudomonas putida, Azomonas spp., Bradyrhizobium japonicum TAL337 and SUD110, Azospirillum brasilense, A. amazonas and Klebsiella planticola were obtained from the Environment and Natural Resources Research Institute (ENRRI), the National Centre for Research, Khartoum.

Striga hermonthica seeds conditioning and germination:

Glass fiber filter papers (GF/C) discs (8 mm diameter) were cut, wetted thoroughly with water and placed in an oven at 100 [degrees]C for 1 h to be sterilized and ready for further use. The sterilized discs, placed in 9 cm petri dishes lined with glass fiber filter papers (GF/C), were moistened with 5 ml distilled water or inoculated with the respective bacterium isolate or strains. About 25-50 surface disinfected S. hermothica seeds were sprinkled on each of the glass fiber discs in each petri dish. The dishes, sealed with para film, placed in black polythene bags were incubated at 30 [degrees]C in the dark for 10 days.

Effects of bacterial strains and isolates on S. hermonthica:

This experiment was conducted at ENRRI laboratory in the period August to October 2007. Sorghum seeds, Wad Ahmed (Striga tolerant) and Abu Sabeen (Striga susceptible) were surface sterilized as previously described. The sterilized seeds were germinated and allowed to grow in paper rolls for 3-7 days prior to transfer to trays containing distilled water. The seedlings, allowed to grow for 2 days in sterilized distilled water, were transferred to filter papers placed on sterilized moist rock-wool in Petri dishes. A hole was made in each Petri dish to permit shoot growth and access to light. The Petri dishes, wrapped in aluminum foil were allowed to stand at room temperature for 2 days. Striga seeds (120-200) conditioned in presence of bacterial isolates, were plotted dry on filter papers and sprinkled on roots in each Petri dish. A control treatment using Striga seeds conditioned in water was included for comparison. Germination, haustoria initiation and attachment were recorded over a period of 5 days.

Data on percentage germination, haustorial initiation and attachment were calculated and subjected to analysis of variance (ANOVA) [7].

Results and Discussion

Striga seeds conditioned in water and placed in close proximity of Abu Sabeen and Wad Ahmed roots displayed 74 - 50% germination, respectively. In among all bacterial isolates S22, GSL, S23, S19, S10 and strains A. brasilense and P. putida were the most inhibitory to germination. Striga seeds conditioned in presence of these isolates and strains displayed significantly low germination (5 - 23 %) in comparison to the control treatment (Fig 1 and 2).

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Striga germilings resulting from seeds placed near Abu Sabeen and Wad Ahmed roots produced 38 and 19% haustoria, respectively. Of all bacterial isolates and strains G14, GSL, S22, P. putida, and A. brasilense were the most suppressive to haustorium initiation on both sorghum cultivars (Fig 3 and 4). The bacterial isolate M34 on the other hand enhanced haustorium initiation. Striga germilings resulting from seeds conditioned in the presence of isolate M34 displayed 43 and 47 % haustorium initiation on Abu Sabeen and Wad Ahmed, respectively (Fig. 3).

Striga germilings resulting from seeds conditioned in water and induced to germinate in situ by root exudates displayed 15 and 4 % attachment on Abu Sabeen and Wad Ahmed, respectively (Fig. 5 and 6). In among all bacterial strains and isolates A. brasilense, P. putida, Bradyrhizobium spp. and GSL were the most inhibitory to Striga attachment (Fig. 5 and 6). The bacterial isolate (GSL) reduced attachment by 78 to 81%, in comparison to the control.

Discussion:

The present investigation was undertaken to evaluate the potentials of native soil borne bacteria to perturb early stages of Striga growth. The study focused on inhibition and/or perturbation of early growth stages of the parasite in an endeavor to develop an integrated control strategy. Ethylene is claimed to be the actual inducer of germination in Striga seeds and that all Striga germination stimulants act through promotion of ethylene biosynthesis in the parasite seeds [9,2]. In conditioned Striga seeds germination stimulants induce ACC synthase and increased capacity of the seeds to oxidize ACC to ethylene [2]. Both inhibition and promotion of Striga germination can be achieved by manipulation of ethylene biosynthesis, ethylene action, or by promotion of ethylene metabolism or that of its immediate precursor ACC.

Aminoethoxyvinyl glycine (AVG), an ACC synthase inhibitor, curtails ethylene biosynthesis and germination in Striga. Norbornadiene, silver thiosulphate and high concentrations of C[O.sub.2], competitive inhibitors of ethylene action, also inhibit Striga germination. In microorganisms ACC is degraded to [alpha]- aminobutyric acid and ammonia [10,8]. The inhibitory effects of the bacterial strains and isolates applied during conditioning could be attributed to a direct effect of the isolate on the seed or indirectly through production of chemical (s) that is/are toxic to the seeds, inhibitors of ethylene biosynthesis, inhibitors of ethylene action, promoters of ethylene deactivation and promoters of ethylene biosynthesis. Azotobacter spp., P. putida, A. brasilense and Klebsiella spp. are known to produce auxin and auxin - like compounds in plants rhizosphere [6]. Differential production of the enzyme catalase, which disproportionate H2O2 to H2O and molecular oxygen, by bacterial isolates would lead to differential production of DMBQ and hence differential reduction in haustorium initiation [11]. The reduced infestation suggests that an integrated Striga management comprising tolerant and/or resistant crop cultivars together with bacterial inoculation may provide adequate control of the parasite.

References

[1.] Abbasher, A.A., J. Sauerborn, 1992. Fusarium nygamai, a potential bioherbicide for Striga hermonthica control in sorghum. Biocontrol, 2: 291-296.

[2.] Babiker, A.G.T., Y. Ma, Y. Sugimoto, S. Inanaza, 2000. Conditioning period, CO2 and GR24 influence ethylene biosynthesis and germination of Striga hermonthica. Physiologia Plantarum, 109: 75-80.

[3.] Babiker, A.G.T., L.G. Butler, G. Ejeta, W.R. Woodson, 1993. Ethylene biosynthesis and strigol-induced germination of Striga asiatica. Physiologia Plantarum, 88: 359-365.

[4.] Babiker, A.G.T, 2007. Striga: The spreading scourge in Africa. The Japanese Society for Chemical Regulation of Plants, 42: 74- 87.

[5.] Ciotola, M., A. Ditommaso and A.K. Watson, 2000. Chlamydospore production, inoculation methods and pathogenicity of Fusarium oxysporum M12-4 A, a biocontrol for Striga hermonthica. Biocontrol Science and Technology, 10: 129-145.

[6.] Frankenberger, W.T. and J.R. Muhammed Arshad, 1995. Phytohormones in soil microbial production and function. Marcel Deker, New York pp: 503.

[7.] Gomez, K.A. and A.A. Gomez. 1984. Statistical Procedures for Agricultural Research. 2nd ed. A Wiley-Interscience Publication. John Wiley and Sons, Inc., Singapore, pp: 734.

[8.] Hassan, M.M., M.E. Abdel gain and A.G.T. Babiker, 2009. Management of Striga hermonthica in sorghum using soil rhizosphere bacteria and host plant resistance. Int. J. Agric. Biol, 11: 367-373.

[9.] Hsiao, A., A.D. Worsham and D.E. Moreland, 1981. Regulation of witcheed (Striga asiatica) conditioning and germination by dl-strigol

. Weed Science, 29: 101-104

[10.] Imaseki, H., 1991. The biochemistry of ethylene biosynthesis. In: The Plant Hormone Ethylene (Mattoo, A.K. and Suttle, J.C. eds) : pp: 1-21.

[11.] Keyes, W.J., R.O. Malley, D. Kim and D.G. Lynn, 2000. Signaling organogenesis in parasitic angiosperms: xenognosin generation, perception and response. Plant Growth Regulators, 19: 217231.

[12.] Lagoke, S.T.O., V. Parkinson and R.M. Agunbiade, 1991. Parasitic weeds and control methods in Africa. In: Combating Striga in Africa (Kim, S.K. ed.). workshop organized by IITA, ICRISAT, and IDRC, Ibadan Nigeria., pp: 3-14.

[13.] Parker, C. and C.R. Riches, 1993. Parasitic Weeds of the World: Biology and Control. CAB International, Wallingford, UK., pp: 332.

[14.] Worsham, A.D., 1987. Germination of witchweed seeds. In: Parasitic Weeds in Agriculture,. ISBN 0-8493-6272-5 CRC Press, Boca Raton, FL, 1: 45-61.

Mohammed Mahgoub Hassan, Migdam El Sheik Abdel gani and Abdel Gabar Tayeb Babiker

Environment and Natural Resources, Sudan University of National Centre for Research, Khartoum, Sudan science and technology faculty of Agriculture

Mohammed Mahgoub Hassan, Migdam El Sheik Abdel gani and Abdel Gabar Tayeb Babiker: Effects of Bacterial Strains and Isolates on in Situ Germination, Subsequent Developmental Stage of Striga sermonthica onto Sorghum Roots

Corresponding Author

Mohammed Mahgoub Hassan, Environment and Natural Resources. Sudan University of science and technology faculty of Agriculture

Tel: 0122255050

E-mail: mohkadis@yahoo.com
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Title Annotation:Original Article
Author:Hassan, Mohammed Mahgoub; gani, Migdam El Sheik Abdel; Babiker, Abdel Gabar Tayeb
Publication:Advances in Environmental Biology
Article Type:Report
Geographic Code:6SUDA
Date:Sep 1, 2011
Words:1883
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