Avenacin A-1 Content of Some Local Oat Genotypes and the In Vitro Effect of Avenacins on Several Soil-Borne Fungal Pathogens of Cereals
Avenacins are a mixture of 4 major (avenacin A-1, B-1, A-2 and B-2) autofluorescent compounds that are accumulated in the roots of oats (Avena spp.), especially root tips, and that have antimicrobial properties. In this research, we screened 189 genotypes of the family Gramineae for autofluorescence and also quantified 35 Avena genotypes for avenacin A-1 content, which is the most abundant and toxic avenacin type. Screening under UV transillumination proved that none of the species, except for Avena spp. accumulated avenacins in their roots. We aimed to find a genotype that lacks avenacin A-1 in order to investigate fungus-oat interaction in that particular interaction. The avenacin A-1 contents of Avena spp. varied between 4.7 and 6.5 mg g-1 fresh weight of root tips. Although there was significant statistical variation in means of avenacin A-1 contents, the search for a genotype that lacks avenacin A-1 was unsuccessful. A soil-borne fungi collection from cereals (Culvularia sp., Drechslera victoriae, Rhizoctonia solani (A-6 type), Pythium ultimum, Fusarium culmorum, F. nivale, F. oxysporum and F. poae) was also included briefly in this research to assess the antifungal activity of avenacins. According to the bioassay, all fungi exhibited inhibition zones around the oat root extract with the exception of P. ultimum. This result suggests that avenacins might contribute to fungal disease resistance and could be used for disease resistance breeding for some major root colonizing fungi.
Avenacin A-1 Content of Some Local Oat Genotypes and the In Vitro Effect of Avenacins on Several Soil-Borne Fungal Pathogens of Cereals
Avenacins are a mixture of 4 major (avenacin A-1, B-1, A-2 and B-2) autofluorescent compounds that are accumulated in the roots of oats (Avena spp.), especially root tips, and that have antimicrobial properties. In this research, we screened 189 genotypes of the family Gramineae for autofluorescence and also quantified 35 Avena genotypes for avenacin A-1 content, which is the most abundant and toxic avenacin type. Screening under UV transillumination proved that none of the species, except for Avena spp. accumulated avenacins in their roots. We aimed to find a genotype that lacks avenacin A-1 in order to investigate fungus-oat interaction in that particular interaction. The avenacin A-1 contents of Avena spp. varied between 4.7 and 6.5 mg g-1 fresh weight of root tips. Although there was significant statistical variation in means of avenacin A-1 contents, the search for a genotype that lacks avenacin A-1 was unsuccessful. A soil-borne fungi collection from cereals (Culvularia sp., Drechslera victoriae, Rhizoctonia solani (A-6 type), Pythium ultimum, Fusarium culmorum, F. nivale, F. oxysporum and F. poae) was also included briefly in this research to assess the antifungal activity of avenacins. According to the bioassay, all fungi exhibited inhibition zones around the oat root extract with the exception of P. ultimum. This result suggests that avenacins might contribute to fungal disease resistance and could be used for disease resistance breeding for some major root colonizing fungi.
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- Arneson, P.A. and R.D. Durbin. 1968. The sensitivity of fungi to α- tomatine. Phytopathology, 58: 536-537.
- Carter, J.P., J. Spink, P.F. Cannon, M.J. Daniels and A.E. Osbourn. 1999. Isolation, characterization and avenacin sensitivity of a diverse collection of cereal-root-colonizing fungi. Appl. Environ. Microb, 65: 3364-3372.
- Crombie, W.M. and L. Crombie. 1986a. Distribution of Avenacins A-1, A-2, B-1 and B-2 in oat roots: Their fungicidal activity towards take-all disease. Phytochemistry, 25: 2069-2073.
- Crombie, W.M. and L. Crombie. 1986b. Pathogenicity of the take-all fungus to oats: its relationship to the concentration and detoxification of the four avenacins. Phytochemistry, 25: 2075- 2083.
- Keukens, E.A.J., T. De Vrije, C. Van Den Boom, P. de Waard, H.H. Plasmna, F. Thiel, W.M.F. Jørgen and B. de Kruijff. 1995. Molecular basis of glycoalkaloid induced membrane disruption. Biochim. Biophys. Acta, 1110: 127-136.
- Long, M., P. Barton-Willis, B.J. Staskawicz, D. Dahlbeck and N.T. Keen. 1985. Further studies on the relationship between glyceollin accumulation and the resistance of soybean leaves to Pseudomonas syringae pv. glycinea. Phytopathology, 75: 235- 239.
- Lyon, F.M. and R.K.S. Wood. 1975. Production of phaseollin, coumestrol and related compounds in bean leaves inoculated with Pseudomonas spp. Physiol. Mol. P. Pathol, 6: 117-124.
- Mansfield, J.W. 2000. Antimicrobial compounds and resistance: the role of phytoalexins and phytoanticipins. In: Mechanisms of resistance to plant diseases. Eds. AJ Slusarenko, Fraser RSS and Loon LC. Kluwer.
- Mert-Türk, F., M.H. Bennett, J.W. Mansfield and E.B. Holub. 2003a. Quantification of camalexin in several accessions of Arabidopsis thaliana following inoculation with Peronospora parasitica and UV-B irradiation. Phytoparasitica, 31(1): 81-89.
- Mert-Türk, F., M.H. Bennett, J.W. Mansfield and E.B. Holub. 2003b. Camalexin accumulation in Arabidopsis thaliana following abiotic elicitation or inoculation with virulent or avirulent Hyaloperonospora parasitica. Physiol. Mol. P. Pathol, 62: 137- 145.
- Morrissey, J.P. and A.E. Osbourn. 1999. Fungal resistance to plant antibiotics as a mechanism of pathogenesis. Microbiol. Mol. Biol. Rev, 63: 708-724.
- Nishikawa, M., S. Nojima, T. Akiyama, U. Sankawa, K. Inoue. 1984. Interaction of digitonin and its analogs with membrane cholesterole. J. Biochem. Tokyo, 96: 1231-1239.
- Osbourn, A.E., B.R. Clarke, J.M. Dow and M.J. Daniels, 1991. Partial characterization of avenacinase from Gaeumannomyces graminis var. avenae. Physiol. Mol. P. Pathol, 38: 301-312.
- Osbourn, A.E., B.R. Clarke, P. Lunness, P.R. Scott and M.J. Daniels. 1994. An oat species lacking avenacin is susceptible to infection by Gaeumannomyces graminis var. tritici. Physiol. Mol. P. Pathol, 45: 457-467.
- Osbourn, A.E. 2001. Plant mechanisms that give defense against soil borne diseases. Australas. Plant Path, 30: 99-102.
- Papadopoulou, K., R.E. Melton, M. Leggett, M.J. Daniels and A.E. Osbourn. 1999. Compromised disease resistance in saponindeficient plants. P. Natl. Acad. Sci. USA, 96: 12923-12928.
- Rossall, S., J.W. Mansfield and R.A. Hutson. 1980. Death of Botrytis cinerea and B. fabae following exposure to wyerone derivatives in vitro and during infection development in broad bean leaves. Physiol. Plant Pathol, 16: 135-146.
- Sandrock, R.W. and H.D. Van Etten. 1998. Fungal sensitivity to and enzymatic degradation of the phytoanticipin α-tomatine. Phytopathology, 88: 137-143.
- Van Etten, H.D., J.W. Mansfield, J.A. Bailey and E.E. Farmers. 1989. Phytoalexin detoxification: importance for pathogenicity and practical implications. Annu. Rev. Phytopathol, 27: 143-164.