Criblage d\'inducteurs de réactions de défense chez le blé (Triticum aestivum) contre l\'oïdium (Blumeria graminis f.sp. tritici)

Cette étude a consisté à rechercher des substances biologiques capables d\'induire les défenses naturelles du blé (Triticum aestivum) contre l\'oïdium (Blumeria graminis f.sp. tritici (Bgt)). Des fractions non purifiées dérivées de la plante et/ou des agents pathogènes du blé (broyats foliaires de blé ou de spores de Bgt, hydrolysat du mycélium de Septoria nodorum (Sn)) ainsi que des produits purifiés (tréhalose et salicylate d\'heptanoyle (SH)) ont été testés lors d\'un traitement préventif. L\'intensité des protections obtenues a varié en fonction de la nature et de la concentration du produit utilisé. La protection obtenue lors de la pulvérisation du broyat foliaire de blé non infecté a été inférieure (33 %) à celle enregistrée après pulvérisation d\'un broyat foliaire de blé infecté par Bgt (46 %). La protection obtenue, suite à la pulvérisation de la plante avec une suspension de spores de Bgt inactivées, a été de 44 %. La diminution d\'infection enregistrée après pulvérisation d\'un hydrolysat de mycélium d\'un autre agent pathogène foliaire du blé (Sn) a été de 33 %. Alors que des pulvérisations préventives de tréhalose à des concentrations de 10 et 15 g/l sur des plants de blé entraînent des diminutions de l\'infection de 50 à 60 %, des concentrations de 1 et 5 g/l ne permettent d\'enregistrer aucune protection. La pulvérisation préventive de deux autres diholosides, le maltose et le cellobiose à 15 g/l ne permet pas de déceler une protection. Le traitement préventif du blé par le SH a permis d\'obtenir une protection très forte (80 %) pour de faibles concentrations en produit (0,1 g/l). L\'application de chacun des deux constituants de la molécule pris séparément induit une protection 2 fois plus faible que celle du SH avec l\'acide salicylique (AS) et aucune protection avec l\'acide heptanoïque (AH).Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most damaging diseases of wheat (Triticum aestivum) especially in Northern France. The study was aiming at screening biological molecules of fungal or plant origin that could enhance resistance to powdery mildew in wheat as an alternative to chemical fungicides. The protection confered by several non purified fractions originating from leaves of wheat (contaminated or not with Bgt) or from the pathogen agents (Bgt and Septoria nodorum (Sn)) were assessed. Protection obtained after treatment with no infected wheat leaves was less important (33 %) than with infected leaves (46 %). The protection recorded after application of inactivated Bgt spores or Sn were about 44 and 33 % respectively. Two other purified molecules, trehalose and heptanoyl salicylic acid (HS), were selected because of their nontoxicity to the environment. Treatment of wheat leaves with the different substances, prior to fungal inoculation, resulted in different levels of protection against Bgt depending on the nature and the concentrations used. The treatment with HS at low concentration (0,1 g/l) allowed a high protection reaching 80 %. Whereas trehalose at 10 and 15 g/l reduced the infection by 50 and 60 % respectively, no protection was observed at 1 and 5 g/l. Keywords: Blé, Blumeria graminis f.sp. tritici, oïdium, inducteurs de défense naturelle, résistance acquise.Agronomie Africaine Vol. 20 (2) 2008: pp. 191-19

Characterization of selected strains of mucorales using fatty acid profiles Caracterização de linhagens de mucorales através do perfil de ácidos graxos

The fatty acid profiles of several fungi of the order Mucorales (Zygomycetes), including Backusella lamprospora (Lendner) Benny and R.K. Benj., Benjaminiella youngii P.M. Kirk, Circinella simplex van Tieghem, Cunninghamella blakesleeana Lendner, Mortierella ramanniana (Möller) Linnem., Mucor circinelloides f. janssenii (Lendner) Schipper, Mycotypha microspora Fenner, Rhizomucor miehei (Cooney and R. Emerson) Schipper and Rhizomucor pusillus (Lindt) Schipper, and of Volutella sp. Fr., from the class Ascomycetes, were qualitatively analysed by gas-liquid chromatography in order to determine the taxonomic value of these chemotaxonomic markers. The fatty acids present in all strains were palmitic (16:0), oleic (18:1), linoleic (18:2) and <FONT FACE="Symbol">g</FONT>-linolenic (18:3) acid, with the exception that the latter was not found in Volutella sp. Chemotaxonomic markers for some species and genera were obtained, including a non-identified fatty acid, FAME8 (minimum and maximum retention times of 27.92 and 28.28 minutes) for Rhizomucor miehei CCT 2236 and Rhizomucor pusillus CCT 4133, and FAME3 (minimum and maximum of 16.53 and 16.61 minutes) for Benjaminiella youngii CCT 4121. The chemotaxonomic marker of the order Mucorales was the fatty acid 18:3<FONT FACE="Symbol">w</FONT>6, confirming previous data from literature. The results of the present study suggest that qualitative fatty acid analysis can be an important chemotaxonomic tool for the classification of fungi assigned to the order Mucorales (Zygomycetes).<br>O perfil de ácidos graxos de Backusella lamprospora (Lendner) Benny e R.K. Benj., Benjaminiella youngii P.M. Kirk, Circinella simplex van Tieghem, Cunninghamella blakesleeana Lendner, Mortierella ramanniana (Möller) Linnem., Mucor circinelloides f. janssenii (Lendner) Schipper, Mycotypha microspora Fenner, Rhizomucor miehei (Cooney e R. Emerson) Schipper e Rhizomucor pusillus (Lindt) Schipper, da ordem Mucorales (Zygomycetes), e Volutella sp. Fr., da classe Ascomycetes, foram analisados qualitativamente por cromatografia gás-líquida, tendo como objetivo determinar o valor taxonômico destes marcadores quimiotaxonômicos. Os ácidos palmítico (16:0), oléico (18:1), linoléico (18:2) e <FONT FACE="Symbol">g</FONT>-linolênico (18:3) foram encontrados em todas as linhagens, com exceção do último, o qual não foi encontrado na linhagem de Volutella analisada. Foram obtidos marcadores quimiotaxonômicos para algumas espécies e gêneros estudados, incluindo um ácido graxo não-identificado, FAME8 (tempos de retenção mínimo e máximo de 27,92 e 28,28 minutos) para Rhizomucor miehei CCT 2236 e Rhizomucor pusillus CCT 4133 e FAME3 (tempos de retenção mínimo e máximo de 16,53 e 16,61 minutos) para Benjaminiella youngii CCT 4121. Para a ordem Mucorales, o marcador quimiotaxonômico obtido foi o ácido graxo 18:3<FONT FACE="Symbol">w</FONT>6, confirmando dados da literatura. Os resultados do presente estudo sugerem que a análise qualitativa do perfil de ácidos graxos pode ser uma ferramenta importante na classificação de fungos da ordem Mucorales (Zygomycetes)