Fatty acid composition from a non-pathogenic binucleate Rhizoctonia, and pathogenic Rhizoctonia solani AG-3.

ROLDÁN H. ; WOLSKI E.A.; DALEO. G.R.; ANDREU A. B.

Mar del Plata

Congreso; VIII CONGRESO ARGENTINO DE. MICROBIOLOGIA GENERAL. -SAMIGE-; 2012

SAMIGE

Non-pathogenic binucleate Rhizoctonia isolates (BNR) have been characterized as effective biocontrol agents against several plant diseases, caused by the pathogenic fungus Rhizoctonia solani Khün, including in potato against Rhizoctonia canker, the disease caused by Rhizoctonia solani AG-3. The objective of this work was to study the composition of fatty acids presents in isolates of BNR and pathogenic Rhizoctonia solani AG-3. Total lipids were extracted from isolates and purified by a modification of Bligh Dyer procedure. The total lipids were hydrolyzed for 10 ? at 90 º C under nitrogen (N2) in NaOH 0.5 N in methanol. Fatty acids were converted to their methyl esters (FAME) by refluxing for 10 ? at 90 º C under N2 in 14% (wt/vol) boron trifluoride in methanol, extracted with hexane and analyzed in a CP-Varian 3800 gas chromatograph on a fused silica capillary column coating with CP-Sil 88 (25 m x 0.32mm I.D, 0,2 µm film thickness). The individual FAME were identified by comparing the retention times with those of standard methyl ester mixtures, and also by a semilogarithmic plot of retention time vs carbon number (Ackman 1969). Four major fatty acids were extracted from BNR and AG-3 isolates: linoleic (18:2w6, cis 9,12); oleic (18:1w9, cis 9); palmitic (16:0), and stearic (18:0). These four fatty acids accounted for 87% of the fatty acids of BNR isolates, and comprised between 71% and 74% of those identified in AG-3 isolates. Other fatty acids present in minor amounts in these isolates included: myristic (14:0), pentadecanoic (15:0), palmitoleic (16:1w7, cis 9), α-linolenic (18:3w3, cis 9,12,15), arachidonic (20:4w6 cis 5,8,11,14), eicosapentaenoic (20:5w3, cis 5,8,11,14,17), and docosahexaenoic (22:6w3, cis 5,8,11,14,17,20) It was found in isolates from BNR and AG-3 that: unsaturated fatty acids saturated fatty acids and also monoenoic fatty acids. The first most common polyenoic acid was18:2w6 in both. The values of linoleic varied within a range since 29.7% to 37,6% for BNR, while that the relative percentage of 18:2w6 founded in AG-3 were between 33.6% and 41,2%. In our study, 18:1 w9 in BNR constituted about twice higher than that of AG3 isolates. On the other hand, AG3 contained more w3 fatty acids than BNR. These results sugest that some contribution to pathogenicity of AG3 should not be dismissed.