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 MICROBIOLOGÍA GENERAL SAMIGE (SAMIGE); 2012

SOCIEDAD ARGENTINA DE MICROBIOLOGÍA GENERAL SAMIGE (SAMIGE)

Non-pathogenic binucleate Rhizoctonia isolates (BNR) have beencharacterized as effective biocontrol agents against several plant diseases,caused by the pathogenic fungus Rhizoctoniasolani Khün, including in potato against Rhizoctonia canker, the diseasecaused by Rhizoctonia solani AG-3. Theobjective of this work was to study the composition of fatty acids presents inisolates of BNR and pathogenic Rhizoctoniasolani AG-3. Total lipids were extracted from isolates and purified by amodification of Bligh Dyer procedure. The totallipids were hydrolyzed for 10 ? at 90 º Cunder nitrogen (N2) in HONa 0.5 N in methanol. Fatty acids wereconverted to their methyl esters (FAME) by refluxing for 10 ? at 90 º C under N2in 14% (wt/vol) boron trifluoride in methanol, extracted with hexane and analyzedin a CP-Varian 3800 gas chromatograph on a fused silica capillary columncoating with CP-Sil 88 (25 mx 0.32mm I.D, 0,2 µm film thickness). The individual FAME were identified bycomparing the retention times with those of standard methyl ester mixtures, andalso by a semilogarithmic plot of retention time vs carbon number (Ackman1969). Four major fatty acids were extractedfrom BNR and AG-3 isolates: linoleic (18:2w6, cis 9,12); oleic (18:1w9, cis9); palmitic (16:0), and stearic (18:0). These four fatty acids accounted for87% of the fatty acids of BNR isolates, and comprisedbetween 71% and 74% of those identified in AG-3isolates. Other fatty acids present in minor amounts in these isolatesincluded: 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 inisolates from BNR and AG-3 that: unsaturated fatty acids > saturated fattyacids and also > monoenoic fatty acids. The first most common polyenoic acidwas18:2w6 in both. The values of linoleic varied within a range since 29.7% to37,6% for BNR, while that the relative percentage of 18:2w6 founded in AG-3were between 33.6% and 41,2%. In our study, 18:1 w9 in BNR constituted abouttwice higher than that of AG3 isolates. On the other hand,  AG3 contained more w3 fatty acids than BNR.These results sugests that some contribution to pathogenicity should not bedismissed.