Assessment of the genetic diversity of the causal agent of Asian soybean rust in the Mercosur countries using AFLP

C.M.L. ROCHA, G. VELLICCE, M.G. GARCÍA, E.M. PARDO, A. DE LUCÍA, J. GILLI, C. GHIONE, N. BOGADO, S. GERMAN, V. BONNECARRERE, F. MARCELINO, L.D. PLOPER AND A.P. CASTAGNARO

Durban

Conferencia; World Soybean Conference South-Africa; 2013

Asian soybean rust (SBR), caused by the fungus Phakopsora pachyrhizi Syd. & Syd, is regarded as one of the most destructive diseases of soybean [Glycine max (L.) Merr.], resulting in yield losses of up to 80% under conditions that favour disease development. SBR was first reported in Japan in 1902 and afterwards it spread to other parts of the world. In the Mercosur countries, it was reported in Paraguay and Brazil in 2001, in Argentina in 2002, and in Uruguay in 2004 (Stewart et al., 2005).The objective of this study was to assess the genetic diversity of P. pachyrhizi isolates from Mercosur countries using a direct methodology based on AFLP technique. Isolates from Argentina, Brazil, Paraguay and Uruguay were collected from fields. Genera and species identification were accomplished by PCR. From 23 isolates of P. pachyrhizi, a total of 3,014 alleles were amplified with 33 pair of AFLP primers.From a total of 1,550 loci, 1,545 were polymorphic (99.68%). Analysis of molecular variance (AMOVA) showed high genetic differentiation of P. pachyrhizi within countries, with 87.64% of variation. Variance among countries represented only the 12.36 % of the total variation, suggesting the existence of a gene flow among countries; such flow was confirmed by a PhiST value of 0.12. PhiST values of 0.15 and 0.14 were obtained for the 2007/08 and 2008/09 seasons, respectively; while the comparison between years resulted in a PhiST value of 0.22 that implies that each year genetic diversity changes. A dendogram analysis, based on Jaccard coefficient, showed similar results: two separated clusters grouped according to the collection year (2007/08-2008/09). The pathogen capability to breakdown successively the soybean resistance genes in this important production area (Yamanaka et al., 2010) may be explained by the high genetic diversity described in the present study.