Differential reaction of two soybean cultivars to Asian soybean rust

GONZALEZ, V.; DIAZ, C.G.; RUIZ, S.; ROMERO, M.B.; REZNIKOV, S.; PLOPER, L.D.

Beijing, China

Conferencia; World Soybean Research Conference VIII (WSRC VIII); 2009

Institute of Grop Science, Chinese Academy of Agricultural Sciences

Asian soybean rust, caused by Phakopsora pachyrhizi, was first detected in Argentina in the northeastern region near Paraguay and Brazil during the 2001-02 growing season, but did not reach major soybean production areas until the end of the 2003-04 season. Yield losses caused by this disease during the past five growing seasons have been highly variable among provinces and years.  No cultivars with resistance to soybean rust are available in northwestern Argentina.  However, in various field trials and commercial fields, one of the maturity group (MG) VIII cultivars, Munasqa RR (M), consistently showed lower levels of the disease than cultivars of similar maturity during most of the growing period. To characterize this reaction, disease progress was studied during the 2005-06, 2006-07 and 2007-08 growing seasons in M in comparison to another MG VIII cultivar, A 8000 RG (A), at Puesto del Medio, Province of Tucumán.  Severity readings were taken at 7-10 day intervals and the area under the disease progress curves (AUDPC) were calculated.  In addition, during the third season, fungicides were applied in separate plots to evaluate the effect of chemical control on both cultivars.  The cultivar M showed a slower progress of rust than A, as evidenced by the AUDPC values in the three seasons (1664 vs. 2411, 838 vs. 2435, and 489 vs. 728).  The application of fungicide reduced final severity levels in both cultivars compared to the untreated controls (5.3% vs. 37.5% in M and 8% vs. 36.0% in A).