Phenotypic and Genotypic Variability in Cercospora kikuchii Isolates from Santa Fe Province, Argentina

Abstract

More than 100 fungal diseases affecting soybean (Glycine max (L.) Merr.) culture have been found worldwide, though only 35 of them are of great economic concern since they cause a 10 to 15% yield decrease (Ivancovich & Botta, 2003; Yeh & Sinclair, 1980). In Argentina, “Late-cycle diseases” (LCD) constitute a complex of infections affecting the culture of this leguminous, particularly in the reproductive stages. The first symptoms appear from the onset of carpel formation, thus producing premature plant maturation, a reduction in yield (5 to 8%) and seed quality loss. Due to the climate conditions of the region, leaf blight and purple seed stain, is one of the LCD prevailing in the central-northern region of Santa Fe Province (Formento, 2005; Ivancovich & Botta, 2003). The causal agent of the disease is the fungus Cercospora kikuchii (T. Matsumoto & Tomoyasu) M.W. Gardner, which produces irregular injuries on the leaves, forming reddish-purple necrotic areas, pale pink to dark purple stains on the seeds, together with cracks on the outer coat (Formento, 2005). C. kikuchii belongs to the Cercospora taxonomic complex, which is assumed to be host-specific (Crous & Braun, 2003), and therefore its species are normally identified from the phenotypic characteristics they show when grown on their natural substrate, being much more difficult to be characterized from artificial media (Almeida et al., 2005; Gams et al., 2007). One of the most important factors determining the pathogenicity of this fungus is the production of cercosporin, a red exotoxin (Kuyama & Tamura, 1957; Upchurch et al.,1991). Another aspect to consider is the genetic variability found in some fungi, which has determined the description of different races; that is why the use of some methodology to detect interand intraspecific variations between isolates is recommended (Kuyama & Tamura, 1957). In this sense, the Random Amplified Polymorphic DNA (RAPD) technique allows the differentiation between strains since amplification focuses only on the whole genome (Tigano et al., 2003; Williams et al., 1990). Although some Brazilian research groups have been studying aspects related with this phytopathogen (Almeida et al., 2003) only a few reports have been found in Argentina and, in particular in Santa Fe Province, about epidemiology and population structure of C. kikuchii.