Pathogenic diversity of soybean rust in Argentina, Brazil, and Paraguay

Abstract

Phakopsora pachyrhizi, the cause of soybean rust, is an economically important pathogen of soybean in South America. Understanding the pathogenicity of indigenous fungal populations is useful for identifying resistant plant genotypes and targeting effective cultivars against certain populations. Fifty-nine rust populations from Argentina, Brazil, and Paraguay were evaluated for pathogenicity in three cropping seasons, 2007/2008-2009/ 2010, using 16 soybean differentials. Only two pairs of P. pachyrhizi populations displayed identical pathogenicity profiles, indicating substantial pathogenic variation in the rust populations. Comparative analysis of 59 South American and five Japanese samples revealed that pathogenic differences were not only detected within South America but also distinct between the P. pachyrhizi populations from South America and Japan. In addition, seasonal changes in rust pathogenicity were detected during the sampling period. The differentials containing resistance genes (Rpp: resistance to P. pachyrhizi) Rpp1, Rpp2, Rpp3, and Rpp4, except for Plant Introduction (PI) 587880A, displayed a resistant reaction to only 1.8-14, 24-28, 22, and 36 % of South American P. pachyrhizi populations, respectively. In contrast, PI 587880A (Rpp1), Shiranui (Rpp5), and 3 Rpp-unknown differentials (PI 587855, PI 587905, and PI 594767A) showed a resistant reaction to 78-96 % of all populations. This study demonstrated that P. pachyrhizi populations from South America vary geographically and temporally in pathogenicity and that the known Rpp genes other than Rpp1 in PI 587880A and Rpp5 have been less effective against recent pathogen populations in the countries studied.

Asian soybean rust in Brazil: past, present, and future

“…A set of differential germplasm was used to determine the types of reaction of soybean plants, considering the presence or absence of lesions, number of uredinia per lesion, and sporulation level on inoculated plants. The results showed that the fungi populations from South America vary geographically and temporally in pathogenicity, and that Rpp1 (PI 587880A) and Rpp5 were the most effective against ASR (Akamatsu et al, 2013). and BRS, by Embrapa (Brasília, DF, Brazil).…”

Resistance to Asian soybean rust in soybean lines with the pyramided three Rpp genes

“…The development of soybean varieties resistant to ASR is considered the most economical control strategy; therefore it is important to facilitate its management (Twizeyimana et al 2007, Pierozzi et al 2008. However, resistance is not always durable due to pathogen variability (Oliveira et al 2005), and there is a large regional pathogenic diversity in the ASR pathogen population in Brazil (Freire et al 2008, Kato and Yorinori 2008, Soares et al 2009, Akamatsu et al 2013). …”

From Select Agent to an Established Pathogen: The Response to Phakopsora pachyrhizi (Soybean Rust) in North America

“…Soybean cultivars with resistance to P. pachyrhizi would be a valuable component in a sustainable soybean rust management program. The development of soybean cultivars with broad resistance to P. pachyrhizi has been complicated by extensive pathogen diversity (Table 2), and the ability of the fungus to evolve genetic diversity despite the apparent lack of a sexual stage (Vittal et al 2012b) contributes to temporal and geographic differences and shifts in the pathogenicity of P. pachyrhizi populations (Akamatsu et al 2013;Paul et al 2013;Walker et al 2014a).…”