Differential Responses of Resistant Soybean Entries to Isolates of Phakopsora pachyrhizi

Abstract

Soybean rust, caused by the fungus Phakopsora pachyrhizi, was detected in the continental United States in 2004. Several new sources of resistance to P. pachyrhizi have been identified in soybean (Glycine max); however, there is limited information about their resistance when challenged with additional U.S. and international isolates. Resistance of 20 soybean (G. max) entries was compared after inoculation with 10 P. pachyrhizi isolates, representing different geographic and temporal origins. Soybean entries included 2 universal susceptible cultivars, 4 sources of soybean rust resistance genes (Rpp1–4), and 4 and 10 resistant entries selected from field trials in Paraguay and Vietnam, respectively. Of the known Rpp1–4 sources of resistance, plant introduction (PI) 459025B (Rpp4) produced reddish-brown (RB) lesions in response to all of the P. pachyrhizi isolates, while PI 230970 (Rpp2) produced RB lesions to all isolates except one from Taiwan, in response to which it produced a susceptible tan (TAN) lesion. PI 200492 (Rpp1) and PI 462312 (Rpp3) produced TAN lesions in response to most P. pachyrhizi isolates. The resistant entries selected from Paraguay and Vietnam varied considerably in their responses to the 10 P. pachyrhizi isolates, with M 103 the most susceptible and GC 84058-18-4 the most resistant. The reaction patterns on these resistant entries to the P. pachyrhizi isolates were different compared with the four soybean accessions with the Rpp genes, indicating that they contain novel sources of rust resistance. Among the P. pachyrhizi isolates, TW 72-1 from Taiwan and IN 73-1 from India produced the most susceptible and resistant reactions, respectively, on the soybean entries.

Pathogenic Variation of South American <i>Phakopsora pachyrhizi</i> Populations Isolated from Soybeans from 2010 to 2015

“…In contrast, the P. pachyrhizi isolates collected in Alabama in 2004 induced a susceptible reaction in Rpp1-carrying PI 200492. Pham et al (2009) confirmed that the rust isolates resulting in a susceptible reaction in PI 200492 already existed in Brazil by 2001. These findings suggest that initial entry of the pathogen was achieved by its long distance movement from Central or South America (Isard et al 2005, Pan et al 2006.…”

“…The US isolates expressing the same pathogenicity profile as US isolates collected in 2004 when soybean rust was first found in the US (Schneider et al 2005), have not been detected in subsequent US samples (Paul et al 2015, Paul & Hartman 2009, Pham et al 2009). Therefore, it has been suggested that P. pachyrhizi isolates existing in 2004 disappeared or were suppressed due to the subsequent winter, likely resulting in unfavorable conditions for pathogen survival a resistant reaction in response to 5%-53% of the rust populations.…”

“…Yorinori (2008) Brazil, and Paraguay (Akamatsu et al 2013). Similarly, a P. pachyrhizi isolate from Taiwan collected in 1972 produced a resistant reaction in an Rpp2-carrying PI, and an isolate collected in 1980 caused a susceptible reaction in the same PI (Bonde et al 2006, Pham et al 2009). Bonde et al (2006) reported that P. pachyrhizi isolates collected in South America, Africa, and Thailand in 2001 were more virulent and/or aggressive than older isolates collected from 1972 to 1994.…”

Asian Soybean Rust – Meet a Prominent Challenge in Soybean Cultivation

“…These resistance genes have been identified genetically but not yet cloned. Screening for resistance against P. pachyrhizi is generally done using three different infection phenotypes: the highest degree of protection was observed in the so-called "immune" response where no disease symptoms were found on soybean leaves upon inoculation with the pathogen (Bromfield, 1984;Pham et al, 2009). By contrast, susceptible interactions are characterized by tan-colored lesions, referred to as "TAN"-type, in which 2-5 uredia (syn.…”

Asian Soybean Rust Resistance: An Overview

“…These genes are not effective against all populations of P. pachyrhizi [22]. The transfer of resistance genes through classical breeding or through marker-assisted selection allow to develop resistant varieties and their use as an efficient and costeffective method for soybean rust control.…”