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

Abstract

Soybean rust caused by Phakopsora pachyrhizi is one of the most serious economic threats to soybean production in South America. A previous study using South American P. pachyrhizi populations collected between 2007/2008 and 2009/2010 revealed the pathogenic diversity in Argentinean, Brazilian, and Paraguayan rust populations. Because such pathogenic diversity has been a major constraint to the breeding program for soybean rust resistance, pathogen populations were continuously monitored throughout the 2010/2011 to 2014/2015 seasons using the same method of evaluating pathogenicity as used in the previous study. None of the 83 P. pachyrhizi samples collected from the three countries from 2010/2011 to 2014/2015 yielded identical pathogenicity patterns in the 16 differentials, thus demonstrating the pathogenic diversity of more recent South American rust populations. Cluster analysis using a total of 145 rust populations from 2007 to 2015 demonstrated that the Argentinean, Brazilian, and Paraguayan populations were not assigned to three distinct country-based groups. The analysis indicated that a majority of South American populations differed in pathogenicity compared with Japanese rust races. The rates of resistance to the rust populations varied among the 13 differentials carrying Rpp genes; the most effective resistance gene was Rpp1-b followed by Rpp5, and the least effective was Rpp1.

Pyramiding three rust‐resistance genes confers a high level of resistance in soybean (Glycine max)

“…Eight Rpp loci for resistance to P. pachyrhizi have been identified to date ( Rpp1–Rpp7 and Rpp1‐b ) and mapped at different loci (Chakraborty et al, ; Childs et al, ; Garcia et al, ; Hossain et al, ; Hyten et al, , ; Li, Smith, Ray, & Frederick, ; Silva et al, ). These genes are now available for marker assisted breeding but are only effective against specific P. pachyrhizi races and so rarely offer durable resistance to the highly variable ASR pathogen (Oliveira, Godoy, & Martins, ), which limits their use for developing ASR‐resistant soybean, particularly in areas where the pathogen is highly virulent (Akamatsu et al, , ; García‐Rodríguez, Morishita, Kato, & Yamanaka, ; Stewart, Rodrígue, & Yamanaka, ; Yamanaka et al, , ). However, pyramiding specific combinations of resistance genes in a single variety can confer a higher level of broad‐spectrum resistance, representing an ideal breeding strategy for the production of ASR‐resistant soybean (Lemos et al, ; Maphosa, Talwana, & Tukamuhabwa, ; Yamanaka et al, , ).…”

Pathotypic variation of Phakopsora pachyrhizi isolates from Uruguay

“…Disease evaluations were made two weeks after inoculation on at least one leaflet from two or three plants per genotype. Thirty individual lesions from these leaflets were evaluated for sporulation level (SL) and number of uredinia (NoU) following Yamanaka et al (2010). SL was rated using a 0 to 3 scale, where 0 is no sporulation and 3 is abundant sporulation .…”

“…Temporal and geographic comparisons of pathogenicity have been made; isolates collected from Africa and South America in 2001 were more virulent than Asian and Australian isolates from the 1970s (Bonde et al 2006). Moreover, higher virulence was also revealed in the Brazilian P. pachyrhizi populations compared to Japanese populations (Yamanaka et al 2010).…”

Evaluating the Contribution of Soybean Rust- Resistant Cultivars to Soybean Production and the Soybean Market in Brazil: A Supply and Demand Model Analysis

“…The cost of fungicide accounted for 7.09% of total production cost of soybeans in the 2016/2017 crop year [6], while the average production cost of Brazil in 2013/2014 was approximately twice as high as that in the USA and Argentina [7]. Some studies have suggested that adopting SBR-resistant cultivars could reduce the cost of fungicide use [4,[8][9][10]. SBR-resistant cultivars have been introduced in Brazil [2], but the highly virulent rust populations have made it difficult to cope with SBR by only one genotype of cultivar [2].…”

“…SBR-resistant cultivars have been introduced in Brazil [2], but the highly virulent rust populations have made it difficult to cope with SBR by only one genotype of cultivar [2]. Therefore, SBR-resistant cultivars corresponding to several types of rust population have been developed [2,9,10]. By adopting these cultivars, the cost of applying fungicide can be reduced [2,5].…”