Pathotypic variation of Phakopsora pachyrhizi isolates from Uruguay

Abstract

Soybean rust, caused by Phakopsora pachyrhizi, is one of the most important foliar diseases threatening soybean production in Uruguay. Knowledge of pathogenic variation among Uruguayan rust populations is necessary to guide development of resistant soybean cultivars in national breeding programs. To assess pathogenic variation,12 P. pachyrhizi isolates were collected from fields across the country over a four-year period and were inoculated onto a set of 12 differential soybean genotypes. All Uruguayan rust isolates (URPs) were highly virulent on differential soybean plants carrying resistance genes Rpp1, Rpp3, and Rpp4. Conversely, all isolates showed resistant reactions on soybean differentials with Rpp1-b and on a line carrying the genes Rpp2, Rpp4, and a Rpp5 allele. The pathogenic variation of the URPs was compared to that of a collection of 157 P. pachyrhizi isolates from other Latin American countries and Japan. All URPs clustered together and with other fungal isolates from South America. Of the seven different pathotypes that were found, four shared identical virulence patterns with isolates from South America, and three were associated with unique virulence patterns, which mainly resulted from the reactions they caused on plants carrying Rpp3, Rpp4 and especially Rpp6. The results indicate that the URPs can overcome the resistance of a larger number of Rpp genes than P. pachyrhizi isolates from neighboring countries. The resistant genes Rpp1-b and Rpp5 proved to be effective against the pathogen and will be introgressed into local soybean lines.

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

“…Therefore, these two combinations of Rpp genes appear to be extremely useful for conferring high resistance to BdRPs. Especially No6‐12‐1 line ( Rpp2 + Rpp4 + Rpp5 ) have been reported its high resistance to ASR pathogens from Latin America as well as Bangladesh (García‐Rodríguez et al, ; Hossain & Yamanaka, ; Stewart et al, ), it may have potential for wide spectrum resistance to P. pachyrhizi in various regions.…”

“…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, , ).…”

Análises genéticas revelam oportunidades e obstáculos da tolerância ao fungo da ferrugem asiática da soja

“…Esses esporos surgem entre 5 e 8 dias após a inoculação (Goellner et al, 2010). Muito embora não existam relatos de reprodução sexuada, principal mecanismo de liberação da variância genética, a existência de variabilidade patogênica do fungo é rotineiramente reportada (Stewart et al, 2019), bem como supressão da resistência conferida por genes de efeito maior [genes R] (Yorinori et al, 2005). Isso se deve a um importante mecanismo compartilhado por fungos filamentosos, conhecido como anastomose hifal (hibridização somática) e formação de heterocários (Vittal et al, 2012).…”

“…Uruguai (Stewart et al, 2019) e nos três principais produtores da América do Sul (Akamatsu et al, 2013).…”

“…Usando genótipos diferenciadores, i.e., àquelas com diferentes genes de resistência à ferrugem da soja (genes Rpp: resistance to P. pachyrhizi), Stewart et al (2019) identificaram um espectro de virulência amplo nos isolados de P. pachyrhizi coletados no Uruguai. Além disso, observaram que os padrões de virulência foram idênticos a patótipos coletados ao longo do continente.…”