Development of classification criteria for resistance to soybean rust and differences in virulence among Japanese and Brazilian rust populations

Abstract

In recent years soybean rust, caused by Phakopsora pachyrhizi has become one of the most serious threats to soybean production in Brazil. Breeding lines and varieties have been selected for resistance to soybean rust in Asia. However, differences in virulence between Asian and Brazilian rust populations should be considered in order to select and use resistant resources from Asia. Here, we suggest criteria for distinguishing resistant from susceptible types by the analysis of four resistance characters: frequency of lesions having uredinia, number of uredinia per lesion, frequency of open uredinia, and sporulation level, determined by the utilization of 63 genotypes. Under growth chamber conditions, a set of 13 soybean varieties were exposed to three rust populations-one from Japan and two from Braziland evaluated for the resistance characters mentioned above. The Japanese and Brazilian populations clearly differed in virulence, as did the two Brazilian populations. Only two resistance genes, Rpp4 from PI459025 and Rpp5 from Shiranui, commonly conferred resistance on all three rust populations. The number of resistant varieties or resistance genes useful in both countries appears limited. Therefore, a resistant cultivar that is universally effective against soybean rust should be developed by pyramiding some major resistance genes and by introducing horizontal resistance. Keywords: Phakopsora pachyrhizi, lesion type, pathogenicity, resistant variety. RESUMO Desenvolvimento de critério de classificação da resistência à ferrugem asiática da soja e diferenças de virulência entre populações do Japão e do BrasilNos últimos anos a ferrugem asiática, causada pelo fungo Phakopsora pachyrhizi tornou-se uma das mais sérias ameaças a produção de soja Brasileira. Linhagens melhoradas e variedades têm sido selecionadas para a resistência à ferrugem da soja na Ásia, entretanto para a seleção e utilização dessas fontes de resistência, diferenças de virulência entre populações Asiáticas e Brasileiras desse fungo devem ser consideradas. Neste trabalho sugerimos um critério para se distinguir resistência de susceptibilidade pela análise de quatro caracteres de resistência: freqüência de lesões contendo urédias, número de urédias por lesão, freqüência de urédias abertas e nível de esporulação determinados pela utilização de 63 genótipos. Sob condições controladas em câmaras de crescimento, treze variedades de soja foram expostas a três populações de fungos -uma população proveniente do Japão e duas populações provenientes do Brasil-e avaliadas quanto aos caracteres de resistência mencionados acima. As populações Brasileiras diferiram entre si claramente quanto a virulência e em relação à população de isolados do Japão. Apenas dois genes de resistência, Rpp4 presente na variedade PI459025 e Rpp5 presente na variedade Shiranui conferiram resistência as três populações da ferrugem. O número de variedades ou genes resistentes úteis em ambos os países parece ser limitado. Assim, um cultivar universalmente efetivo contra a ferru...

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

“…By using such differences in the host-plant responses, a method of evaluating soybean resistance to P. pachyrhizi and assessing the pathogenicity of P. pachyrhizi has been established (Akamatsu et al 2013, Yamanaka et al 2010). In addition, P. pachyrhizi samples from Argentina, Provinces of Argentina, states of Brazil, and departments of Paraguay are shown on each map.…”

Inducers of resistance and silicon on the activity of defense enzymes in the soybean-Phakopsora pachyrhizi interaction

“…The initial symptoms of ASR are chlorosis of polygonal shape in the leaves delimited by the veins that evolve later to brown lesions where uredia containing numerous urediniospores arise (Sinclair and Hartman, 1999). ASR is a difficult disease to control due to the highly aggressive nature of the pathogen and the absence of cultivars with satisfactory levels of resistance (Yamanaka et al, 2010). The greatest damage caused by ASR is the early defoliation of the plants (Li et al, 2010), which results in a reduction in the number of pods, number…”

Asian Soybean Rust Resistance: An Overview

“…The effectiveness of the racespecific resistance is often of short duration, especially in biotrophic pathogens like P. pachyrhizi, with high virulence variability. Varieties with two pyramided resistance genes tend to express greater durability of resistance than varieties with a single gene [73,74]. Lemos et al [75] and Yamanaka et al [76] reported that a variety with three resistance genes (Rpp2, Rpp4 and Rpp5) showed significantly higher resistance than its ancestor, showing that pyramiding strategy is effective to increase the rust resistance.…”