Rust effect estimation in soybean crosses for tolerance to Asian rust

Abstract

Asian soybean rust is an important disease that has deeply troubled farmers and researchers since it was first reported. The causal agent, biotrophic fungus Phakopsora pachyrhizi Sydow & P. Sydow, has found extremely favorable conditions for its dissemination in Brazil. The most characteristic symptom of infection appears in the leaves, initially on the adaxial leaf surface, as small angular points less than 1mm in diameter, together with gray-colored uredospores (spores). Management involves a set of practices that guarantee coexistence between the plant and the pathogen without significant damage to the crop. The objective of this research was to evaluate tolerance to Asian rust by estimating losses caused by natural infection in the field. Experiments with generation F4 (2014/15) plants were established in a randomized blocks design with four replicates, with two types of genotypes (crosses and parents) and two schemes for disease management using fungicides. For analysis of the data, a test was applied on two dependent samples to verify the significance of the estimate of the rust effect. With regard to grain yield and tolerance, the most outstanding crosses were 104 (USP14-01-20 × EMGOPA313) and 149 (USP93-05.552 × EMGOPA313). Crosses 147 (USP93-05552 × PI153.282) and 137 (USP70.108 × PI153.282) were graded as tolerant in the evaluation of both yield reduction and seed size. We found evidence of tolerance to Asian rust in both crosses and parents. The statistical test revealed the significance of the rust effect estimates in soybean.

Impact of Asian soybean rust on vegetable soybean, considering two stages of development

“…A tolerant plant is phenotypically similar to a susceptible one, which makes identification difficult (Newton, 2016). However, some studies have identified tolerant genotypes and crosses that can be used in soybean breeding programs (Espolador et al., 2020; Oloka et al., 2009; Pereira et al., 2018). To date, no studies in the literature have focused on the tolerance of vegetable soybeans to ASR.…”

“…According to Pereira et al. (2018), Rust effect is the difference among the adjusted means of each genotype and between the two disease management schemes. The rust effect (RE) was estimated for all 10 traits evaluated at the R 6 and R 8 stages as RE = X (without ASR) – Y (with ASR), where X is the mean of the plots without ASR and Y is the mean of the plots with ASR.…”

“…Some breeding programs aimed at obtaining tolerant genotypes have sought efficient strategies for assessing tolerance in the field (Hartman et al., 2005; Rimbaud et al., 2021). One strategy is to use management strategies with different fungicides to compare genotypes in the presence and absence of rust, estimating the losses caused by rust (Levy, 2004; Pereira et al., 2018; Schafer, 1971).…”

Capacidade combinatória de genótipos de soja sob condições de cerrado de baixa latitude

“…Vários estudos têm sido realizados para avaliar a capacidade combinatória de genótipos de soja, visando o estabelecimento de estratégias eficientes de seleção de indivíduos superiores em condições de baixas latitudes. Entre esses trabalhos, destacamse aqueles voltados à obtenção de linhagens superiores quanto à produção de grãos (Daronch et al, 2014), teor de óleo e proteína (Del Conte, 2017), e quanto à tolerância a ferrugem asiática (Pereira et al, 2018). Entretanto, a demanda por novos cultivares-elite de soja é constante, e os programas de melhoramento têm que ser dinâmicos para superar os atuais índices de produtividade e desempenho exigidos pelo mercado.…”

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

“…A tolerância, como uma alternativa de redução dos impactos negativos causados pela ferrugem tem sido tema de pesquisas com resultados proeminentes (Kawuki et al, 2004;Jarvie e Shanahan, 2009;Oloka et al, 2009;Araujo e Vello, 2010;Melo et al, 2015;Pereira et al, 2018). Avaliando 51 linhagens de soja na Uganda, Kawuki et al (2004) (Meuwissen et al, 2001).…”