No abstract

Phakopsora pachyrhizi is an obligatory biotrophic fungus that causes Asian soybean rust (ASR) disease. ASR control primarily involves chemical control and the use of resistant soybean cultivars carrying an Rpp (resistance to P. pachyrhizi) gene. This study aimed to characterize the ASR resistance of three soybean Asian landraces. By screening the world core collection (WC) of soybean, which consists of 80 varieties, three landraces were identified in Southeast Asia as resistant to ASR. Genetic mapping using the F2 population derived from a cross with an ASR-susceptible variety, BRS 184, indicated that KS 1034 (WC2) has ASR resistance conferred by a single dominant resistance gene, mapped on chromosome 18, in the same region where Rpp1 was mapped previously. The BRS 184 × WC61 (COL/THAI/1986/THAI-80) F2 population, on the other hand, showed an ASR resistance locus mapped by quantitative trait locus analysis on chromosome 6, in the region where the resistance conferred by PI 416764 Rpp3 resides, with a logarithm of the odds score peak at the same position as the marker, Satt079, while the BRS 184 × WC51 (HM 39) population showed the resistance to ASR allocated between Satt079 and Sat_263 markers, also in the region where Rpp3 was mapped previously. Both WC51 and WC61 have the same infection profile as FT-2 and PI 462312 when tested against the same ASR isolate panel. These three WCs can be used in MAS programs for introgression of Rpp1 and Rpp3 and the development of ASR-resistant cultivars in the breeding program.

Asian soybean rust (ASR), caused by the obligate biotrophic fungus Phakopsora pachyrhizi, is one of most important diseases in the soybean (Glycine max (L.) Merr.) agribusiness. The identification and characterization of genes related to plant defense responses to fungal infection are essential to develop ASR-resistant plants. In this work, we describe four soybean genes, GmbZIP62, GmbZIP105, GmbZIPE1, and GmbZIPE2, which encode transcription factors containing a basic leucine zipper (bZIP) domain from two divergent classes, and that are responsive to P. pachyrhizi infection. Molecular phylogenetic analyses demonstrated that these genes encode proteins similar to bZIP factors responsive to pathogens. Yeast transactivation assays showed that only GmbZIP62 has strong transactivation activity in yeast. In addition, three of the bZIP transcription factors analyzed were also differentially expressed by plant defense hormones, and all were differentially expressed by fungal attack, indicating that these proteins might participate in response to ASR infection. The results suggested that these bZIP proteins are part of the plant defense response to P. pachyrhizi infection, by regulating the gene expression related to ASR infection responses. These bZIP genes are potential targets to obtain new soybean genotypes resistant to ASR.

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is one of the most serious soybean (Glycine max) diseases in tropical and subtropical regions. To facilitate the development of resistant varieties using gene pyramiding, DNA markers closely linked to seven resistance genes, namely, Rpp1, Rpp1-b, Rpp2, Rpp3, Rpp4, Rpp5, and Rpp6, were identified. Linkage analysis of resistance-related traits and marker genotypes using 13 segregating populations of ASR resistance, including eight previously published by our group and five newly developed populations, identified the resistance loci with markers at intervals of less than 2.0 cM for all seven resistance genes. Inoculation was conducted of the same population with two P. pachyrhizi isolates of different virulence, and two resistant varieties, ‘Kinoshita’ and ‘Shiranui,’ previously thought to only harbor Rpp5, was found to also harbor Rpp3. Markers closely linked to the resistance loci identified in this study will be used for ASR-resistance breeding and the identification of the genes responsible for resistance.