Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is one of the most serious diseases of soybean. The soybean landraces PI 594767A, PI 587905 and PI 416764 previously showed high levels of resistance to a wide range of ASR fungus, while the genetic basis of the resistance has yet to be understood. In this study, the ASR resistance loci were mapped using three independent mapping populations, POP‐1, POP‐2 and POP‐3 derived from crosses BRS184 × PI 594767A, BRS184 ×  PI 587905 and BRS184 × PI 416764, respectively. In each population, the resistance to ASR segregated as a single gene, but the resistance was dominant in PI 594767A and PI 587905 and incompletely dominant in PI 416764. The resistance genes from both PI 594767A and PI 587905 were mapped on chromosome 18 corresponding to the same location as known resistance locus Rpp1. Quantitative trait locus (QTL) analysis performed on POP‐3 identified the putative ASR resistance locus in PI 416764 on the defined region of chromosome 6 where Rpp3 was located. The QTLs detected by the mapping explained about 67–72% of the phenotypic variation in POP‐3. Cluster analysis based on disease reactions to 64 ASR populations demonstrated the presence of at least two types of functional resistant Rpp1 alleles: strong and weak allele(s), e.g. soybean accession PI 594767A and PI 587905 carry the strong resistant Rpp1 allele(s). Introducing or pyramiding strong Rpp1 allele(s) in elite soybean cultivars is expected to be useful against the South American rust population.

The spider mite sub-family Tetranychinae includes many agricultural pests. The internal transcribed spacer (ITS) region of nuclear ribosomal RNA genes and the cytochrome c oxidase subunit I (COI) gene of mitochondrial DNA have been used for species identification and phylogenetic reconstruction within the sub-family Tetranychinae, although they have not always been successful. The 18S and 28S rRNA genes should be more suitable for resolving higher levels of phylogeny, such as tribes or genera of Tetranychinae because these genes evolve more slowly and are made up of conserved regions and divergent domains. Therefore, we used both the 18S (1,825–1,901 bp) and 28S (the 5′ end of 646–743 bp) rRNA genes to infer phylogenetic relationships within the sub-family Tetranychinae with a focus on the tribe Tetranychini. Then, we compared the phylogenetic tree of the 18S and 28S genes with that of the mitochondrial COI gene (618 bp). As observed in previous studies, our phylogeny based on the COI gene was not resolved because of the low bootstrap values for most nodes of the tree. On the other hand, our phylogenetic tree of the 18S and 28S genes revealed several well-supported clades within the sub-family Tetranychinae. The 18S and 28S phylogenetic trees suggest that the tribes Bryobiini, Petrobiini and Eurytetranychini are monophyletic and that the tribe Tetranychini is polyphyletic. At the genus level, six genera for which more than two species were sampled appear to be monophyletic, while four genera (Oligonychus, Tetranychus, Schizotetranychus and Eotetranychus) appear to be polyphyletic. The topology presented here does not fully agree with the current morphology-based taxonomy, so that the diagnostic morphological characters of Tetranychinae need to be reconsidered.

Since Asian soybean rust (ASR) isolates in South America are highly virulent, diverse, and distantly related to Japanese ones, limited numbers of resistance resources are available in soybean breeding in that region. Pyramiding of available ASR resistance genes (Rpp) in a single soybean genotype may provide wider spectrum and higher level of ASR resistance to soybean. However, the desired combinations of genes conferring adequate resistance to highly virulent or distantly related ASR isolates have not yet been studied. In this study, seven pyramided lines carrying multiple Rpp genes have been developed and evaluated for their resistance against one ASR isolate from Japan and two from Brazil. Significantly higher resistance was observed in the pyramided lines, No6-12-B (Rpp4 + Rpp5), Oy49-4 (Rpp2 + Rpp3 + Rpp4), and No6-12-1 (Rpp2+Rpp4+Rpp5) compared to the original resistance sources, PI 230970 (Rpp2), Hyuuga (Rpp3), PI 459025 (Rpp4), and Kinoshita (Rpp5) carrying single Rpp genes. Although infection of the resistance sources with the highly virulent Brazilian ASR isolates resulted in susceptible phenotypes with moderate to abundant sporulation, highly resistant phenotypes with almost no sporulation were observed in the three Rpp-pyramided lines. Therefore, pyramided lines carrying these Rpp gene combinations are useful in soybean breeding for conferring broad spectrum, high resistance to ASR isolates that are virulent to the varieties carrying single resistance genes.

Asian soybean rust (ASR) caused by Phakopsora pachyrhizi is one of the most serious soybean (Glycine max) diseases in tropical and subtropical areas. A soybean line, PI 587855, showed a resistance phenotype against ASR pathogens in Japan and South America at high frequency; however, little is known of the genetic control of this resistance and chromosomal location of the corresponding locus. Therefore, the aim of this study was to study the inheritance of PI 587855 resistance and map the corresponding locus with SSR markers aiming to use the linked markers in marker‐assisted selection. In the segregating population, resistance to ASR appeared to be controlled by a single dominant gene. The ASR resistance locus was mapped near to the chromosomal region where the resistant loci, Rpp1 and Rpp1‐b, were previously mapped. Comparative genetic mapping and disease reaction profiles of other seven lines carrying Rpp1 or Rpp1‐b to four Brazilian ASR isolates revealed that the resistance reaction exhibited by PI 587855 was similar to that of Rpp1‐b‐carrying varieties which have useful resistance to South American ASR strains.

Brown algae produce alginate that has various ratios and diverse sequences of two uronic acids, β-D-mannuronic acid and α-L-guluronic acid, compared with those of alginate produced by bacteria. This diversity of alginate in brown algae is caused by mannuronan C5-epimerases (MC5Es), which catalyze the conversion of β-D-mannuronic acid to α-L-guluronic acid. Although several bacterial MC5E enzymes have been well characterized, to date, there exists no information on the biochemical properties of eukaryotic MC5E. In this study, MC5E expression was detected in a brown alga Saccharina japonica sporophyte by immunoblot analysis. We also searched for MC5E mRNA from S. japonica by RT-PCR and revealed eight partial amino acid sequences, SjC5-I to-VIII. We focused on the highest frequency clone, SjC5-VI, and elucidated its full-length cDNA and putative gene structure. The translated SjC5-VI protein consists of 499 amino acids, with the N-terminal 21 amino acids predicted as a secretion signal sequence. Functional recombinant SjC5-VI (rSjC5-VI) was successfully expressed as a secreted protein using an insect-cell expression system, and we determined the optimal temperature, pH, and NaCl concentrations to be 35°C, 7.0-8.2, and 300 mM, respectively, using the Ca 2+-induced gel-formation assay. In addition, Ca 2+ enhanced gelation by 1.7-fold following rSjC5-VI activity. Furthermore, 1 H-NMR spectroscopy of rSjC5-VI-treated polyM revealed alternate epimerization of β-D-mannuronic acid to 3 α-L-guluronic acid. To the best of our knowledge, this is the first report on the characterization of MC5E activity in eukaryotes.