Complete nucleotide sequence of soybean leaf rugose mosaic virus, an atypical member of the genus Bymovirus.

The host range of previously reported bymoviruses is restricted to plants belonging to the family Poaceae. Soybean leaf rugose mosaic virus (SbLRMV) from non-Poaceae plants is related to bymoviruses based on a partial genome sequence. However, unlike bymoviruses, this virus infects plants of at least four dicotyledonous families, including Fabaceae, and causes disease in soybean. Complete nucleotide sequences of two variants of SbLRMV were determined, and its taxonomic position was clarified. RNA1 is 7109 nucleotides (nt) long with one large open reading frame (ORF), possibly encoding a polyprotein of 257 kDa. This polyprotein is likely processed into eight mature proteins. The entire RNA1 ORF shares 52%-55% nucleotide sequence identity and 27%-43% amino acid sequence identity, and the coat protein shares 49%-54% nucleotide sequence identity and 30%-34% amino acid sequence identity to other bymoviruses. The similarity to other viruses in the family Potyviridae is generally lower. RNA2 is 3413 or 3415 nt long and putatively encodes a polyprotein of 108 kDa. This protein is probably cleaved into two mature proteins. The sequences of these two RNAs are very similar to those of bymoviruses. Phylogenetic analysis of members of the family Potyviridae showed that RNA1 and RNA2 of SbLRMV formed a basal clade with known bymoviruses. Inoculation tests using leaf samples suggested that SbLRMV RNA1 can systemically infect and cause disease in soybean without the presence of RNA2. In conclusion, SbLRMV is an atypical member of the genus Bymovirus that infects soybean (Fabaceae) and other dicots rather than gramineous hosts.

Comparative analysis of the inverted repeat of a chalcone synthase pseudogene between yellow soybean and seed coat pigmented mutants.

In soybean, the I gene inhibits pigmentation over the entire seed coat, resulting in yellow seeds. It is thought that this suppression of seed coat pigmentation is due to naturally occurring RNA silencing of chalcone synthase genes (CHS silencing). Fully pigmented seeds can be found among harvested yellow seeds at a very low percentage. These seed coat pigmented (scp) mutants are generated from yellow soybeans by spontaneous recessive mutation of the I gene. A candidate for the I gene, GmIRCHS, contains a perfect inverted repeat (IR) of a CHS pseudogene (pseudoCHS3) and transcripts of GmIRCHS form a double-stranded CHS RNA that potentially triggers CHS silencing. One CHS gene, ICHS1, is located 680 bp downstream of GmIRCHS. Here, the GmIRCHS-ICHS1 cluster was compared in scp mutants of various origins. In these mutants, sequence divergence in the cluster resulted in complete or partial loss of GmIRCHS in at least the pseudoCHS3 region. This result is consistent with the notion that the IR of pseudoCHS3 is sufficient to induce CHS silencing, and further supports that GmIRCHS is the I gene.

Long-term blast control in high eating quality rice using multilines.

Combining genetic heterogeneity and crop homogeneity serves a dual purpose: disease control and maintaining harvest quality. Multilines, which consist of a genetically uniform mixture of plants, have the potential to suppress disease while maintaining eating quality, yet practical methods that facilitate commercial use over large geographical areas are lacking. Here, we describe effective rice multiline management based on seed mixture composition changes informed by monitoring virulent blast races in Niigata Prefecture, Japan. The most elite nonglutinous cultivar, Koshihikari, was converted into the multiline, Koshihikari BL (blast resistant lines) and planted on 94,000 ha in 2005. The most destructive rice disease, blast, was 79.4% and 81.8% less severe in leaves and panicles, respectively, during the 2005-2019 period compared to the year 2004. In addition, fungicidal application was reduced by two-thirds after the introduction of BL. Our results suggest that seed mixture diversification and rotation of resistant BL provides long-term disease control by avoiding virulent race evolution.

Screening and Field Trials of Virus Resistant Sources in Capsicum spp.

Thirty-seven Capsicum accessions containing cultivated and wild species were screened for resistance to Cucumber mosaic virus (CMV), and were also investigated for their response to Tomato aspermy virus (TAV), Tomato mosaic virus (ToMV), Pepper mild mottle virus (PMMoV), and Tomato spotted wilt virus (TSWV). C. baccatum PI 439381-1-3 (PI 439381-1-3), C. frutescens LS 1839-2-4 (LS 1839-2-4), and C. frutescens cv. Tabasco (cv. Tabasco) showed a hypersensitive reaction against CMV-Y, and thus were not systemically infected. Only inoculated leaves of C. annuum cv. Sapporo-oonaga and cv. Nanbu-oonaga were infected with CMV-Y, and viral infection did not spread systemically. These five accessions (PI 439381-1-3, LS 1839-2-4, cv. Tabasco, cv. Sapporo-oonaga, and cv. Nanbu-oonaga) were considered resistant to CMV-Y. These accessions were also resistant to other CMV isolates, but not to the TAV isolate. PI 439381-1-3, LS1839-2-4, cv. Sapporo-oonaga, and cv. Nanbu-oonaga were susceptible to PMMoV, while PI 439381-1-3 and LS1839-2-4 showed systemic necrosis. All CMV-resistant accessions were susceptible to TSWV. Field tests of eight Capsicum accessions, including CMV, PMMoV, and/or TSWV-resistant accessions, demonstrated that most of the PI 439381-1-3 plants were not infected with CMV and PMMoV among the virus-infested fields. As occurred with mechanical inoculation, LS 1839-2-4, cv. Tabasco, cv. Sapporo-oonaga, and cv. Nanbu-oonaga were hard to infect with CMV in the field.