On the cover

Gibberellin-induced internode elongation enables grafting and promotes floral transition in Brassicaceae crops. Left: Elongated internodes induced by gibberellin treatment. The background shows paraffin sections of the elongated internode and hypocotyl of a radish. Center: A grafted plant that successfully flowered following internode elongation. Right: Longitudinal section of the graft junction observed using confocal laser scanning microscopy (This issue, p. 133–143).

(H. Takagi: Ishikawa Prefectural University)

Cottonseeds are rich in proteins with high nutritional value. In this study, a genome-wide association study involving six methods was performed to dissect the genetic architecture of the cottonseed protein content (CPC) in Upland cotton (Gossypium hirsutum L.). The CPC exhibited typical characteristics of a quantitative trait. The six methods revealed 1, 4, 4, 31, 10, and 30 CPC-related quantitative trait nucleotides (QTNs), among which 17 were detected by at least two methods. Notably, TM40095 on A12 and TM59869 on D06 were detected by three methods, thus being considered stable QTNs. Five QTN-by-environment interactions (QEIs) and 29 QTN-by-QTN interactions (QQIs) were detected. The regions flanking the SNPs of two stable QTNs, five QEIs, and four significant QQIs included 49, 174, and 269 candidate genes, respectively. A functional enrichment analysis indicated that 12 and 48 non-redundant genes related to the two stable QTNs and five QEIs, respectively, were associated with significantly enriched functions. Moreover, eight protein (gene)–protein (gene) interactions were predicted. According to RNA-seq expression data, GH_D06G1049 (related to QTNs) and GH_A06G1663, GH_D13G0601, and GH_A05G0236 (related to QEIs) were preferentially expressed in multiple ovule tissues, suggesting that they may contribute to seed protein synthesis and accumulation. These findings provide new clues regarding the genetic basis of CPC and may accelerate the molecular breeding of cotton with ideal protein content.

In Brassicaceae crops such as cabbage and turnip, which are harvested for their vegetative organs, floral induction can reduce the eating quality of these organs. Therefore, developing late-flowering varieties that are insensitive to vernalization is a key breeding objective. However, a major challenge in breeding these cultivars lies in the contradiction between the late-flowering trait and the need to induce flowering for crossing. To address this, we developed a flowering induction technique using grafting, in which gibberellin-induced elongated internodes are used as scions and grafted onto the flower stalk of Brassica rapa cv. ‘CHOY SUM EX CHINA 3’, which constitutively expresses FLOWERING LOCUS T (FT), as the rootstock. This method is applicable even to rosette-type Brassicaceae plants with short internodes. Histological and radioisotope analyses confirmed the reconnection of vascular bundles and the functionality of component transport across the graft junction. Additionally, gibberellin treatment was found to promote flowering in the presence of FT, most likely through an activation of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 3, a gene known to promote floral meristem development. This rapid flowering system offers a practical strategy for accelerating the breeding of late-flowering Brassicaceae crops.

Vigna luteola, a wild legume species, shows remarkable variation in salinity tolerance across its natural habitats, with coastal populations exhibiting high tolerance and riverbank populations being sensitive. This intraspecific variation provides a valuable system for investigating the genetic basis of salt tolerance. A major QTL for salt tolerance was previously identified by crossing salt-tolerant and salt-sensitive accessions, but the responsible genes remain unknown. In this study, grafting experiments between the two accessions revealed that the root plays a primary role in salt tolerance by suppressing Na⁺ transport to the shoot. We then conducted root transcriptome analysis and identified four candidate genes located within the QTL and highly expressed under salt stress in the tolerant accession: CBL-INTERACTING PROTEIN KINASE 6 (CIPK6), CAFFEOYL SHIKIMATE ESTERASE (CSE), FCS-LIKE ZINC FINGER PROTEIN 13 (FLZ13), and DROUGHT-INDUCED 21 (DI21). Promoter analysis revealed that the CIPK6 promoter contains transcription factor binding motifs unique to the salt-tolerant accession, which may contribute to its high expression under salt stress. These findings suggest that CIPK6 is regulated by cis-regulatory differences and is the most promising candidate for the salt-tolerance QTL. The identified genes in this study provide a foundation for developing salt-tolerant crops in the future.

Fusarium head blight (FHB) is a severe disease that affects wheat production. ‘Sumai 3’ has been used as the FHB resistance genetic resource, and DNA markers linked to known quantitative trait loci (QTL) located on 3BS, 6BS, 5AS, or 2DL have been used to detect the ‘Sumai 3’-derived allele. We first developed a near-isogenic line (NIL) of a Japanese cultivar, ‘Kitahonami’, with ‘Sumai 3’ FHB resistant allele at the 2DL-located QTL by recurrent backcrossing. Although the ‘Sumai 3’ allele improved resistance to FHB, it reduced yield and thousand-grain weight (TGW) to unacceptable levels. During the genotype of FHB-resistant QTL in FHB-resistant breeding lines K-1932 and K-1976, we found both lines have a novel allele at the 2DL-located QTL introduced from ‘Asakaze’. We confirmed the co-segregation between the FHB resistance phenotype and the novel ‘Asakaze’-derived allele in the three breeding populations. Furthermore, we developed two sets of NILs, with and without the ‘Asakaze’-derived allele, and examined the FHB resistance, yield, and TGW. The results show that the ‘Asakaze’-derived allele improved FHB resistance similar to the ‘Sumai 3’-derived allele. Surprisingly, the ‘Asakaze’-derived allele did not negatively affect yield and TGW, contrary to the ‘Sumai 3’-derived allele. Wheat breeders can improve FHB resistance without reducing yield and TGW using the ‘Asakaze’-derived QTL allele.

Wheat yellow mosaic (WYM) disease, caused by the wheat yellow mosaic virus (WYMV), significantly affects wheat production. Three WYMV pathotypes—I, II, and III—have been identified in Japan, each with a distinct geographical distribution and pathogenicity. To investigate the historical and geographical distribution of infection-resistant wheat varieties in Japan and the relevant genetics, we comprehensively evaluated the response to WYMV pathotypes and the genotypes conferring resistance in accessions of the Japanese wheat core collection. In the experimental fields harboring WYMV, most of the varieties that showed stable resistance were breeders lines; only a few were traditional varieties. Resistant accessions are particularly prevalent in northern Japan. These results suggest that resistant varieties have been developed through modern breeding, in which crossbreeding with foreign varieties has played a major role. Resistance-conferring genes on the chromosome 2DL and 5AL appeared to have been introduced during this breeding process, and the 5AL locus became widely distributed in Japanese varieties. Through genome-wide association studies, we identified a novel resistance-conferring locus on chromosome 7AS. Furthermore, the resistant haplotype on 7AS confers robust resistance to pathotype I when combined with the haplotype carried on 5AL. The results of this study contribute to the understanding of resistance-associated genetics in the context of WYM disease, highlighting the potential of particular genomes to confer robust and durable resistance in breeding efforts.

Optimizing heading date to suit local conditions is key to maximizing yield potential. ‘Haruka Nijo’, a two-rowed barley (Hordeum vulgare L.) cultivar developed for the Kyushu region of Japan, is early-heading and has superior yield performance compared to the standard cultivar ‘Nishinohoshi’. To identify genomic regions associated with early-heading in ‘Haruka Nijo’, we conducted analysis of quantitative trait loci (QTLs) using recombinant progeny of ‘Haruka Nijo’ × ‘Nishinohoshi’ (heading date difference: 2.4–6.0 days). A stable QTL, designated QHD.HN-5H, was detected near the centromere of chromosome 5H. This QTL explained 30.3–46.1% of the phenotypic variance and consistently conferred 2–5 days earlier heading across three seasons. Pedigree analysis indicated that the QHD.HN-5H region in ‘Haruka Nijo’ likely originated from the Tohoku six-rowed cultivar ‘Haganemugi’ and was probably co-introduced into Kyushu cultivars together with the Barley yellow mosaic virus resistance gene rym3. Whole-genome sequencing and Gene Ontology analysis identified non-synonymous differences between ‘Haruka Nijo’ and ‘Nishinohoshi’ in five heading-related genes within the QTL region. Four of these genes shared identical genotypes between ‘Haganemugi’ and ‘Haruka Nijo’, supporting their candidacy. These findings provide new breeding tools to adapt the heading date of barley to the climate and cultivation environment.

We developed a new reddish-purple fleshed sweetpotato (RFSP) cultivar, ‘Sakurahonoka’, with high yield for processing use. Released in 2025, the most distinctive characteristic of Sakurahonoka is its flesh color. The dominant aglycone (anthocyanidin-moiety) of anthocyanin (aglycone) in Sakurahonoka is pelargonidin, which distinctly varied from the purple-fleshed sweetpotato (PFSP) cultivars, whose dominant aglycones were peonidin or cyanidin. Sakurahonoka demonstrated a higher marketable root yield than the two major PFSP cultivars in the Kyushu region of Japan: ‘Ayamurasaki’ and ‘Murasakimasari’. Additionally, Sakurahonoka showed a higher resistance to sweetpotato foot rot disease than Ayamurasaki. Furthermore, the color of Sakurahonoka processed as fried chips and steamed paste was unique and brighter than that of the PFSP cultivars. Food manufacturers have found that Sakurahonoka is suitable as an ingredient in fried chips and boiled-diced sweetpotato. It can be processed into a paste; however, its steamed sweetpotato is fibrous and requires effort to be strained. Thus, Sakurahonoka is an epoch-making RFSP that improves the color variation in sweetpotato-processed foods.

We developed a new sweetpotato variety, ‘Michishizuku’, as the raw material for imo-shochu, a traditional Japanese distilled liquor made from sweetpotaoes, and for starch production. Michishizuku was selected from a cross between ‘Konaishin’ and Kyukei 09187-14 and was released in 2021. Its total yield was higher than that of ‘Koganesengan’, slightly higher than that of ‘Shiroyutaka’, and slightly lower than that of Konaishin. The starch content of Michishizuku was significantly higher than those of the other varieties, and its starch yield was 146–147% that of Koganesengan and 93–102% that of Konaishin. Shochu brewing tests confirmed that the alcohol yield of Michishizuku was higher than that of Koganesengan. In addition, the flavor of shochu made from Michishizuku (Michishizuku shochu) was similar to that of Koganesengan shochu, and its sensory evaluation score was slightly higher than that of Koganesengan shochu. Based on these results, Michishizuku is highly suitable for shochu brewing. The viscosity characteristics of the starch of Michishizuku were similar to those of Shiroyutaka and Konaishin, and its whiteness was as high as that of Shiroyutaka. Therefore, Michishizuku is also suitable as a raw material for starch production. Michishizuku exhibited moderately strong resistance to foot rot, which causes severe damage to sweetpotato in the Southern Kyushu area. These characteristics suggest that Michishizuku will contribute to reductions in damage caused by foot rot and the stable production of shochu and starch.