We attempted to backcross Carica papaya as a pollen donor to previously developed intergeneric hybrid plants (C. papaya × Vasconcellea cundinamarcensis) showing Papaya leaf distortion mosaic virus (PLDMV) resistance (Tarora et al. 2016). By employing embryo culture technique, 45 seeds with embryos were obtained from 5,762 seeds in the matured fruits (180 to 210 days after pollination) of backcrossed plants. Finally, 32 independent plants were regenerated from these embryos. Of these regenerated plants, 19 individuals were confirmed to have the Y chromosome from the pollen donor (papaya), indicating that backcross was succeeded. All the backcrossed plants also had both sex chromosomes of C. papaya and V. ‍cundinamarcensis, derived from the intergeneric hybrids as female parents, suggesting that unreduced gametes might be produced in the intergenic hybrid plants. By inoculation of PLDMV to leaves, 66% of the backcrossed plants showed no symptoms and the remaining plants showed necrotic lesions on the upper leaves, which prevented virus proliferation. Therefore, all the infected backcrossed plants were resistant to PLDMV. These results showed that the developed backcrossed plants are valuable materials for developing PLDMV-resistant cultivars in papaya.

Barley grains contain high amounts of health-promoting constituents represented by a dietary fiber, β-glucan. In order to further reinforce the health benefits of barley, there have been demands for cultivars containing higher levels of multiple health-promoting compounds. Here, we report that a barley line, ‘Tanikei QM-1’, harbors a novel mutant allele of the Lys5 gene and contains higher amounts of several health-promoting constituents. ‘Tanikei QM-1’, which is derived from the mutagenesis of ‘Shikokuhadaka 97’, and several progeny lines obtained by crossing ‘Tanikei QM-1’ and ‘Hokuriku 48’ or ‘Hokuriku 49’, produces shrunken seeds in which the starch granules and their equatorial grooves show abnormal morphology. Analyses of the health-promoting constituents revealed that the shrunken seed lines contain higher amounts of β-glucan, fructan, arabinoxylan, resistant starch and GABA, and lower starch accumulation in the grains. In particular, β-glucan, fructan and arabinoxylan contents in the lines are higher than those in the high-β-glucan cultivar ‘Beau Fiber’. Conversely, the normal seed progeny lines contain almost the same level of those constituents as the standard cultivars ‘Fiber-Snow’ and ‘Shikokuhadaka 97’. Since the starch granule morphology and reduced starch content in the shrunken seed lines are quite similar to those of ‘Beau Fiber’, which harbors a mutant allele of the Lys5 gene encoding ADP-glucose transporter, we performed a sequence analysis of a 1.5-kbp genomic region of the Lys5 gene and found a novel nonsynonymous substitution common in the shrunken seed lines but not in the normal seed lines. These results strongly suggest that the substitution is the causal mutation for the higher amounts of several health-promoting compounds in the shrunken seed lines. In addition, we developed a dCAPS marker that makes it possible to genotype the mutant allele. The novel allele of the Lys5 gene in ‘Tanikei QM-1’, designated as lys5.i, is expected to provide useful breeding material for the production of barley cultivars with higher health benefits.