Soybean dwarf virus (SbDV) causes serious dwarfing, yellowing and sterility in soybean (Glycine max). The soybean cv. Adams is tolerant to SbDV infection in the field and exhibits antibiosis to foxglove aphid (Aulacorthum solani), which transmits SbDV. This antibiosis (termed “aphid resistance”) is required for tolerance to SbDV in the field in segregated progenies of Adams. A major quantitative trait locus, Raso1, is reported for foxglove aphid resistance. Our objectives were to fine map Raso1 and to reveal whether Raso1 alone is sufficient to confer both aphid resistance and SbDV tolerance. We introduced Raso1 into cv. Toyomusume by backcrossing and investigated the degree of aphid antibiosis to foxglove aphid and the degree of tolerance to SbDV in the field. All Raso1-introduced backcross lines showed aphid resistance. Interestingly, only one Raso1-introduced backcross line (TM-1386) showed tolerance to SbDV in the field. The results demonstrated Raso1 alone is sufficient to confer aphid resistance but insufficient for SbDV tolerance. Tolerance to SbDV was indicated to require additional gene(s) to Raso1. Additionally, Raso1 was mapped to a 63-kb interval on chromosome 3 of the Williams 82 sequence assembly (Glyma1). This interval includes a nucleotide-binding site–leucine-rich repeat encoding gene and two other genes in the Williams 82 soybean genome sequence.
A wide range of genotypes suitable for a plant regeneration system is needed when utilizing genetic transformation techniques to develop new crop cultivars. We examined the regeneration efficiencies for somatic embryogenesis in 61 genetically diverse sugar beet (Beta vulgaris L.) breeding lines developed in Japan using a previously reported procedure. Frequencies of embryogenic callus formation from seedling leaf and petiole explants ranged from 0 to 89% and those of somatic embryo formation from the calli ranged from 0 to 99%. There was no clear correlation between the two frequencies, suggesting that different genetic backgrounds are involved in the two formation mechanisms. To evaluate each breeding line's capability for somatic embryogenesis, we proposed a somatic embryogenesis capability index based on four parameters. Based on the values of this index, only 21 breeding lines were suitable materials for regeneration via somatic embryogenesis. These breeding lines include four lines with moderate or better resistance to three major sugar beet diseases in Japan and one line with strong resistance to these diseases, and these lines will be useful materials with superior characteristics for developing transgenic breeding lines. To increase the regeneration efficiencies in the other 40 breeding lines, we examined other types of explants from seedlings and the effects of various plant growth regulators. We found that cotyledon explants generally showed improved callus formation and that using thidiazuron instead of N 6 -benzylaminopurine improved somatic embryo formation in some lines.
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