An efficient transformation method for soybean [Glycine max (L.) Merr.] using meristematic tissues of germinating seeds has been established. The embryonic axes were excised from germinating seeds of Korean soybean cultivar, Iksannamulkong and 0.5-2 cm long segment containing meristematic tissues were prepared by cutting hypocotyl region. The explants were inoculated with Agrobacterium tumefaciens strain LBA4404 harboring a binary vector with the bar gene as a selectable marker gene and a β-glucuronidase (GUSINT) reporter gene, and then co-cultured for 7 days on co-cultivation medium (CCM). The meristematic tissues were cultured on shoot induction medium (SIMP6) supplemented with 0.4 mg/l N6-benzylaminopurine (BAP) and 0.1 mg/l indolebutyric acid (IBA) in the presence of 6 mg/l L-phosphinotricin (PPT) for 2 weeks and the surviving explants were transferred to shoot elongation medium (SEMP6). Transformation was confirmed by Southern blot analysis and the transformation efficiencies ranged from 1.48 to 2.07%. The new modified transformation method was successfully implemented for obtaining several transgenic lines with SMV-CP gene. It is expected that this method could efficiently be used for the transformation of recalcitrant soybean cultivars.

Barley Yellow Dwarf Virus (BYDV), an aphid-borne luteovirus, is a major plant pathogenic disease causing a huge economic loss in the grain production of a wide range of Gramineae species throughout the world. It has been recently reported that BYDV also occurred frequently in wheat field of Korea. Here, we performed to develop the detection and classification methods of BYDV strains that were accomplished by reverse transcription-polymerase chain reaction (RT-PCR). Since there are high variations among BYDV strains, three pairs of primers were designed to detect BYDV strains such as PAV (Vic-PAV and CN-PAV) and MAV (primer A) simultaneously, specifically Vic-PAV(primer B), and MAV (primer C) based on the genomic RNA sequences of BYDV strains previously published. The validity of the primers was confirmed using several BYDV strains obtained from CIMMYT. Though three BYDV strains were able to be detected using primer A, PCR products were not distinguished between two PAV strains. It was possible to separate them with a restriction enzyme, EcoRI, whose restriction site was present in the amplified DNA fragment from Vic-PAV, but not from CN-PAV.

Soybean mosaic virus (SMV) resistance of Korean recommended soybeans was evaluated naturally and by mechanical inoculation in Suwon. Based on the differential reaction of forty-four soybean genotypes tested to nine different SMV strains, soybeans were classified into twenty-four groups. Myeongjunamulkong and Ilpumgeom-jeongkong showed a high degree of resistance to nine SMV strains, having no symptom. The other cultivars produced various reactions according to inoculation of each SMV strain: symptomless, mosaic or systemic necrosis. Only five cultivars such as Kwangankong, Eunhakong, Tawonkong, Namhaekong, Sobaegnamulkong were totally susceptible to every strain. There was variation in disease incidence. Soybeans, having the highest levels of resistance to G5H and G7H in the greenhouse, showed the lowest levels of SMV incidence in the field of Suwon. Myeong-junamulkong, Ilpumgeomjeongkong, Soyangkong, Pungsannamulkong, Sodamkong, Jangmikong, Geomjeong-kong2, Pureunkong, Sinpaldalkong2, Duyoukong, and Geumgangkong were fairly resistant to SMV. And SMV incidence of Taekwangkong, Saealkong and Baegunkong was over 45% with symptom of bud necrosis. And soybeans, highly resistant to SMV in the field and the greenhouse, were mainly derived from Jangyeobkong and Hwang-keumkong resistant to G1-G7.

Reverse transcription and polymerase chain reaction (RT-PCR) assay was used to detect SMV strains. A pair of oligonucleotide primers were designed to include the cylindrical inclusion (CI) coding region between 4,176 to 5,560 nt. Amplification from the total RNA extracted from infected plants with SMV yielded a 1,385 bp DNA fragment. RT-PCR was shown to be 103 times more sensitive than the ELISA assay and it could detect a virus in 10-6 dilution. Restriction enzyme analysis of RT- PCR products using EcoR I showed that SMV isolates were classified into six groups according to the patterns of restriction fragments.