Detection of novel QTLs for foxglove aphid resistance in soybean.

KEY MESSAGE: The Raso2 , novel QTL for Korea biotype foxglove aphid resistance in soybean from PI 366121 was identified on chromosome 7 using GoldenGate SNP microarray. Foxglove aphid, Aulacorthum solani (Kaltenbach), is a hemipteran insect that infects a wide variety of plants worldwide and causes serious yield losses in crops. The objective of this study was to identify the putative QTL for foxglove aphid resistance in wild soybean, PI 366121, (Glycine soja Sieb. and Zucc.). One hundred and forty-one F4-derived F8 recombinant inbred lines developed from a cross of susceptible Williams 82 and PI 366121 were used. The phenotyping of antibiosis and antixenosis resistance was done through choice and no-choice tests with total plant damage and primary infestation leaf damage; a genome-wide molecular linkage map was constructed with 504 single-nucleotide polymorphism markers utilizing a GoldenGate assay. Using inclusive composite interval mapping analysis for foxglove aphid resistance, one major candidate QTL on chromosome 7 and three minor QTL regions on chromosomes 3, 6 and 18 were identified. The major QTL on chromosome 7 showed both antixenosis and antibiosis resistance responses. However, the minor QTLs showed only antixenosis resistance response. The major QTL mapped to a different chromosome than the previously identified foxglove aphid resistance QTL, Raso1, from the cultivar Adams. Also, the responses to the Korea biotype foxglove aphid were different for Raso1, and the gene from PI 366121 against the Korea biotype foxglove aphid was different. Thus, the foxglove aphid resistance gene from PI 366121 was determined to be an independent gene from Raso1 and was designated as Raso2. This result could be useful in breeding for new foxglove aphid-resistant soybean cultivars.

Molecular cloning of the gyrA gene and characterization of its mutation in clinical isolates of quinolone-resistant Edwardsiella tarda.

Knowing the entire sequence of the gene encoding the DNA gyrase Subunit A (gyrA) of Edwardsiella tarda could be very useful for confirming the role of gyrA in quinolone resistance. Degenerate primers for the amplification of gyrA were designed from consensus nucleotide sequences of gyrA from 9 different Gram-negative bacteria, including Escherichia coli. With these primers, DNA segments of the predicted size were amplified from the genomic DNA of E. tarda and then the flanking sequences were determined by cassette ligation-mediated polymerase chain reaction. The nucleotide sequence of gyrA was highly homologous to those of other bacterial species, in both the whole open-reading frame and the quinolone-resistance-determining region (QRDR). The 2637-bp gyrA gene encodes a protein of 878 amino acids, preceded by a putative promoter, ribosome binding site and inverted repeated sequences for cruciform structures of DNA. However, the nucleotide sequence of the flanking region did not show any homologies with those of other bacterial DNA gyrase Subunit B genes (gyrB) and suggested the gyrase genes, gyrA and gyrB, are non-continuous on the chromosome of E. tarda. All of the 12 quinolone-resistant isolates examined have an alteration within the QRDR, Ser83 --> Arg, suggesting that, in E. tarda, resistance to quinolones is primarily related to alterations in gyrA. Transformation with the full sequence of E. tarda gyrA bearing the Ser83 --> Arg mutation was able to complement the sequence of the gyrA temperature-sensitive mutation in the E. coli KNK453 strain and to induce increased resistance to quinolone antibiotics at 42 degrees C.