Items from Japan.

ITEMS FROM JAPAN

IBARAKI UNIVERSITY

College of Agriculture, 3-21-1 Chuo, Ami, Inashiki, Ibaraki 300-0393, Japan.

 

Nobuyoshi Watanabe.

Cytological and microsatellite mapping of the gene for brittle rachis in a Triticum aestivum–Aegilops tauschii introgression line. [p.43]

Aegilops tauschii, a wild relative of wheat, has been considered to be a valuable source of variation for the improvement of cultivated wheat. However, undesirable genes can be incorporated into the cultivars from wild relatives. The spontaneous spike shattering caused by the brittle rachis character is of adaptive value in wild grass species, but not in cultivars. The rachis of R-61, which was derived from the cross of T. aestivum subsp. aestivum cultivar Bet Hashita with an accession of Ae. tauschii, was brittle. Using telosomic stocks, the brittle rachis gene Br61 (tentatively designated) of R-61 was located on the short arm of chromosome 3D. The distance between Br61 and the centromere was 31.9 cM. The distance of Br61 from the centromeric marker Xgdm72 was 25.3 cM on the short arm of chromosome 3D. The location of Br61 was similar to that of Br1, whose location was determined by telosomic mapping and microsatellite mapping. A discrepancy of disarticulation type was found between R-61 and Ae. tauschii, suggesting that recombination around the regions of the Br1 locus and Brt locus created the wedge-type disarticulation of R-61.

 

Genetic mapping of the gene affecting polyphenol oxidase activity in durum wheat. [p. 43]

The quality of durum wheat is influenced by polyphenol oxidase (PPO) activity and its corresponding substrates. A saturated, molecular-marker linkage map was constructed previously using a set of RILs derived from a cross between the durum wheat cultivars Jennah Khetifa and Cham 1. Quantitative trait loci for PPO activity in seeds were mapped in this population. PPO activity in seeds of the parents and 110 RILs was measured spectrophotometrically. The PPO activity of Cham 1 was significantly lower than that of Jennah Khetifa. QTL analysis of these data indicated that most of PPO activity was associated with major loci on the long arm of chromosome 2A. The trait was found to be strongly associated with the SSR marker Xgwm312@2A. With this knowledge, marker-assisted selection can be used to select genotypes with lower PPO activity in durum wheat populations.

 

Microsatellite mapping of the genes for brittle rachis on homoeologous group-3 chromosomes in tetraploid and hexaploid wheats. [p. 43]

The brittle rachis character, which causes spontaneous shattering of spikelets, has an adaptive value in wild grass species. The loci Br1 and Br2 in durum wheat and Br3 in hexaploid wheat determine disarticulation of the rachis above the junction of the rachilla with the rachis such that a fragment of the rachis is attached below each spikelet. Using microsatellite markers, the loci Br1, Br2, and Br3 were mapped on the homoeologous group-3 chromosomes. The Br2 locus was located on the short arm of chromosome 3A and linked with the centromeric marker Xgwm32 at a distance of 13.3 cM. The Br3 locus was located on the short arm of chromosome 3B and linked with the centromeric marker Xgwm72 (at a distance of 14.2 cM). The Br1 locus was located on the short arm of chromosome 3D. The distance of Br1 from the centromeric marker Xgdm72 was 25.3 cM. Mapping the Br1, Br2, and Br3 loci of the brittle rachis suggests the homoeologous origin of these three loci for brittle rachis. Because the genes for brittle rachis have been retained in the gene pool of durum wheat, the more closely linked markers with the brittle rachis locus are required to select against brittle rachis genotypes and then to avoid yield loss in improved cultivars.

 

Publications. [p. 44]

  • Watanabe N, Takesada N, Fujii Y, and Martinek P. 2006. Cytological and microsatellite mapping of the gene for brittle rachis in a Triticum aestivum-Aegilops tauschii introgression line. Euphytica 151:63-69.
  • Watanabe N, Akond ASMGM, and Nachit MM. 2006. Genetic mapping of the gene affecting polyphenol oxidase activity in tetraploid durum wheat. J Appl Genet 47:201-205.
  • Watanabe N, Fujii Y, Kato N, Ban T, and Martinek P. 2006. Microsatellite mapping of the genes for brittle rachis on homoeologous group 3 chromosomes in tetraploid and hexaploid wheats. J Appl Genet 47:93-98.