Breeding Science 60: 286–292 (2010) Note Differential effects of Aegilops tauschii genotypes on maturing-time in synthetic hexaploid wheats Yuki Fujiwara1), Sanae Shimada1), Shigeo Takumi2) and Koji Murai*1) 1) Department of Bioscience, Fukui Prefectural University, 4-1-1 Matsuoka-Kenjojima, Eiheiji, Yoshida, Fukui 910-1195, Japan 2) Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe, Hyogo 657-8501, Japan Bread wheat (Triticum aestivum) is a hexaploid species with A, B and D genomes. Therefore, most bread wheat genes are present in the genome as triplicated homoeologous genes (homoeologs) derived from the an- cestral A, B, and D genome diploid species. Maturing-time, which is associated with flowering-time and the grain-filling period, is one of the most important agronomic traits for wheat breeding. Here, the effects of homoeologs derived from D genome diploid species on maturing-time in bread wheat were examined in syn- thetic hexaploid wheats obtained by crossing tetraploid durum wheat T. turgidum ssp. durum cv. Langdon and three accessions of the D genome diploid species (Aegilops tauschii). After vernalization, the synthetic hexaploid wheat derived from an early-flowering D genome donor showed an early-flowering phenotype among the synthetic hexaploids, whereas the synthetic wheat derived from a late-flowering D genome donor was late-flowering among the synthetic hexaploids. This suggests that the early-flowering phenotype in hexaploid wheat is affected by the homoeolog for early-flowering in the D genome donor. In contrast, maturing-time and grain-filling period in the synthetic hexaploids did not correspond with those of the D genome donors, suggesting that these traits are controlled by the interaction between homoeologs on the A, B and D genomes in hexaploid wheat. Key Words: maturing-time, grain-filling period, hexaploid, wheat, Triticum aestivum, Aegilops tauschii, homoeolog. Introduction and Vrn-D1, have been shown to be located on chromo- somes 5A, 5B and 5D, respectively, of bread wheat. The A In cereal crops such as wheat and barley, maturing-time, genome of hexaploid bread wheat came from T. urartu, the which includes flowering-time and the grain-filling period, B genome from Aegilops speltoides or another species is an important character because of its influence on adapt- classified in the Sitopsis section, and the D genome from ability to different environmental conditions. Bread wheat Ae. tauschii (Feldman 2001). As a consequence of its (Triticum aestivum, 2n = 6x = 42, genome constitution origin, the hexaploid wheat genome contains triplicated AABBDD) is grown in a wide range of environments all homoeologous genes (homoeologs) derived from the ances- over the world, and its wide adaptability results from the tral diploid species. Vrn-A1, Vrn-B1 and Vrn-D1 are the variation in maturing-time among cultivars (reviewed in homoeologs of the Vrn-1 gene. Vrn-A1 of the diploid Worland and Snape 2001). einkorn wheat T. monococcum (2n = 2x = 14, AmAm) has Many genetic studies have been performed to investigate been identified as a homolog of APETALA1/FRUITFULL of the genetic control of heading/flowering-time in wheat and Arabidopsis (Yan et al. 2003). The Vrn-1 genes of hexaploid three component factors have been identified: vernalization wheat have been identified as either WAP1 (wheat AP1) requirement, photoperiod sensitivity, and narrow-sense (Murai et al. 2003, Trevaskis et al. 2003) or TaVRT-1 earliness (earliness per se) (Yasuda and Shimoyama 1965, (Triticum aestivum vegetative to reproductive transition-1) reviewed in Murai et al. 2005). Vernalization requirement is (Danyluk et al. 2003) that are now uniformly called VRN1. concerned with the sensitivity of the plant to cold tempera- The photoperiod (long-day) response in wheat is determined ture for accelerating spike primordium formation. The ver- by the dominant genes Ppd-A1, Ppd-B1 and Ppd-D1, which nalization insensitivity (spring habit) genes, Vrn-A1, Vrn-B1 control sensitivity to day length and are located on chromo- somes 2A, 2B and 2D, respectively. Wheat is a quantitative Communicated by T. Komatsuda long-day plant, and short day conditions delay the heading Received May 28, 2010. Accepted August 4, 2010. time. Ppd acts to reduce the delay in heading under short day *Corresponding author (e-mail: [email protected]) conditions (Murai et al. 2003). Ppd-H1 of barley (Hordeum Diploid donor genotype affects maturing-time in hexaploid wheat 287 vulgare, 2n = 2x = 14, HH) was identified as a pseudo- sions PI476874, CGN10768, and AT80, respectively, and response regulator (PRR) that showed most similarity to the were selected for use in this study. Syn 6256 was described Arabidopsis circadian clock-associated gene, PRR7 (Turner in our previous report (Takumi et al. 2009), but the other two et al. 2005). Orthologous PRR genes were identified in the lines are unpublished. The synthetic hexaploids contain the A, B and D genomes of hexaploid wheat (Beales et al. A and B genomes from the female parent Langdon and the D 2007). Narrow-sense earliness, which corresponds to the au- genome from the respective Ae. tauschii male parents. All tonomous flowering pathway in Arabidopsis, is defined as hexaploid lines have the normal chromosome set, 2n = 42 earliness in flowering of fully vernalized plants grown under (data not shown), and grow normally (described here). long-day conditions. Several QTLs have been identified in barley and wheat for this characteristic (reviewed in Evaluation of agronomic characters including maturing- Cockram et al. 2007), and a major locus, Eps-1, was reported time in the field in wheat (Faricelli et al. 2009). In contrast our understanding The three synthetic hexaploid wheat lines and Langdon of the genetics of heading/flowering-time, little is known of were grown in season 2008–2009 at Fukui, Japan (latitude that for maturing-time or grain-filling period. 36N, longitude 136E). Seeds were sown on 23 Oct. 2008 in Ae. tauschii is widely distributed in Eurasia, ranging from the experimental field of Fukui Prefectural University. The Turkey to China, and shows considerable genetic variation plants were thinly distributed with 10 cm spacing in a single (Dvorak et al. 1998, Matsuoka et al. 2005, Mizuno et al. row. Seven characters were observed: heading date, matur- 2010). The birthplace of hexaploid wheat is believed to lie ing date, plant height (cm), ear length (cm), spikelet number within the area comprising Transcaucasia and the southern per ear, fertility (%), and grain number per spikelet. With the coastal region of the Caspian Sea. This indicates that the exception of fertility and maturing time, these characters Ae. tauschii populations involved in the origin of hexaploid were measured on the main shoot and ear of each plant, and wheat would have had a narrow range of genetic variation averages of three plants were used for statistical analyses. compared to that present in the species as a whole. Thus, this Analyses of variance were used to identify significant differ- diploid species contains a large amount of genetic diversity ences among lines. Fertility (%) was estimated by the seed that is not represented in hexaploid wheat, and, therefore, setting rate of the first and second florets of all spikelets. offers agronomic potential for improving modern varieties of Heading date was the day when 50% of the ears of five hexaploid wheat. In this study, synthetic hexaploid wheats plants had appeared from flag leaf. Maturing date was the obtained by crossing tetraploid durum wheat and a D ge- day when 80% of the ears of five plants had turned yellow. nome diploid species (Ae. tauschii) (Takumi et al. 2009, and unpublished lines) were examined to investigate the effect of Evaluation of heading, flowering, and maturing-times using homoeologs derived from the D genome diploid species on a growth chamber maturing-time in bread wheat. This analysis showed that Seeds that sprouted after being soaked on wet filter paper maturing-time and grain-filling period in hexaploid wheat is at 20°C were sown in small soil-filled containers at a spac- affected by the D genome genotype of the diploid species. ing of 2 cm, and then vernalized at 4°C (24 h light condition) for 35 days. After vernalization, they were placed in a Materials and Methods growth chamber under a 16 h/8 h light/dark regime at 20°C (12,000 lux light intensity). For non-vernalization experi- Plant materials ment, sprouted seeds were place in a growth chamber under Three Aegilops tauschii accessions, PI476874, the same long-day condition as the vernalization experi- CGN10768 and AT80, were used as the D genome donor in ments. Three to seven plants comprised the experimental the construction of the synthetic hexaploid wheats. The sample group for each genotype. The first leaf unfolded dur- PI476874, CGN10768 and AT80 accessions originated in ing the 35 day vernalization treatment. Therefore, the num- Afghanistan, Pakistan and China, respectively. They all ber of days from unfolding of the second leaf to heading have a winter habit, and carry recessive alleles of VRN1 (DH) of the main tiller was scored for each plant. Similarly, (Vrn1) (data not shown). When grown under either vernal- the number of days from unfolding of the second leaf to ized or non-vernalized conditions, PI476874 is an early- flowering (DF) was scored for each plant. For experiments maturing accession while AT80 is late-maturing (shown in in the growth chamber, maturing-times (dates) were deter- this study). CGN10768 has an intermediate maturing-time mined in two ways. One maturing date was defined as the (shown in this study). The tetraploid durum wheat Triticum day when the ear neck of the main shoot turned yellow (ma- turgidum ssp. durum cv. Langdon was used as the AB ge- turing date 1).