| Consumption of wheat product has been increasing because of burgeoning World’s population and changes in food habits in the past decades. In the second place, the stability and sustainability of wheat production have been challenged by global climate changes, shrinking arable land and deteriorating environment. Therefore, global food security will remain a worldwide concern. To raise wheat yield, genetic improvement and cultivar development will be the most efficient way in a long term. As a critical trait, the yield itself is rather complex and thus often divided into two major numerical components:the number of grains per unit land area and average individual grain weight. Unlike grain number, individual grain weight has not been improved since Green Revolution. One can expect largely increased wheat yield through better utilization of excess photoassimilates during grain filling by larger grain size. In order to achieve this, the related species of wheat in Triticeae can be used to transfer desirable genes. Rye (Secale cereale) and Psathyrostachys huashanica, known as two important members in tertiary gene pool, have been exploited for wheat improvement. In this study, an attempt to introduce both genetic resources into wheat for grain weight improvement was initiated. Meanwhile, the mitotic and meiotic behaviour of rye chromosomes in wheat was investigated to facilitate the transfer of valuable traits.Two amphiploids, wheat-P huashanica (AABBDDNsNs,2n=56,"PHW-SA") and hexaploid triticale ("Zhongsi828’", AABBRR,2n=42), were utilized as the donors of P. huashanica and rye chromosomes, respectively.15derivative lines with large grains were obtained from the F3progeny derived from the F1hybrids. The chromosome constitutions of these lines were subsequently identified using molecular cytogenetic techniques. Also, a subset composing33F3lines were selected for analysis of rye chromosome behavior during mitosis and meiosis. The results were showed as the following.1. A total of239F3lines were produced via consecutive selfing.15were selected on the basis of their apparently higher thousand-grain weight (TGW) than the mean of two parents. TGW varied from26.6-40.7g, outperforming the mean of two parents by63-150%.2. Correlation analysis between the15lines showed that TGW was only highly significantly correlated with the length of flag leaf (r=-0.75, P<0.01).3. Cytogenetic characterization revealed that the somatic chromosome number ranged from41to44, Among them,10lines had42chromosomes. At meiotic metaphase1, a number of univalents (0.16-10.26) were found existing in most of the pollen mother cells (PMCs). Bivalent number varied from15.74to21.10. and9lines showed multivalents. Lines928-6and953-3(2n=42) exhibited normal meiosis. Across all the lines, the averaged chromosome configuration was3.35univalents,15.85ring bivalents,3.49rod bivalents,0.06trivalents and0.02tetravalents per PMC.4. Giemsa C-banding patterns showed that, of15lines, nine had each pair of1R-7R of rye chromosomes, and four had13rye chromosomes. In addition,12rye chromosomes were characterized in line943-3. Interestingly, in the line951-13, ten rye chromosomes and a translocation between wheat and rye chromosomes were observed (2RS-6DS). However, only three lines, namely938-1,940-6and944-6, were distinguished to carry1Ns and3Ns,3Ns,5Ns and7Ns of P. huashanica, respectively.5. The results from genomic in situ hybridization (GISH) on the chromosomes of root tips were consistent with that from Giemsa C-banding. That is,9,4and1lines had14, 13and12chromosomes showing signals, respectively, as labeled by the probe of the DNA of rye. The remaining line951-13contained not only10rye chromosomes but also a chromosome fragment from rye. On the other hand, only three lines, i.e.938-1,940-6and944-6, carried2,1and2chromosomes from P. huashanica. respectively.6. GISH on chromosome preparations in meiosis was conducted in three experiments. In the first experiment, all lines were detected only by R-genome DNA as the probe.1-7bivalents and0--12univalents were labeled in the progeny. With regard to line951-13, it had5bivalents and a chromosome fragment from rye. The remainders (928-6and953-3) possessed7bivalents (mostly ring) from rye, which could be transmitted normally to daughter cells. When Ns-genome DNA was used as the probe along, there were1-2univalents showing hybridization signals. Finally, we employed the mixture of R-and Ns-genomes DNA as probes. The resulting number of chromosomes showing yellow-green fluorescent signals was in line with that of rye chromosomes annotated previously in the first experiment, but not in lines938-1,940-6and944-6. In the three lines,1-7bivalents and a number of univalents emitted yellow-green fluorescent signals in the most PMCs.7. Observation of rye chromosome behavior in cell cycles in the subset was carried out. Mitotic analysis showed that rye chromosomes progressed normally with the wheat counterparts without loss. However, abnormal meiosis was found in almost all lines. It was at anaphase1that many rye univalents lagged behind those of wheat, followed by equational division. Some of the sister chromatids remained lagged and this resulted in the formation of chromosomal segments and micronuclei at telophase Ⅰ or Ⅱ. Part of the two daughter cells yielded unreduced gametes as a result of difference in the rhythm. Synapsis and translocations between wheat and rye genomes, and rye chromosome bridges were also detected.8. Assessment of stripe rust resistance showed that all the tested lines were immune or highly resistant to stripe rust with incidence of0-10%, severity of0-1%and infection type of0-1. |
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