4.1 | Identification of natural hybrids
R. stricta and R. turczaninovii were planted in the experimental base of SAGS. We collected the seeds of the two species and planted them individually. We found that there were randomly distributed sterile plants in the experiment field. These sterile plants grew stronger than around plants and their seed set is very low (Figures 1a-c and 3). They were morphologically intermediate between R. strictaand R. turczaninovii , such as pubescence of leaf, basal leaf sheath and stem node (Figures 1d-o). We hypothesized that the plants were hybrids of R. stricta and R. turczaninovii .
Karyotype analysis showed that 57 putative natural hybrids were tetraploids, 2n=4x=28 (Figure 4). Chromosomal pairing analysis showed that meiosis of R. stricta and R. turczaninovii were more regular than the putative hybrids (Figure 5). Except for hybrid RH2-31, all hybrids had univalent at MI. Univalent varying from 0.42 to 2.00 in hybrids RH1, whereas it varying from 0 to 3.45 in hybrids RH2 (Table S2). In all hybrids, the c-value was higher than 0.81, indicating that chromosome pairing of the hybrids was comparatively regular, and had two sets of homology genomes.
FISH analysis using St2-80 showed that the 14 chromosomes of R. stricta , R. turczaninovii and the natural hybrids displayed St type (Figures 6a, c, e and 7a, c, e), indicating that they contained one set of the St genome. This result was confirmed by GISH, where 28 chromosomes were hybridized with the StY probe from R. ciliaris (Figures 6b, d, f and 7b, d, f). The results of in situ hybridization showed that the genomic constitution of the parents and hybrids was StY .
The above results indicated that these hybrids were tetraploids with theStY genome.