Cytogenetic and molecular characterization of intergeneric hybrids betweenBrassica napusandOrychophragmus violaceus

Abstract

Twenty-two intergeneric hybrids from a cross between Brassica napus (AACC, 2n = 38) cultivar Oro and the ornamental crucifer Orychophragmus violaceus (OO, 2n = 24) were produced without embryo rescue. The plants were classified into three groups based on morphological and cytological observations and RAPD banding patterns. Plants of Group I had morphological traits of both parents and 2n = 29 chromosomes. In these plants, 62.1% of the pollen mother cells (PMCs) had the pairing configuration 1 III + 9 II + 8 I; the remaining PMCs had 10 II + 9 I. The plants possessed 97.6-98.8% B. napus specific and 9.2-11.7% O. violaceus specific RAPD fragments. Plants of Group II exhibited novel morphological traits and possessed 2n = 35, 36, or 37 chromosomes. Plants of Group III were morphologically similar to B. napus and possessed 2n = 19, 37, 38, or 39 chromosomes. Plants of Group II and Group III had 94.1-99.4% B. napus specific RAPD fragments and no O. violaceus specific RAPD fragments. Chromosome fragments were observed in PMCs of most of the F1 plants in all groups. Based on the cytological results and RAPD analysis, it is suggested that genome doubling and chromosome elimination occurred in the intergeneric hybrids of B. napus x O. violaceus.

Extraction of the Constituent Subgenomes of the Natural Allopolyploid Rapeseed (Brassica napus L.)

“…Subsequently, with the loss of all C-subgenome chromosomes and the alien individual chromosome or segments in the hybrids, the alien introgression would decrease further, i.e., from 3.48% in the hybrid to 1.64% in RBR ZS11 (Table 1). However, the A-C homeologous pairing (1III + 9II + 8I, other than 10II + 9II) in the hybrids (2n = 29) could probably move certain segments of the C-subgenome chromosomes to the specific A-subgenome chromosome, as the trivalent occurred in 60% PMCs (Cheng et al 2002;Tu et al 2010; present study). The exchange rate should be much reduced as more C-subgenome chromosomes were eliminated.…”

“…After B. napus was pollinated by several crucifers out of the Brassiceae tribe, including Orychophragmus violaceus (Cheng et al 2002;Hua and Li 2006), Capsella bursa-pastoris (Chen et al 2007), Lesquerella fendleri (Du et al 2008), I. indigotica (Tu et al 2010) and C. abyssinica (present study), only nonclassical hybrids were identified and contained the variable chromosome numbers (2n = 19-38) from B. napus and few alien chromosomes or DNA sequences. The chromosomes from the pollinators were likely eliminated mostly during certain stages of embryo or hybrid plant development, because of their distant relationships with B. napus.…”

“…Of relevance for the extraction of the A subgenome, the C-subgenome chromosomes were also lost to different extents in individual hybrids, together with those from pollinators that functioned as inducers (Figure 1). Specially, the hybrids with 2n = 29 were recurrently obtained in all crosses with these pollinators, and only two representative pairings (1III + 9II + 8I and 10II + 9I) showed that 10 duplicated and 9 individual chromosomes were maintained (Cheng et al 2002;Chen et al 2007;Tu et al 2010;present study). The A-subgenome origin of 10 paired chromosomes and C-subgenome origin of unpaired ones were speculated (Chen et al 2007) but confirmed by the derivation of the restituted B. rapa from the hybrids after two more rounds of the induced chromosome eliminations (Tu et al 2010;present study).…”

“…The introgression of alien DNA elements into the extracted A subgenome probably occurred at a low rate, for such sequences specific for pollinators were detected at low frequencies in the hybrids (2n = 29) with Oro pollinated by O. violaceus (Cheng et al 2002) and I. indigotica (Tu et al 2010). Subsequently, with the loss of all C-subgenome chromosomes and the alien individual chromosome or segments in the hybrids, the alien introgression would decrease further, i.e., from 3.48% in the hybrid to 1.64% in RBR ZS11 (Table 1).…”

Karyotypic Variability in Experimental Diploid and Triploid Hybrids of Aloe vera*A. saponaria

“…tuberosus (Natali et al 1998), Cucumis hystrixϫC. sativus (Chen et al 2004) and in intergeneric hybrids of Brassica napusϫOrychophagmus violaceus (Cheng et al 2002). If this were the case concerning A. saponaria and A. vera, it could explain at least in part the origin of the aneuploidy 2nϭ3xϪ1ϭ20 (11Lϩ9S) and (12Lϩ8S).…”