N. Arumugam et al., SYNTHESIS OF HEXAPLOID (AABBCC) SOMATIC HYBRIDS - A BRIDGING MATERIALFOR TRANSFER OF TOUR CYTOPLASMIC MALE-STERILITY TO DIFFERENT BRASSICASPECIES, Theoretical and Applied Genetics, 92(6), 1996, pp. 762-768
Most of the alloplasmic cytoplasmic male sterility (CMS) systems are k
nown to be associated with a number of floral abnormalities that resul
t from nuclear-cytoplasmic incompatibilities. One such system, 'tour',
which is derived from Brassica tournefortii, induces additional flora
l abnormalities and causes chlorosis in Brassica spp. While the restor
er for this CMS has been reported to be present in B. napus, in B. jun
cea, where the abnormalities are more pronounced, no restorer has yet
been identified. Rectification of these floral abnormalities through m
itochondrial recombinations and chloroplast replacement might result i
n the improvement of this CMS system. As organelle recombinations can
possibly be achieved only by somatic cell hybridization, fusion experi
ments were carried out between hygromycin-resistant B. juncea AABB car
rying 'tour' cytoplasm and phosphinotricin-resistant, normal B. olerac
ea CC to generate AABBCC hexaploid somatic hybrids. The presence of se
lectable marker genes facilitated the selection of hybrids in large nu
mbers. The resulting hybrids showed wide variation in floral morpholog
y and organelle composition. Regenerants with normal, male-sterile flo
wers having recombinant 'tour' or 'oleracea'-type mitochondria and 'ol
eracea'-type chloroplasts were obtained. Hybrids with male-fertile flo
wers were also obtained that had recombined 'tour' mitochondria. The A
ABBCC hexaploid hybrids synthesized in the present study were successf
ully utilized as a bridging material for transferring variability in t
he organelle genome simultaneously to all the digenomic Brassica speci
es, and all of these hybrids are now being stabilized through repeated
backcrosses to the allo-polyploid crop brassicas.