SOMATIC HYBRIDS BETWEEN BRASSICA-JUNCEA (L) CZERN AND DIPLOTAXIS-HARRA (FORSK) BOISS AND THE GENERATION OF BACKCROSS PROGENIES

An attempt to transfer genes from drought tolerant Diplotaxis harra, a wild relative of Brassica species, to an elite oil-yielding cultivar, B-85, of mustard (Brassica juncea) was made through protoplast fusion , as the two plant systems are sexually incompatible. By following the standard protocol for PEG-mediated protoplast fusion followed by high pH, high Ca++, DMSO treatment and appropriate cell-culture technique, 16 presumptive somatic hybrid plants could be regenerated. Chromosoma l analysis of four such somatic hybrids revealed that three of them we re asymmetric. Analysis of morphological characters, meiotic chromosom es, and esterase isoenzyme pattern revealed that all the somatic hybri ds were different from each other. Furthermore four chromosomes of eac h genome could undergo homoeologous pairing at meiosis indicating the possibilities for genetic recombination and chromosomal rearrangements . Irregular distribution of chromosomes at anaphase-II at meiosis has been a consistent feature of these plants. Eventually, pollen of all t he somatic hybrids showed complete infertility preventing the recovery of any selfed seed. Nevertheless, ovule fertility of one somatic hybr id was not totally impaired as it had set some seeds upon backcrossing with the B. juncea parent. The esterase isoenzyme banding pattern of 24 individual progeny plants of this backcross provided evidence for t heir recombinant nature. It was thus confirmed that a transfer of gene tic traits from Diplotaxis harra to B. juncea had indeed taken place. Furthermore, it was conceptualised that a transfer of alien genes thro ugh the protoplast-fusion technique is primarily possible in situation s where meiotic pairing of the chromosomes of the two participating ge nomes generates recombinant gametocytes which can pass through subsequ ent filial generations.