Somatic hybrids between Brassica juncea (L). Czern. and Diplotaxis harra (Forsk.) Boiss and the generation of backcross progenies

Abstract

An attempt to transfer genes from droughttolerant 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. Chromosomal analysis of four such somatic hybrids revealed that three of them were asymmetric. Analysis of morphological characters, meiotic chromosomes, and esterase isoenzyme pattern revealed that all the somatic hybrids were different from each other. Furthermore four chromosomes of each 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 the somatic hybrids showed complete infertility preventing the recovery of any selfed seed. Nevertheless, ovule fertility of one somatic hybrid 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 their recombinant nature. It was thus confirmed that a transfer of genetic traits from Diplotaxis harra to B. juncea had indeed taken place. Furthermore, it was conceptualised that a transfer of alien genes through the protoplast-fusion technique is primarily possible in situations where meiotic pairing of the chromosomes of the two participating genomes generates recombinant gametocytes which can pass through subsequent filial generations.

Intergeneric hybrid between Brassica napus and Diplotaxis harra through ovary culture and the cytogenetic analysis of their progenies

“…These intergeneric hybrids were characterized by hybrid morphological features and contained more than 2n = 58 chromosomes. Further studies of the progenies were not reported (Klimaszewsla & Keller, 1988;Begum et al, 1995).…”

“…Plants consisted of 2n = over 58 chromosomes (Begum et al, 1995). The hybrid plant obtained by protoplast fusion between B. napus and D. harra, exhibited hybrid features and consisted of 2n = over 60 chromosomes (Klimaszewsla & Keller, 1988).…”

Intergeneric somatic hybridization and its application to crop genetic improvement

“…Incorporation of total genomes of the two parents, especially nuclear ones, in a hybrid has two obvious disadvantages, introduction of too much exotic genetic material accompanying the expected gene(s) and genetic imbalance leading to somatic incompatibility. These limitations could cause either abnormal growth and development of the somatic hybrids or regeneration of hybrids with low fertility (Wang et al, 1989;Sherraf et al, 1994;Spangenberg et al, 1994;Begum et al, 1995;Kisaka et al, 1998;Hu et al, 2002b;Wang et al, 2003). For example, the somatic hybrids between Arabidopsis thaliana and Brassica napus, Lycium barbarum and tobacco (Nicotiana tabacum) did not develop roots (Bauer-Weston et al, 1993;Liu et al, 1995b).…”

“…Isoenzymes of esterase (Bauer-Weston et al, 1993), peroxidase (Begum et al, 1995;Xia et al, 1998;Xu et al, 2003), phosphoglucose isomerase (Fahleson et al, 1994b), phosphoglucomutase (Ochatt et al, 1989), glutamate aspartic aminotransferase (Jain et al, 1988), phosphatase (Yamaguchi and Shiga, 1993), menadione reductase (Klimaszewska and Keller, 1988) and leucine aminopeptidase (Hansen and Earle, 1997) have been used for confirming hybrid nature of regenerants from intergeneric fusions. Subunits of Fraction-I protein, RUBPCase, have been used to characterize somatic hybrids based on isoelectric focusing (Shepard et al, 1983).…”

Mixing of maize and wheat genomic DNA by somatic hybridization in regenerated sterile maize plants

“…Resistance genes were transferred against bacterial (Hansen and Earle 1995;Laferriere et al 1999), fungal (Hansen and Earle 1997) and virus diseases (Austin et al 1985;Gibson et al 1988), or even nematodes (Lelivelt et al 1993). Somatic transfer of cytoplasmic male sterility (Kyozuka et al 1989;Akagi et al 1995) has been achieved and improvement of drought (Begum et al 1995) or cold tolerance (Louzanda et al 1993) was also attempted via somatic hybridization.…”