Intergeneric Hybridization between Raphanus sativus L. and Brassica nigra KOCH. and Alloplasmic Radish Derivative

Abstract

Cytological and morphological observations were made on the intergeneric new hybrids between Raphanus sativus and Brassica nigra and the derived progenies. Chromosomes of Fl hybrids in the meiosis of the pollen mother cells (PMC) were amphihaploid except for an amphidiploid plant (NiR F₁-3) in B, nigraxR. sativus. Amphihaploids showed the pairing type of (0-4)II+(9-17)I at metaphase I(MI) and the chromosome number of most of the PMCS at metaphase II(MII) ranged from 5 to 12 with a modal value of 8 or 9. An amphidiploid plant showed a relatively regular meiosis with 17II at MI and PMCS With 17 chromosomes at MII. The morphology of the amphihaploids was intermediate between that of the parent cultivars except for the presence of white flowers. Due to the meiotic abnormalities, amphihaploids failed to produce viable pollen and seed. An amphidiploid of NiR F₁-3 was very large and showed seed fertility. Backcrossed generations with R.sativus and B, nigra were sesquidiploids of BRR (2n=26) and BBR (2n=25) showing pairing types of 9 II+8I and 8II+9I at MI, respectively. The BRR plants preserved their seed fertility not only in open pollination but in further backcrossing to two cultivars of R. sativus. Derived plants were euploid (2n=18) or hyperploid (2n=19-22). Prevailing occurrence of univalents and bivalents in both amphiploids and derived progenies suggested the occurrence of more frequent autosyndetic pairings than allosyndetic ones at MI. Subsequently new alloplasmic radish lines, viz. R, sativus with B, nigra cytoplasm were bred. These lines produced fertile seeds in the next backcrossing to R. sativus.