Transfer of resistance against the beet cyst nematode from radish (Raphanus sativus) to rape (Brassica napus) by monosomic chromosome addition.

In rape ( Brassica napus), no resistance to the beet cyst nematode (BCN) Heterodera schachtii is available. This study was carried out to determine the specific chromosome(s) of resistant radish ( Raphanus sativus) carrying the gene(s) for nematode resistance as a prequisite to convert rape from a host into a trap crop for this pest. A Raphanobrassica progeny of 25 plants was analyzed which segregated for all nine chromosomes of the Raphanus genome in a genetic background of synthetic rape. The number of radish chromosomes was determined by fluorescence in situ hybridization, using the Raphanus-specific DNA probe pURsN; and their type was identified by chromosome-specific randomly amplified polymorphic DNA markers. Five different multiple rape-radish chromosome additions (comprising the whole set of nine radish chromosomes, a-i) were selected and crossed to rape. For each cross-progeny, the number of cysts on plant roots was counted 42 days after inoculation with a L2 larvae suspension. Simultaneously, the plants were characterized for the presence or absence of individual radish chromosomes, using sets of chromosome-specific markers. Thus, the effect of each radish chromosome on cyst number was tested. Chromosome d had a major resistance effect, whereas the presence/absence of the other radish chromosomes had nearly no influence on cyst number. Plants with added chromosome d showed a resistance level comparable with that of the radish donor parent. The analysis in the cross to rape of a plant monosomic only for chromosome d confirmed the strong effect of this chromosome on nematode resistance. A further experiment comprising seven crosses using winter rape breeding lines and monosomic addition line d as pollen parent provided the same results on a broader genetic basis. In each case, the added chromosome d in a single dosage caused nearly the full resistance of the radish donor. Resistance was independent of the glucosinolate content in the roots. The possibilities for stabilizing BCN resistance in rape and its use for other crops and nematodes are discussed.

Transfer of a male-sterility-inducing cytoplasm from onion to leek ( Allium ampeloprasum).

Two interspecific triploid (AAC) hybrids (84/1-94 and 99/1-94) from crosses between onion [ Allium cepa (2 n=2 x=16, CC)] and leek [ A. ampeloprasum (2 n=4 x=32, AAAA)] were backcrossed to leek in order to transfer a male-sterility-inducing cytoplasm from onion that would enable the production of hybrid leek. GISH evaluations of meiosis in the interspecific hybrids revealed irregularities due to univalent onion chromosomes producing micronuclei from onion chromatin, whereas the pairing of the two sets of leek chromosomes was nearly normal. Attempts to use colchicine to double the chromosome number of the hybrids failed. Backcrosses of 84/1-94 to leek as the pollen parent were not successful. The first backcross of 99/1-94 to tetraploid leek produced 11 BC(1) plants with chromosome numbers between 38 and 41. Identification of parental chromosomes by GISH showed that all eight onion chromosomes and 30-33 leek chromosomes were transmitted to the backcross progenies due to unreduced egg cells. Onion chromosomes were eliminated during the second backcross. Southern hybridization confirmed the transfer of the T-cytoplasm like source of CMS from onion to the BC(2) progenies. After the third backcross to leek, 158 plants were obtained with varying numbers of onion chromosomes and some intergenomic recombinant chromosomes. Alloplasmic leek plants without onion chromatin were selected for further characterization of male sterility and quality traits.