Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/26/2001
Publication Date: N/A
Citation: Interpretive Summary: Hybrid leek offers significant advantages to growers, especially increased yield and uniformity. At present, the only way to produce hybrid leek is by the asexual propagation of individual male-sterile leek plants. This is a time consuming and labor intensive procedure adding greatly to the cost of hybrid production. The production of hybrid leek would greatly benefit from a source of cytoplasmic male sterility (CMS), allowing for the seed propagation of the female parent of the hybrid. Unfortunately, no source of CMS exists in leek. To overcome this deficiency, a known source of CMS from onion was backcrossed for three generations to leek to produce plants with the nuclear genome of leek and the cytoplasm of CMS onion. The transfer of the onion cytoplasm was established using molecular markers in the chloroplast genome. These plants will be evaluated for male fertility and quality attributes. This work will provide a source of male sterility for the production of more uniform and valuable hybrid leek.
Technical Abstract: Two interspecific triploid (AAC) hybrids (84/1-94 and 99/1-94) from crosses between onion, Allium cepa (2n=2x=16, CC), and leek, A. ampeloprasum (2n=4x=32, AAAA), were backcrossed to leek to transfer a male-sterility-inducing cytoplasm from onion to 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 two sets of leek chromosomes paired nearly normal. Attempts to use colchicine to double the chromosome number of hybrids failed. Backcrosses of 84/1-94 to leek as pollen parent were not successful. The first backcross of 99/1-94 to tetraploid leek produced 11 BC1 plants with chromosome numbers between 38 and 41. Identification of parental chromosomes by GISH showed that all eight onion chromosomes were transmitted to each backcross progeny. The number of leek chromosomes varied from 30 to 33, possibly due to unreduced egg cells. Onion chromosomes were eliminated during the second backcross. Polymorphisms in the chloroplast DNA confirmed the transfer of the T-cytoplasmic-like source of onion CMS to the BC2 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 sterilit and quality traits.