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Dr. Si-Jun Zheng
Wageningen-UR, Plant Research International
P.O. Box 16, 6700 AA Wageningen, the Netherlands
++ 31 317 477001
++ 31 317 418094
s.zheng@plant.wag-ur.nl
www.plant.wag-ur.nl/expertise/alliumresearch
Gene transfer in Allium: recent developments and future prospects
S-J. Zheng
Wageningen-UR, Plant Research International, P.O. Box 16, 6700 AA Wageningen, the Netherlands
This review outlines recent developments of gene transfer systems in Allium crops. Gene transfer can be
realized via sexual hybridization, somatic hy(cy)bridization and genetic transformation. Sexual
hybridization has always been an important tool for the introduction of genetic variation needed for
plant improvement. Much of the research carried out in this context is done within and between onion
and its wild relatives. In contrast to onion, other important Allium crops like leek (A. porrum) and garlic
(A. sativum) received less attention. The latest developments in this area, like the genepool approach to
introgress agronomically important traits from wild relatives in onion, and the possibilities for sexual
hybridization in garlic will be discussed.
If sexual hybridization is not possible to transfer genes, somatic hy(cy)bridization and genetic
transformation can provide a way forward. Somatic hy(cy)bridization was succesfully used to transfer
cytoplasmic male sterility (CMS) from onion to leek and also in bridging the gap between onion and
garlic. However until present the perspectives of this technique in Allium breeding is not clear. Recently
an exiting breakthrough was made in opening up genetic transformation technology for Allium crops.
Both Agrobacterium-mediated and biolistic gene transfer systems have been developed in onion, shallot
(A. cepa L. group Aggregatum) and garlic (A. sativum). Detailed molecular characterization of
transgenic Allium crops to prove their transgenic status have been carried out, using molecular
biological techniques like PCR (conventional and adaptor-ligation), DNA blot hybridization and
fluorescence in situ hybridization (FISH) and cell biological techniques like GUS and green fluorescent
protein (GFP) expression. Currently transgenic Allium plants are available harbouring bar or
acetolactate synthase (ALS) genes for herbicide resistance, Bt genes for insect resistance and antisense
alliinase genes for a milder taste. Transgenic onion, shallot and garlic plants proved to have a normal
phenotype, were fertile, had a normal ploidy level and inherited their genes in a Mendelian fashion. As
a last topic in this review safety assessment of genetically modified (GM) Allium crops will be
discussed.