Gene Bank & Genetic Diversity of Wild lettuce species
Dr. Alex Beharav
Institute of Evolution (IOE), University of Haifa, Israel
The IOE's Crop Wild Relatives (CWRs) Gene Bank harbor collections of the wild species of genus Lactuca (Compositae (Asteraceae), tribe Cichorieae, a subclade Lactucinae). This genus comprises about 100 wild species, mainly distributed in the Northern Hemisphere. The Wild Lettuce Gene Bank (WLGB) led by Dr. Alex Beharav - aims to survey, collect and characterize rare wild Lactuca spp. - who is leading in these topics, and has a proven record in such types of bio-statistical and population genetic analyses.
Cultivated lettuce, Lactuca sativa L., is one of the most important and widely distributed leafy vegetables. Domestication has resulted in limited genetic variation in the cultivated crop making it vulnerable to diseases, pests, and environmental stresses. L. sativa is part of a reproductively isolated group that includes the wild species L. serriola L., L. saligna L., and L. virosa L. However, of these three wild species, only L. serriola represents the primary Lettuce Gene Pool (LGP-1).
In recent years we initiated extensive studies on the characterization of the population structure of wild Lactuca spp. originating from Southwest Asia, the center of diversity for wild species closely related to cultivated lettuce (Wild Lactuca Relatives, WLRs). Unique new collections - of four out of seven wild species that according previous literature represents the LGP-1: L. serriola, L. aculeata Boiss., L. georgica Grossh., and L. altaica Fisch. & C.A. Mey., as well as L. saligna that represents the Secondary Lettuce Gene Pool (LGP-2) - from Israel and Armenia have been investigated, as well as a few samples collected in past from Jordan, Turkey and other countries. We have produced also a minor collections of: (1) other four wild lactuca spp. that are within the natural distribution region of Israel, but taxonomically far from the cultivated lettuce. (2) Two wild Cichorium (Compositae, tribe Cichorieae, a subclade Cichoriinae) species.
The objectives of our research are related to the identification, collection, conservation and sustainable use of these rich genetic sources for lettuce improvement. Specifically, our research is devoted to: species definition; taxonomic validation; genetic, morphological and phenological diversity; identification of natural putative hybrids (Fig. 1); diseases resistance; and sesquiterpene lactones content. Novel (e.g. complete resistance of single L. aculeata accession to five California isolates and five European Bremia lactucae races) and even some unexpected results (e.g. various characterization of trichomes that were absolutely similar to L. aculeata in plants from a single L. serriola population) were obtained due to our rule of screening a detailed, large scale of natural populations and individuals for germplasm variation. Notably, our results question some commonly-accepted “facts” that have been cited for over one hundred years in the literature, such as the definition of L. georgica as an absolutely biennial or perennial plant, as well as placement of this species into the LGP-1.
Described and ongoing results from the WLGB project suggest that the studied species are largely untapped sources for breeding resistances against biotic and a-biotic stresses, as well as other traits, into the cultivated lettuce.
Fig. 1 (a) Natural field in Malkiya, Upper Galilee, Israel (33°06'10.4"N; 35°30'49.3"E "E; 668 m a.s.l.), showing coexistence of both L. aculeata (right) and L. serriola (left) plants; Results of natural hybridization between both parental species: (b) F1 plants (in bags), and (c) segregation of F2 family, progenies of individual L. aculeata plant no. 450-3 that were collected in Zefat, Upper Galilee, Israel (32°57'38.1"N; 35°30'53.7"E; 760 m a.s.l.)