Abstract
Broad phenotypic variations were obtained previously in derivatives from the asymmetric somatic hybridization of cauliflower “Korso” (Brassica oleracea var. botrytis, 2n = 18, CC genome) and black mustard “G1/1” (Brassica nigra, 2n = 16, BB genome). However, the mechanisms underlying these variations were unknown. In this study, 28 putative introgression lines (ILs) were pre-selected according to a series of morphological (leaf shape and color, plant height and branching, curd features, and flower traits) and physiological (black rot/club root resistance) characters. Multi-color fluorescence in situ hybridization revealed that these plants contained 18 chromosomes derived from “Korso.” Molecular marker (65 simple sequence repeats and 77 amplified fragment length polymorphisms) analysis identified the presence of “G1/1” DNA segments (average 7.5%). Additionally, DNA profiling revealed many genetic and epigenetic differences among the ILs, including sequence alterations, deletions, and variation in patterns of cytosine methylation. The frequency of fragments lost (5.1%) was higher than presence of novel bands (1.4%), and the presence of fragments specific to Brassica carinata (BBCC 2n = 34) were common (average 15.5%). Methylation-sensitive amplified polymorphism analysis indicated that methylation changes were common and that hypermethylation (12.4%) was more frequent than hypomethylation (4.8%). Our results suggested that asymmetric somatic hybridization and alien DNA introgression induced genetic and epigenetic alterations. Thus, these ILs represent an important, novel germplasm resource for cauliflower improvement that can be mined for diverse traits of interest to breeders and researchers.
Highlights
Cauliflower (Brassica oleracea var. botrytis, 2n = 18, CC genome) is a major vegetable crop valued worldwide for its nutrition and flavor
The low genetic diversity in modern Brassica varieties is concerning because it reduces potential genetic gains in breeding programs
introgression lines (ILs) containing fragments from related species can be used to generate improved cultivars. This method has proven successful in many crops, including wheat (Liu et al, 2007), rice (Rangel et al, 2008), potato (Chavez et al, 1988), eggplant (Mennella et al, 2010), B. napus (PrimardBrisset et al, 2005; Leflon et al, 2007), barley (Johnston et al, 2009), tomato (Menda et al, 2014), and rye grass (Roderick et al, 2003)
Summary
As with other modern crop species, intense selection for preferred traits, and a tendency for inbreeding have resulted in low genetic diversity among cauliflower breeding resources To address this problem, related species such as black mustard. Innovation of Cauliflower Germplasm (Brassica nigra, 2n = 16, BB genome), with a large reservoir of genes conferring desirable characteristics, have been proposed as a valuable source of genetic diversity for Brassica crop improvement. In principle, this diversity can be transferred into crops via sexual hybridization and subsequent backcrossing. Agronomically important traits, such as disease resistance and specific fatty acid compositions, have been successfully integrated into the crops (Gerdemann et al, 1994; Hansen and Earle, 1994, 1995, 1997; Wang et al, 2003; Tu et al, 2008; Scholze et al, 2010)
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