Genetic variability of Canadian elite cultivars of summer turnip rape (Brassica rapa L.) revealed by simple sequence repeat markers

Abstract

. 2009. Genetic variability of Canadian elite cultivars of summer turnip rape (Brassica rapa L.) revealed by simple sequence repeat markers. Can. J. Plant Sci. 89: 865Á874. Canadian public oilseed breeding programs have played a leading role in the development of canola-quality Brassica rapa oilseed cultivars, but the genetic variability of the cultivars developed over the past 60 yr is poorly understood. Simple sequence repeat (SSR) markers were applied to assess the genetic variability of 294 plants representing one landrace introduced from Poland ca. 1940 and nine Canadian elite B. rapa cultivars released by Agriculture and Agri-Food Canada since 1964. Application of 18 SSR primer pairs detected 27 likely loci on five or more linkage groups and 123 polymorphic alleles. The allelic frequencies ranged from 0.003 to 0.997 and averaged 0.262. The estimates of mean heterozygosity for these cultivars ranged from 0.126 to 0.197 and averaged 0.165. Significant decreases of SSR alleles and average dissimilarities were observed over the 60 yr of breeding effort. The proportion of total SSR variation residing among the cultivars was 10.4%; between high vs. low erucic acid cultivars 5% and between high-vs. low-glucosinate cultivars 5%. Pairwise genetic differentiation ranged from 0.025 to 0.184 and averaged 0.104. Genetic clustering of these cultivars revealed AC Sunbeam to be a genetically unique cultivar, and two distinct groups of the other nine cultivars were separated by high-vs. low-glucosinate content. Several distinct genotypes, largely derived from the landrace Polish, were identified. These findings are useful for broadening the genetic base of elite B. rapa germplasm, selecting genetically diverse genotypes for synthetic and hybrid combinations, and conserving this germplasm. L'he´te´rozygotie moyenne estime´e pour ces cultivars varie de 0,126 a`0,197, pour une moyenne de 0,165. Les auteurs ont note´une diminution importante des alle`les SSR et des dissemblances moyennes durant les soixante anne´es qu'a dure´le programme d'hybridation. La variation des SSR s'e´tablissait a`10,4% pour l'ensemble des cultivars, soit 5% pour ceux ah aute ou a`faible concentration d'acide e´rucique et 5% pour ceux a`forte ou a`basse concentration de glucosinolates. La diffe´renciation ge´ne´tique par paire varie de 0,025 a`0,184, pour une moyenne de 0,104. Le regroupement ge´ne´tique des cultivars indique qu'AC Sunbeam est un cultivar unique, ge´ne´tiquement parlant; les neuf autres cultivars ont e´te´divise´s en deux groupes distincts selon leur concentration, faible ou e´leve´e, de glucosinolates. Plusieurs ge´notypes diffe´rents, de´coulant dans une large mesure de la race polonaise, ont pu eˆtre identifie´s. Ces re´sultats contribueront a`e´largir la base ge´ne´tique du mate´riel e´lite de B. rapa, la se´lection de ge´notypes diffe´rents en vue de la cre´ation de cultivars par synthe`se ou hybridation, ainsi que la conservation du mate´riel ge´ne´tique.

Genetic structure and diversity of a collection ofBrassica rapasubsp.rapaL. revealed by simple sequence repeat markers

“…The diversity found within B. rapa populations analysed in the present study was higher than in the work reported by Fu & Gugel (2009), who detected levels of heterozygosity from 0•120 to 0•197 in 10 cultivars of B. rapa subsp. oleifera analysed by SSR markers.…”

“…oleifera analysed by SSR markers. The lower level of diversity found by Fu & Gugel (2009) can be explained because the populations analysed were related by origin. The heterozygosity found by Ofori et al (2008) in three openpollinated cultivars of B. rapa subsp.…”

“…High levels of within-population variation (0•90 and 0•83) were found in cultivars of B. rapa subsp. oleifera (Ofori et al 2008;Fu & Gugel 2009). Zhao et al (2005), applying AFLP markers, reported comparable genetic diversity among and within different cultivars belonging to different B. rapa crops, including leafy vegetables, oilseed, root vegetables and fodder collected world-wide.…”

Unusually low pour point of fatty acid methyl esters with low saturated fatty acid content

“…For example, genetic diversity was reported in B. rapa cv. Echo, a cultivar selected from the cultivar Polish in 1964 . It was hypothesized that selection of variants in fatty acid composition within a rapeseed cultivar provides the opportunity to study the impact of fatty acid composition on oxidative stability.…”

Genome-wide identification of SSR markers in the Brassica A genome and their utility in breeding

“…Their value as markers arise from their ease of detection, the co-dominance of their multiple alleles, as well as the fact that they are often designed from specific sequences (Powell et al 1996). This marker type was found to be useful in various breeding applications, such as analysis of genetic diversity among the different accessions of B. napus (e.g., Hasan et al 2006;Bus et al 2011;Gyawali et al 2013) and B. rapa (e.g., Ofori et al 2008;Fu and Gugel 2009;Annisa et al 2013), assessment of the extent of allelic diversity introgressed from the exotic gene pool into crop germplasm (e.g., Kebede et al 2010), and molecular mapping of traits for identification markers for use in breeding (e.g., Kebede et al 2012;Rahman et al 2014;Kebede and Rahman 2014). SSR markers can be developed from expressed sequence tags (ESTs), the ends of bacterial artificial chromosomes (BACs), and genome sequence surveys (GSS); however, these markers must be mapped against each other to localize them in the genome (Ramchiary et al 2011;Li et al 2013;Yu et al 2013).…”