Genetic diversity of kale (Brassica oleracea L. var acephala) using agro-morphological and simple sequence repeat (SSR) markers

Genet Resour Crop Evol https://doi.org/10.1007/s10722-023-01686-6 RESEARCH ARTICLE Genetic diversity of kale (Brassica oleracea L. var acephala) using agro‑morphological and simple sequence repeat (SSR) markers Barbara Pipan · Mohamed Neji · Vladimir Meglič · Lovro Sinkovič Received: 18 May 2023 / Accepted: 12 July 2023 © The Author(s) 2023 Abstract Kale (Brassica oleracea. var. acephala) is a nutrient-rich green leafy vegetable consumed as food and used in traditional medicine worldwide. An essential step in describing the available genetic resources and ensuring their effective use in breeding programs is to characterize the genetic diversity of available germplasm. In this study, the genetic diversity and structure of 26 kale accessions from South-East Europe were examined using 26 agromorphological traits collected in the field and 12 simple sequence repeat (SSR) markers. Considerable agro-morphological variability was found in most quantitative (CV = 17.26–42.42%) and qualitative (H’ = 0.61–1.79) traits. Multifactorial analysis (MFA) showed that country of origin (33.01%) and morphotype (32.30%) significantly influenced kale diversification. Leaf blade shape (20.62%), leaf incision (19.43%), anthocyanin distribution (16.43%), and leaf colour (15.55%) were the traits that most clearly differentiated accessions. The three common commercial kale cultivars were identified as independent outliers that differed from the other kale accessions in Supplementary Information The online version contains supplementary material available at https://doi. org/10.1007/s10722-023-01686-6. B. Pipan (*) · M. Neji · V. Meglič · L. Sinkovič Crop Science Department, Agricultural Institute of Slovenia, Hacquetova ulica 17, 1000 Ljubljana, Slovenia e-mail: both MFA and UPGMA clustering analysis. The SSR markers were highly informative with 108 alleles and polymorphic information content ranging from 0.395 to 0.856. Strong genetic diversity was detected at the accession level (H’ = 0.58) while genetic differentiation was low (Fst = 0.05). Similar to UPGMA clustering, Bayesian clustering suggests that the kale collection can be divided into four clusters with a high degree of admixture and no geographic grouping pattern is apparent. Overall, the study showed that the kale collection studied represents a valuable reservoir of genetic and agro-morphological variability that could be used for future breeding initiatives. Keywords Kale · Genetic differentiation · Allelic diversity · SSR markers · Plant descriptors Introduction The diploid species (2n = 18) Brassica oleracea L. (Brassicaceae), the most diverse species in the genus Brassica, includes several vegetable crops with a long history of cultivation and domestication worldwide, such as cauliflower, cabbage, broccoli, Brussels sprouts, kohlrabi, and kale (Golicz et al. 2016). In particular, kale leaves (B. oleracea var. acephala) has attracted great interest due to its excellent nutritional value compared to other crops. It is considered an ideal source of vitamins, essential minerals, and fatty acids (Pathirana et al. 2017). Therefore, it occupies Vol.: (0123456789) 13 Genet Resour Crop Evol a privileged position in the cuisine and diet of European, Asian and American populations (Gonçalves et al. 2012). Moreover, it is widely used in traditional medicine for the treatment of rheumatism, liver diseases, eye problems, bone weakness, anaemia, and obesity (Gonçalves et al. 2012; Kuerban et al. 2017; Thavarajah et al. 2016) and also as an animal feed (Cartea et al. 2003). Brassica species are known as a highly diverse group of plants due to their ability of spontaneous cross-pollination and gene flow among sexually compatible relatives (Meglič and Pipan 2018; Pipan et al. 2013, 2011). B. oleracea var. acephala is classified into different morphotypes based on morphological characteristics. For example, kale (B. oleracea L. var. acephala DC.) has dark green and crinkled leaves, Scotch kale (B. oleracea L. var. acephala (DC.) Alef. var. sabellica L.) is characterized by grey-green and highly crinkled and wrinkled leaves, while Marrow stem kale (B. oleracea L. var. acephala (DC.) Alef. var. medullosa L.) is characterized by a soft and thick stem and different leaf types. In addition to variation among morphotypes, populations/cultivars within the same morphotype may also exhibit wide morphological variation due to a long history of domestication and adaptation to environmental conditions (Hahn et al. 2022). According to Hahn et al. (2022), three types of kale are distinguished according to their origin: curly kale (Scotch type, Brassica oleracea covar. acephala var. sabellica), Italian kale (Lacinato type, Brassica oleracea covar. acephala var. palmifolia), and collard (Brassica oleracea covar. acephala var. viridis). Indeed, in B. oleracea var. acephala, large morphological variation could occur both within populations as a result of cross-pollination and between populations due to extensive selection by farmers and/or adaptation to local environments (Cartea et al. 2003; Šamec et al. 2019a; Thavarajah et al. 2016). Detailed agro-morphological characterization and assessment of patterns of genetic variability based on quantitative and qualitative traits is the first and crucial step in describing available genetic resources and their efficient use in breeding programs (Balkaya and Yanmaz 2005; Oumata et al. 2023). However, although agro-morphological traits can be controlled at the genetic level, they may be nonspecific and nonpolymorphic, and their variation could be strongly influenced by environmental factors (Choudhury et al. 2022; Petit et al. 2020; Terlević et al. 2023). In Vol:. (1234567890) 13 contrast, DNA-based molecular markers are stable, intact, abundant in the genome, and free from environmental influences. Therefore, they are a powerful tool not only for comprehensive depiction the genetic diversity patterns, but also for other advanced analyses such as gene mapping and molecular markerassisted breeding (Zhu et al. 2019). Although various molecular markers have been developed to date, simple requence Repeats (SSRs) or microsatellites remain the most attractive for genetic variability research and plant breeding because they are codominantly inherited, abundant, multi-allelic and highly polymorphic (Riangwong et al. 2020; Rivera et al. 2016), and are also easy to handle in the laboratory or automated by capillary sequencers (Schuelke 2000). Therefore, assessment of genetic variation using agro-morphological traits and SSR markers has proven to be a very powerful approach for genetic resources management, utilization, and conservation in many crops, including chickpea (Ghaffari et al. 2014), tomato (Mercati et al. 2015), pepper (Rivera et al. 2016), leafy mustard (Sharma et al. 2020), and cauliflower (Rakshita et al. 2021). In the present study, a large set of quantitative and qualitative agro-morphological traits and (...truncated)