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

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 agro-morphological 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 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.