Evaluation of forty-five cultivars as affected by bulb initiation, bulb and scale characteristics, and bulb minerals and organic compounds of intermediate-day yellow onion (Allium cepa L.) in South Korea

Abstract

We evaluated and classified forty five onion cultivars according to bulb initiation, bulb and scale characteristics, minerals and organic compounds contents, and storage quality in South Korea during 2016/2017 and 2017/2018 growing seasons. Field experiment was conducted in randomized block design with three replications. Bulb initiation ranged from 153 days after transplanting (DAT, April 2) to 177 DAT (April 26). Fresh bulb weight (FBW) and bulb index (BI) were 285.5 ± 18.5 g/individual, 0.93 ± 0.05, respectively. Number of scales (NS), number of center (NC), and scale thickness (ST) were 7.6 ± 0.2, 2.3 ± 0.2, and 5.5 ± 0.2 mm/scale, respectively. Chroma and Lightness of bulb skin were 27.1 ± 1.9, 61.2 ± 2.3, respectively. Storage loss (SL) on December 12 was 19.4 ± 5.9%. Nitrogen (N), Carbon (C) and sulfur (S) contents were 1.36 ± 0.14, 37.9 ± 3.2 and 0.40 ± 0.06 mg kg−1 on a fresh weight basis. Total soluble solids (TSS) and total phenolics content (TPC) were 8.6 ± 0.6 °Bx, 164.8 ± 15.6 mg GE kg−1 on a fresh weight basis. Days from transplanting to bulb initiation was significantly positively correlated with bulb height, NC, dry matter, N, C, S, TSS, TPC, total flavonoids content (TFC) etc., while it was negatively correlated with rot loss and SL. Dry matter content was significantly positively correlated with N, C, S, TSS, TPC, TFC etc., while it was negatively correlated with SL. Storage loss was negatively correlated with N, S, Potassium and TSS. Dendrogram of agglomerative hierarchical clustering for the forty five cultivars based on bulb initiation, bulb and scale characteristics, and bulb minerals and organic compounds contents classified five cultivar groups. Cluster 1 featured the earliest bulb initiation and the greatest SL. Cluster 2 featured the fewest NS and NR, and the thickest ST. Cluster 3 featured the greatest FBW, and the most NS and NC. Cluster 4 featured the greatest BI and the thinnest ST. Cluster 5 featured the lowest SL, and the highest minerals and antioxidant compounds contents. This information should be helpful for onion growers to decide onion cultivar and for onion breeders to promote new cultivars depending on their purpose.