Multivariate Analysis Based on Agronomic Traits of 95 Bulb Onion (Allium cepa L.) Cultivars

Abstract

Annual produntion of bulb onion (Allium cepa L.) is the third largest among vegetables in Japan. In Japan, bulb onion cultivars are mainly divided into two groups: spring-sowing (late-maturing) and autumn-sowing (early-maturing) cultivars. The cultivars belonging to these groups have been difficult to compare regarding their morphological traits under the same cultivation conditions, but now we can evaluate their traits under newly developed spring-sowing cultivation in the Tohoku region. We extracted a total of 50 traits using 95 domestic and foreign cultivars/genetic resources through two trials each of spring-sown and autumn-sown cultivation. Because most of the trait data obtained from the spring-sown trial were correlated with those from the autumn-sown trial, the spring-sown cultivation is considered effective for reproducible evaluation of cultivar traits, especially in cases of severe conditions during winter due to climate instabilities such as heavy snow (freezing) and a warm winter. Principal component analysis of 30 traits revealed a 51.3% cumulative contribution of the primary and secondary components, with the former determining earliness and latter determining bulb traits. A scatter diagram of the primary and secondary components indicated some specific clusters according to conventional cultivar classification. The principal component and cluster analyses obtained from our data representing each cultivar group may be useful as references for objective evaluation of the characteristics of bulb onion cultivars.