Evaluation of bulb shape and fresh-weight of different onion cultivars

The relationship between bulb shape and fresh-weight were examined in 6-17 phenologically different onion varieties over a period of three consecutive years (1997-2000). Cultivars which are recommended for production in different agricultural areas of Southwestem Japan, were classified according to their maturity in early, midearly and late varieties were examined. Onion bulb shape, expressed as the proportionality existent between the diameter and height, was found to be lower in the early local varieties, such as Kaizuka-wase (1.8 =+- 0.04) and Shizuoka-wase (1.8 =+- 0.03), thus reflecting their flattened form. In the later varieties, such as Osakamaru and Yamaguchi-kodaka, the value was 1.1 =+- 0.02, demonstrating 'their complete globular shape. Conversely, for the F1 varieties Apollo, Advance and OL, the ratio value was higher (1.3 =+- 0.05) and was lower for Momiji (1.0 =+- 0.01). In general, they presented less oblateness than the local varieties. Amongst the local varieties, the highest bulb weights recorded were 365. 8 and 356. 9 g / bulb for Awajichyukou and Sensyu-nakate, respectively, while the remaining five cultivars weighed less than 300 g each. In contrast, with the exception of Momiji, all F1 hybrids registered weight values superior to 300 g, beginning with Advance that yielded 470 g. Significant varieties x year interactions were detected for all morphological traits, suggesting that phenotypic yield stability of a particular variety might be affected by the nutrient application schedule over the years. Modest fertilization reduction during the third year of cultivation may have been responsible for the observed lower values in morphological traits.