2020 Volume 19 Issue 3 Pages 229-235
‘Koyama New Summer’ is a bud mutation of ‘Hyuganatsu’ (Citrus tamurana hort. ex. Tanaka), which has the characteristic of producing more seedless fruits than ‘Hyuganatsu’. We examined the cause of seedlessness in ‘Koyama New Summer’. In the self-pollination process of ‘Koyama New Summer’ and ‘Hyuganatsu’, the pollen tube elongation stopped in the upper part of the style, and there was no significant difference between the two. This indicates that ‘Koyama New Summer’ has self-incompatibility like ‘Hyuganatsu’. The fruit setting rate after physiological fruit drop of ‘Koyama New Summer’ under the non-pollen condition was 60.8%, being higher than in ‘Nishiuchi Konatsu’, ‘Muroto Konatsu’, and ‘Hyuganatsu’. This indicates that ‘Koyama New Summer’ has highly parthenocarpic traits compared with ‘Nishiuchi Konatsu’, ‘Muroto Konatsu’, and ‘Hyuganatsu’. In addition, parthenocarpy in ‘Koyama New Summer’ gives rise to autonomic parthenocarpic traits because it was induced under non-pollen and non-agent-administered conditions. In conclusion, after examining the causes of seedlessness in ‘Koyama New Summer’, it was determined that it exhibits not only self-incompatibility but also highly autonomic parthenocarpic traits.
