Post-zygotic arrest of embryo development induces seedless fruits in kabosu (Citrus sphaerocarpa hort. ex Tanaka)
Katsuhisa Futagami is an MS student in the Graduate School of Bioresource and Bioenvironmental Sciences at Kyushu University, Fukuoka, Japan. He has been studying the theme during undergraduate and postgraduate courses in Kyushu University, under the supervision of Professor Yukio Ozaki and Assistant Professor Yuki Mizunoe. He attended the III Asian Horticultural Congress with the research entitled “Post-zygotic arrest of embryo development induces seedless fruits in kabosu (Citrus sphaerocarpa hort. ex. Tanaka)”. Kabosu is one of polyembryonic and flavorful acid citruses, and its juice is used as an alternative to table vinegar in Japan. Seedless kabosu ‘Sobo-No-Kaori’ and ‘Kami-No-Kawa’ were established from bud mutations of seeded ‘Oita No.1’ and commercially highly evaluated. The fruits are, however, commonly smaller than those of ‘Oita No.1’ and occasionally contain several seeds. New superior seedless kabosu cultivars are, therefore, required. In the current study, the factor of the seedlessness in kabosu was determined by investigating the fertility of male and female gametes, and self-incompatibility for the basis of the breeding of seedless kabosu cultivars. Plant materials of ‘Oita-No.1’, ‘Sobo-No-Kaori’ and ‘Kami-No-Kawa’ were provided from Oita Prefectural Agriculture, Forestry and Fisheries Research Center, Oita, Japan. High pollen germination rate was revealed in ‘Oita No.1’, and moderate values enough for pollination were observed in ‘Sobo-No-Kaori’ and ‘Kami-No-Kawa’. One hundred or more pollen tubes elongated and reached to lower styles of seedless cultivars eight days after self- and cross-pollination with ‘Oita No.1’. These results showed that both seedless cultivars are male fertile and self-/cross-compatible before fertilization. The number of perfect seeds, and the number of embryos in perfect seeds per fruit in seedless cultivars were lower than those in ‘Oita No.1’ regardless of pollen parents. On the other hand, seedless cultivars produced many imperfect seeds containing undeveloped embryos as compared with ‘Oita No.1’. These results indicated that seedless cultivars show imperfect embryo development. Seedlessness in kabosu is primarily caused by female sterility resulting in arrested embryo development after fertilization. The new findings of this study will inform the breeding of novel seedless cultivars in citrus.
Katsuhisa Futagami won the ISHS Young Minds Award for the best poster at the III Asian Horticultural Congress (AHC2020) in Thailand in December 2020.
Katsuhisa Futagami, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, 422, West 5, 744 Motooka, Nishiku, Fukuoka City 819-0395, Japan, e-mail: firstname.lastname@example.org
The article is available in Chronica Horticulturae