Adventitious shoot regeneration in cotyledons from Japanese pear and related species

An efficient method for the generation of adventitious shoots from the cotyledons of Japanese pear and related species was developed. Cotyledons from seeds of the Japanese pear “Okusankichi” and the Asian pea pear “Hokushimamenashi” were used to determine the optimum concentrations of phytohormones in the medium. The rates of generation of adventitious shoots and the numbers of adventitious shoots per explant were highest when the media contained 5 μM 1-naphthaleneacetic acid combined with 10 or 25 μM 6-benzylaminopurine. These growth regulators were used to generate adventitious shoots from the cotyledons of 33 cultivars of Japanese, Chinese, Asian pea, and European pears. A high number of adventitious shoots per explant (1.3–2.3) and high rates of regeneration of adventitious shoots (60–76 %) were obtained from the cotyledons of Japanese pears “Imamuraaki” and “Agenosho Shinanashi.” Although pollination was not controlled, cotyledons from mother trees of old Japanese cultivars and Chinese pears tended to be more regenerable than those from other pear species. Since the rooting ability of the adventitious shoots was very low, micro-grafting was applied to obtain regenerated potted plants from adventitious shoots. Grafted regenerated plants were recovered at a rate of more than 60 %, regardless of cultivar. To our knowledge, this is the first report to evaluate shoot regeneration from cotyledons of major Pyrus species.