The effect of gamma-irradiation on the changes of photosynthetic efficiency in Kanpei ( Citrus unshiu × C. sinensis )

Fruit trees are perennial plant to have a characteristic requiring a long juvenile period until fruit set in general. Developing to release a new fruit cultivar is a laborious and cost- and time-consuming work. Especially, citrus breeding is not always feasible due to its cross-incompatible, sterile, and polyembryonic characteristics. Therefore, mutagenesis has been widely applied to citrus breeding to increase mutation frequency and genetic variability enabling development of new genotypes as an alternative method. Recently, various tangor ( Citrus unshiu × C. sinensis ) cultivars were released through interspecific hybridization. Many attempts have been made to induce mutations in developing tangor cultivars, while their physiological effects have not been verified yet. To investigate the effect of gamma-irradiation exerted on tangor cultivar ‘Kanpei’, its scions were irradiated with 20, 40, 60, 80, and 100 Gy of gamma-rays. Then, we examined the SPAD values between the gamma-irradiated M 0 plants comparing with control ‘Kanpei’ (0 Gy). Interestingly, we found that there are variations in SPAD values among different treatments. This implies that mutation breeding should consider different factors other than the target traits.