Radiation Mutagenesis And Tissue Culture Applications In Strawberry Breeding

Strawberry (Fragaria ananassa Duch.) is one of the most important berry fruit in China, whose yield and cultivated area are the second abundant only less than grape. Strawberry fruit is nutritious and delicious, and popular. It is the prominent problem of strawberry production in China that there is lack of excellent varieties with high quality and disease resistance, and with intellectual proprietary. Most of the varieties in southern cultivated area were introduced from Japan, while the varieties in northern cultivated area were from Europe and America. Usually, Japanese varieties have better quality, but they are inferior to the European and American varieties in disease resistance. Therefore, it is an urgent duty to breed new strawberry varieties with high quality and disease resistance. At present, strawberry breeding work is mostly depended on traditional methods both in China and abroad. In addition, molecular marker technique and genetic engineering have been applied as well. Compared with above methods, the radiation mutagenesis in connection with tissue culture for breeding has many advantages. 'Toyonoka' and ' Akihime' strawberry, two of the dominating cultivated varieties in China, were used as materials in present study. Studies on radiation mutagenesis in connection with tissue culture for compound breeding technology have been performed. The results were summarized as follows.1. Effects of radiated with gamma rays pretreatment on inductivity and plant differentiation of strawberry anther1) The treatment of gamma irradiation could increase the callus inductivity and plant regeneration rate of anther. 20 Gy was the best dose. The callus inductivity of 'Akihime' and 'Toyonoka' were 39.09% and 35.68% more than that of control, respectively.2) After pretreatment of radiation by gamma rays, the difference between two induction media on the frequency of callus formation was significantly smaller than that of the control. Selectivity for induction medium had been reduced after pretreatment.3) On the same medium, the plant differentiation rates of 'Akihime' and 'Toyonoka' were also 6.67%-6.72% and 4.73%-6.45% higher than that of the control, respectively.4) The media composition significantly affected plant differentiation rate. The plant differentiation rate on M2 was 4.46%-10.53% higher than that on M1.5) The callus inductivity and plant regeneration rate of 'Akihime' was higher than that of 'Toyonoka' with the same treatment.2. Effects of gamma irradiation on shoot regeneration from leaf and bud growth in vitro of strawberry1) The leaf was very sensitive to the gamma irradiation, and 'Toyonoka' was more sensitive than 'Akihime'. The LD₅₀ (50% decrease of generation) of strawberry leaf was between 10 and 20 Gy.2) Strawberry leaves were inoculated in vitro at 8 d-15 d after gamma rays irradiation, and the shoot regeneration rate from of 'Toyonoka' increased at 10 Gy and almost no difference from 20 Gy to 40 Gy. The positive effect dose for 'Akihime'.was from 10 Gy to 30 Gy, however, 40 Gy decreased shoot regeneration rate.3) Suitable dose of gamma rays acted as a stimulus to the multiplication of strawberry in vitro.3. Effects of ⁶⁰Coγrays on in vitro mutagenesis of strawberry1) All treatments had effects on the growth and development of strawberry, but different cultivars had different sensitivity to the irradiation of gamma rays. The LD50 was 55 Gy for 'Toyonoka' and 64.6 Gy for 'Akihime'.2) Inhibition was obviously produced by ⁶⁰Co gamma rays for 'Toyonoka' strawberry, in which the plant became short in height, delayed blooming and reduced flower number.3) The effect of ⁶⁰Co gamma rays on flowering was more distinct than that on growth for 'Akihime'. According to the aberrance, the optimal dose was 20 Gy for 'Akihime' strawberry, which produced 36.53% higher aberrance and more excellent aberrance.