Breeding and Evaluation of New Iron Yam （Dioscorea opposita Thunb） Varieties

[Objective] This study was conducted to develop some new iron yam （Dioscorea opposita） varieties with excellent cooking, eating and nutritional qualities. [Method] The fresh weight per plant, drying rate, dry weight per plant, yield, allan- toin content, water soluble extract content and disease resistance of seven new iron yam cultivars （No.1, No.2, No.4, No.6, No.8, No.9 and No.10） obtained through spaceflight mutation breeding were measured and compared with control （No.11）. Then, the nutrition quality of two elite cultivars No. 6 and No.10 was determined by comparing with the control. [Result] The eight iron yam cultivars ranked in descend- ing order of their fresh weight per plant as follows： No.6（0.255 kg）〉No.10（0.254 kg）〉 No.4（0.242 kg）〉No.9（0.237 kg）〉No.1（0.233 kg）〉No.11（0.206 kg）〉No.2（0.191 kg）〉No.8 （0.157 kg）. There was no significant difference in fresh weight per plant between No.6 and No.10, but extremely significant difference between No.6 and the control, No.10 and the control. The eight iron yam cultivars ranked in descending order of their drying rate as follows： No.2 （32.641%）〉No.10 （32.230%）〉No.9 （28.223%）〉No.6 （25.174%）〉No.8（25.122%）〉No.11 （25.043%）〉No.1 （24.291%）〉No.4（20.234%）. The dry- ing rate of both No.6 and No.10 was higher than that of the control. The eight iron yam cultivars ranked in descending order of their dry weight per plant as follows： No.10（0.082 kg）〉No.9（0.067 kg）〉No.6（0.064 kg）〉No.2（0.062 kg）〉No.1（0.056 kg）〉No.11 （0.052 kg）〉No.4 （0.049 kg）〉No.8 （0.039 kg）. The dry weight per plant of both No.6 and No.10 is higher than that of the control. The eight iron yam cultivars ranked in descending order of their allantoin content as follows No.6 （0.484%）〉No.4 （0.467%）〉 No.10 （0.399%）〉No.ll （0.386%）〉No.9 （0.378%）〉No.8 （0.350%）〉No.2 （0.342）〉No.1 （0.325%）. The allantoin content of No.6 was significantly higher than that of No.10 and the control. There was significant difference in allantoin content between No.6 and No.10, but no significant difference between No 10 and the control. The eight iron yam cultivars ranked in descending order of their extract content as follows No. 6（20.49%）〉No.2（16.01%）〉No.4（15.54%） 〉No. 10（15.35%）〉No. 1 （14.48%）〉No. 11 （14.10%） 〉No.9（13.88%）〉No.8（11.87%）. The extract content of No.6 exhibited extremely sig- nificant difference with that of No.10 and the control, and the extract content of No. 10 was also significantly different from that of the control. The taste of No.10 was dry, soft, floury, sweet