[en] Some clonal lines of resistance to black rot were obtained from M₁V₃ of Xu-18 variety. Through some regional tests, provincial yield trial and production test, the mutant line Nong-Da 601 (12-11-8) as spring sweet potato showed a better yield than the control, the dry matter content of Nong-Da 601 was also better than that of control, further more, the resistance to black rot of mutant selected in M₁V₃ could be passed onto their progeny. The analysis of esterase isozyme showed zymogram variation between Nong-Da 601 and Xu-18. From the observation of the root tip cells, the chromosome bridge appeared obviously after irradiation, but the frequency of chromosome aberration in M₁V₆ was decreased almost to the level of control (Xu-18). It seems that the changes of disease resistance from susceptible to resistant by irradiation was not due to chromosome aberration but due to gene mutation