Abstract:Haploid Triticale callus did not grow on N6 medium with pH adjusted to 10 by 1% NaOH or with 1% NaC1, and was killed totally after culture for 40–50 days. However, living spots could be found in few dead inoculated calluses. When these living spots were transferred to the same medium, some of them will continue to grow and others dying off. These media are called screening media and the calluses growing more or less normally on them, variants. It is supposed that each variant came from a single callus cell. One gram of fresh callus contains about 1.65×106 cells, and the variation rate for resistance to 1% NaCl, as calculated from total quantity of inoculum, is 0.86 per million cells, and for resistance to pH 10, 0.81. R4 is a variant resistant to pH 10. The variation rate of IL for resistance to pH 11 is 1.01 per million cells. If selection is made directly from the normal callus, the variation rate for resistance to pH 11 could be estimated as (0.81×10–6)× (1.01×10–6), or 0,82 per 10" cells. For such a low rate of variation, it would be impossible to isolate them under the usual condition of laboratory. However, it could be achieved easily if a stepwise selection schedule is adopted. The variation rate can be increased one to two tithes by pretreatment of callues cells with 0.4% EMS aqueous solution for two hours. When the variants were cultured in normal medium far 3 to 5 passages (28 days between two subcultures), 23–33% of variants could not maintain their resistance, However, the two-third or more variants are stable and maintain their resistance through passages in normal media. Besides, plantlets induced from the callus of pH 10 resistant line TR4, could grow on the pH 10 medium. And callus induced from these plantlets explant maintains the resistance. These facts indicate that the stable resistant variants selected from the callus cells would be valuable for breeding purpose.