1973 年 38 巻 4 号 p. 699-706
In this investigation an attempt was made to find the cause of restricted oc-currence of natural polyploids in the genus Iberis, (Cruciferae) and efforts were made to see if aberrant types with extra chromosomes could be obtained and stabilised by polyploidization.
Three methods using colchicine were compared in treatments involving seven species viz. I. amara gp. (I. amara varieties and I. odorata), and I. pectinata, all annuals with chromosome number 2n=14; I. welwitschii and I. bernadiana both perennials with 2n=14; I. umbellata an annual with 2n=18 and I. sempervirens a perennial with 2n=22. In the annual species (2n=14 and 18), a high proportion of polyploid tissues was induced in mixoploid C1 plants. The treated perennials (2n=14 and 22) failed to flower and could not be assessed for polyploidy. In the subsequent generation or C2, only I. umbellata produced a high number of reasonably stable tetraploid plants. Triploid seeds were obtained from C1 plants and from crosses between 4 n female plants and 2 n males in I. umbellata, while the reciprocal crosses gave only diploid seeds or failed. No aberrant types with extra chromosomes were recovered from the triploid or other generations.
Cytological abnormalities were observed which may help to explain instability of polyploids in nature, but it is believed that there is a strong genetic control factor which acts to spontaneously reduce polyploid genomes to haploid ones. Tolerance to higher ploidies appears to increase with change in basic numbers from x=7 to x=9 to x=11.