Haploids and homozygous diploids, triploids and tetraploids in sugar beet

Attempts to induce haploid parthenogenesis in sugar beet by pollination with wild beet pollen and irradiated sugar beet pollen resulted in five haploid plants. Seven additional haploids were found among inbred lines, and still another in the C 1 generation after colchicine treatment of an inbred line. The frequency of haploids in different kinds of sugar beet seed, also studied, was higher in offspring from diploids pollinated by tetraploids (about 0.2%) than in diploid crosses. The haploids and homozygous diploid and tetraploid lines synthesized from three of the haploids are briefly described. In a greenhouse experiment with diploids, triploids and tetraploids, which originated from one and the same haploid, the diploids and the euploid triploids did not differ in root weight, while euploid tetraploids weighed on an average 7 per cent less than the diploids. At both the triploid and tetraploid levels, aneuploidy had a much greater negative influence on root development than the physiological imbalance caused by the increase in genome number. Contrary to the root weight, the weight of the leaves increased with the increase in genome number, even when including the aneuploids. These results are discussed in relation to the influence of heterozygosity on the performance of autotetraploids and the present situation in polyploid breeding in sugar beet.