SELF-FERTILITY AND AGAMOSPERMY IN SUGAR-B EET, BETA-VULGARIS L

Experimental data on self-fertility in pollen-sterile sugar beet plant s are reported. These plants form seeds via agamospermy. An embryologi cal study of two agamospermous strains revealed embryos that developed from unfertilized cells of embryo sacs before pollination. The agamos permous seedlings had diploid chromosome sets and were segregated by m arker locus Rr (red hypocotyl), which controlled hypocotyl pigmentatio n in seedlings. The ratio between the frequencies of two seedling phen otypes was 11 : 3; i.e., it was equal to that of the gametic frequenci es in the case of tetrasomic segregation in duplex heterozygotes (RRrr ). A conclusion was drawn that in the studied strains, the archespore complex was a mixoploid cell population containing diploid and tetrapl oid cells. Embryo sacs with unreduced (diploid) chromosome sets were f ormed from tetraploid cells; these embryo sacs were prone to parthenog enetic development. It was revealed that the rate of self-fertility wa s almost the same in pollen-fertile and pollen-sterile plants. However , the proportion of plants that set seeds when their floral shoots wer e isolated from alien pollen was significantly higher in pollen-fertil e beets. It is probable that, in self-incompatible, pollen-fertile pla nts, some seeds are also formed via agamospermy. An explanation is sug gested for the drastic increase in the proportion of self-fertile plan ts that was revealed in beet populations grown at a low temperature in the late 1930s [3]; it is suggested that agamospermous embryos (which appear regularly in any population) have a greater possibility of com pleting embryogenesis at a low than at a high temperature because of h igher embryonic mortality in the latter case.