DISOMIC AND DITELOSOMIC ALIEN CHROMOSOME ADDITIONS IN BEET (BETA-VULGARIS), CARRYING AN EXTRA CHROMOSOME OF BETA-PROCUMBENS OR TELOSOME OF B-PATELLARIS

Alien chromosome transmission through the female germ line as well as meiosis in pollen mother cells were studied in disomic and ditelosomic alien chromosome additions of beet, Beta vulgaris, carrying an extra pair of chromosomes or telosomes of B. procumbens or B. patellaris, re spectively. The alien chromosomes carried genes for resistance to the beet cyst nematode, Heterodera schachtii, and screening for this resis tance was used to select plants with or without the alien chromosomes. A great variation for alien chromosome transmission was recorded and plants carrying two extra alien chromosomes were recovered in the back cross progenies of the disomic or ditelosomic additions. However, in t hese progenies the average frequencies of plants without alien chromos omes (86%) did not clearly differ from that in similar progenies of th e original monosomic or monotelosomic chromosome additions, indicating that doubling the number of the alien chromosome did not enlarge thei r transmission to the next generation. The alien chromosomes fully pai red at pachytene and desynapsed again before diakinesis, indicating de creased chiasma formation. At second metaphase nearly 60% of the cells had one extra chromosome, and the remaining cells carried two or no e xtra chromosomes in about equal proportions. The tetrads looked fully normal. The expected relation between the average number of alien chro mosomes in the germ cells and in the plants of the progenies did not s how up, indicating a strong selection favouring the female gametes wit hout alien chromosomes.