CYTOLOGICAL BEHAVIOR AND GENETIC-EFFECTS OF THE B-CHROMOSOMES OF RYE IN TETRAPLOID WHEAT, TRITICUM-DURUM DESF

Cytogenetical studies on tetraploid wheat, Triticum durum Desf. with B chromosomes of rye were conducted and a comparison was made with hexaploid wheat, T. aestivum with an equal number of B chromosomes of the same origin. The B chromosomes of rye in the tetraploid wheat create severe abnormalities on the meiotic behaviour of the A chromosomes. They significantly decreased the frequency of chiasma per cell by decreasing the number of ring bivalent and by increasing the frequency of rod bivalent and univalent per cell. The increased frequency of univalents at metaphase-I also led to the occurrence of laggards at anaphase-I and micronuclei at dyad and tetrad. Pollen and seed fertility were sharply decreased with an addition of a single B chromosome in the plants. They also had a significant negative influence on the kernel characters. Besides these all negative effects, the B chromosomes had a strong positive effect on most of the morphological characters influencing vegetative development of the plants. The effects of B chromosomes in the tetraploid wheat were more pronounced than the hexaploid wheat might be related to the absence of chromosomes of the D genome in the former species.