Cytogenetics of cultivated Bougainvilleas. V. Induced tetraploidy and restoration of fertility in sterile cultivars

Abstract

Induced tetraploidy restores fertility in sterile cultivars of Bougainvillea. However, like the fertile diploid cultivars induced tetraploids are self-incompatible, but set seeds readily on crossing. Diploid progenitors show irregular meiosis, while in tetraploid counterparts there is predominant bivalent pairing. Low frequency of quadrivalents at 4x level implies that pairing at diploid level is between chromosomes heterozygous for cryptic structural changes. This also accounts for lower number of chiasmata per chromosome in diploids in comparison with their tetraploid counterparts. Sterility at 2x level appears to be due to recombination of cryptic structural differences and/or unequal distribution or aberrant behaviour of univalents. Predominant bivalent pairing accompanted by high fertility is a strong pointer towards preferential pairing in induced tetraploids.