Autopolyploids of Helianthus annuus L. var. morden

Abstract

Autopolyploid plants of Helianthus annuus var. morden were obtained by treating seedlings (2-5 d old) with 0.4%, 0.5% and 0.6% colchicine for 12h. The autopolyploids exhibited reduction in the height, girth, leaves and flowers of the plants but increase in the size of stomata, pollen grains and meiocytes. Pollen and seed fertility were reduced. There was increase in seed weight from diploids to C1 and then to C2 generations in tetraploids, but increase in C1 and decrease in C2 generation in octoploids. Low seed setting in C1 generation which, however improved in C2 generation only in tetraploids. C2 generation was absent in hexa-decaploids. The chromosome number in diploids, tetraploids, octoploids and hexa-decaploids were found to be 2n=34, 68, 136 and 272, respectively. Meiotic observations showed various associations of chromosomes such as univalents, bivalents and quadrivalents and abnormalities such as laggards, unequal separation of chromosomes, bridges, stickiness in C1 generation which lessened in C2 generation in tetraploids but increase in octoploids. These irregularities appeared to be the major factors responsible for high pollen sterility in autopolyploids. High or number of bivalents and lower frequency of abnormalities at metaphase in tetraploids in C2 generation led to an improvement in pollen and plant fertility.