CYTOLOGICAL STUDIES IN THE GENUS PHASEOLUS .2. MEIOTIC ANALYSIS OF 16 SPECIES

Meiotic studies in sixteen species of the. genus Phaseolus have been made. In all these the haploid number of chromosomes was found to be eleven (11). In all the species, except P. acutifolius, P. aconitifolius, P. coccineus, P. aborigineus, regular formation of eleven bivalents was noted, but they differed in the number of ring and rod bivalents-per pollen mother cells. The univalents were recorded in P. acutifolius, P. aconitifolius, P. aborigineus, and P. coccineus. These species differed in the value of 1/3 chiasma per chromosome and the coefficient of terminalisation also. From the analysis of inter class variance, it was noted that there existed a significant variation in their chiasma frequency. A positive correlation was recorded in all these species except P. aureus and P. trilobus, in which a negative correlation was noted. Such observations indicated that there was a variation in the distribution of chiasmata even in the same nucleus. The species P. acutifolius, P. aborigineus and P. coccineus showed the presence of bridges and laggards at anaphase I and II. The analysis of pollen grains revealed that the pollen fertility was lower (70-75%) in P. coccineus, P. aborigineus, P. aconitifolius and P. acutifolius, whereas in the rest of the species it was found to be in between 80 to 85%. The relationship of the species, and their evolutionary tendencies were analysed on the basis of the meiotic behaviour. The meiotic data, obtained from sixteen species of Phaseolus, confirmed that karytotype asymmetry and the change in the morphology of the chromosomes were instrumental in speciation within the genus Phaseolus. The presence of a few spontaneous chromosomal aberrations in some of the species could also be regarded as one of the factors of variation and speciation within this genus. © 1979, Japan Mendel Society, International Society of Cytology. All rights reserved.