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Summary A population of cultivated Aloe barbadensis Mill. displayed various types of chromosomal configurations at anaphase/telophase-I and II due to inversion heterozgosity. The population was characterized by the presence of bridges and fragments because of various numbers and positions of cross-overs in the inversion loop. The inversion heterozygote had very low pollen fertility.

Summary A population of cultivated Haworthia limifolia displayed various types of chromosomal configurations at anaphase/telophase-I and -II due to inversion heterozygosity. It was characterized by the presence of bridge and fragment because of various numbers and positions of crossovers in the inversion loop. The heterozygous condition led to reduced pollen fertility.

Bulbs of Allium cepa L. were treated with 0.2% ethyl methane sulphonate (EMS) for various durations: 6, 12, 18 and 24 h. Two mutants were isolated in a population raised from 0.2% EMS for 12 h (translocation heterozygote) and 18 h (inversion heterozygote) treated bulbs of Allium cepa. The translocation heterozygote exhibited the formation of a chain of four chromosomes in majority of the pollen mother cells (PMCs) at diakinesis/metaphase-I. At anaphase-I, the translocation heterozygote displayed various abnormalities such as laggards, unequal distribution, micronuclei, etc. The inversion heterozygote plant displayed various types of chromosomal configurations at anaphase/telophase-I and II in meiosis. It was characterized by the presence of bridge and fragment because of various numbers and the position of crossovers in the inversion loop. Pollen fertility was found to be very low in both the translocation heterozygote and inversion heterozygote.

SummaryPolyploidy was induced by colchicine in Allium cepa L. Five plants of Allium cepa (AC1-AC5) were isolated from the 0.2% colchicine treated inflorescences. The meiotic stages were analyzed in treated buds. Various cytological features like chromosomal associations (quadrivalents, bivalents and univalents), chiasmata frequency and terminalization coefficient were recorded at diakinesis/metaphase-I. Anaphase/telophase-I/II were studied in all the cholchitetraploids. In all these plants, the anaphase/telophase-I were abnormal showing unequal distribution, laggards, micronuclei and multipolar at telophase-II. Pollen mitosis was studied in these plants. The chromosomes (n=16) were found at metaphase. Pollen fertility was low (40.9 to 56.9%) in all colchitetraploids.Key words Induced colchitetraploid, Allium cepa L., Pollen fertility, Colchicine, Chromosome.The importance of polyploid plants in agriculture is well known. Colchicine has been largely used to alter ploidy level frequencies in cell populations to obtain tetraploid plants, starting with diploid material. In fact, polyploid plants usually have larger and thicker leaves, stems or roots, and also flowers, fruits and seeds, and then, a greater yield (Gao et al. 1996).The genus Allium consists of 700 species in the world (Friesen et al. 2005). Allium cepa L. is one of the most important plant species which was cultivated thousands of years ago as an edible plant (Jamila et al. 2009). Its chromosome number is low (2n=16), and it has a relatively large size and is susceptible to cytological manipulations (Mercykutty and Stephen 1980). The present investigation was planned to induce polyploidy in Allium cepa by colchicine treatment and identify the ploidy level by counting the chromosome number. Materials and methods Colchicine treatmentYoung inflorescences were treated with 0.2% colchicine solution for 6, 12, 18, or 24 h also by using the cotton swab method . After treatment inflorescences were thoroughly washed with water. Study of meiosisFor meiotic studies, young flower buds of appropriate size were collected between 10 to 11 AM and fixed in freshly prepared Carnoy s fluid (absolute alcohol and acetic acid in 3 : 1 ratio). Anthers were separated, teased in a drop of 2% iron acetocarmine on a clean slide and squashed under a cover glass. Pollen mother cells (PMCs) were analyzed for suitable stages of meiosis. Temporary slides were analyzed for different stages of meiosis like diakinesis, metaphase-I, anaphase-I, telophase-I and -II. Chromosomal associations, chiasmata frequency, distribution of chromosomes and other features were recorded. Chiasma frequency was calculated according to Ward (1979).