Cytogenetic Effects of Gamma Rays on Indica Rice Radha-4

The present study was conducted to understand the effects of different doses of radiations by gamma rays of Co60 on cytogenetics of indica rice, Radha-4 at the Central Lab, Institute of Agriculture and Animal Science, Rampur, Nepal. The immature PMC of M1 generation plants were analyzed performing the usual smearing and squashing technique. Radiation had a significant effect causing different types of cytogenetic aberrations, such as univalent and multivalent association of chromosomes, chromatin-bridges, laggards, fragments, stickiness, and multinucleated cells. An increasing number of aberrant cells with increasing dose of radiation was identified. The greatest share of aberration was identified due to multivalent association as a result of translocation followed by bridges and laggards, and the least effect for the stickiness of the chromosomes. Finally, 35 KR doses of gamma rays was the most potent dose inducing cytogenetic aberrations in meiotic pollen mother cell of rice compared to other dose spectrum.J. Inst. Agric. Anim. Sci. 27:25-36 (2006)

Cytogenetic studies of aneuploids in rapeseed. II. Morphology, fertility, and cytology of self-pollinated progenies of monosomic plants of Brassica napus L.

Cytogenic studies were conducted on self-pollinated progenies from two monosomic lines of Brassica napus to ascertain the mode of transmission of the monosomic chromosome. An approximately 1:1 ratio of disomic to monosomic plants was obtained. Only one nullisomic plant was found among a total of 71 plants analyzed. The 1:1 ratio and the anaphase I disjunction (19–18) suggest that the gametes (n) were twice as competitive or functional as their counterpart (n − 1). Since quadrivalents were observed in the disomic plants and only trivalents in the monosomics, the monosomic chromosomes were believed to be the ones that were involved in the formation of multivalents. The percentage of multivalent association in monosomic plants was almost double that in disomic plants. In the disomic plants, an average of 11.96% of pollen mother cells had one to two quadri-valents. The average frequency of trivalents in the monosomics was 23.63%. It was suggested that pairing of these homologs was genetically controlled with a dosage effect. The absence of one chromosome increased the frequency of multivalents. Key words: monosomic, Brassica, rapeseed, aneuploid.

Meiotic studies of some South African cultivars of Lantana camara (Verbenaceae)

Lantana camara L. is a polyploid species with a basic chromosome number of 11 (x = l l ) . Chromosome association in 39 cultivars indicated the occurrence of univalents to heptavalents with bivalents predominating. Multivalent association analysis revealed the presence in South Africa of at least four different groups of L. camara at the diploid level. The potential for sexual reproduction must exist, at least at the diploid level, to account for differences in chromosomal behaviour that can only be attributed to hybridization. The possibility exists that the basic chromosome number may be lower than 11, or else postspeciation genomic evolution must have occurred. No cytogenetical correlation exists between the South African and Indian cultivars. The number of chiasmata per genome increases with an increase in the polyploid level. Most multivalents are of the chain type. Univalents during diakinesis are the result of asynapsis. Triploid and pentaploid plants display a markedly abnormal meiosis. L. camara is a segmental allopolyploid species.