|HOSSAIN, M. - UNIVERSITY OF MARYLAND
Submitted to: Journal of Heredity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/1997
Publication Date: N/A
Interpretive Summary: Improvement of alfalfa has lagged behind other crops due a lack of knowledge of the location of agriculturally important genes. Genes are located on chromosomes, thus it is important to know which genes are located on which chromosome. Alfalfa chromosomes are very small, they look alike structurally, and there are 32 of them, thus it is very difficult to identify each individual chromosome. We have studied the chromosomes of two closely related subspecies of alfalfa (Medicago sativa ssp. caerulea and ssp. falcata) which have only 16 chromosomes. We modified a Giemsa staining procedure for differentially banding the chromosomes called N-banding. This is the first report of the successful use of N-banding to identify alfalfa chromosomes. The banding patterns of ssp. falcata were all very similar and of little value for identifying individual chromosomes of this subspecies. However, the banding pattern of ssp. caerulea contained very distinct banding patterns and we were able to distinguish each individual chromosome even in hybrid cells. Identification of the chromosomes of alfalfa will enable scientist the opportunity to map specific genes on individual chromosomes of the improvement of alfalfa.
Technical Abstract: Chromosomes of two diploid (2n=2x=16) subspecies of Medicago sativa, ssp. caerulea and ssp. falcata, and their hybrid were studied using a N-banding technique. This study was undertaken to develop a N-banded karyotype of ssp. caerulea and ssp. falcata, and to determine if the same N-banding technique could be useful to identify individual chromosomes in hybrid cells between these two subspecies. The chromosomes of ssp. falcata have only centromeric N-bands and thus this technique is not useful for identifying individual chromosomes. However, a multitude of bands were observed in the N-banding pattern of ssp. caerulea enabling the precise identification of each of the eight pairs of chromosomes and the development of a karyotype. The differences in banding patterns between these subspecies makes it possible to distinguish chromosomes from each subspecies in hybrid cells. This is the first report of the use of N-banding to identify the diploid chromosomes of M. sativa ssp. caerulea and ssp. falcata. Using this N-banding technique it will be possible to detect the introgression of chromosomal material from ssp. falcata into cultivated alfalfa.