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Title: IDENTIFICATION OF B CHROMOSOMES USING GIEMSA BANDING IN MEDICAGO.

Author
item HOSSAIN, M
item Bauchan, Gary

Submitted to: Journal of Heredity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: We have learned from previous studies, that some of the accessions in the U. S. Germplasm Collection of Medicago species have been incorrectly classified as having 16 chromosomes. Therefore, during a routine cytogenetic investigation of chromosome counting, we discovered that two accessions, PI 115365 and PI 486207 contained three plants each that had 17 chromosomes. Upon further investigation using Giemsa C-banding techniques it was determined that the extra chromosomes were B- chromosomes. Giemsa C-banding involves the differential staining of protein which is tightly bound to DNA thus producing a characteristic band on the chromosome. B chromosomes are chromosomes which are usually much smaller than the normal chromosomes, stain well when C-banded and can cause a reduction in fertility. This is the first verified report of the existence of B chromosomes in the genus Medicago. We are in the process of isolating individual plants from the accessions which contain the B chromosome for detailed analysis. Identification of plants with B chromosomes may be used to isolate plants which are either male or female sterile for use by plant breeders in the production of hybrid alfalfa.

Technical Abstract: This is the first verified report of the existence of B chromosomes in the genus Medicago. During a routine cytogenetic investigation of diploid M. sativa ssp. falcata (L.) Arcangeli accessions contained in the US National Plant Germplasm System, we discovered two accessions PI 115365 and PI 486207 which contained three plants each that were aneuploid with 2n=17. Upon further investigation of root tip cells using C-banding techniques it was determined that the extra chromosomes were B-chromosomes that were highly heterochromatinized. The Giemsa banding pattern of the A chromosome complement in the aneuploid cells was not altered from the banding patterns which was observed in normal cells. We are in the process of isolating individual plants from the accessions which contain the B chromosome for detailed analysis.