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ARS Home » Research » Publications at this Location » Publication #107541
Title: DISTRIBUTION AND CHARACTERIZATION OF HETEROCHROMATIC DNA IN 'AFRICAN' ALFALFA

Author
item Bauchan, Gary
item HOSSAIN, AZHAR - MISC

Submitted to: Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: 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. Genes are located on chromosomes, thus it is important to know which genes are located on which chromosome. We have studied the chromosomes an 'African' germplasm source which is one of the nondormant germplasm sources used in the US. We utilized chromosome banding techniques and image analysis techniques in this study. Chromosome analysis of tetraploid alfalfa revealed that alfalfa has four similar sets of chromosomes based on their chromosome morphology and chromosome banding patterns. This C-banding technique will now be applied to other alfalfa types with the expectation that the banded chromosomes will be different enough to allow us to distinguish the individual chromosomes of alfalfa. The utilization of chromosome banding and image analysis can have multiple applications in the field of cytogenetics and plant breeding. They can be used to study the evolutionary relationships and genome analysis among and between Medicago species; identification of chromosomal modifications; and the visualization of the incorporation of alien genetic material from wild species into alfalfa for the improvement of alfalfa.

Technical Abstract: A standard karyotype of tetraploid alfalfa (Medicago sativa ssp. sativa) 'African' germplasm source was constructed using the combined techniques of C-banding and image analysis. C-banding is a powerful diagnostic tool for distinguishing the homologous chromosomes of alfalfa. Chromosome analysis of tetraploid alfalfa revealed that alfalfa has four similar sets s of chromosomes based on their chromosome morphology and C-banding patterns. A standard karyotype of 'African' alfalfa consists of one set of satellited chromosomes, four sets of submetacentric chromosomes, and three sets of small metacentric chromosomes. All of the chromosomes have centromeric bands and a terminal band on the short arm. Interstitial bands were observed on each of the short arms with the exception of chromosome 7. Chromosomes 1, 2, and 3 have interstitial bands on their long arms. There exists a lot of variability in the number, intensity and location of the constitutive heterochromatic DNA, however there is not sufficient variability to make it impossible to recognize the homologous chromosomes. The 'African' karyotype of alfalfa developed in this study should become the standard for the development of additional karyotypes for diverse alfalfa populations.