Skip to main content
ARS Home » Research » Publications at this Location » Publication #118905


item Bauchan, Gary
item Campbell, Travis

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Alfalfa productivity has not increased significantly over the past several years due to the lack of knowledge of the genetics of the crop. Genes are located on chromosomes, thus it is important to know the location of the genes on chromosomes in order to manipulate and enhance genes of agronomic importance. Alfalfa chromosomes are very small and they look alike structurally thus it is very difficult to identify each individual chromosome and even more difficult to identify the location of genes on each chromosome. We therefore developed a computerized image enhancement and analysis system to enlarge the chromosomes and perfected a chromosome banding technique to identify individual chromosomes based on their unique banding pattern. We have studied the chromosomes of a 'Chilean' germplasm source which is one of the non- dormant germplasm sources used in the US. Chromosome analysis revealed that there is a lot of variability in the number, intensity and location the chromosome bands, however, it is still possible to recognize the individual chromosomes. There is a small number, 1%, of individuals that have a different chromosome number from the normal. These plants can be very helpful in determining the location of agriculturally important genes. The utilization of chromosome banding and image analysis techniques can have multiple applications for plant breeders for the improvement of alfalfa and other crops.

Technical Abstract: A cytogenetic investigation was conducted on tetraploid alfalfa (Medicago sativa ssp. sativa) 'Chilean' germplasm source (PI 536534) using the combined techniques of C-banding and image analysis. Chromosome analysis of tetraploid 'Chilean' alfalfa revealed that there are polymorphisms for heterochromatic DNA in the nineteen plants observed and there were 1% aneuploids in the population. There is a lot of variability in the number, intensity and location of the constitutive heterochromatic DNA, however, there was not sufficient variability to make it impossible to recognize the homologous chromosomes. The aneuploids were either 2n=4x+1=33 or 2n=4x-1=31with the additional or missing chromosome being the satellite chromosomes. The 'Chilean' karyotype resembles the standard karyotype of tetraploid alfalfa, however, there is a reduction in the total amount of heterochromatic DNA.