Karyological Study on Genetic Variation in Annual Alfalfa

  Annual species of Medicago are important pasture legumes in western parts of Iran. Due to limited karyotypic reports on annual Medicago species, the present study was conducted on accessions available in gene bank of Iran. Total length of chromosomes, size of long and short arms and their ratio were the basis for karyological measurement. Karyotypic studies showed that M. radiata 29 , M. radiata 588, M. minima 316, M. polymorpha 1123, M. orbicularis 449, M . li tiralis 1038, M. trancatulla 1146 and M. polymorpha 612, carried 2n=2x=16 chromosomes and Medicago rigidula 2n=2x=14 chromosomes. Among species with 2n=2x=14, M. rigidula 1126 had the highest total chromosomal length and M. rigidula 454 the least total length. Species M. littoralis 1038 and M. minima 316 both with 2n=2x=16, had the highest and the lowest total chromosomal length, respectively. Total chromosome length and mean of chromosome length in most of exotic species were more than those of landraces. Species and varieties with larger karyotype had larger seed size. B chromosome found only in the M. littoralis and M. polymorpha species. Satellite chromosome observed in varieties 606, 1126 and 1199 of M. rigidula, 1123 and 612 of M. polymorpha and M. radiata 588. Resultes of cluster analysis revealed that varieties and species with similar karyotypice size and mean chromosomal length, did not show any significant differences, hence they were located in one group. Factor analysis revealed that chromosomes number 5, 6, 7 (2x=14) and 7, 5, 2 (2x=16) showed maximum structural change among accessions. Karyotype symmetry were determined by using coefficient of variation (CV) and total form percentage (%TF). Resultes of CV showed that the most of variation between chromosomes belongs to M. polymorpha 612 and the least of variation between chromosom es belongs to M. rigidula 1128. According to TF, M. minima 316 had the most karyotype symmetry and M. rigidula 1126 showed the least karyotype symmetry.