Karyomorphology of Different Strains of Maydeae

Abstract

The present investigation was undertaken with a view to explore the variational patterns of the mitotic chromosomes of maize and to examine the intergeneric re-lationships within the Maydeae. Twenty two cultivars of maize, mostly of Indian origin and one each of teosinte and Coix were analysed, employing the refined techniques of chromosome analysis.
A wide variation was observed in the total chromatin lengths of the haploid complements. The cultivar CM-105 has the longest complement while Synthetic-B23 has the shortest complement. The karyotype is graded. The qualitative features of the ideograms are relatively uniform. The position of primary constriction varies from median to nearly submedian. Three types of chromosomes with secondary constriction were recognized, depending on the relative position of the two constrictions. Certain other variations were observed such as heteromorphic satellited chromosomes and haploid chromosome number in roots. The karyo-types of teosinte and Coix do not differ more than those of cultivars of maize.
The gross chromosome uniformity of maize is well known and is the resultant of judicious human selection. The presence of gross chromosomal aberrations as the possible cause of the wide range of length variation in the chromosome comple-ments can be ruled out. Addition or deletion of nucleotypic DNA during the for-mation of the cultivars might possibly have played a role in causing the observed variation. Differential condensation patterns of the chromosomes, reflecting dif-ferent degrees of genetic activity have also been suggested to result in alterations of chromosome characteristics. In addition, several other factors such as minor aberrations, genetic differences, inherent length variability, nature of formation of the cultivars and differential response to the treatment may have acted individually and interacted with each other to produce the wide variation. Thus it has been shown that mitotic chromosome analysis, when carried at with appropriate tech-niques, brings out significant differences in maize.
Evidences from several fields such as pachytene cytology, archaeology, paly-nology and comparative biochemistry indicate the close similarity of maize and teosinte. The present investigation does not warrant the segregation of maize and teosinte into distinct genera. The observations further support the inclusion of maize, teosinte and Coix in the Maydeae.