Cytogenetic studies in the genus Zea : 1. Evidence for five as the basic chromosome number

Area of Science:

• Cytogenetics
• Plant breeding
• Evolutionary biology

Background:

• The genus Zea, encompassing maize and its relatives, exhibits complex polyploidy.
• Understanding the basic chromosome number is crucial for deciphering Zea's evolutionary history and genetic relationships.

Purpose of the Study:

• To provide new cytological evidence for the basic chromosome number of the genus Zea.
• To analyze meiotic configurations in various Zea species and their hybrids.
• To investigate the phylogenetic implications of observed chromosomal behaviors.

Main Methods:

• Analysis of meiotic configurations during meiosis in Zea mays ssp. mays, Z. diploperennis, Z. perennis, and four F1 interspecific hybrids.
• Observation of bivalent (II), trivalent (III), and quadrivalent (IV) formations, along with univalents (I).
• Assessment of secondary association between bivalents at diakinesis-metaphase I.

Main Results:

• Zea mays ssp. mays (2n=20) showed regular meiosis with 10 bivalents, typical of an allotetraploid.
• Z. diploperennis (2n=20) exhibited some multivalents, suggesting segmental allotetraploid nature.
• Z. perennis (2n=40) displayed 5IV + 10II, indicative of an auto-allooctoploid.
• Interspecific hybrids showed varying configurations, with secondary associations observed in tetraploid taxa, highlighting homoeologous genome affinities.

Conclusions:

• The collective cytological data strongly support x = 5 as the basic chromosome number for the genus Zea.
• The observed polyploid patterns and interspecific hybrid behaviors provide insights into the evolutionary pathways within Zea.
• The findings contribute to a better understanding of the phylogenetic relationships among Zea species.