Chromosome C‐banding of the teosinte Zea nicaraguensis and comparison to other Zea species

摘要

The genus Zea is divided into two sections, section Zea consisting of the four subspecies Zea mays L. ssp mays, Zea mays L. ssp. mexicana (Schrad.) H.H. Iltis, Zea mays ssp. parviglumis H.H. Iltis & J.F. Doebley and Zea mays ssp. huehuetenangensis (H.H. Iltis & J.F. Doebley) J.F. Doebley and section Luxuriantes consisting of Z. diploperennis H.H. Iltis, J.F. Doebley & R. Guzman, Z. perennis (Hitch.) Reeves & Mangelsd., Z. luxurians (Durieu & Asch.) R.M. Bird and the recently discovered Z. nicaraguensis H.H. Iltis & B.F. Benz (Molina and Garcia 1999; Iltis and Benz 2000). The wild species of the genus Zea have the common name teosinte.Both cultivated maize and the teosinte species are diploids (2n=20) with a tetraploid origin (except for Z. perennis which is a tetraploid) with the basic chromosome number X=10 (Molina and Garcia 1999). The chromosome number of Z. nicaraguensis has not been reported before. Today, this species is found at only two locations in Pacific Coastal Nicaragua, but was much more common and widespread just some 20?years ago. Young plants of Z. nicaraguensis are consumed by cattle while mature plants, which can grow as high as 5?m, are used to make fences and shelters. The species occurs at 6–15?m above sea level, and has the ability to grow in standing or slowly moving water. Because of this ability, due to a high capacity to form root aerenchyma and adventitious roots, it may be useful in wide hybridisations with maize, in order to improve maize growth in water-logged soils (Iltis and Benz 2000; Mano et al. 2006).Z. nicaraguensis is to a large extent an unutilised genetic resource and its properties in terms of adaptation, disease resistance etc. have to be phenotypically and genetically characterized in order to determine its potential in maize improvement. Crosses between maize and Z. nicaraguensis have already been performed and hybrids have been obtained in an ongoing project of the authors. Mano et al. (2005) have in teosinte identified Quantitative Trait Loci (QTL) for adventitious root formation and efforts to transfer such QTLs from teosinte into maize are underway (Mano et al. 2006).The closest relative to Nicaraguan teosinte, Z. nicaraguensis, is the Guatemalan teosinte, Z. luxurians (Doebley and Iltis 1980). The two species show close morphological similarity but the developmental behaviour differs considerably between the two, supporting a taxonomic segregation. Nicaraguan teosinte has longer and more abundant tassel branches, a larger number of spikelets per branch and a habitat differing from its Guatemalan counterpart (Iltis and Benz 2000).The aims of this study was (1) to verify the chromosome number of Z. nicaraguensis, (2) to compare the C-banding pattern of Z. nicaraguensis with that of its close relative Z. luxurians as well as with Z. diploperennis and cultivated maize in order to see if similarities in banding pattern reflect their relationships.