MULTIPLE CHARACTER ANALYSIS AND CHROMOSOME STUDIES IN THE TRIPSACUM LANCEOLATUM COMPLEX.

The genus Tripsacum is related to maize (Zea mays L.), one of the important crop plants of the world. Even though natural hybrids of maize and Tripsacum have not been reported so far, these two genera can be crossed artificially. Based on cytogenetic studies of maize-Tripsacum and maize-teosinte hybrids, Mangelsdorf and Reeves (1931, 1939) proposed that Tripsacum introgression played an important role in the evolution of maize both directly and via teosinte. Since the original studies of Mangelsdorf and Reeves, several investigators have repeated the hybridization and studied the F1 and backcross progenies of maize-Tripsacum hybrids (Randolph, 1950; Galinat, 1961, 1962; Galinat and Mangelsdorf, 1965, 1966; Maguire, 1957, 1960, 1961, 1962; Chaganti, 1965). The cytogenetic data obtained from these studies established that synapsis and crossing-over takes place between the chromosomes of maize and Tripsacum (Mangelsdorf and Reeves, 1939; Maguire, 1957; Chaganti, 1965). Several homologous loci have been discovered between maize and Tripsacum (Chaganti, 1965; Maguire, 1962). When a segment of Tripsacum chromosome was exchanged for a corresponding segment of maize chromosome, the Tripsacum segment was found to take over the function of the maize segment; when this segment was brought to homozygous condition the plants were found to be fertile and morphologically different (Maguire, 1961). The archaeological and botanical evidence that has accumulated in the quarter of a century since Mangelsdorf and Reeves reported their results has firmly established the presence and importance of Tripsacum introgression in archaeological and modern races of maize (Mangelsdorf, 1961; Mangelsdorf et al., 1964; Wellhausen et al., 1952). Recently Galinat et al. (1964) proposed that Tripsacum itself originated as an amphidiploid of wild maize and Manisuris. This hypothesis is based on morphological and cytogenetic studies. The evidence suggests that nine chromosomes of maize possess at least one recessive allele for the corresponding loci situated on nine of the 18 chromosomes of Tripsacum thus showing the possible presence of a genome of maize in Tripsacum. These observations make the relationship between Tripsacum and maize much closer than had been thought. In view of this close relationship, an understanding of the evolutionary trends in Tripsacum is essential to a better understanding of the phylogenetic relationships of Zea (maize and teosinte) and Tripsacum. Even though a considerable amount of information is available on the cytogenetics of maize-Tripsacum hybrids and on the presence of Tripsacum introgression in maize, until recently the information on the genus itself was fragmentary (see Tantravahi, 1968). The genus Tripsacum contains nine recognized species, all of which are native to the New World. The range of their distribution extends from northern South America through Central America and Mexico into the United States (Fig. 1). Polyploidy has played an important role in the evolution of the genus. There are four diploid (2n = 36) species (T. floridanum Porter ex. Vasey; T. australe Cutler and Anderson; T. maizar Hernandez-Xolocotzi and Randolph; T. zopilotense Hernandez-Xolocotzi and Randolph). Randolph (unpublished) considers that there may be naturally occurring autotetraploid