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A trispecific hybrid, MTP (hereafter called tripsazea), was developed from intergeneric crosses involving tetraploid Zea mays (2n = 4x = 40, genome: MMMM), tetraploid Tripsacum dactyloides (2n = 4x = 72, TTTT), and tetraploid Z. perennis (2n = 4x = 40, PPPP). On crossing maize-Tripsacum (2n = 4x = 56, MMTT) with Z. perennis, 37 progenies with varying chromosome numbers (36-74) were obtained, and a special one (i.e., tripsazea) possessing 2n = 74 chromosomes was generated. Tripsazea is perennial and expresses phenotypic characteristics affected by its progenitor parent. Flow cytometry analysis of tripsazea and its parents showed that tripsazea underwent DNA sequence elimination during allohexaploidization. Of all the chromosomes in diakinesis I, 18.42% participated in heterogenetic pairing, including 16.43% between the M- and P-genomes, 1.59% between the M- and T-genomes, and 0.39% in T- and P-genome pairing. Tripsazea is male sterile and partly female fertile. In comparison with previously synthesized trihybrids containing maize, Tripsacum and teosinte, tripsazea has a higher chromosome number, higher seed setting rate, and vegetative propagation ability of stand and stem. However, few trihybrids possess these valuable traits at the same time. The potential of tripsazea is discussed with respect to the deployment of the genetic bridge for maize improvement and forage breeding.

—The wild species of the genus Zea comprise nine different taxa, including annual and perennial, diploid and tetraploid species, distributed from northern Mexico to Costa Rica. Due to the great variability existing among species, the aim of this work was to evaluate the morphological and climatic variability patterns and phylogenetic relationships among species, based on morphological characters. Two hundred and seventy-six populations of known species and races were included; 15 individuals per population were planted. From each individual, 19 morphological and physiological traits were measured, and at each collection site 23 climatic descriptors were obtained. Both data sets were analyzed with multivariate analysis. For the phylogenetic analysis 17 morphological variables were transformed to character states using GAP-WEIGHTING. With multivariate analyses, it was possible to determine the existence of well-defined groups. Species, and races of different subspecies, were found to be clearly delimited by geographic regions, climatic characteristics, altitudes, and distinct morphological features. The phylogenetic relationships found are congruent with those identified in similar studies based on molecular data. Morphological data on their own cannot give enough information to infer divergence times. In this context, multivariate and phylogenetic analyses with morphological data are taxonomically of great importance for identifying species and subspecies of genus Zea. At species level, the study has added elements to distinguish between Zea diploperennis from the states of Nayarit and Jalisco, between Zea perennis from Michoacán and Jalisco, and between Zea luxurians from Oaxaca and Guatemala.

El teocintle representa una fuente importante de genes para el mejoramiento del maíz (Zea mays L.); sin embargo, poco se ha avanzado en la caracterización de sus respuestas a diversas condiciones ambientales, incluyendo el desarrollo del teocintle en función de la temperatura, siendo ésta una variable clave para su adaptación y distribución. La temperatura base (Tb), temperatura óptima (To) y temperatura umbral máxima (Tu) son conocidas también como temperaturas cardinales del desarrollo y son particulares para cada especie, genotipo y etapa fenológica. El objetivo del presente estudio fue determinar las temperaturas cardinales de poblaciones de los teocintles Zea perennis, Zea diploperennis, Zea mays subsp. mexicana razas Chalco, Durango, Mesa Central y Nobogame y Zea mays subsp. parviglumis o raza Balsas. Se utilizaron datos de experimentos de campo realizados entre 1986 y 2005 donde se monitorearon datos de días a antesis (F), datos de temperatura y precipitación. Se utilizaron modelos lineales y curvilíneos para explicar la variación de la tasa de desarrollo de la etapa siembra-antesis (1/F) en función de la variación de la temperatura media (Tm) del período siembra-floración. Los resultados mostraron que la relación entre Tm y 1/F es descrita por una función curvilínea, ajustándose en todos los casos un modelo cuadrático-exponencial, con un valor de r2> 0.73. El valor de Tb varió de 8.02 a 14.31 °C, el de To entre 23.5 y 31.67 °C y el de Tu entre 29.43 y 40.61 °C. Se concluye que los valores de temperaturas cardinales del teocintle varían entre y dentro de razas, lo que indica adaptación a diversas condiciones térmicas para las razas de teocintle estudiadas.

Little is known about parasitoids that attack insect pests on wild host plants, including wild teosintes. Sentinel teosinte plants with eggs of the specialist herbivore pest, the corn leafhopper, Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae), were used to attract and capture egg parasitoid species in natural habitats of annual teosinte Zea mays ssp. parviglumis Iltis & Doebley, which is the direct ancestor of maize (Zea mays ssp. mays L.), and perennial teosinte Zea perennis (Hitchc.) Reeves & Mangelsdorf in central Mexico. In annual teosinte, eggs of D. maidis were parasitized by Anagrus incarnatus Haliday and Anagrus columbi Perkins (Hymenoptera: Mymaridae), as well as Paracentrobia sp. near subflava (Girault) and Pseudoligosita sp. near longifrangiata (Viggiani) (Hymenoptera: Trichogrammatidae); in perennial teosinte, they were parasitized by A. incarnatus and Pseudoligosita sp. near longifrangiata. All the egg parasitoids, recorded for the first time from wild teosintes, have been previously known from the same leafhopper pest on cultivated maize. Thus, their conservation in wild teosinte habitats may be important for enhancing natural biological control of the corn leafhopper in adjacent maize fields.

Invertebrate herbivores prefer younger over older plant stages. Therefore, defensive traits against herbivores during early plant ontogeny are important. Defensive chemical and physical traits are well-studied in domesticated plants, but not in their wild relatives. Little is known about the function of trichomes, a physical defense against herbivore arthropods that damage cultivated plants and their wild ancestors. Maize is one of the most important crops in the world, but few studies have been conducted on the physical defenses during early ontogeny of maize and its wild relative teosinte. Therefore, the objective of this study was to characterize the density of trichomes (macrohairs) in maize and teosintes, and to evaluate the chewing damage by Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) larvae on the 6-leaf stage of 1) perennial teosinte Zea perennis (Poaceae), 2) annual teosinte Zea mays ssp. parviglumis , 3) landrace maize, and 4) on the 2-leaf stage of the landrace maize. Significantly less damage occurred in both teosinte species, which showed pubescence (trichomes) on the upper leaf-blade, but not on the midrib leaf surface. The highest trichome density was found on Z. perennis , followed by Z. mays ssp. parviglumis at the 6-leaf stage. No trichomes were found on the landrace maize, at the 6-leaf stage or 2-leaf stage. Results suggest that trichomes play an important role in preventing damage by chewing larvae on the ancestors of maize. Genes that promote macrohair initiation in teosintes during early vegetative development could be incorporated into maize plants in the future.

Little is known about insect pest ontogeny, with respect to fecundity, on domesticated plants and their wild relatives, and the effect of fecundity on parasitoids. The aim was to determine fecundity in young (2 wk old) and mature (8 wk old) females of the pest Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae) on maize, Zea mays ssp. mays , and its wild relative, teosinte. The effect of fecundity on parasitoid attraction was also evaluated. First, the fecundity of young D. maidis females and their attractiveness to parasitoids was evaluated in the native maize race “maiz ancho” and in the teosinte Zea perennis . Next, the fecundity of mature females and their attractiveness to parasitoids was evaluated in the native maize race “maiz ancho” at two juvenile stages, and in the teosintes Zea mays ssp. parviglumis and Z. perennis . Whereas young females laid more eggs on maize than on Z. perennis , mature females laid similar numbers of eggs on all plants studied. Anagrus incarnatus Haliday (Hymenoptera: Mymaridae) was the most abundant egg parasitoid. Eggs from young versus mature D. maidis females attracted more parasitoids. Furthermore, more parasitoid adults emerged from eggs produced by young D. maidis females on maize than on Z. perennis , whereas no difference was seen in the number of parasitoid adults emerging from eggs produced by mature D. maidis females from any of the four plant treatments. These results indicate that fecundity changes with herbivore pest age and egg parasitoid attraction depends on herbivore density; in this case, attraction was higher for young D. maidis females.

Tripsacum dactyloides is closely related to Zea mays since Zea perennis and the MTP tri- species hybrid have four possible reproductive modes. Eastern gamagrass (Tripsacum dactyloides L.) and tetraploid perennial teosinte (Zea perennis) are well known to possess genes conferring resistance against biotic and abiotic stresses as well as adaptation to flood and aluminum toxic soils. However, plant breeders have been hampered to utilize these and other beneficial traits for maize improvement due to sterility in their hybrids. By crossing a tetraploid maize-inbred line × T. dactyloides, a female fertile hybrid was produced that was crossed with Z. perennis to yield a tri-genomic female fertile hybrid, which was backcrossed with diploid maize to produce BC1 and BC2. The tri-genomic hybrid provided a new way to transfer genetic material from both species into maize by utilizing conventional plant breeding methods. On the basis of cytogenetic observations using multi-color genomic in situ hybridization, the progenies were classified into four groups, in which chromosomes could be scaled both up and down with ease to produce material for varying breeding and genetic purposes via apomixis or sexual reproduction. In the present study, pathways were found to recover maize and to obtain specific translocations as well as a speedy recovery of the T. dactyloides–maize addition line in a second backcross generation. However, phenotypes of the recovered maize were in most cases far from maize as a result of genetic load from T. dactyloides and Z. perennis, and could not be directly used as a maize-inbred line but could serve as an intermediate material for maize improvement. A series of hybrids was produced (having varying chromosome number, constitution, and translocations) with agronomic traits from all three parental species. The present study provides an application of overcoming the initial interspecific barriers among these species. Moreover, T. dactyloides is closely related to Z. mays L. ssp. mays since Z. perennis and the MTP tri- species hybrid have four possible reproductive modes.

Cytological diploidization process is different in autopolyploid and allopolyploid species. Colchicine applied at the onset of meiosis suppresses the effect of pairing regulator genes resulting multivalents formation in bivalent-forming species. Colchicine treated maizes (4x = 2n = 20, AmAmBmBm) showed up to 5IV, suggesting pairing between chromosomes from genomes homoeologous Am and Bm. In untreated individuals of the alloautooctoploid Zea perennis (8x = 2n = 40, ApApAp´Ap´Bp1Bp1Bp2Bp2) the most frequent configuration was 5IV +10II (formed by A and B genomes, respectively). The colchicine treated Z. perennis show up to 10IV revealing higher affinity within genomes A and B, but any homology among them. These results suggest the presence of a paring regulator locus (PrZ) in maize and Z. perennis, whose expression is suppressed by colchicine. It could be postulated that in Z. perennis, PrZ would affect independently the genomes A and B, being relevant the threshold of homology, the fidelity of pairing in each genomes and the ploidy level. Cytological analysis of the treated hexaploid hybrids (6x = 2n = 30), with Z. perennis as a parental, strongly suggests that PrZ is less effective in only one doses. This conclusion was reinforced by the homoeologous pairing observed in untreated dihaploid maizes, which showed up to 5II. Meiotic behaviour of individuals treated with different doses of colchicine allowed to postulate that PrZ affect the homoeologous association by controlling entire genomes (Am or Bm) rather than individual chromosomes. Based on cytological and statistical results it is possible to propose that the cytological diploidization in Zea species occurs by restriction of pairing between homoeologous chromosomes or by genetical divergence of the homoeologous chromosomes, as was observed in untreated Z. mays ssp. parviglumis. These are independent but complementary systems and could be acting jointly in the same nucleus. Fil: Poggio, Lidia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: González, Graciela Esther. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina

The present work compares the molecular affinities, revealed by GISH, with the analysis of meiotic pairing in intra-and interspecific hybrids between species of Zea obtained in previous works. The joint analysis of these data provided evidence about the evolutionary relationships among the species from the paleopolyploid genus Zea (maize and teosintes). GISH and meiotic pairing of intraspecific hybrids revealed high genomic affinity between maize (Zea mays subsp. mays) and both Zea mays subsp. parviglumis and Zea mays subsp. mexicana. On the other hand, when Zea mays subsp. huehuetenanguensis DNA was probed on maize chromosomes, a lower affinity was detected, and the pattern of hybridization suggested intergenomical restructuring between the parental genomes of maize. When DNA from Zea luxurians was used as probe, homogeneous hybridization signals were observed through all maize chromosomes. Lower genomic affinity was observed when DNA from Zea diploperennis was probed on maize chromosomes, especially at knob regions. Maize chromosomes hybridized with Zea perennis DNA showed hybridization signals on four chromosome pairs: two chromosome pairs presented hybridization signal in only one chromosomal arm, whereas four chromosome pairs did not show any hybridization. These results are in agreement with previous GISH studies, which have identified the genomic source of the chromosomes involved in the meiotic configurations of Z. perennis × maize hybrids. These findings allow postulating that maize has a parental genome not shared with Z. perennis, and the existence of intergenomic restructuring between the parental genomes of maize. Moreover, the absence of hybridization signals in all maize knobs indicate that these heterochromatic regions were lost during the Z. perennis genome evolution. Fil: González, Graciela Esther. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Poggio, Lidia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina

Allopolyploidization plays the special role in the evolution of many crops. Moreover, the evolution in early stage of some allopolyploidization events is predicted to be effected by nuclear-cytoplasmic interactions. Maize and teosintes are well model system for study of genetic recombination in allopolyploidization. In order to investigate the effects of genome organization and cytoplasm on genome evolution in newly synthesized allopolyploids (neoallopolyploids), a series of neoallopolyploids were produced by reciprocal crosses of maize and Zea perennis. By using dual-color genomic in situ hybridization, intra- and intergenomic meiosis pairing of these polyploids were quantified and compared with regard to its genome organization and cytoplasm background. In the four neoallopolyploids, the stability of maize genome is consistently lower than that of Z. perennis genome. Additional, the stability of maize genome is affected by genome ploidy. The cytoplasm, genome composition and their interaction do have the special role in chromosome paring and the meiosis behaviors in Zea allopolyploids vary significantly and showed non-diploidization. Z. perennis cytoplasm may give a relatively relaxed environment for maize genome.

Hybridization, which allows for gene flow between crops, is difficult between maize and Zea perennis. In this study, we aim to initiate and study gene flow between maize and Z. perennis via a special aneuploid plant (MDT) derived from an interspecific hybrid of the two species. The chromosome constitution and morphological characters of MDT as well as certain backcross progenies were examined. Results from genomic in situ hybridization (GISH) indicate that aneuploid MDT consisted of nine maize chromosomes and 30 Z. perennis chromosomes. The backcross progenies of MDT×maize displayed significant diversity of vegetative and ear morphology; several unusual plants with specific chromosome constitution were founded in its progenies. Some special perennial progeny with several maize chromosomes were obtained by backcrossing MDT with Z. perennis , and the first whole chromosome introgression from maize to Z. perennis was detected in this study. With this novel material and method, a number of maize-tetraploid teosinte addition or substitution lines can be generated for further study, which has great significance to maize and Z. perennis genetic research, especially for promoting introgression and transferring desirable traits.

This project examines the relationships within the genus Zea using complete plastid genomes (plastomes). While Zea mays has been well studied, congeneric species have yet to be as thoroughly examined. For this study four complete plastomes and a fifth nearly complete plastome were sequenced in the five species (Zea diploperennis, Zea perennis, Zea luxurians, Zea nicaraguensis, and Zea mays subsp. huehuetenangensis) by Sanger or next-generation methods. An analysis of the microstructural changes, such as inversions, insertion or deletion mutations (indels) and determination of their frequencies were performed for the complete plastomes. It was determined that 193 indels and 15 inversions occurred across the examined plastomes of Zea. Tandem repeat indels were the most common type of microstructural change observed. Divergence times were estimated using a noncorrelated relaxed clock method. Divergence dates for specific nodes relative to Zea were calculated to fall between 38,000 years before present (YBP) for the subspecies included in this study and 23,000 YBP for section Luxuriantes included in this study. The stem lineage of all Zea species was calculated to have diverged at 176,000 YBP. The calculated mutation rates for the genus fell within the range of 1.7E-8 to 3.5E-8 microstructural changes per site per year. These rates of change are not uniform, despite the close relationships of taxa in this study. Phylogenomic analyses using full plastome alignments were also conducted to compare tree topologies from different types of mutations. In most cases, the previous work examining Zea mitochondrial and nuclear data was confirmed.

The genus Zea (teosinte) has a native distribution from Mexico to Nicaragua (Meso-America region) and studies on teosinte species may help improve our understanding of maize genetics, population genetics, genome evolution and crop evolution. Moreover, since F1 hybrids between teosinte and maize are fertile, all teosinte species can potentially contribute to maize breeding in the form of traits such as resistance or tolerance to heavy metals in the soil and other adverse environmental conditions. Gene flow between maize and teosinte occurs in Mexico and Central America. This study analysed the genetic diversity of teosintes by using the microsatellite technique on a total of 120 individuals from six different species and 21 Simple Sequence Repeats (SSR). A total of 109 alleles were found and the number of alleles per locus ranged from 2 to 7. The genetic diversity varied between all species from 0.514 to 0.572, with a mean value of 0.548 (Nei index). Rare and unique alleles were detected in all species, with the highest frequencies found in Zea diploperennis Iltis, Doebley et Guzman, Zea perennis (Hitchc.) Reeves et Mangelsdorf and Zea nicaraguensis Iltis et Benz, which had more than seven rare alleles each. Analysis of molecular variance revealed that 19.87% of the variation between species was statistically significant (P

Adaptation of crops to climate change has motivated an increasing interest in the potential value of novel traits from wild species; maize wild relatives, the teosintes, harbor traits that may be useful to maize breeding. To study the ecogeographic distribution of teosinte we constructed a robust database of 2363 teosinte occurrences from published sources for the period 1842-2016. A geographical information system integrating 216 environmental variables was created for Mexico and Central America and was used to characterize the environment of each teosinte occurrence site. The natural geographic distribution of teosinte extends from the Western Sierra Madre of the State of Chihuahua, Mexico to the Pacific coast of Nicaragua and Costa Rica, including practically the entire western part of Mesoamerica. The Mexican annuals Zea mays ssp. parviglumis and Zea mays ssp. mexicana show a wide distribution in Mexico, while Zea diploperennis, Zea luxurians, Zea perennis, Zea mays ssp. huehuetenangensis, Zea vespertilio and Zea nicaraguensis had more restricted and distinct ranges, representing less than 20% of the total occurrences. Only 11.2% of teosinte populations are found in Protected Natural Areas in Mexico and Central America. Ecogeographical analysis showed that teosinte can cope with extreme levels of precipitation and temperatures during growing season. Modelling teosinte geographic distribution demonstrated congruence between actual and potential distributions; however, some areas with no occurrences appear to be within the range of adaptation of teosintes. Field surveys should be prioritized to such regions to accelerate the discovery of unknown populations. Potential areas for teosintes Zea mays ssp. mexicana races Chalco, Nobogame, and Durango, Zea mays ssp. huehuetenangensis, Zea luxurians, Zea diploperennis and Zea nicaraguensis are geographically separated; however, partial overlapping occurs between Zea mays ssp. parviglumis and Zea perennis, between Zea mays ssp. parviglumis and Zea diploperennis, and between Zea mays ssp. mexicana race Chalco and Zea mays ssp. mexicana race Central Plateau. Assessing priority of collecting for conservation showed that permanent monitoring programs and in-situ conservation projects with participation of local farmer communities are critically needed; Zea mays ssp. mexicana (races Durango and Nobogame), Zea luxurians, Zea diploperennis, Zea perennis and Zea vespertilio should be considered as the highest priority taxa.

Waxy maize is a special type of cultivated maize and has grown in China for long history. However, the evolution and origin of waxy maize still remain unknown. We analyzed the origin and evolution of waxy maize by sampling DNA sequences from four taxa with eight populations: waxy maize and other maize cultivars from Southwest China or America (Zea mays L. ssp. mays), parviglumis (Z.mays L. ssp.parviglumis Iltis et Doebley), three more distant species within this genus (Z. luxurians (Durieu et Ascherson) Bird, Zea perennis (Hitchcock) Reeves et Mangelsdorf, and Zea diploperennis Iltis, Doebley et Guzman), and a representative of sister genus (Tripsacum dactyloides L.). We sequenced 20 sequences and downloaded 26 sequences from NCBI for the glb1 locus, which encodes a nonessential seed storage protein. Within the Zea genus samples, the waxy maize has the minimum sequence diversity, which contains 31.1% of the level of diversity of parviglumis and 58.5% of the level of diversity of normal maize from Southwest China. Sequence variation within glb1 locus is consistent with neutral evolution in all four taxa according to Tajima’D test. From the NJ tree for glb1 sequences waxy maize formed two main groups which are intermixed with normal maize sequences. These results suggest that the Chinese waxy maize originate from a single gene mutation from normal maize. Combined with the history of maize dispersal in China we can even think that Chinese waxy maize was divergenced from Chinese flint maize.

Propagation of perennial diploid teosinte, Zea diploperennis Iltis, Doebley and Guzman (2n = 2x = 20), and tetraploid teosinte, Z. perennis (Hitchc.) Reeves and Magelsdorf (2n = 4x = 40), is limited by seed availability. For plants grown in the field, a photoperiod response delays flowering until fall, and seeds may not reach maturity. The objective of this study was to develop an in vitro micropropagation protocol for field grown teosinte. Shoot proliferation was induced from nodes split longitudinally and plated on Murashige and Skoog's (MS) medium supplemented with 5 μM 6-benzyl amino purine and 3% (w/v) sucrose. Both species possess a single axillary bud that generated multiple plants on division. Rooting of shoots was achieved in half-strength MS medium with and without the addition of 0.4 μM indole-3-butyric acid and 2% (w/v) sucrose. Nodes and younger branches of the tetraploid generated significantly more plants than those of the diploid.

In this study we have analysed and compared the genomic composition, meiotic behaviour, and meiotic affinities of Zea perennis and Zea mays ssp. mays. To do so we studied the parental taxa and the interspecific hybrid Zea perennis x Zea mays ssp. mays, using classical cytogenetic methods, as well as GISH and FISH. GISH enabled us to recognize the genomic source of each chromosome involved in the meiotic configurations of this hybrid, and established the genomic affinities between their parental species. The results obtained here reinforce the hypothesis of the amphiploid origin of Zea perennis and, together with previous research, indicate that the chromosomes with divergent repetitive sequences in maize and Zea luxurians could be the remnants of a relict parental genome not shared with Zea perennis.

To transfer desirable characters from perennial teosinte [Zea perennis (Hitchc.) Reeves & Mangelsd.] into maize (Z. mays L.), we have generated an interspecific hybrid and its backcross generations (BC 1 F 3 ). The maize x perennial teosinte BC 1 F 3 (MZI202) resembled maize, with chromosome number 2n = 20. MZI202 was studied by multicolor genomic in situ hybridization (McGISH) and simple-sequence repeat (SSR) microsatellites markers. The McGISH experiments provided direct evidence that MZI202 was a maize-perennial teosinte substitution line with introgression of three alien chromosomes from perennial teosinte. The SSR assay further confirmed that a single chromosome 6 and the pair of chromosome 10 of maize were replaced by perennial teosinte chromosomes in MZI202.

Genomic formulae, fertility, chromosome pairing, and the cryptic intergenomic pairing (induced by using diluted colchicine solution) were analysed in the tri-hybrid (MDP), obtained by crossing DP40 (2n=40, which was inferred in previous studies to have originated from the fusion of an unreduced gamete of Zea diploperennis with a normal gamete of Z. perennis) with the maize inbred line Zm40 (2n=40). MDP (2n=40) showed a higher fertility (90% of the seeds are viable) than Zm40 (60%) and DP40 (80%). A regular migration of 20 chromosomes to each pole occurred in 92% of the cells in anaphase I, while bridges were observed in the other 8% of the cells. When Zm40 was used as female of the crossing (Zm40×DP40), ears were similar to corn. Conversely, ears resembled those of the wild species when cytoplasm was donoured by Zd. Then, it can be stated the existence of cytoplasmic influence on MDP ear type. MDP had almost no I or III, with an average of 0.04I+10.90II+0.01III+4.50IV. The most frequent meiotic configuration was 10II+5IV (43.93% of the cells). On average, 33.81 chiasmata/cell were observed (17.34, 0.05 and 16.42 average numbers of chiasmata/cell in bivalents, trivalents and tetravalents, respectively). It can be inferred that the 5IV were the product of homoeologous chromosome pairing of A genomes from the three species. On the other hand, the 10II configuration suggests separate pairing of the 5 homologous B chromosomes from maize and the 5 homoeologous B chromosomes from Zp and Zd.

Two patterns of plant defense gene evolution are emerging from molecular population genetic surveys. One is that specialist defenses experience stronger selection than generalist defenses. The second is that specialist defenses are more likely to be subject to balancing selection, i.e., evolve in a manner consistent with balanced-polymorphism or trench-warfare models of host-parasite coevolution. Because most of the data of specialist defenses come from Arabidopsis thaliana, we examined the genetic diversity and evolutionary history of three defense genes in two outcrossing species, the autotetraploid Zea perennis and its most closely related extant relative the diploid Z. diploperennis. Intraspecific diversity at two generalist defenses, the protease inhibitors wip1 and mpi, were consistent with a neutral model. Like previously studied genes in these taxa, wip1 and mpi harbored similar levels of diversity in Z. diploperennis and Z. perennis. In contrast, the specialist defense hm2 showed strong although distinctly different departures from a neutral model in the two species. Z. diploperennis appears to have experienced a strong and recent selective sweep. Using a rejection-sampling coalescent method, we estimate the strength of selection on Z. diploperennis hm2 to be ∼3.0%, which is approximately equal to the strength of selection on tb1 during maize domestication. Z. perennis hm2 harbors three highly diverged alleles, two of which are found at high frequency. The distinctly different patterns of diversity may be due to differences in the phase of host-parasite coevolutionary cycles, although higher hm2 diversity in Z. perennis may also reflect reduced efficacy of selection in the autotetraploid relative to its diploid relative.

The physical locations of the 5S and 45S rDNA sequences were examined in three types of teosinte, Zea mays ssp. mexicana (2n = 20), Zea diploperennis (2n = 20) and Zea perennis (2n = 40) by biotinylated fluorescence in situ hybridization (FISH). The tested materials only showed one hybridization site of 5S rDNA on their genomes, but they were different in the position of the signals. The hybridization site of Zea mays ssp. mexicana was located on the long arm of chromosome 2, indicating that it is the same as the cultivated maize in the position of 5S rDNA, while the sites of Zea diploperennis and Zea perennis were on the short arms of other chromosomes. For 45S rDNA, one hybridization site was detected at secondary constriction region of the satellite chromosomes in Zea mays ssp. mexicana and Zea diploperennis, while in Zea perennis, besides the site located at the secondary constriction region, a second site on the short arm of another chromosome pair was observed. Our results provide additional evidence for Zea mays ssp. mexicana being a subspecies of Zea mays.

To evaluate the performance of microsatellites or simple sequence repeats (SSRs) for evolutionary studies in Zea, 46 microsatellite loci originally derived from maize were applied to diverse arrays of populations that represent all the diploid species of Zea and 101 maize inbreds. Although null phenotypes and amplification of more than two alleles per plant were observed at modest rates, no practical obstacle was encountered for applying maize microsatellites to other Zea species. Sequencing of microsatellite alleles revealed complex patterns of mutation including frequent indels in the regions flanking microsatellite repeats. In one case, all variation at a microsatellite locus came from indels in the flanking region rather than in the repeat motif. Maize microsatellites show great variability within populations and provide a reliable means to measure intraspecific variation. Phylogeographic relationships of Zea populations were successfully reconstructed with good resolution using a genetic distance based on the infinite allele model, indicating that microsatellite loci are useful in evolutionary studies in Zea. Microsatellite loci show a principal division between tropical and temperate inbred lines, and group inbreds within these two broad germplasm groups in a manner that is largely consistent with their known pedigrees.

A teosinte gene or gene cluster, Teosinte crossing barrier1 (Tcb1), that restricts crossability with maize mapped 6 centiMorgans distal to sugary-1 on chromosome 4. Tcb1 is loosely linked with the gametophyte-1 locus whose Ga1-s allele, present in many popcorns, confers nonreceptivity to the pollen of other maize varieties (ga1). Full-strength Tcb1 (positive modifiers present) was nonreceptive to Ga1-s as well as to ga1 pollen. Attenuated Tcb1 (positive modifiers absent) was detectably more receptive to Ga1-s than to ga1, suggesting cross recognition between the two systems of incompatibility. Reciprocally, homozygous Ga1-s was unreceptive both to Tcb1 and tcb1 pollen, but heterozygous Ga1-s/ga1 plants were somewhat more receptive to Tcb1 than to tcb1. Discrimination by Tcb1/− females against tcb1 pollen is prezygotic, accomplished without the loss of viable ovules. When introduced into maize, Tcb1 incompatibility may be useful for isolating one category of commercial varieties from another.

Polyploidy has been an extremely common phenomenon in the evolutionary history of angiosperms. Despite this there are few data available to evaluate the effects of polyploidy on genetic diversity and to compare the relative effects of drift and selection in polyploids and related diploids. We investigated DNA sequence diversity at four nuclear loci (adh1, glb1, c1, and waxy) from the tetraploid Zea perennis and the closely related diploid Z. diploperennis. Contrary to expectations, we detected no strong evidence for greater genetic diversity in the tetraploid, or for consistent differences in the effects of either drift or selection between the tetraploid and the diploid. Our failure to find greater genetic diversity in Z. perennis may result from its relatively recent origin or demographic factors associated with its origin. In addition to comparing genetic diversity in the two species, we constructed genealogies to infer the evolutionary origin of Z. perennis. Although these genealogies are equivocal regarding the mode of origin, several aspects of these genealogies support an autotetraploid origin. Consistent with previous molecular data the genealogies do not, however, support the division of Zea into two sections, the section Zea and the section Luxuriantes.

Auxin-binding protein 1 subsp. mays (ABP1) has been suggested as a receptor mediating auxin-induced cell expansion and differentiation. In maize (Zea mays), ABP1 is encoded by a single gene, Abp1. The TATA and CAAT promoter elements as well as the transcriptional start site were previously identified and all were found to be located within a transposable element (TE),Tourist-Zm11. In this study we report the cloning and characterization of the Abp1 5′-flanking region in maize and its wild relatives, the teosintes. We provide evidence for insertion polymorphism corresponding to Tourist-Zm11 and two novel TEs, Batuta and Pilgrim. Despite this polymorphic structure, the Abp1 core promoter in maize and the teosintes is conserved, is located downstream of the TE insertions in the 5′-flanking region, and is TATA-less. We discuss the potential evolutionary impact of these TEs on the regulation of Abp1 gene expression.

Teosinte comprises different Zea species (Zea mays, Zea diploperennis, Zea perennis, Zea luxurians) that can be crossed with cultivated maize (Z. mays ssp. mays). Nine microsatellites from maize were applied to different teosinte species in order to evaluate their usefulness in marker-based exploitation of these genetic resources. The same microsatellites were tested with rye, barley, and sorghum as potential molecular markers for these species. Almost all microsatellite × teosinte combinations yielded polymerase chain reaction (PCR) fragments in the range of cultivated maize. Using an F 2 population of a cross between maize inbred A188 and an individual of Zea mays ssp. mexicana, amplification products for maize and teosinte originated from the same genomic location for each of nine microsatellites investigated. PCR fragments of reduced intensity were generally obtained by applying maize microsatellites to rye, barley and sorghum. Polymorphisms among accessions within teosinte (sub)species occurred frequently. In contrast, no polymorphisms were obtained within rye, barley, and sorghum. Hence, application of maize microsatellites to teosinte for fingerprinting or marker-assisted introgression of genomic regions from teosinte into cultivated maize appears promising.

Alien cytoplasm substitution effects on quantitative agronomic characters in maize breeding germplasm have been studied many times, but few cytoplasmic effects have been found. This research was conducted to evaluate the importance of nuclear sources of variation often confounded with cytoplasmic effects, and to study effects of substituting teosinte cytoplasms into Zea mays ssp. mays hybrids. Cytolines were developed by transferring 11 cytoplasms to maize inbreds A619 and W23 by at least six generations of backcrossing. Reciprocal testcrosses were made between cytolines and three testers as well as between A619 and W23 and the same testers. Nuclear effects on reciprocal cross differences and effects of incomplete recovery of cytoline nuclear genotypes were large enough to cause bias in estimates of cytoplasmic effects, had appropriate comparisons not been available to account for these sources of variation. The 11 teosinte cytoplasms reduced grain yield by an average of 0.20 Mg ha -1 or 2.2%. Cytoplasmic effects averaged across all cytoplasms and hybrids were not significantly different from zero for any other trait. One of 11 cytoplasms studied had stable effects on hybrid performance. Four additional cytoplasms had appreciable effects that varied widely with the nuclear genotype. Direct substitution of any of these cytoplasms into maize hybrids would not likely be of great benefit because desirable effects were generally small and difficult to predict in different nuclear-cytoplasmic combinations.

Cytoplasmic variation in maize (Zea mays L.) is known to influence qualitative phenotypes such as male sterility and teosinte-cytoplasm-associated miniature. Cytoplasmic influences on quantitative characters such as grain yield have been difficult to document. The objective of this research was to study effects of diverse teosinte cytoplasmic genomes on quantitative agronomic characters in two maize inbreds. Ten diverse cytoplasms derived from three subspecies of Z. mays and one Z. perennis cytoplasm were substituted for the cytoplasms of inbreds A619 and W23 by at least six generations of backcrossing. Inbreds with teosinte cytoplasms were compared with A619 and W23 in a replicated field trial in three environments. Five of the 11 cytoplasms had quantitative influences. Three of these five cytoplasms decreased yield, with one of the cytoplasms reducing yield of the A619 nuclear genotype by 1.07 Mg ha -1 or 20%. Many effects were specific to either the A619 or W23 nuclear background indicating that teosinte cytoplasmic genomes interacted with maize nuclear genomes. Cytoplasmic effects tended to be small and unfavorable in the context of a maize breeding program.

Little is known about the natural enemies of the leafhopperDalbulus spp. (Homoptera: Cicadellidae). Searches for its dryinid (wasps) parasitoids were made in Jalisco, Mexico. Jalisco contains the greatest number ofDalbulus species, and is considered to be near to the center of origin of this leafhopper genus and its host plants: maize, teosintes (Zea spp.) and gamagrasses (Tripsacum spp.). The dryinidGonatopus bartletti was found parasitizingD. maidis on maize and on annual teosinteZea mays spp.parviglumis. G. flavipes was found parasitizingD. elimatus on perennial teosinteZ. perennis; and a new speciesG. moyaraygozai andAnteon ciudadi parasitizingD. quinquenotatus onTripsacum pilosum andT. dactyloides. Parasitism by dryinids was found at altitudes of 680–2,000 m.Dalbulus maidis, the leafhopper species which causes the greatest losses in maize in Latin America, was found to be parasitized from 680–1,760 m. TheDalbulus species associated with annual host plants (maize andZ. mays spp.parviglumis) were parasitized by dryinids during the rainy season, while theDalbulus species associated with perennial host plants (Z. perennis andTripsacum) were parasitized by dryinids during both the rainy and dry season. The greatest diversity of dryinid parasitoids ofDalbulus spp. and the highest levels of parasitism were recorded from perennial plants, indicating that such species are reservoirs of natural enemies ofDalbulus spp.

Genetic relationship of a newly discovered teosinte from Nicaragua, Zea nicaraguensis with waterlogging tolerance, was determined based on randomly amplified polymorphic DNA (RAPD) markers and the internal transcribed spacer (ITS) sequences of nuclear ribosomal DNA using 14 accessions from Zea species. RAPD analysis showed that a total of 5,303 fragments were produced by 136 random decamer primers, of which 84.86% bands were polymorphic. RAPD-based UPGMA analysis demonstrated that the genus Zea can be divided into section Luxuriantes including Zea diploperennis, Zea luxurians, Zea perennis and Zea nicaraguensis, and section Zea including Zea mays ssp. mexicana, Zea mays ssp. parviglumis, Zea mays ssp. huehuetenangensis and Zea mays ssp. mays. ITS sequence analysis showed the lengths of the entire ITS region of the 14 taxa in Zea varied from 597 to 605 bp. The average GC content was 67.8%. In addition to the insertion/deletions, 78 variable sites were recorded in the total ITS region with 47 in ITS1, 5 in 5.8S, and 26 in ITS2. Sequences of these taxa were analyzed with neighbor-joining (NJ) and maximum parsimony (MP) methods to construct the phylogenetic trees, selecting Tripsacum dactyloides L. as the outgroup. The phylogenetic relationships of Zea species inferred from the ITS sequences are highly concordant with the RAPD evidence that resolved two major subgenus clades. Both RAPD and ITS sequence analyses indicate that Zea nicaraguensis is more closely related to Zea luxurians than the other teosintes and cultivated maize, which should be regarded as a section Luxuriantes species.

We present data on evolution of the Ac/Ds family of transposable elements in select grasses (Poaceae). An Ac-like element was cloned from a DNA library of the grass Pennisetum glaucum (pearl millet) and 2387 bp of it have been sequenced. When the pearl millet Ac-like sequence is aligned with the corresponding region of the maize Ac sequence, it is found that all sequences corresponding to intron II in maize Ac are absent in pearl millet Ac. Kimura's evolutionary distance between maize and pearl millet Ac sequences is estimated to be 0.429 +/- 0.020 nucleotide substitutions per site. This value is not significantly different from the average number of synonymous substitutions for coding regions of the Adh1 gene between maize and pearl millet, which is 0.395 +/- 0.051 nucleotide substitutions per site. If we can assume Ac and Adh1 divergence times are equivalent between maize and pearl millet, then the above calculations suggest Ac-like sequences have probably not been strongly constrained by natural selection. The level of DNA sequence divergence between maize and pearl millet Ac sequences, the estimated date when maize and pearl millet diverged (25-40 million years ago), coupled with their reproductive isolation/lack of current genetic exchange, all support the theory that Ac-like sequences have not been recently introduced into pearl millet from maize. Instead, Ac-like sequences were probably present in the progenitor of maize and pearl millet, and have thus existed in the grasses for at least 25 million years. Ac-like sequences may be widely distributed among the grasses. We also present the first 2 Ds1 controlling element sequences from teosinte species: Zea luxurians and Zea perennis. A total of 10 Ds1 elements had previously been sequenced from maize and a distant maize relative, Tripsacum. When a maximum likelihood network of genetic relationships is constructed for all 12 sequenced Ds1 elements, the 2 teosinte Ds1 elements are as distant from most maize Ds1 elements and from each other, as the maize Ds1 elements are from one another. Our new teosinte sequence data support the previous conclusion that Ds1 elements have been accumulating mutations independently since maize and Tripsacum diverged. We present a scenario for the origin of Ds1 elements.

Premeiotic colchicine treatment brings about the production of one to five quadrivalents in Zea mays ssp. mays (maize, 2n=20) and an increase in the number of quadrivalents from five to ten in Zea perennis (2n=40). The results confirm the allotetraploid nature of maize and suggest that the species possesses two homoeologous genomes (A2A2 B2B2) that fail to pair, probably due to the presence of Ph-like genes. Moreover, the autoallooctoploid nature of Zea perennis, with a genome formula A'1A'1 A″1A″1 C1C1 C2C2, is supported by the present results.

Seeds of 49 accessions of corn (Zea mays ssp. mays), 9 accessions of teosinte (Zea species that are thought to be ancestors and probable progenitors to corn), and 3 accessions of Job's tears (Coix lacryma), obtained from a germplasm repository, were ground and extracted with hexane. Whole kernel oil yields and levels of four phytonutrients (free phytosterols, fatty acyl phytosterol esters, ferulate phytosterol esters, and gamma-tocopherol) in the oils were measured. Among the seeds tested, oil yields ranged from 2.19 to 4.83 wt %, the levels of ferulate phytosterol esters in the oil ranged from 0.047 to 0.839 wt %, the levels of free phytosterols in the oil ranged from 0.54 to 1.28 wt %, the levels of phytosterol fatty acyl esters in the oil ranged from 0.76 to 3.09 wt %, the levels of total phytosterols in the oil ranged from 1.40 to 4.38 wt %, and the levels of gamma-tocopherol in the oil ranged from 0.023 to 0.127 wt %. In general, higher levels of all three phytosterol classes were observed in seed oils from accessions of Zea mays ssp. mays than in seed oils from accessions of the other taxonomic groups. The highest levels of gamma-tocopherol were observed in teosinte accessions.

The aim of this work was to analyse: a) the phenotypic and cytogenetic differences of Zea mays and Zea perennis hybrids 2n=30 and 40; b) the effect of colchicine on their chromosomes pairing in meiosis. The plant materials used for these studies were Z. mays (Zm20) 2n=20, Z. mays (Zm40) 2n=40 and Z. perennis (Zp) 2n=40 and the hybrids Zm20 ×Zp (MP30) 2n=30 and Zm40 × Zp (MP40) 2n=40. Some characteristics of Z. perennis such as rhizomes, distic ears, perennially and profuse tillering were only observed in MP40 plants. In the other hand, MP30 plants had maize like phenotype; they were annual, with 4 round ears and low tillering. Therefore, phenotypic expression of several traits depends upon the dose of genes from each parent in the hybrid. The genomic formulae proposed for these species and hybrids were Zm20: AmAm BmBm; Zm40: AmAmAmAm BmBmBmBm; Zp: ApApApAp Bp1Bp1 Bp2Bp2; MP30: AmApAp Bp1Bp2 Bm; MP40: AmAmApAp BmBm Bp1Bp2. Prezigotene colchicine treatment increased the frequency of quadrivalents in Zm20, Zp and Mp40 and trivalents in MP30. These results suggest homoeology between Bm and Bp1Bp2 genomes from maize and Zp, respectively., Facultad de Ciencias Agrarias y Forestales, Comisión de Investigaciones Científicas de la provincia de Buenos Aires

To date, mobile Mu transposons and their autonomous regulator MuDR have been found only in the two known Mutator lines of maize and their immediate descendants. To gain insight into the origin, organization, and regulation of Mutator elements, we surveyed exotic maize and related species for cross-hybridization to MuDR. Some accessions of the mexican land race Zapalote chico contain one to several copies of full-length, unmethylated, and transcriptionally active MuDR-like elements plus non-autonomous Mu elements. The sequenced 5.0-kb MuDR-Zc element is 94.6% identical to MuDR, with only 20 amino acid changes in the 93-kD predicted protein encoded by mudrA and ten amino acid changes in the 23-kD predicted protein of mudrB. The terminal inverted repeat (TIR) A of MuDR-Zc is identical to standard MuDR; TIRB is 11.2% divergent from TIRA. In Zapalote chico, mudrA transcripts are very rare, while mudrB transcripts are as abundant as in Mutator lines with a few copies of MuDR. Zapalote chico lines with MuDR-like elements can trans-activate reporter alleles in inactive Mutator backgrounds; they match the characteristic increased forward mutation frequency of standard Mutator lines, but only after outcrossing to another line. Zapalote chico accessions that lack MuDR-like elements and the single copy MuDR a1-mum2 line produce few mutations. New mutants recovered from Zapalote chico are somatically stable.

We have characterized two promoters of the cytochrome oxidase subunit 2 (cox2) gene in Zea perennis mitochondria present in maize lines. Initiation at a site 907 bases upstream of the start codon results in the major approximately 1900 nt cox2 transcript. A sequence just upstream of this site conforms to the consensus described for maize mitochondrial promoters and its transcription is correctly initiated in a maize mitochondrial in vitro transcription extract. A second transcription initiation site (-347) is used only when the dominant allele of a nuclear gene, Mct, is present and its use results in an additional, shorter major transcript. Sequences flanking the Mct-dependent transcription initiation site, which we have termed the conditional promoter of cox2 (cpc), do not fit the maize mitochondrial promoter consensus and do not function in the maize in vitro transcription extract. The cpc region does not hybridize with mitochondrial, chloroplast or nuclear DNAs from most maize or teosinte lines. However, the cpc sequence is found in the same position upstream of the cox2 gene in Zea diploperennis mtDNA and it has striking similarity to the previously reported 'ORF of unknown origin' fused to the ATPase subunit 6 gene in maize CMS-C mitochondria. cpc appears to represent a new type of mitochondrial promoter. Further analysis of both conditional and constitutive promoters should help us to better understand the control of transcription in plant mitochondria.

We have isolated a new family of moderately repetitive nucleotide sequences (about 2500 copies per haploid genome) specific to the genus Zea and absent in other graminaceous species. These sequences are interspersed in the genome and they show the same genomic organization pattern and similar copy number in all the Zea species examined. These two facts, consistency in the copy number and the same organization pattern, would indicate on the one hand that these sequences were amplified before the divergence of Zea species, and on the other hand that maize and all the teosintes could be considered as the same evolutionary population. Independent clones corresponding to the repetitive sequences have been isolated and sequenced from a genomic library of the teosinte, Zea diploperennis . The repeats, flanked by Hae III sites, are more than 70% G + C-rich, on average 253 bp long and show 78% similarity to each other. These repetitive sequences are in a highly methylated-C context and they present some features resembling those of coding sequences, such as high CpG and low TpA content, and similar codon usage to maize genes in one of the reading frames. Moreover, the repetitive probe hybridizes with RN A extracted from different tissues of maize and from teosinte, indicating that these repeats or similar ones are present in transcribed sequences.

The genus Zea is here divided into the Sect. LUXURIANTES Doebley & Iltis sect. n., including the perennials Z. diploperennis (2n = 20) and Z. perennis (2n = 40) and the annual Z. luxurians (2n = 20); and Sect. ZEA, including the wildZ. mays ssp.parviglumis andZ. mays ssp. mexicana (both 2n = 20), and Z. mays ssp. mays (2n = 20), the highly domesticated and tremendously variable derivate of the latter. This division is verified by a multivariate analysis of a large number of morphological characters of the male inflorescence. Cytogenetic and chemotaxonomic evidence supports the morphological conclusions. A consideration of the phylogeny of Zea within the conceptual framework offered by this new sectioning of the genus points convincingly to annual teosinte (Z. mays ssp. mexicana) as the ancestor of cultivated maize. THE GENUS Zea contains, according to its latest taxonomic treatment (Iltis & Doebley, 1980), six distinct taxa classified into four species: 1) Z. mays L., sensu lato, including Z. mays ssp. mays, the cultivated maize; Z. mays ssp. mexicana (Schrader) Iltis, and Z. mays ssp. parviglumis Iltis and Doebley, the latter two the widespread annual teosintes from Mexico and west central Guatemala; 2) Z. luxurians (Durieu and Ascherson) Bird, the annual teosinte from southeastern Guatemala and Honduras; 3) Z. perennis (Hitchc.) Reeves and Mangelsdorf, the tetraploid perennial teosinte; and, finally, 4) Z. diploperennis Iltis, Doebley and Guzmain, the recently discovered diploid perennial teosinte, the latter two both highly local species from southern Jalisco, Mexico. These taxa could be arranged subgenerically in several ways, depending on one's criteria. Thus, if one follows the only taxonomic system so far published (Post and Kuntze 1903; cf. Wilkes, 1967), the genus would be divided into Sect. ZEA, containing only the cultigenZ. mays sensu stricto, and Sect. EUCHLAENA (Schrader) Kuntze, containing all five remaining taxa, the teosintes. The reasons the genus was thus I Received for publication 19 October 1979; revision accepted 19 December 1979. Support for this work provided in part by grants (to H.H.I.) from NSF (BM S74-21861), the Research Committee of the Graduate School, the Davis Fund and the 0. N. Allen Herbarium Fund, Department of Botany, University of Wisconsin-Madison, and Pioneer Hi-Bred International, Inc. For help and support with various aspects of this research our thanks go to Donald Duvick, Robert Kowal, Walton Galinat, Frederick J. Hermann, Karen Lind, Norman Borlaug, and Linda Ainsworth of the Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT); and especially to Maria L. Puga, Rafael Guzman M., Enrique Estrada F., and the Instituto de Botanica, Universidad de Guadalajara, Mexico. John Lonnquist grew much of our material. D. Davidse, F. G. Gould and T. Soderstrom made helpful comments on the manuscripts. divided are obvious enough. First, not only are the gigantic, polystichous, many-seeded, nondisarticulating female ears of maize totally unique in the Andropogoneae (or, for that matter, in the Gramineae), but the slender, distichous, few-seeded, disarticulating female spikes of all teosinte species are so similar to each other as to nearly defy taxonomic discrimination. Similarly with the tassel, the male inflorescence. Maize tassels are always easily recognized by their thick and highly condensed central (terminal) spike (i.e., with many spikelets per unit length), the lateral branches in contrast being always slender and uncondensed. Teosinte tassels, on the other hand, have uniformly slender and uncondensed branches, with the central (terminal) spike scarcely if at all differentiated from the lateral branches. As a matter of fact, experienced "teosinte hunters" can soon learn to distinguish teosinte and maize from a car window at quite some distance by scanning the cornfield "skyline" with binoculars and looking for the central branch of the tassel. If uncondensed and slender, it's teosinte; if stiff and thick, it's maize! Thus, simply on the basis of spikelet arrangement in both male and female inflorescences, Kuntze's taxonomic division would seem, on the face of it, to be correct and unassailable. The uniqueness of the maize ear notwithstanding, any classification of an economic genus which places the object of human desire into one subgeneric category and all its wild relatives in another is, a priori, open to suspicion. In other words, we may state as a general principle that the fundamental systematic classification of economic genera should never be based primarily on those morphological features deliberately selected for by man. To do so leads to a taxonomy where the generally largeand many-seeded cultivars are placed in

(1988). The history and evolution of Maize. Critical Reviews in Plant Sciences: Vol. 7, No. 3, pp. 197-220.

Nineteen accessions selected from the four species and three subspecies of the genus Zea and one accession from the related genus Tripsacum were surveyed for variation with 21 restriction endonucleases. In all, 580 restriction sites were assayed in each chloroplast (cp)DNA, this representing 2.2% of the genome. Twenty-four of the 580 sites were variable in one or more of the cpDNAs. The number of nucleotide substitutions per site (p) between Zea and Tripsacum (0.0056) approximates that between other closely related angiosperm genera. The range in values of p among Zea species (0.0003-0.0024) is on the lower end of the range reported for other angiosperm genera. Analysis of the distribution of restriction site mutations throughout the genome indicated that the inverted repeat evolves more slowly than either the small or large unique sequence regions. Parsimony phylogenetic analysis of the restriction site data produced a tree consistent with isoenzymatic and morphological measures of affinity among the species. Chloroplast DNA analysis was not useful in discriminating the subspecies within Zea mays. The lack of any detectable differences between the cpDNA of maize (Z. mays subsp. mays) and some teosintes (Z. mays subsps. mexicana and parviglumis) is consistent with the hypothesis that maize is a domesticated form of teosinte. Comparison of the degree of sequence divergence for Z. mays cpDNA and the Adh1 locus suggests the latter may be evolving at 10 times the rate of the former. Comparison of rates of sequence evolution for the mitochondrial and chloroplast genomes was inconclusive and could not clarify whether these two genomes have dissimilar rates of sequence evolution.

A compromise classification of the genus Zea, reflecting both phylogeny and practical needs, recognizes six taxa, as follows: Section LUXURIANTES: Zea perennis, Zea diploperennis, Zea luxurians. Section ZEA: Zea mays ssp. mexicana (Neo-volcanic Plateau), Zea mays ssp. parviglumis Iltis & Doebley ssp. n. var. parviglumis (Rio Balsas drainage, Pacific slope from Guerrero to Jalisco), Zea mexicana ssp. parviglumis var. huehuetenangensis Iltis & Doebley var. n. (Pacific slope, western Guatemala, Prov. Huehuetenango), Zea mays ssp. mays. The new subspecies is distinguished by smaller spikelets and rachis joints, the varieties by different habitats, blooming dates and their genetic behavior in relation to cultivated Zea mays. Zea mays ssp. mexicana is the ancestor of corn. THE CULTIVATED "CORN" OR "MAIZE" of the American Indians and world commerce, Zea mays ssp. mays, is a species whose taxonomic circumscription has never been questioned. Its wild relatives, the "teosintes," however, have for quite some time now been considered by many workers to present a number of taxonomic problems. This study attempts to resolve some of these. Most modern but orthodox systems of clas

Scanning electron microscopy was used to examine the wall sculpturing of pollen from Zea mays L. ssp. mays (maize), Zea mays ssp. mexicana (Schrad.) Iltis (teosinte), Zea perennis (Hitchc.) Reeves and Mangelsdorf (perennial teosinte), and two species of Tripsacum L. The Zea taxa are shown to possess similar pollen types, with spinules scattered regularly over the exine surface. Tripsacum exhibits a distinctly reticuloid pattern, with spinules clumped into isolated lacunae. Hybrids between Zea and Tripsacum are either intermediate in exine pattern or similar to Tripsacum, depending on the genome combination.