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Inflorescence development in a newly discovered teosinte, Zea nicaraguensis (Poaceae), from Nicaragua has been investigated using scanning electron microscopy (SEM). The SEM examination revealed that the pattern of both male and female inflorescence development was similar to previously described inflorescence in other Zea taxa. Branch primordia were initiated acropetally in a distichous pattern along the rachis of male and female inflorescences. Spikelet pair primordia bifurcated into pedicellate and sessile spikelet primordia. Predictably, pedicellate spikelet development was arrested and aborted in the female teosinte inflorescence. Organogenesis of functional spikelets and florets was similar to that previously described in maize and teosintes. The results were consistent with our hypothesis that both femininity and masculinity share a common mechanism of inflorescence development in Zea and Tripsacum and are in accord with a putative common mechanism of sex determination in the Andropogoneae. Interestingly, this population of teosinte, unique in its ability to grow in water-logged soils, showed a stable pattern of early inflorescence development. Our results also revealed the uncharacteristic presence of inflorescence polystichy in this population of Zea nicaraguensis. We propose this novel phenotypic variation raises the possibility that a domestic evolution of polystichy in maize was enabled by an occasional polystichous phenotypic in teosinte. Key words: development; evolution; inflorescence; maize; organogenesis; Poaceae; teosinte; Zea.

Some have postulated that highland Mexican maize was derived from an ancient high-altitude teosinte and that later introgression between the two taxa occurred. We used scanning electron microscopy to examine the inflorescence development in both the tassel and ear of a high-altitude Toluca teosinte. One of the most interesting observations was the presence of atypical multiranked orthostiches in the central spike of some male Toluca teosinte inflorescences. Most tassels exhibited a central spike with a pure, four-ranked, tetrastichous phyllotaxy or an intermediate (distichous/tetrastichous) phyllotaxy. A few [A.sub.1] tassels had a more typical distichous (two-ranked) central spike. Most ears showed the two-rank condition expected for teosintes. However, three ears displayed an intermediate (distichous/tristichous or distichous/tetrastichous) phyllotaxy and one ear was tetrastichous. Our analysis of spikelet and floret development in all Toluca inforescences revealed a pattern similar to that in landrace and U.S. maize, as well as to their close relatives, the teosintes. We suggest that this investigation may reveal inflorescence development in a natural maize-teosinte hybrid. This study further supports our hypothesis that both maleness and femaleness in the Zea inflorescences are derived from a common developmental pathway and underpins a proposal that andropogonoid grasses share a common pattern of inforescence development. Key words: development; inflorescence; Mexico; organogenesis; Poaceae; teosinte; Zea.

The ontogeny of staminate tassels and pistillate ears in the maize mutant Fascicled ear was examined using scanning electron microscopy. The normal pattern of inflorescence development is perturbed by the Fascicled ear mutation at the transition stage. The Fascicled ear mutation promotes the development of an abnormal transition stage axis that is both shorter and broader than the wild type. The inflorescence apical meristem then undergoes a bifurcation, and two inflorescence axes arise in place of a single axis. Each derived inflorescence apical meristem may undergo a similar perturbation sequence. This expression of the Fascicled ear mutation may be repeated one to several times, which leads to the development of a fascicled pistillate inflorescence and a fascicled central spike in the staminate inflorescence. The apical meristems of some tassel branches are also bifurcated. Subsequent organogenesis during paired-spikelet and floral development in Fascicled ear plants follows the pattern of normal maize. However, triplet spikelets are occasionally observed. The organogenic disruption by the Fascicled ear mutation that we describe will aid genetic and molecular analysis on the regulation of inflorescence development in maize and other members of the genus Zea. Key words: apical meristem; development; inflorescence; maize mutant; organogenesis; Poaceae; Zea mays.

Tassel and ear primordia were collected from greenhouse-grown specimens of the Mexican maize landrace Chapalote and prepared for scanning electron microscopic (SEM) examination. Measurements of inflorescence apices and spikelet pair primordia (spp) were made from SEM micrographs. Correlation of inflorescence apex diameter with number of spikelet ranks showed no significant difference between tassels and ears, except at the two-rank level where the ear apical meristem had a significantly smaller diameter than corresponding two-ranked tassels. Within individual inflorescences, spp in different ranks enlarged at comparable rates, although the rates from one ear to the next along the stem differed. In both tassels and ears, spp divide to form paired sessile and pedicellate spikelet primordia when the spp is [approximately equal to]150 [[micro]meter] wide; ear axes are significantly thicker than tassel axes at the time of bifurcation. The similarities in growth between ear and tassel primordia lend further support to the hypothesis that both the maize tassel and ear are derived from a common inflorescence pattern, a pattern shared with teosinte. Inflorescence primordial growth also suggests that a key character difference between teosinte and maize, distichous vs. polystichous arrangement of spikelets, may be related to size of the apical dome and/or rate of primordium production by the apical meristem. There appears to be more than a single morphological event in the shift from vegetative to reproductive growth. The evocation of axillary buds (ears) is independent of, and temporally separated from, the transition to flowering at the primary shoot apex (tassel). Key words: development; evolution; flowering; inflorescence; maize; Poaceae; Zea.

The ontogeny of tassels and ears in a perennial Mexican teosinte, Zea perennis (Hitchc.) Reeves and Mangelsdorf, was examined using scanning electron microscopy and light microscopy. Ear development follows a pattern previously described for two annual teosintes, Z. mays subsp. mexicana and Z. mays subsp. parviglumis var. parviglumis (race Balsas), and for the bisexual mixed inflorescence in a diploperennial teosinte, Z. diploperennis; it differs from that described for the ear of Z. diploperennis plants grown at the latitudes of Iowa and Wisconsin. Common bud primordia of the ear are initiated in the axil of distichously arranged bracts along the ear axis. These common primordia bifurcate to form paired pedicellate and sessile spikelet primordia. Development of the pedicellate spikelets in the ear is arrested leaving the sessile spikelets, along with the adjoining rachis segment, to form solitary grains enclosed within cupulate fruitcases. The organogenesis of the central spike of the tassel is similar to that previously described in other Zea taxa. This developmental study supports the hypothesis that both femaleness and maleness are derived from and expressed on a common background; it is consistent with the view that the maize ear was derived from the central spike of a male inflorescence terminating a primary branch of the main axis of the inflorescence.

Inflorescence organogenesis of a wild-type and a gynomonoecious (pistillate) mutant in Tripsacum dactyloides was studied using scanning electron microscopy. SEM (scanning electron microscope) analysis indicated that wild-type T. dactyloides (Eastern gamagrass) expressed a pattern of inflorescence organogenesis that is observed in other members of the subtribe Tripsacinae (Zea: maize and teosinte), family Poaceae. Branch primordia are initiated acropetally along the rachis of wild-type inflorescences in a distichous arrangement. Branch primordia at the base of some inflorescences develop into long branches, which themselves produce an acropetal series of distichous spikelet pair primordia. All other branch primordia function as spikelet pair primordia and bifurcate into pedicellate and sessile spikelet primordia. In all wild-type inflorescences development of the pedicellate spikelets is arrested in the proximal portion of the rachis, and these spikelets abort, leaving two rows of solitary sessile spikelets. Organogenesis of spikelets and florets in wild-type inflorescences is similar to that previously described in maize and the teosintes. Our analysis of gsf1 mutant inflorescences reveals a pattern of development similar to that of the wild type, but differs from the wild type in retaining (1) the pistillate condition in paired spikelets along the distal portion of the rachis and (2) the lower floret in sessile spikelets in the proximal region of the rachis. The gsf1 mutation blocks gynoecial tissue abortion in both the paired-spikelet and the unpaired-spikelet zone. This study supports the hypothesis that both femaleness and maleness in Zea and Tripsacum inflorescences are derived from a common developmental pathway. The pattern of inflorescence development is not inconsistent with the view that the maize ear was derived from a Tripsacum genomic background. Key words: development; Eastern gamagrass; gynomonoecious mutant; inflorescence; organogenesis; Poaceae; Tripsacum dactyloides.