Resumen El maíz dosmesano (Zea mays L.) es un tipo de maíz nativo utilizado en el sistema milpa de Tabasco, México, apreciado por su calidad de tortilla y por su gran adaptación a las condiciones del trópico mexicano. Es necesario generar recomendaciones de manejo agronómico para mejorar su aprovechamiento. El objetivo de este estudio fue evaluar el potencial productivo del maíz tropical dosmesano nativo de Tabasco, México bajo diferentes densidades de población, generadas con variantes de arreglos topológicos de distancia entre surcos (0.8 y 1.0 m), distancia entre matas (0.20 y 0.25 m) y número de semillas por mata (una y dos); adicionalmente, se incluyeron un testigo regional (TR) a 1.0 m entre surcos, 1.0 m entre matas y cuatro semillas/mata, y otro modificado (TRM) con 0.8 m entre surcos, 1.0 m entre matas, cuatro semillas/mata. Se utilizó un diseño experimental de bloques completos al azar con tres repeticiones, con arreglo factorial de tratamientos. Se registraron las variables días después de la siembra a 50 % de floración masculina (50 % FM) y 50 % de floración femenina (50 % FM), altura de mazorca (AM, cm), altura de planta (AP, cm), relación AP/AM, porcentaje de acame (PA), relación (AP/AM)/PA, porcentaje de plantas jorras (PPJ), porcentaje de prolificidad (PP) y rendimiento de grano (RG, kg ha-1). Se detectó interacción significativa de distancia entre surcos × número de semillas/mata para RG (P ≤ 0.01) y PPJ (P ≤ 0.01). El mayor RG (3869 kg ha-1) se observó en 1.0 m de distancia entre surcos y dos semillas por mata, con 80,000 plantas ha-1, y superó a TR que rindió 2198 kg ha-1. El mayor PPJ, 73 %, se observó en distancia entre surcos de 0.8 m y dos semillas por mata. Hubo triple interacción significativa en AP (P ≤ 0.01) y AM (P ≤ 0.01), ambas con distancia entre surcos de 0.8 m, distancia entre matas de 0.2 m y una semilla por mata, con media de 2.67 y 1.26 m, respectivamente. Existió efecto simple significativo del número de semillas por mata para PP (P ≤ 0.05), con 17 y 4 %, con una y dos semillas por mata, respectivamente. No se detectaron efectos significativos para 50 % FM, 50 % FF, PA, en la relación AP/AM y (AP/AM)/PA (P > 0.05). El RG observado indica alto potencial del cultivo bajo alta densidad poblacional, en comparación con el sistema tradicional de siembra.

Summary Bimonthly maize (Zea mays L.) is a type of native maize used in the milpa system of Tabasco, Mexico. This maize is appreciated for its tortilla quality and great adaptation to the conditions of the Mexican tropics. Recommendations for its agronomic management need to be created to improve its use. This study evaluated the productive potential of bimonthly tropical maize native to Tabasco, Mexico at different populations densities created by alteration of the distance between rows (0.8 and 1.0 m), the distance between hills (0.20 and 0.25 m) and the number of seeds per hill (one and two). A regional control (RC) at 1.0 m between rows, 1.0 m between hills and four seeds per hill, as well as a modified control at 0.8 m between rows, 1.0 m between hills and four seeds per hill were included. A randomized complete block experimental design with three replications was used, with a factorial arrangement of treatments. The recorded traits were days to 50 % anthesis (50 % A) and 50 % silking (50 % S) after planting, ear height (EH, cm), plant height (PH, cm), PH/EH ratio, lodging percentage (LP), (PH/EH)/LP ratio, barren plants percentage (BPP), prolificacy percentage (PP) and grain yield (GY, kg ha-1). A significant interaction of distance between rows × seeds per hill was detected for GY (P ≤ 0.01) and BPP (P ≤ 0.01). The highest GY, 3836 kg ha-1, was observed at 1.0 m distance between rows and two seeds per hill, with 80,000 plants ha-1, which exceeded RT controls yield of 2198 kg ha-1. The highest BPP, 73 %, was observed in rows at 0.80 m and two seeds per hill. There was significant triple interaction for PH (P ≤ 0.01) and EH (P ≤ 0.05), both in rows at 0.80 m, 0.20 m between plants, and one seed per hill, with mean 2.67 and 1.26 m, respectively. There was a significant simple effect of seed number per hill for PP (P ≤ 0.05), with 17 and 4 % for one and two seeds per hill, respectively. No significant effects were detected for 50 % A, 50 % S, LP, and the PH/EH and (PH/EH)/LP ratios (P > 0.05). The observed GY indicates a high potential for the crop under high population density, compared to the traditional planting system.

El género Tripsacum (Poaceae) tiene afinidad filogenética con el maíz y se distribuye ampliamente en América. El número básico de cromosomas es x=18 y existen poblaciones naturales desde diploides (2n=2x=36) hasta hexaploides (2n=6x=108). Las plantas de este género se reproducen de manera sexual y asexual y, en poliploides, ocurre la apomixis. Se realizó un estudio citológico en plantas con diferente nivel de ploidía. En espigas se hizo análisis de la meiosis, y de semillas se obtuvieron plántulas a las cuales se determinó el número cromosómico en ápices radicales y por cuantificación de ADN mediante citometría de flujo. Se encontraron poblaciones constituidas únicamente por triploides o tetraploides, y otras que contienen una mezcla de diploides hasta hexaploides. En diacinesis, los cromosomas de los diploides se asocian en bivalentes; en los triploides se forman univalentes, bivalentes y trivalentes; mientras que en tetraploides en univalentes, bivalentes, trivalentes y cuadrivalentes. En profase II, los diploides forman, en alta frecuencia, grupos cromosómicos segregantes de 18; los triploides desde 21 hasta 33; y los tetraploides desde 32 hasta 38. El número de cromosomas en progenies de plantas diploides fue 2x=36 y 3x=54; de triploides, 3x=54, 4x=72, 5x=90 y 6x=108; y de tetraploides, 4x=72, 5x=90 y 6x=108. Los resultados indican que los diploides tienen un origen sexual y que los triploides y tetraploides posiblemente sean apomícticos facultativos.

The Tripsacum (Poaceae) genus has phylogenetic affinity with maize and is widely distributed in America. The basic number of chromosomes is x=18, and there are natural populations ranging from diploids (2n=2x=36) to hexaploids (2n=6x=108). The plants of this genus reproduce sexually and asexually and, in polyploids, apomixis occurs. A cytological study was conducted in plants with different ploidy level. Analysis of meiosis was made in tassels, and seedlings were obtained whose chromosomal number was determined in root tips and by DNA quantification using flow cytometry. Populations made up only of triploids or tetraploids were found, and others containing a mixture from diploids to hexaploids. During diakinesis, diploid chromosomes associate in bivalents; in triploids, univalents, bivalents, and trivalents are formed; and in tetraploids, univalents, bivalents, trivalents, and quadrivalents are formed. In prophase II, the diploids form with high frequencies segregating chromosomal groups of 18; the triploids, groups from 21 to 33; and tetraploids, from 32 to 38. The chromosomal number in progenies of diploid plants was 2x=36 and 3x=54; of triploids 3x=54, 4x=72, 5x=90, and 6x=108; and from tetraploids, 4x=72, 5x=90, and 6x=108. Results indicate that the diploid individuals have sexual origin and the triploids and tetraploids may be apomictic.

O gênero Tripsacum (Poaceae) tem afinidade filogenética com o milho e se distribui amplamente na América. O número básico de cromossomas é x=18 e existem populações naturais desde diplóides (2n=2x=36) até hexaplóides (2n=6x=108). As plantas deste gênero se reproduzem de maneira sexual e asexual e, em poliplóides, ocorre a apomixia. Realizou-se um estudo citológico em plantas com diferente nível de ploidia. Foi realizada análise em espigas da meiose e das sementes foram obtidas plântulas nas quais se determinou o número cromossômico em ápices radicais e por quantificação de DNA mediante citometria de fluxo. Encontraram-se populações constituídas unicamente por triplóides ou tetraplóides, e outras que contêm uma mistura de diplóides até hexaplóides. Em diacinese, os cromossomas dos diplóides se associam em bivalentes; nos triplóides se formam monovalentes, bivalentes e trivalentes; enquanto que em tetraplóides em monovalentes, bivalentes, trivalentes e tetravalentes. Na profase II, os diplóides formam, em alta frequência, grupos cromossômicos segregantes de 18; os triplóides desde 21 até 33; e os tetraplóides desde 32 até 38. O número de cromossomas em progênies de plantas diplóides foi 2x=36 e 3x=54; de triplóides, 3x=54, 4x=72, 5x=90 e 6x=108; e de tetraplóides, 4x=72, 5x=90 e 6x=108. Os resultados indicam que os diplóides têm uma origem sexual e que os triplóides e tetraplóides possívelmente sejam apomícticos facultativos.

Phenotypic variation in different populations of Opuntia cantabrigiensis, O. leucotricha, O. rastrera, O. robusta and O. streptacantha was evaluated by examining 28 anatomical and morphologic variables through discriminant analysis. These populations are separated from each other by distances ranging between 32 and 110 km. Altitude and annual average temperature showed no variation in the study area. Discriminant analysis separated populations of O. cantabrigiensis, which is the species having the lowest density (13 individuals ha-1), whilst some populations of other Opuntia species, whose densities were as high as 1,852 individuals ha-1, overlapped. No different ploidy levels were found among populations, although we recorded levels of ploidy between species that ranged from diploid (O. rastrera) to octoploid (O. streptacantha). Therefore, phenotypic differences between populations appear to be related to the density of individuals rather than to environmental variables, given the lack of environmental gradients or change in level ploidy.

Se evaluó la variación fenotípica a través de 28 variables anatómicas y morfológicas mediante análisis discriminantes en poblaciones de Opuntia cantabrigiensis, O. leucotricha, O. rastrera, O. robusta y O. streptacantha que se encuentran separadas entre sí por distancias de entre 32 y 110 km. La altitud y la temperatura media anual no mostraron variación en el área de estudio. El análisis separa las poblaciones de O. cantabrigiensis, que es la especie con menor densidad (13 individuos ha-1), mientras que para el resto de las especies, cuyas poblaciones pueden alcanzar hasta 1,852 individuos ha-1, algunas poblaciones se yuxtaponen. No hay diferencias en los niveles de ploidía entre las poblaciones, a pesar de que se registraron niveles de ploidía entre diploide (O. cantabrigiensis) a octoploide (O. streptacantha). Por lo tanto, las diferencias fenotípicas entre las poblaciones parecen estar relacionadas con la densidad de individuos y no con variables ambientales, dada la falta de gradientes ambientales o a cambios en el nivel de ploidía de las distintas especies.

El estudio se llevó a cabo en recolectas de Rhoeo spathacea realizadas en Veracruz, Chiapas, Tabasco, Yucatán, Quintana Roo y Michoacán, México. Las plantas presentaron número diploide de cromosomas (2n=12) en mitosis. En meiosis los individuos formaron anillo y/o cadenas en metafase I, con excepción de varios mutantes desinápticos-RSD (separación de cromosomas apareados). En meiosis de Rhoeo no se observan bivalentes ni hay posibilidades de entrecruzamiento, y consecuentemente no habrá quiasmas ya que no hay cuatro cromátidas de las cuales dos deberían ser no-hermanas. Sin embargo, en anafase I hay disyunción altamente regular 6:6 que se presentan como "anillos o donas" con los brazos cortos hacia el interior de esas figuras. De la autofecundación de un mutante desináptico-RSD (GAVA 1.1) se obtuvo una progenie F2 de 123 individuos: 90 diploides-formadores de anillos y 1 acrotrisómico (2n=13). Esto es, 91 individuos "revirtieron" el comportamiento y 29 fueron diploandróginos tetraploides desinápticos (2n=24) y 3 hipertetraploides (2n=25 desinápticos). Este comportamiento diferente entre hermanos confirma que Rhoeo es dicarión: los diploides- con anillo tendrán el subgenoma A, y los tetraploides el B, que incluyen cromatidas hermanas en la restitución en segunda división (2n).

This study was carried out with collected material of Rhoeo spathacea in the states of Veracruz, Chiapas, Tabasco, Yucatan, Quintana Roo and Michoacan, Mexico. All material exhibited a diploid chromosome number (2n =12) in mitosis. In meiosis, all individuals showedring and /or chains at metaphase I. Exceptionally several desynaptic mutants resulted desynaptic - SDR (dissociation of paired chromosomes). Therefore, in meiosis Rhoeo did not exhibit synapsis in parallel-fashion instead the chromosomes are united in end-to-end (no chiasmata-) fashion. Then, there are not bivalents, no chiasmata-achiasmata- as there are not four chromatids two of which resulted sister-chromatids. But in anaphase I, there is high regular 6:6 disyuction and observed as "Rings or donuts". In which short arms are oriented to the center of those figures. From selfed a desynaptic- SDR (GAVA 1.1) mutant, a progeny of 123 individuals resulted: 90 diploid-ring forming, 1 acrotrisomic (2n=13) equally ring-forming reverts its "meiotic behavior", but 29 diplandrogynous tetraploids (2n=24) and 3 hypertetraploids (2n=25) resulted desynaptics. The cytological behaviour is due to the fact that Rhoeo Is a dikaryon: diploids-ring forming and the trisomic also and present subgenome A, but polyploids present subgenome B which includes a desynaptic gene in both sister chromatids as result of restitution at second division(2n).

Os objetivos deste trabalho foram avaliar a freqüência da poliembrionia e indentificar os seedlings zigóticos e nucelares de Citrus volkameriana usando RAPD. Cultivaram-se in vitro 25 sementes poliembriônicas e 8 monoembriônicas, por seis meses. Extraiu-se o DNA dos seedlings e usou-se em combinação com cinco primers RAPD para identificar a origem zigótica e nucelar das plântulas. Os resultados mostraram que as condições ambientais do ano afetaram significativamente (P<0,05) as características morfológicas dos frutos e o número de embriões por semente. Os índices de sementes poliembriônicas variaram nos três anos de avaliação (30,9%, 44,8% e 54,4%). As características morfológicas não se correlacionaram com a poliembrionia. A cultura in vitro possibilita que todos os embriões de cada semente cresçam, favorecendo os seedlings identificados como zigóticos. Nas sementes poliembriônicas e monoembriônicas, 25,9% e 87,5% dos seedlings, respectivamente, originaram-se sexualmente. Nem todos os seedlings zigóticos foram produzidos por embriões localizados no micrófilo das sementes poliembriônicas.

The objectives of this work were to evaluate the frequency of polyembryony, and to identify zygotic and nucellar seedlings of Citrus volkameriana using RAPD. Twenty-five polyembryonic and eight monoembryonic seeds were cultivated in vitrofor six months. DNA from seedlings was extracted and used in combination with five RAPD primers to identify zygotic or nucellar origin of the seedlings. Environmental conditions of the year affected significantly (P<0.05) the morphological characteristics of fruitsand the number ofembryos per seed. Polyembryonic seeds ranged from 30.9%, 44.8% to 54.4% over three years. Morphological characteristic was not correlated with polyembryony. In vitro culture enable all embryos of each seed to grow, favoring the percentage of seedlings identified as zygotic. In polyembryonic and monoembryonic seeds, 25.9% and 87.5% of the seedlings, respectively, were sexually originated. In polyembryonic seeds, not all zygotic seedlings were produced by small embryos located at the micropyle.