Paenibacillus polymyxa NMA1017 as a potential biocontrol agent of Phytophthora tropicalis, causal agent of cacao black pod rot in Chiapas, Mexico.

Cacao represents an important source of income for farmers in the south of Mexico. However, phytosanitary problems have disrupted the production over the years. The use of antagonistic microorganisms as biocontrol agents might improve the production of cacao. In this study, Paenibacillus polymyxa NMA1017, isolated from the rhizosphere of Opuntia ficus-indica L., was used as a biocontrol agent for black pod rot of Theobroma cacao L. cultivated in Chiapas, Mexico. The experiments were carried in vitro and in vivo using pear fruit (Pyrous communis) as model and cacao pods in the field, respectively. The effect of NMA1017 on the phytopathogen was observed by electron microscopy and the production of enzymes was tested as a potential mechanism of action. The bacterium inhibited the radial growth of Phytophthora tropicalis PtCa-14 by 85.9 ± 0.12%. The strain NMA1017 affected mycelial development, as observed by the damage to the cell wall of the oomycete. In pear fruit, the biocontrol agent controlled the production of mycelium on the pear fruit surface, indicating an inhibitory effect exerted. Cacao pods infected with P. tropicalis in the field resulted in a reduction in disease incidence from 86 to 33% and in infection from 68 to 6%. Moreover, strain NMA1017 produced hydrolytic enzymes such as cellulases, xylanases, chitinases and proteases. The results obtained highlight P. polymyxa NMA1017 as an organism of interest for the biocontrol of P. tropicalis, as a method to rescue this important crop in Mexico.

Optimization of Paenibacillus sp. NMA1017 Application as a Biocontrol Agent for Phytophthora tropicalis and Moniliophthora roreri in Cacao-Growing Fields in Chiapas, Mexico.

In Mexico, cacao production is endangered by pathogenic fungi, such as Phytophthora spp. and Moniliophthora rorei, that cause black pod rot and moniliasis, respectively. In this study the biocontrol agent Paenibacillus sp. NMA1017 was tested in cacao fields against the previous diseases. The treatments applied were shade management, inoculation of the bacterial strain with or without an adherent, and use of chemical control. The statistical analysis showed that the incidence of black pod rot in tagged cacao trees diminished when the bacterium was applied (reduction of 44.24 to 19.11%). The same result was observed with moniliasis when the pods were tagged (reduction of 66.6 to 27%). The use of Paenibacillus sp. NMA1017 with an integrated management might be a solution to cacao diseases and to having a sustainable production of cacao in Mexico.

Varietal Descriptors for the Distinction of Underutilized Varieties of Sechium edule (Jacq) Swartz.

Sechium edule (Jacq.) Sw. (Cucurbitaceae) is a species native to Mexico and Central America. The collection, characterization, and evaluation of accessions maintained in genebanks is essential for the conservation of this species. However, there are no specific varietal descriptors that differ from those used in a phenetic approach and are adapted to international registration guidelines to help distinguish, improve, cluster, and protect intraspecific variants of common use and those obtained by breeding. Therefore, 65 morphological descriptors (qualitative and quantitative) were evaluated in 133 accessions obtained from Mexico, Guatemala, and Costa Rica located in the National Germplasm Bank of S. edule in Mexico. These characteristics were observed to be phenetically stable for five generations under the same agroclimatic conditions. In addition, an analysis of amplified fragment length polymorphism (AFLP) was applied to 133 samples from a set of 245 accessions. According to the multivariate analysis, 26 of the 65 descriptors evaluated (qualitative and quantitative) enabled differentiation of varieties of S. edule. The AFLP analysis showed a high level of polymorphism and genetic distance between cultivated accessions and their corresponding wild ancestor. The variations in S. edule suggest that the morphological characteristics have differentiated from an essentially derived initial edible variety (ancestral original variety), but unlike other cucurbits, there is no evidence of the ancestral edible for Sechium since the seed is unorthodox and there are no relicts.

Actividad antioxidante en genotipos de Theobroma spp. (Malvaceae) en México / Antioxidant activity in genotypes of Theobroma spp. (Malvaceae) in Mexico

Abstract Introduction: The organoleptic qualities of aromatic species and their derived products are directly related to some characteristics of flavor, color and nutritional value and depend largely on their genetic origin and content of secondary metabolites. Objective: The antioxidant activity of different genotypes of Theobroma spp. from Mexico was evaluated in order to distinguish promising qualities for genetic improvement, and to differentiate phylogenetic traits, considering biochemical variables. Methods: The amount of phenols, flavonoids and antioxidant activity was determined by ABTS and DDPH, in addition to the content of anthocyanins, theobromine and caffeine in four species of Theobroma L., and 50 genotypes derived from T. cacao. The results were analyzed using an analysis of variance, means test, principal component analysis and cladistic analysis. Results: There are highly significant differences between genotypes. The phenol content ranged from 7.5-85 mg g-1; flavonoids 6.57-69.6 mg g-1, antioxidant activity by ABTS of 17.3-86.1 and by DDPH of 40.0-53.3; anthocyanin content of 0.01-3, caffeine of 1.8-6.7-and theobromine of 2.9-9.8 mg g-1. Principal component and cladistic analysis helped explain the variation found and distinguish evolutionary characters and phylogenetic brotherhoods. The variation in content of phenols, flavonoids, antioxidant activity, anthocyanins, theobromine and caffeine was mainly due to the degree of domestication, while for the group of genotypes derived from T. cacao (forastero, trinitario and criollo) it was the origin of the seeds. Conclusions: The degree of domestication influences the content of phenols and antioxidant capacity. The results suggest that the evaluated variables can help to form criteria for genetic improvement in the complex derived from T. cacao oriented to the selection of higher phenol content and greater antioxidant activity.

Resumen Introducción: Las cualidades organolépticas de las especies aromáticas y sus productos derivados se relacionan directamente con algunas características del sabor, color y valor nutricional y dependen en gran medida de su origen genético y contenido de metabolitos secundarios. Objetivo: Se evaluó la actividad antioxidante de diferentes genotipos de Theobroma spp. de México, con el fin de distinguir cualidades promisorias para el mejoramiento genético, y diferenciar rasgos filogenéticos, considerando variables bioquímicas. Métodos: Se determinó la cantidad de fenoles, flavonoides y actividad antioxidante mediante ABTS y DDPH, además de contenido de antocianinas, teobromina y cafeína en cuatro especies de Theobroma L., y 50 genotipos derivados de T. cacao. Resultados: Los resultados fueron analizados mediante un análisis de varianza, prueba de medias, análisis de componentes principales y análisis cladístico. Existen diferencias altamente significativas entre genotipos. El contenido de fenoles varió de 7.5-85 mg g-1; flavonoides 6.57-69.6-mg g-1, actividad antioxidante por ABTS de 17.3-86.1 y por DDPH de 40.0-53.3; el contenido de antocianinas de 0.01-3, cafeína de 1.8-6.7 y teobromina de 2.9-9.8 mg g-1. El análisis de componentes principales y cladístico ayudó a explicar la variación encontrada y distinguir caracteres evolutivos y hermandades filogenéticas. La variación en contenido de fenoles, flavonoides, actividad antioxidante, antocianinas, teobromina y cafeína estuvo dada principalmente por el grado de domesticación, mientras que para el grupo de genotipos derivados de T. cacao (forastero, trinitario y criollo) fue el origen de las semillas. Conclusión: El grado de domesticación influye en el contenido de fenoles y actividad antioxidante. Los resultados sugieren que las variables evaluadas pueden ayudar a formar criterios para el mejoramiento genético en el complejo derivado de T. cacao orientado a la selección de mayor contenido de fenoles y mayor actividad antioxidante.

Estudio citológico en poblaciones diploides y poliploides del género tripsacum / CYTOLOGICAL STUDY IN DIPLOID AND POLIPOID POPULATIONS OF THE Tripsacum GENUS / ESTUDO CITOLÓGICO EM POPULAÇÕES DIPLÓIDES E POLIPLÓIDES DO GÊNERO Tripsacum

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.

Respuesta a la selección para resistencia a sequía en maíz (Zea mays L.) / drought resistance Selection response in corn (Zea mays L.)

Se estudió la respuesta a la selección masal para componentes del rendimiento de grano y la estabilidad en dos variedades originales de maíz, Zacatecas 58 y Cafime, en las cuales se aplicaron 19 y 16 ciclos de selección masal para resistencia a sequía, respectivamente. Ambos materiales genéticos se evaluaron en dos localidades (Montecillo y Tecámac, Estado de México) con tres ambientes de humedad del suelo (riego, temporal y sequía). Los estimadores del avance genético por ciclo de selección y los parámetros de estabilidad utilizados indican que en el ambiente de sequía se encontraron los avances genéticos más altos por ciclo para ambas variedades, pero la mayor ganancia acumulada en unidades para los caracteres evaluados, se obtuvo en condiciones de riego. Los compuestos de selección de Cafime fueron más consistentes que los de Zacatecas 58. El peso de mazorca promedio por planta se incrementó conforme aumentó el número de ciclos de selección en las dos variedades y de manera concomitante se incrementó el coeficiente de regresión. Se deduce que al aumentar la selección masal visual aumenta el rendimiento y la sensibilidad ambiental lineal (b i), pero no la sensibilidad ambiental no lineal (S²d i). Finalmente, el aumento del rendimiento y de sus componentes estuvo positivamente correlacionado con el coeficiente de regresión lineal del rendimiento sobre el número de ciclos de selección, pero no hubo correlación con las desviaciones de regresión.

The response to masal selection for components of grain yield, and stability, were studied in two original varieties of corn, Zacatecas 58 and Cafime, in which 19 and 16 cycles of masal selection for drought resistance were applied, respectively. Both genetic materials were evaluated in two localities (Montecillo and Tecámac, State of Mexico) in three soil moisture environments (irrigation, rainfall and drought). The genetic advance estimates for a selection cycle and the stability parameters used indicate that in the drought environment the highest genetic advances in a cycle were found for both varieties, but the largest accumulated profit in units for the evaluated traits, was obtained under irrigation conditions. The selection compounds of the Cafime variety were more consistent than those of Zacatecas 58. In both varieties, the ear corn average weight increased as the selection cycle number increased and, thus, the coefficient of regression also increased. It is deduced that an increase of visual masal selection increases the yield and the environmental linear sensibility (b i), but not the environmental nonlinear sensibility (S²d i). Finally, the yield increase and its components were positively correlated with the linear regression coefficient of the yield concerning the selection cycles number, but there was no correlation with the regression deviation.

Estudou-se a resposta à seleção massal para componentes do rendimento de grão e a estabilidade em duas variedades originais de milho, Zacatecas 58 e Cafime, nas quais foram aplicadas 19 e 16 ciclos de seleção massal para resistência à seca, respectivamente. Ambos materiais genéticos foram avaliados em duas localidades (Montecillo e Tecámac, Estado do México) com três ambientes de umidade do solo (irrigação, temporal e seca). Os estimadores do avanço genético por ciclo de seleção e os parâmetros de estabilidade utilizados indicam que no ambiente de seca se encontraram os avanços genéticos mais altos por ciclo para ambas as variedades, mas o maior ganho acumulado em unidades para os caracteres avaliados, foi obtido em condições de irrigação. Os compostos de seleção de Cafime foram mais consistentes que os de Zacatecas 58. O peso médio de espiga por planta se incrementou na medida em que aumentou o número de ciclos de seleção nas duas variedades e de maneira concomitante se incrementou o coeficiente de regressão. É deduzido que ao aumentar a seleção massal visual aumenta o rendimiento e a sensibilidade ambiental linear (b i), mas não a sensibilidade ambiental não linear (S²d i). Finalmente, o aumento do rendimento e de seus componentes esteve positivamente correlacionado com o coeficiente de regressão linear do rendimento sobre o número de ciclos de seleção, mas não houve correlação com as desviações de regressão.

Comparación de la tolerancia a la sequía de cuatro variedades de maíz (zea mays L) y su relación con la acumulación de prolina / Comparison of drought tolerance in four maize varieties (zea mays L) and its relation to proline accumulation

Se comparó la tolerancia a la sequía con base en los potenciales hídricos, acumulación de prolina y biomasa, en las variedades de maíz Zacatecas 58 original (Zo), Cafime original (Co) y sus respectivas variedades mejoradas para resistencia a la sequía, Zacatecas 58 Selección Masal 19 (Z19) y Cafime Selección Masal 16 (C16) en condiciones de sequía y riego en invernadero. En la quinta hoja de las cuatro variedades los potenciales hídrico (Psi Pi) y osmótico (Psi pi) disminuyeron conforme se prolongó la sequía; las variedades mejoradas presentaron menores Psiw y Psi pi con respecto a las originales. La acumulación de prolina aumentó conforme se prolongó el periodo de sequía en las cuatro variedades, en diferente proporción. Las variedades mejoradas presentaron mayor acumulación de prolina que las originales, con excepción de la Z19, que a los 38 días de sequía mostró menor acumulación que Zo y mayor acumulación de biomasa. Los resultados permiten establecer que las variedades mejoradas por selección masal en condiciones de humedad restringida en el suelo, han desarrollado un mecanismo de resistencia a sequía semejante al propuesto inicialmente por otros autores, al cual han llamado latencia o resurrección, que les permite sobrevivir en condiciones extremas de sequía, recuperarse completamente y reiniciar su metabolismo normal y crecimiento una vez que hay humedad, donde la prolina juega un papel preponderante