Morpho-agronomic evaluation of native maize races associated with Mexican tropical climate agroforestry systems.

Maize (Zea mays L.) is native to Mexico, in which wide genetic diversity can be found; however, maize is at risk of genetic erosion, and agroforestry systems (ASs) can be a strategy for conservation and sustainable use of this crop. The objective of this study was to evaluate the variation in the morpho-agronomic characteristics of three native maize races, Tuxpeño, Olotillo × Tuxpeño and Ratón × Tepecintle, cultivated in different AS in a tropical climate of Veracruz, Mexico, as well as its association with microclimatic conditions. In 2019, experiments were established in the localities La Gloria and La Luisa, Veracruz, where the three maize races are cultivated, in a randomized complete block design with three replications in a 3 × 4 factorial scheme (three native maize races and three AS arrrays, plus monoculture). Ten morpho-agronomic variables were recorded in each experiment and were analyzed by analysis of variance (ANOVA; Tukey's post-hoc test, all p ≤ 0.05) and principal component analysis (PCA). Six morpho-agronomic characteristics showed significant differences for the race × system interaction. Consistently standing out both in the Myroxylon with 2.8 m × 2.0 arrays and in the monoculture was the Olotillo × Tuxpeño race, as there were no variations (p ≥ 0.05) in 50% of its morpho-agronomic characteristics. The first three PCs explained 87.7% of the cumulative variance, determined by five variables of the ears, three of the grain and plant height, which were associated with temperature; therefore, the microclimatic conditions of the studied ASs are associated with the morpho-agronomic characteristics of the native maize races. The results show that ASs could be a strategy for the conservation and use of native corn germplasm and could allow the diversification of sustainable production for rural farmers.

Evaluation of Resistance of Eleven Maize Races (Zea mays L.) to the Red Spider Mite (Tetranychus merganser, Boudreaux).

At least 59 maize races (Zea mays L.) have been registered in Mexico. The feeding damage caused by insects and mites to maize crops generates up to ~30% of maize yield losses. Spider-mite-resistant plants are needed. The red spider mite, Tetranychus merganser Boudreaux (Acari: Tetranychidae), is distributed in the United States, China, Mexico, and Thailand. It is considered a potential pest in Mexican agriculture. The aim of this study was to evaluate the resistance mechanisms (antixenosis and antibiosis) of 11 native maize populations, representative of each race of maize grown in Tamaulipas, Mexico, to T. merganser under laboratory conditions. The aim was also to obtain information on the chemical composition and some morphological characteristics of these maize races and to identify resistant maize races for incorporation into a breeding program. Antixenosis was assessed by non-preference for oviposition and feeding. Antibiosis was measured by growth rate (ri). The presence of secondary metabolites in the 11 maize races were different. In the 11 maize races, quantitative analysis of total phenol concentration, total flavonoid concentration, and antioxidant capacity were significantly different. The multivariate analysis of variance showed that there is evidence of antixenosis noted by maize race differences in egg laying and percentage feeding damage but not of antibiosis noted by growth rate. Red spider mites laid significantly more eggs on the Celaya (24 h: 25.67 ± 17.04, 48 h: 42.67 ± 26.86, 72 h: 49.33 ± 28.54) race than on Raton (24 h: 7.00 ± 5.00, 48 h: 12.67 ± 8.02, 72 h: 14.67 ± 9.29) and Elotes Occidentales × Tuxpeño (24 h: 9.67 ± 5.85, 48 h: 15.33 ± 10.69, 72 h: 17.67 ± 10.97) races. However, the growth rate and mortality of T. merganser in the 11 corn races were similar. The Vandeño (24 h: 11.67 ± 2.89, 48 h: 27.67 ± 7.64, 72 h: 30.00 ± 18.03) and Tabloncillo × Tuxpeño (24 h: 18.33 ± 7.64, 48 h: 25.00 ± 8.66, 72 h: 25.00 ± 8.66) races were the most resistant to red spider mite damage, whereas the most susceptible race was Celaya (24 h: 26.67 ± 15.28, 48 h: 48.33 ± 29.30, 72 h: 65.00 ± 30.00). Further analysis by PCA at 24, 48, and 72 h found the Celaya race positively correlated to growth rate and oviposition of T. merganser and to a lesser extent with the percentage of feeding damage, suggesting that the Celaya race was most susceptible to T. merganser. At 24 h, the Vandeño race was most resistant, given a negative correlation to growth rate and oviposition by T. merganser. The PCA at 48 and 72 h noted the Elotes Occidentales × Tuxpeño race was most resistant to red spider mite, with negative relationships to growth rate and oviposition and, to a lesser extent, to feeding damage. This resistance is due to the differences in both its morphological characteristics and the secondary metabolites present in their leaves.

Diversidad y caracterización de maíces nativos de la Reserva de la Biósfera "El Cielo", Tamaulipas, México / Diversity and characterization of native maize from the "El Cielo" Biosphere Reserve, Tamaulipas, Mexico

Resumen La diversidad del maíz en México se fundamenta por la presencia de 59 a 64 razas; Tamaulipas como estado productor contribuye a mantener la variabilidad entre razas, especialmente en las regiones aisladas. La reserva de la Biósfera "El Cielo" localizada en una región montañosa, que comprende los municipios de Jaumave, Ocampo, Gómez Farías y Llera de Canales, ha sido escasamente estudiada, a pesar de que existen riesgos de degradación o extinción de poblaciones nativas de maíz, por factores como cambios de uso de suelo y fenómenos naturales. El objetivo de este trabajo fue analizar la diversidad morfológica de poblaciones nativas de maíz de la Reserva de la Biósfera "El Cielo". Durante los meses de febrero, marzo y abril del 2016, se realizaron recolectas de maíces nativos en los municipios que comprenden la reserva. El tamaño de la muestra varió, entre 20 y 30 mazorcas de cada población, y de estas, se eligieron 10 mazorcas para registrar variables cuantitativas y cualitativas. Se utilizaron los métodos multivariados de análisis de componentes principales y conglomerados. El 62.45 % correspondió a la variación total, la cual fue explicada por los dos primeros componentes principales, y las variables con mayor contribución a la variación fueron longitud de mazorca, número de granos por hilera, peso de mazorca, peso y volumen de 100 granos, diámetro de mazorca y de olote, número de hileras por mazorca y la relación diámetro/longitud de mazorca. En las poblaciones nativas de maíz que aún se cultivan en la Reserva de la Biósfera "El Cielo", se encontró amplia diversidad morfológica de mazorca, así como variación en la combinación de colores de grano y olote, lo que sugiere que las poblaciones nativas representan un amplio potencial como acervo genético y reservorio de genes.

Abstract The diversity of maize in Mexico is based on the presence of breeds that range from 59 to 64 varieties. Tamaulipas is a corn-producing state that contributes to sustain this enormous variation of breeds, especially in isolated regions. The biosphere ecological reserve "El Cielo" is located in a mountainous region, which comprises Jaumave, Ocampo, Gómez Farías and Llera de Canales municipalities. This region has been scarcely studied in spite of the degrada tion or extinction risks of native populations of maize due to factors such as changes in land use and natural phenomena. The objective of this work was to analyze the morphologic diversity of native maize varieties of "El Cielo" biosphere ecological reserve. Native maize harvests were collected in the municipalities that comprise the reserve during the months of February, March and April of 2016. The sample size ranged between 20 and 30 cobs of each variety, out of this sample 10 cobs were selected in order to register quantitative and qualitative variables. A multivariate analysis method of main components and conglomerates was used. Results show that 62.45 % of the samples were correspondent with total variation, which was explained by the first two main compo nents. The variables with greater contribution to the variation were cob length, number of grains per row, cob weight, weight and volume of 100 grains, cob diameter, number of rows per hob and the relation of diameter/length in each cob. The native maize populations that are still cultivated at the biosphere ecological reserve "El Cielo" there was a wide morphological diversity of cob, as well as variation in the com bination of grain and corncob color. This sug gests that native populations possess a substantial potential as a gene pool and gene reservoir.

Social and environmental factors in the diversity of tomato landraces from the South-Central region of Mexico / Influência de fatores sociais e ambientais na diversidade de variedades crioulas de tomateiro da região Centro-Sul do México

ABSTRACT: In the present study, we investigated the influence of social and environmental factors in the genetic diversity of tomato landraces in the South-Central region of Mexico. A total of 30 tomato landraces, collected in 18 villages with different ethnolinguistic affiliations, were analyzed. We reported that the genetic diversity of tomato landraces is associated with the ethnolinguistic group, weather, and soil-type present in the region studied. Our results showed that there are morphological differences between landraces grown by different ethnolinguistic groups; however, there was also evidence of morphological similarities between landraces from groups with different ethnolinguistic affiliations. Finally, different selection criteria, mainly fruit color, size and shape, plays an important role in the phenotypic divergence among landraces grown in different traditional farming systems.

RESUMO: No presente estudo investigamos a relação da afiliação etnolinguística com a diversidade genética de variedades locais de tomate na região Centro-Sul do México. Um total de 30 variedades de tomate, coletadas em 18 aldeias com diferentes afiliações etnolinguísticas, foram analisadas. Verificamos que a diversidade genética das variedades crioulas de tomate está associada ao grupo etnolinguístico presente na região estudada. Nossos resultados mostram que existem diferenças morfológicas entre raças cultivadas por diferentes grupos etnolinguísticos. No entanto, também houve evidências de semelhanças morfológicas entre raças de grupos com diferentes afiliações etnolinguísticas. Finalmente, diferentes critérios de seleção, como, principalmente, cor, tamanho e forma dos frutos, desempenham um papel importante na divergência fenotípica entre as variedades crioulas cultivadas em diferentes sistemas agrícolas tradicionais.