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.

Las condiciones ambientales en zonas semiáridas limitan la productividad de especies forrajeras empleadas en la alimentación animal; sin embargo, el maíz (Zea mays L.) presenta una amplia adaptación a diferentes condiciones ambientales de temperatura, precipitación, altitud, suelo entre otras. El objetivo del presente estudio fue evaluar el rendimiento y composición morfológica de diez genotipos de maíces nativos, un híbrido y una variedad sintética, durante el ciclo primavera-verano de 2017. Se utilizó un diseño experimental de bloques completos al azar y se realizó un análisis de varianza, las medias de los tratamientos se compararon con la prueba de Tukey. Las variables evaluadas fueron: rendimiento de materia seca total (MST) y por componente morfológico: hoja (MSh), tallo (MSt), mazorca (MSmz), panícula (MSp) y materia muerta (MSmm), altura de planta (AP), número de hojas (NH), longitud de hoja (LH), ancho de hoja (AH) y la relación hoja/tallo (H/T). El mayor y menor rendimiento de MST, lo obtuvo el genotipo Ratón×Tuxpeño Norteño y el híbrido A6-069-B, con 8 888 y 3 113 kg MS ha-1, respectivamente. La mayor altura (180 cm) la obtuvieron los genotipos Ratón×Tuxpeño Norteño y Olotillo×Tuxpeño. El mayor número de hojas lo presentó el genotipo Tuxpeño Norteño×Olotillo con 11.6. La mayor relación hoja/tallo (2.1) fue en la variedad sintética breve Padilla. Es necesario realizar más investigación en el mejoramiento por selección recurrente del genotipo Ratón×Tuxpeño Norteño para obtener un mayor rendimiento y valor nutritivo en el forraje de maíz.

Characterizing the genetic diversity of maize (Zea mays L.) populations by their morphological and molecular attributes makes it possible to place populations into specific groups; thus, facilitating the design of procedures for their optimum and sustainable use. In this study, data from two lines of evidence were analyzed simultaneously to robustly classify maize populations and to determine their genetic relationships. Seven maize races of the central high plateau of Mexico were characterized using a combined analysis of 13 morphological traits and 31 microsatellite loci. The germplasm assessed included samples of 119 accessions held at Mexican germplasm banks. Cluster and principal component analyses were performed. Also, genetic and geographic relationships among the accessions were determined. Principal component analysis separated the different accessions into well-defined groups using first three principal components. The accessions of Arrocillo Amarillo and Elotes Cónicos races did not exhibit a grouping pattern, indicating greater genetic complexity. Better grounded grouping and phylogenetic relationships were obtained when traits of both lines of evidence were used simultaneously.

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.

La agricultura en Áreas Naturales Protegidas (ANPs) es vista como potencialmente perjudicial para la biodiversidad. Sin embargo, bajo métodos tradicionales y parcelas pequeñas, se forman mosaicos agrícolas con poca tecnificación, usando variedades locales y conservando conocimientos tradicionales. Esto crea agrodiversidad dinámica en áreas cercanas a ANPs. La falta de comprensión de la interacción entre ANPs y agricultura limita el desarrollo de estrategias y políticas para su coexistencia. Esto descuida el valor del patrimonio biocultural, la seguridad y soberanía alimentaria de las comunidades rurales, dependientes de recursos fitogenéticos. Es crucial estudiar y visibilizar esta dinámica para manejar adecuadamente sus conflictos y prioridades.