Abstract. Chitinase and β-1,3-glucanase play an important role in the defense reaction against fungal pathogens. In Agave americana there is limited information on the behavior of these proteins in response to the Fusarium oxysporum attack. In this study, a scanning electron microscopy (SEM) analysis was performed using roots of A. americana infected with F. oxysporum, and the activity of chitinase and β-1,3-glucanase in roots of A. americana was evaluated to 0, 7, 15 and 30 days after inoculation with F. oxysporum. SEM revealed that 15 days after inoculation (DAI) is enough for the fungus to infect the roots of A. americana. It was observed that the activity of chitinase in infected plants increased significantly at 15 DAI with respect to non-infected plants, while the activity of β-1,3 glucanase did not show a significant statistical difference with control plants. These results suggest that, in response to F. oxysporum infection, the activation of the chitinase-type PRs proteins is induced in A. americana.

Resumen. La quitinasa y β-1,3-glucanasa desempeñan una función importante en la reacción de defensa contra patógenos fúngicos. En Agave americana existe poca información sobre el comportamiento de estas proteínas en respuesta a la infección de Fusarium oxysporum. En este estudio, se realizó un análisis de microscopía electrónica de barrido (MEB) en raíces de A. americana infectadas con F. oxysporum y se evaluó la actividad de quitinasa y β-1,3-glucanasa en raíces de A. americana a 0, 7, 15 y 30 días después de inoculación con F. oxysporum. MEB reveló que 15 días después de la inoculación (DDI) son suficientes para que el hongo infecte las raíces de A. americana. La actividad de quitinasa en plantas infectadas incrementó significativamente a los 15 DDI con respecto a las plantas no infectadas, mientras que la actividad de β-1,3 glucanasa no presentó diferencia estadística significativa con plantas testigo. Los resultados sugieren que, en respuesta a la infección por F. oxysporum, A. americana activa proteínas PRs de tipo quitinasas.

Abstract Background The biological control of phytopathogens is improved by incorporating native strains of biocontrol agents; this is the case of Trichoderma spp. The control effect is higher when are applied groups of organisms and show incompatible interactions with increase antagonism. Objective The objective of the present study was to identify and evaluate in vitro the interspecific relation of native Trichoderma spp., and the antagonistic effect of incompatible species against Meloidogyne incognita. Methods The isolates of Trichoderma spp. were evaluated among them in dual culture, 45 dual cultures were performed, the four with greater incompatibility: T. virens (Th27-08) /T. harzianum (Th33-59), T. citrinoviride (Th33-58) /T. harzianum (Th33-59), T. virens (Th43-13) /T. ghanense (Th26-52) y T. simmonsii (Th09-06) /T. harzianum (Th33-59) and were evaluated against M. incognita in Solanum lycopersicum, in greenhouse. Results and conclusions The results showed interactions incompatible with significant differences (P≤0.01) against the nematode in relation to the control without fungal inoculants, reductions of 50.8-83.0% in the severity of the radical damage were estimated, 25.7-80.3% in the number of eggs and 31.5-94.1% in the number of females. The best effect was observed in the confrontation of T. citrinoviride (Th33-58) /T. harzianum (Th33-59) when compared to the Oxamil 24% control.

Resumen Antecedentes El control biológico de fitopatógenos se mejora al incorporar cepas nativas de agentes biocontroladores; es el caso de Trichoderma spp. El efecto de control es mayor cuando se aplican consorcios y muestran interacciones incompatibles entre sí para incrementar condiciones de antagonismo. Objetivos El objetivo del presente estudio fue identificar y evaluar in vitro la relación interespecífica de especies nativas de Trichoderma spp., así como la efectividad antagónica de especies incompatibles contra Meloidogyne incognita. Métodos Se realizaron 45 enfrentamientos duales in vitro, las cuatro con mayor incompatibilidad fueron: T. virens (Th27-08) /T. harzianum (Th33-59), T. citrinoviride (Th33-58) /T. harzianum (Th33-59), T. virens (Th43-13) /T. ghanense (Th26-52) y T. simmonsii (Th09-06) /T. harzianum (Th33-59). Estos se evaluaron contra M. incognita en Solanum lycopersicum, en condiciones de invernadero. Resultados y conclusiones Los resultados mostraron interacciones incompatibles con diferencias significativas (P≤0.01) contra el nematodo. En éstas, en relación al testigo sin inoculantes fúngicos se estimaron reducciones del 50.8-83.0% en la severidad del daño radical, 25.7-80.3% en el número de huevos y 31.5-94.1% en el número de hembras. El mejor efecto fue observado en el enfrentamiento de T. citrinoviride (Th33-58) /T. harzianum (Th33-59) al ser comparado con el testigo Oxamil 24%.

The whitefly Bemisia tabaci (Gennadius, 1889) is a major plant pest of horticultural crops from the families Solanaceae, Fabaceae and Cucurbitaceae in Neotropical areas. The exploration of host plant resistance and their biochemical mechanisms offers an excellent alternative to better understand factors affecting the interaction between phytophagous insect and host plant. We evaluated the survival of B. tabaci in landrace genotypes of Capsicum annuum L., and the activity of plant defense-related enzymes (chitinase, polyphenoloxidase, and peroxidase). The landrace genotypes Amaxito, Tabaquero, and Simojovel showed resistance to B. tabaci, as we observed more than 50% nymphal mortality, while in the commercial susceptible genotype Jalapeño mortality of B. tabaci nymphs was not higher than 20%. The activities of plant defense-related enzymes were significantly different among pepper genotypes (P < 0.05). Basal activities of chitinase, polyphenoloxidase and peroxidase were significantly lower or equal in landrace genotypes than that of the commercial genotype Jalapeño. The activity of plant enzymes was differential among pepper genotypes (P < 0.05). For example, the activity of chitinase enzyme generally was higher in non-infested plants with B. tabaci than those infested. Instead polyphenoloxidase (’Amaxito’ and ’Simojovel’) and peroxidase enzymes activities (’Tabaquero’) increased in infested plants (P < 0.05). We conclude that basal activities of plant defense-related enzymes could be act through other mechanism plant induction, since plant defense-related enzymes showed a different induction response to B. tabaci. We underlined the role of polyphenoloxidase as plant defense in the pepper genotype Simojovel related to B. tabaci.

The chemical management of the black leaf streak disease in banana caused by Mycosphaerella fijiensis (Morelet) requires numerous applications of fungicides per year. However this has led to fungicide resistance in the field. The present study evaluated the activities of six fungicides against the mycelial growth by determination of EC50 values of strains collected from fields with different fungicide management programs: Rustic management (RM) without applications and Intensive management (IM) more than 25 fungicide application/year. Results showed a decreased sensitivity to all fungicides in isolates collected from IM. Means of EC50 values in mg L-1 for RM and IM were: 13.25 ± 18.24 and 51.58 ± 46.14 for azoxystrobin, 81.40 ± 56.50 and 1.8575 ± 2.11 for carbendazim, 1.225 ± 0.945 and 10.01 ± 8.55 for propiconazole, 220 ± 67.66 vs. 368 ± 62.76 for vinclozolin, 9.862 ± 3.24 and 54.5 ± 21.08 for fludioxonil, 49.2125 ± 34.11 and 112.25 ± 51.20 for mancozeb. A molecular analysis for β-tubulin revealed a mutation at codon 198 in these strains having an EC50 greater than 10 mg L-1 for carbendazim. Our data indicate a consistency between fungicide resistance and intensive chemical management in banana fields, however indicative values for resistance were also found in strains collected from rustic fields, suggesting that proximity among fields may be causing a fungus interchange, where rustic fields are breeding grounds for development of resistant strains. Urgent actions are required in order to avoid fungicide resistance in Mexican populations of M. fijiensis due to fungicide management practices.

Morphological characterization of habanero pepper (Capsicum chínense Jacq.) showed that chilli fruit occasionally contains a small internal fruit (SIF) developing inside the main fruit. SIF morphology showed a normal fruit with pericarp, two locules and small reminiscent ovules joined to placental-like tissues. Histological analysis showed that SIFs maintain physical connexion with the placental tissues of the main fruit through vascular tissues. A Hardy-Weinberg analysis suggested that the frequency of SIF formation in the Capsicum chinense population studied is not the result of natural selection. This is the first report on this morphological abnormality in Capsicum chinense and constitutes an initial attempt to explain SIF formation frequency in this chilli pepper.

La caracterización morfológica del fruto de chile habanero (Capsicum chinense Jacq.) mostró que el fruto principal ocasionalmente contiene un pequeño fruto interno, aquí denominado "small internal fruit" (SIF). La morfología SIF fue normal, pues tiene pericarpio, dos lóculos y reminiscencias de óvulos unidos a una región parecida a la placenta. Los análisis histológicos mostraron que los SIFs mantienen una conexión vascular con el tejido placentario del fruto principal. Un análisis de Hardy-Weinberg en una población de chile habanero indicó que la frecuencia de la formación de SIF no es resultado de la selección natural. Este es el primer reporte de la caracterización de este fruto en Capsicum chinense y constituye un primer esfuerzo para explicar la frecuencia de formación de SIFs, en esta especie.