Phytophthora cinnamomi is among the most destructive plant pathogens that affect many host plants in different ecosystems. Economically important hosts of this pathogen include avocado (Persea americana), and this oomycete may cause large-scale destructive epidemics. This study analyzed the potential geographic distribution of P. cinnamomi (pathogen) and avocado (host), and distribution of the pathogen in relation to multiple hosts in the Americas. Niche overlap between hosts and pathogen were also evaluated, using a multistep process of ecological niche modelling and the MaxEnt algorithm. Niche similarity among pathogen populations in different hosts and related niche similarity were also examined. As a complement, a tool was designed to visualize the risk of this pathogen in avocado. Results showed that the pathogen was randomly distributed in the avocado niche environmental space, but the niche of the pathogenwas narrower than that of its principal host. The niche of the pathogen was largely a function of the host niches. Areas with potential to grow avocado could present low risk of P. cinnamomi, but given the invasiveness of this pathogen, they may be affected in the future.

Banana black leaf streak, caused by Mycosphaerella fijiensis M. Morelet, is a primary phytosanitary concern in export of this fruit around the world. To develop improved cultivars resistant to this disease, an understanding of host response to infection is necessary. In this study, we obtained expression data on 14,872 genes by microarray analysis in the resistant genotype Musa acuminata subsp. burmannicoides ‘Calcutta 4’ after inoculation with Mycosphaerella fijiensis. From these data, 16 genes were analyzed as potential reference genes and 12 genes were identified as potential early indicators of the onset of the host defense response. Subsequently, these genes were analyzed by quantitative reverse-transcription polymerase chain reaction in susceptible ‘Williams’ and resistant Calcutta 4. The 18S and 26S ribosomal subunit genes in both cultivars showed the best characteristics as reference genes. In all, 5 of the 12 defense genes expressed shortly after infection (peroxidase, pathogenesis-related [PR]-4, PR-10, phenylalanine ammonia-liase, and disease resistance response 1) showed overexpression in Calcutta 4 between 6 and 24 h after inoculation as opposed to Williams, which did not show overexpression after 144 h. Early induction of defense-related genes could be a key component of the resistance of the Calcutta 4 genotype against M. fijiensis. In addition, these five genes could be used as indicators of the activation of defense responses in the interaction between banana and M. fijiensis.

El cultivo de aguacate en Colombia ha presentado un incremento en el área sembrada durante la última década, especialmente en clima frío moderado, entre 1.800 y 2.500 msnm. La variedad Hass se destaca por tener la mayor área sembrada en este clima, en el departamento de Antioquia-Colombia. Este cultivo presenta grandes retos tecnológicos para su expansión; entre ellos el manejo de enfermedades ocupa un lugar predominante por las implicaciones que tiene en costos, impacto en la salud, ambiente y restricciones para exportaciones. La marchitez, ocasiona la muerte de numerosos árboles en todas las etapas del cultivo y presenta la mayor incidencia y severidad de las enfermedades identificadas para este cultivo. El desconocimiento de los agentes causales de esta enfermedad, ha llevado a realizar prácticas de manejo encaminadas principalmente al control del oomycete Phytophthora cinnamomi Rands, como único agente causal. Esta investigación tuvo como objetivo identificar los distintos agentes causales de la marchitez del aguacate y la relación de su incidencia con las prácticas de manejo en lotes cultivados en el departamento de Antioquia-Colombia. Los resultados encontrados muestran que la marchitez es el principal problema del cultivo de aguacate. Los microorganismos P. cinnamomi, Phytophthora heveae Thompson, Phytophthora citrícola Sawada, Verticillium sp., y Cylindrocarpon destructans (Zinss) Scholten fueron aislados y reprodujeron los síntomas asociados a marchitez. Las condiciones de bajo contenido de oxigeno el suelo también reprodujeron la sintomatología de marchitez, involucrando también un origen abiótico en la etiología.

Areas cultivated with Hass avocado crops in Colombia have growth rapidly. One of the major limitations is the avocado wilt complex disease (AWC) caused by biotic and abiotic factors which have increased under the El Niño southern oscillation ENSO phenomenon (El Niño, La Niña). The objective of this study was to evaluate different strategies for mitigating the adverse effects associated with the ENSO phenomenon and AWC in avocado crops. We evaluated native materials, mulches, and parameters associated with the production of seedlings and planting practices in the field. The response variables tested were plant development, incidence, severity, mortality, and microbial dynamics, among others. The results indicated that native genotypes of Persea americana had different levels of adaptability to drought and flooding conditions. These genotypes also showed some degree of resistance to Phytophthora cinnamomi and Verticillium sp. infection with several degrees of rootstock-scion incompatibility with the Hass cultivar. In addition, mulch reduced the variability of soil moisture and temperature in the soil profile. Adequate selection of genotypes and new tools for planting have decreased the susceptibility to adverse effects associated with the ENSO phenomenon and the incidence and mortality caused by diseases under drought and flooding conditions. This work presents alternatives to mitigate adverse effects of climate variability in avocado crops under tropical conditions.