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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.

Avocado root rot is the most important disease of this fruit crop worldwide. This pathology may be caused by several biotic and abiotic agents, with the oomycete Phytophthora cinnamomi being the pathogen more frequently associated with poor phytosanitary conditions. There are disease control methods available that can reduce disease severity and allow plants to recover; however, they are not consistently and promptly applied. In addition, only chemical products are used by farmers as the preferred management method. This research aimed to evaluate different root rot management strategies in a commercial orchard. Data suggest that individual control methods are not as effective as when they are applied in combination, as in the T8 treatment (metalaxyl + mancozeb applied in drench; injection of potassium phosphite to each plant stem; potassium silicate applied in drench; addition of a layer of organic mulch and incorporation of 10 kg of composted substrate, both applied to the ground around the base of each tree). Using this strategy, the area under the disease progress curve for the avocado root rot was reduced by up to 68.6%, and the extra-quality avocado fruit class increased by as much as 44% compared to the diseased control plants (T0) (P < 0.01). With the combined treatment T8, farm income showed a 9.5-fold increase, probably due to an increase in the percentage of viable roots by up to 9.4-fold, which would have improved nutrient and water uptake.

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.

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