Summary Since the myrtle rust pathogen (Austropuccinia psidii) was first reported (as Puccinia psidii) in Brazil on guava (Psidium guajava) in 1884, it has been found infecting diverse myrtaceous species. Because A. psidii has recently spread rapidly worldwide with an extensive host range, genetic and genotypic diversities were evaluated within and among A. psidii populations in its putative native range and other areas of myrtle rust emergence in the Americas and Hawaii. Microsatellite markers revealed several unique multilocus genotypes (MLGs), which grouped isolates into nine distinct genetic clusters [C1–C9 comprising C1: from diverse hosts from Costa Rica, Jamaica, Mexico, Puerto Rico, and USA‐Hawaii, and USA‐California; C2: from eucalypts (Eucalyptus spp.) in Brazil/Uruguay and rose apple (Syzygium jambos) in Brazil; C3: from eucalypts in Brazil; C4: from diverse hosts in USA‐Florida; C5: from Java plum (Syzygium cumini) in Brazil; C6: from guava and Brazilian guava (Psidium guineense) in Brazil; C7: from pitanga (Eugenia uniflora) in Brazil; C8: from allspice (Pimenta dioica) in Jamaica and sweet flower (Myrrhinium atropurpureum) in Uruguay; C9: from jabuticaba (Myrciaria cauliflora) in Brazil]. The C1 cluster, which included a single MLG infecting diverse host in many geographic regions, and the closely related C4 cluster are considered as a “Pandemic biotype,” associated with myrtle rust emergence in Central America, the Caribbean, USA‐Florida, USA‐Hawaii, Australia, China‐Hainan, New Caledonia, Indonesia and Colombia. Based on 19 bioclimatic variables and documented occurrences of A. psidii contrasted with reduced sets of specific genetic clusters (subnetworks, considered as biotypes), maximum entropy bioclimatic modelling was used to predict geographic locations with suitable climate for A. psidii which are at risk from invasion. The genetic diversity of A. psidii throughout the Americas and Hawaii demonstrates the importance of recognizing biotypes when assessing the invasive threats posed by A. psidii around the globe.

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Aim of study: Plantations are threatened by an emerging disease called “Gmelina death disease”. The objective of this study was measured the incidence and severity of this disease and were correlated with the characteristics of the plantations, micro- and macronutrients in the soil and climatic parameters.Area of study: The present study evaluated 16 symptomatic fast-growth plantations of different age in Costa RicaMaterial and methods: Fungi were identified from xylem of infected trees. Incidence and severity was measured and correlated with the characteristics of the plantations, micro- and macronutrients in the soil and climatic parameters. Root condition and the quality (specify gravity, mechanical and decay resistance and chemical compositions), of the wood of symptomatic and asymptomatic trees were compared.Main results: Three fungal species (Chaetomella raphigera, Fusarium solani and Rhizomucor variabilis) were identified from diseased samples. Clay content in the soil profile from 10-20 cm deep explained a significant proportion of the variation in the incidence and severity of the disease, and stand density was related to severity. Although two climatic variables, Holdridge’s potential annual evapotranspiration and Thornthwaite’s potential evapotranspiration, showed a relationship between the incidence in the trees and symptoms of the disease. Infected wood turned black in symptomatic trees. Specify gravity and mechanical resistance of infected wood decreased, whereas its natural durability was unaffected. Changes were observed in the quantities of Mg, Fe, Ca, K and Zn in infected wood.Research highlights: Gmelina plantations established in sites with high stand densities and high contents of clay increase susceptibility to this disease.

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Desde 1984, a través del Laboratorio de Protección Forestal del Instituto Tecnológico de Costa Rica se realiza el diagnóstico nacional de plagas y enfermedades forestales en el país. Se informa de un total de 486 especies de insectos (75%), 131 de patógenos (20%), 25 de animales vertebrados (4%) y 9 de muérdagos (1%) en 109 especies árboreas. Los informes se clasifican de acuerdo a la parte del árbol afectada; en el follaje se presentan la mayor parte de dichos informes (52,8%), seguido del fuste (16,4%). Se describen los principales problemas en estructuras reproductivas, follaje, brotes, fuste, ramillas y raíces, como Hyblaea puera y varias especies de crisomélidos en Tectona grandis, Dictyla monotropidia en Cordia alliodora, "royas" de follaje y ramillas (Puccinia cordiae, Melampsoridium alni, Olivea tectonae, Prospodium sp. y Gymnosporangium sp.), barrenadores de brotes (Hypsipylla grandella y Cosmopteryx sp.), el "descortezador" Scolytodes alni en Alnus acuminata, barrenadores (varias especies de cerambícidos) y cancros (Chrysoporte cubensis, Botryosphaeria sp., Nectria sp., Seiridiun sp.) en el fuste y pudriciones radicales.