In 2014, a new and serious leaf and shoot disease of unknown aetiology appeared in Eucalyptus plantations of North Sumatra, Indonesia. The disease is characterized by black necrotic spots that initially appear on young leaves and petioles, which become scab‐like as the lesions age. Infected trees respond to infection by producing shoots with small leaves that commonly appear feathered. Fruiting structures typical of most foliar pathogens are not seen, but using scanning electron microscopy (SEM), fungal spores are evident and associated with the scab‐like structures. Using culture‐dependent methods, cultures resembling a species of Elsinoe were isolated from the lesions. DNA sequence comparisons for four gene regions, as well as morphological observations, showed that the fungus is an undescribed species in Elsinoe, for which the name Elsinoe necatrix sp. nov. is provided. Pathogenicity trials on a Eucalyptus clone with the Elsinoe species resulted in scab‐like structures similar to those observed under field conditions and the fungus was easily reisolated from the resulting lesions. This study includes a description of the pathogen and characterization of the disease, for which the name Eucalyptus scab and shoot malformation is suggested.
The genus Calonectria accommodates many important pathogens of agricultural, horticultural and forestry crops, including Eucalyptus. During 2017 surveys of Eucalyptus diseases in Sabah, Malaysia, typical symptoms of Calonectria leaf blight were observed. A large number of Calonectria isolates were collected from diseased leaves and soils associated with symptomatic trees. The aim of this study was to identify and resolve the phylogenetic relationships between these isolates using morphological characters and DNA 1 sequence comparisons for six gene regions. From a collection of 73 isolates, eight species residing in three species complexes were identified. Among these, four undescribed species were characterized, and are named here as Ca. borneana, Ca. ladang, Ca. pseudomalesiana and Ca. tanah. Results of this study support the view that planted Eucalyptus in tropical and subtropical areas of the world represent niches remarkably rich in Calonectria spp. This also has implications for the management of diseases on these important trees.
Acacia mangium plantations account for more than 50 % of the exotic plantations in Vietnam. A new black butt symptom was discovered in 2012, followed by the wilting sign in Acacia seedlings in Tuyen Quang Province. Isolations recovered two Phytophthora species, the well-known Acacia pathogen P. cinnamomi, and an unknown species. The new species is described here as Phytophthora acaciivora sp. nov. Phylogenetically this species resides in clade 2d and is most closely related to P. frigida. Phytophthora acaciivora is a heterothallic species, oospores are aplerotic and antheridia are amphigynous. It produces predominantly elongated ovoid, semi papillate, persistent sporangia, no hyphal swellings and no chlamydospores. Optimum temperature for the growth is 25–30 °C and the maximum temperature is over 37.5 °C. Studies are underway to determine the impact of this new species on Acacia plantations in Vietnam.
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