In recent decades, commercial Eucalyptus plantations have expanded toward the warm and humid regions of northern and northeastern Brazil, where Calonectria leaf blight (CLB) has become the primary fungal leaf disease of this crop. CLB can be caused by different Calonectria species, and previous studies have indicated that Calonectria might have high species diversity in Brazil. During a disease survey conducted in three commercial plantations of Eucalyptus in northeastern Brazil, diseased leaves from Eucalyptus trees with typical symptoms of CLB were collected, and Calonectria fungi were isolated. Based on phylogenetic analyses of six gene regions (act, cmdA, his3, rpb2, tef1, and tub2) and morphological characteristics, two new species of Calonectria were identified. Five isolates were named as C. paragominensissp. nov. and four were named as C. imperatasp. nov. The pathogenicity to Eucalyptus of both species was confirmed by fulfilling the Koch’s postulates.
Calonectria leaf spot, caused by Calonectria pteridis, is a serious problem in Eucalyptus crops in both nursery and the field. Under ideal conditions, the disease can cause severe defoliation. It is known that calcium and potassium are directly related to the plant's resistance to pathogens. Thus, the knowledge of how a balanced fertilization of Ca and K interferes in the distribution of these nutrients at the infection site would contribute to elucidate the resistance of the plant related to its nutrition. This study investigated the effect of calcium and potassium fertilizer application on the content and distribution of these nutrients in the symptomatic leaf area, transition zone and asymptomatic leaf area over time. Eucalyptus seedlings were grown in nutrient solution under different Ca and K treatments (6 mmol/L K + 4 mmol/L Ca, 6 mmol/L K + 8 mmol/L Ca and 9 mmol/L K + 12 mmol/L Ca) and inoculated with C. pteridis. Leaves were removed at 24, 48 and 72 hr after inoculation (hai) and evaluated by X‐ray microanalysis. The highest calcium content among the different leaf areas was observed in the symptomatic area, and the levels in this area increased over time, with the highest mean value observed at 72 hai in the 6K + 8Ca treatment. In the other treatments, the mean calcium content peaked at 48 hai and then decreased. A similar pattern in asymptomatic tissue was observed for potassium in the 6K + 8Ca treatment. Fertilization with calcium and potassium directly affected the demand and availability of nutrients at different times during infection. These results demonstrate that plant defence responses and their continuity over time during infection rely on balanced calcium and potassium fertilization because these nutrients are directly involved in plant resistance to the pathogen.
One of the most damaging diseases of Eucalyptus is Calonectria leaf blight, and it causes significant economic losses. In March 2021, symptoms of leaf blight disease were observed in a Eucalyptus commercial plantation in northeastern Brazil. The present study aimed to identify the causal agent based on morphological features, phylogenetic analyses and pathogenicity tests. Based on phylogenetic analyses of the cmdA, his3, tef1 and tub2 gene regions and morphological characteristics, the fungal isolates were identified as Calonectria quinqueramosa, and their pathogenicity to Eucalyptus urophylla was confirmed. The results of this study confirmed the importance of multi-locus phylogeny supported by morphological characteristics for the proper identification of Calonectria species. To the best of our knowledge, this study highlights the first report of C. quinqueramosa causing leaf blight on E. urophylla trees in northeastern Brazil. This information will be valuable to promote the development of disease management strategies and to lead the development of Eucalyptus genotypes with resistance to Calonectria.
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