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.
Plant growth-promoting rhizobacteria strains from special formulations have been used to optimize eucalyptus cutting production. To undertake quality control for the formulated products, the rhizobacterial strains should be characterized to assess their purity and authentication. In the present study, we characterized nine strains of rhizobacteria, including three Bacillus subtilis (S1, S2 and 3918), two Pseudomonas sp. (MF4 and FL2), P. putida (MF2), P. fulva (Ca), Frateuria aurantia (R1), and Stenotrophomonas maltophilia (CIIb). The strains were differentiated by colony morphology after 24 h of incubation in three different solid state culture media (glucose-nutritive agar, 523 medium and yeast extract-mannitol agar), sensitivity to a panel of 28 antibiotics (expressed according to the formation of inhibition halos of bacterial growth in the presence of antibiotics), and PCR-RFLP profiles of the 16S rDNA gene produced using nine restriction enzymes. It was possible to differentiate all nine strains of rhizobacteria using their morphological characteristics and sensitivity to antibiotics. The molecular analysis allowed us to separate the strains CIIb, FL2 and R1 from the strains belonging to the genera Bacillus and Pseudomonas. By using these three methods concomitantly, we were able to determine strain purity and perform the authentication.
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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