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Selecting high-quality varieties with disease resistance by artificial crossbreeding is the most fundamental way to address the damage caused by Calonectria spp. in eucalypt plantations. However, understanding the mechanism of disease-resistant heterosis occurrence in eucalypts is crucial for successful crossbreeding. Two eucalypt hybrids, the susceptible EC333 (H1522 × unknown) and the resistant EC338 (W1767 × P9060), were screened through infection with Calonectria isolates, a pathogen that causes eucalypt leaf blight. RNA-Seq was performed on the susceptible hybrid, the disease-resistant hybrid, and their parents. The gene differential expression analysis showed that there were 3912 differentially expressed genes between EC333 and EC338, with 1631 up-regulated and 2281 down-regulated genes. The expression trends of the differential gene sets in P9060 and EC338 were similar. However, the expression trend of W1767 was opposite that of EC338. The similarity of the expression and the advantage of stress resistance in E. pellita suggested that genes with significant differences in expression likely relate to disease resistance. A GSEA based on GO annotations revealed that the carbohydrate binding pathway genes were differentially expressed between EC338 and EC333. The gene pathways that were differentially expressed between EC338 and EC333 revealed by the GSEA based on KEGG annotations were the sesquiterpenoid and triterpenoid biosynthesis pathways. The alternative splicing analysis demonstrated that an AS event between EC338 and EC333 occurred in LOC104426602. According to our SNP analysis, EC338 had 626 more high-impact mutation loci than the male parent P9060 and 396 more than the female parent W1767; W1767 had 259 more mutation loci in the downstream region than EC338, while P9060 had 3107 fewer mutation loci in the downstream region than EC338. Additionally, EC338 had 9631 more mutation loci in the exon region than EC333. Modules were found via WGCNA that were strongly and oppositely correlated with EC338 and EC333, such as module MEsaddlebrown, likely associated with leaf blight resistance. The present study provides a detailed explanation of the genetic basis of eucalypt leaf blight resistance, providing the foundation for exploring genes related to this phenomenon. Full article

Species of Mycosphaerellaceae and Teratosphaeriaceae represent over 40% of the fungi identified on eucalypt leaves worldwide. These include some important pathogens that mainly cause leaf blight and spot, and result in increasingly negative impacts on global commercial eucalypt industries. Eucalyptus plantations are commonly cultivated in southern China for solid wood and pulp products. However, the species diversity and geographic distribution of Mycosphaerellaceae and Teratosphaeriaceae, associated with diseased plantation Eucalyptus leaves in China, have not been clarified. In this study, we conducted the first systematic surveys and sample collections of Mycosphaerellaceae- and Teratosphaeriaceae-like fungi from diseased plantation Eucalyptus leaves in southern China. In total, 558 isolates were obtained from 59 sampled sites in five provinces. One isolate was isolated from each tree. According to the disease symptoms, conidia morphological characteristics, and DNA sequence comparisons of ITS, tef1 and tub2 gene regions. The 558 isolates were identified as Teratosphaeria epicoccoides (312 isolates; 55.9%) and T. destructans (246 isolates, 44.1%). Both species were widely distributed in the sampled regions in southern China. The genotypes of T. epicoccoides and T. destructans were determined based on ITS, tef1, and tub2 sequences. The results showed that multiple genotypes of each species of T. epicoccoides and T. destructans exist in China. Additionally, isolates with multiple genotypes were obtained in all five sampled provinces. These results suggest that both T. epicoccoides and T. destructans are not clonal. This study proved that both T. epicoccoides and T. destructans are dominant species and widely distributed on diseased Eucalyptus leaves in southern China. The wide geographic distribution and potential high genetic diversity pose challenges for the disease management of Teratosphaeria leaf blight and leaf spot in China. Full article

Background and objectives: The global forest economy is threatened by eucalypt pathogens which are often latent or cryptic species that escape common quarantine and detection methods. Plantation forestry using eucalypts is of considerable importance to Paraguay, but knowledge regarding the pests and diseases affecting these plantations is limited. This study identified fungal diseases present in these plantations. Materials and Methods: We surveyed eucalypt plantations in four provinces in Paraguay and collected material from diseased trees for identification of the causal agents. The samples were analyzed using a combination of morphological and molecular methods. Results: Diseases encountered included Botryosphaeria stem canker, Calonectria leaf blight, Chrysoporthe stem canker, myrtle/eucalypt rust, Coniella leaf spot, heartwood rot and Teratosphaeria stem canker. Contrary to expectations, the causal agent of Teratosphaeria stem canker was identified as Teratosphaeria zuluensis (M.J. Wingf., Crous & T.A. Cout.) M.J. Wingf. & Crous and not Teratosphaeria gauchensis (M.-N. Cortinas, Crous & M.J. Wingf.) M.J. Wingf. & Crous, that is commonly documented for the South American region. Conclusions: This study updates the knowledge on forest fungal pathogens in Paraguayan eucalypt plantations and is the first report of T. zuluensis in Paraguay and in South America. Full article