Jorge Luis Badel

‘Ubá’ mango is a fruit crop of great value for farmers in the Zona da Mata region of Minas Gerais state, Brazil. Organic farmers from this region recently reported a severe outbreak of foliar black spots of unknown aetiology in orchards of this mango variety, causing significant concern. The objective of this study was to identify the causal agent of the disease by conducting microbial isolations, biochemical and molecular characterizations, multi‐locus sequence analysis and pathogenicity tests. Bacterial isolates displaying orange‐, yellow‐ and cream‐coloured colonies were recovered from diseased leaves collected in the mango orchards. Upon inoculation of healthy mango plants, a representative isolate of each colony colour was able to reproduce the black spot symptoms typical of the disease. Bacterial isolates with the same colony morphology as those recovered from naturally infected plants were reisolated from the inoculated plants, confirming that they are etiological agents of the disease. In a phylogenetic analysis, the cream‐coloured bacterium clustered in the same clade with the Burkholderia contaminans type strain, whereas the yellow‐ and orange‐bacteria formed independent clades within Sphingomonas and Microbacterium , respectively, indicating the identification of new bacterial genomospecies. These results revealed that the leaf spots of mango trees in Ubá have a complex aetiology, represent the first report of the pathogenicity of these three bacterial species towards mango trees and provide crucial information for the development of diagnostic and control methods.

Tectona grandis (teak) is a tree species highly appreciated for its high‐quality hardwood and versatile industrial applications. Despite clonal teak plantations showing several advantages, such as reduced rotation time and increased wood volume production, the genetic uniformity of plantations makes them more susceptible to diseases. Ceratocystis wilt caused by Ceratocystis manginecans has been the most prevalent disease on teak plantations, reducing tree growth rate, wood quality and value. Planting resistant genotypes is the most effective measure to mitigate losses caused by the disease. Thus, this work aimed to assess the resistance to Ceratocystis wilt of 12 teak clones commercially planted in Brazil, as well as the inheritance of resistance in teak open‐pollinated families. Five teak clones exhibited resistance to Ceratocystis wilt, and all investigated open‐pollinated teak families segregated resistance. The findings support the interpretation that resistance to Ceratocystis wilt in teak is a quantitative trait with additive gene effects in determining this trait. The information obtained in this work is an important contribution to directing the efforts of teak breeding programs in the attempt to reduce the losses caused by Ceratocystis wilt.

Xant homonas axonopodis pv. ricini is the major bacterial pathogen of castor bean ( Ricinus communis L.), an important source for oil production in several countries; only castor bean has been reported as its natural host. Recently, its pathotype strain ICMP 5747 was shown to cause disease in eucalypt plants and to group with Xanthomonas euvesicatoria in a multi-locus sequence analysis (MLSA), raising doubts about its taxonomic position. The objective of this study was to assemble the genome sequence of strain ICMP 5747 and employ it in MLSA using Bayesian inference and maximum likelihood methods with four housekeeping genes, phylogenomics based on conserved homologous genes, and genome sequence comparisons against validly published or proposed Xanthomonas species to elucidate its taxonomic position. A 5.1 Mb draft genome sequence with a 65% GC content and 99.7% completeness was assembled. MLSA, phylogenomic reconstruction based on 368 conserved genes, and genome comparisons demonstrated that strain ICMP 5747 is more closely related to X. euvesicatoria strains than to the X. axonopodis type strain. Serendipitously, it was also found that the X. axonopodis pv . commiphoreae pathotype strain LMG 26789 is also more closely related to X. euvesicatoria strains. This study proposes the transfer of X. axonopodis pvs. ricini and commiphoreae to the X. euvesicatoria species, as X. euvesicatoria pv . ricini comb. nov. and X. euvesicatoria pv . commiphoreae comb. nov. to help establish the phylogenetic relationships among Xanthomonas species and determine the etiology of plant diseases.

Teratosphaeria nubilosa is the predominant causal agent of Teratosphaeria leaf disease (TLD) in experimental plantations of E. globulus in Brazil. It exhibits slow vegetative growth and lack of sporulation in in vitro culture, making it difficult to obtain enough ascospores for mass inoculation. This study aimed to establish an inoculation method based on ascospore ejection from naturally infected leaves and use it to assess the response to T. nubilosa of eucalypt species and interspecific hybrids. First, the optimal temperature and incubation time for ascospores ejection from naturally infected E. globulus leaves were determined in vitro. Then, these optimal conditions were used to assess the response of eight eucalypt genotypes to T. nubilosa inoculation using ejected ascospores. The infected leaves were placed above (T1), above and under (T2) or under (T3) the plants to be inoculated. Significant differences in disease incidence, disease severity and plant defoliation were observed among genotypes and inoculation treatments. Plants exhibited higher incidence, more severe symptoms and more defoliation when exposed to T2. E. globulus and E. globulus × E. nitens clones were the most susceptible whereas an E. benthamii clone was immune. The sources of resistance identified in this work can be used in hybridization programmes with E. globulus to obtain interspecific hybrids expressing resistance to T. nubilosa and retaining the desirable traits for planting in temperate climates. The inoculation method optimized in this work could be used for small and medium‐scale screening of Eucalyptus spp. resistant to TLD. However, periodic validation of the species and genotype of the fungus associated with the naturally infected leaves used for inoculation and confirmation of the resistant phenotype of the selected eucalypt clones or progenies through experimental replications over time must be conducted.

Bacterial leaf blight (BLB) caused by Xanthomonas spp. is an important threat for eucalypt production. Planting of resistant genotypes is the best strategy for eucalypt BLB control. However, selection of resistant clones is challenging since the disease is caused by at least three Xanthomonas species that can be sympatric and cause a range of foliar symptoms. So far, standard area diagrams (SADs) to assess eucalypt BLB severity caused by different Xanthomonas species have not been reported. Here, SADs for eucalypt BLB severity assessment were developed. Plants of five eucalypt genotypes were individually inoculated with different Xanthomonas species and leaves exhibiting lesions varying in colour, shape, and size were digitally scanned for disease assessment. Among 150 scanned leaves, the actual leaf affected area ranged from 0.01% to 55%. Based on these minimum and maximum values and the frequency of severity distribution, the 10 leaves that best represented the distribution of affected leaf area were selected to assemble the SADs. Groups of experienced and inexperienced raters estimated BLB severity on a subset of 50 out of the 150 original leaves without and then with the use of the SADs. Correlation concordance analyses revealed that SADs provided a significant improvement in accuracy, precision and reliability of disease estimates by both rater groups, with higher gains observed for the inexperienced group. The SADs developed in this study will be useful for selection of eucalypt genotypes resistant to BLB under controlled conditions when knowledge on the Xanthomonas species composition is lacking or when local populations are comprised of several species.

Carioca and black bean groups play a significant role in Latin American common bean ( Phaseolus vulgaris ) consumption, serving as excellent sources of nutrients. One of the most significant threats for common bean production is common bacterial blight (CBB), a disease caused by the gram‐negative bacteria Xanthomonas phaseoli pv. phaseoli (Xpp) and Xanthomonas citri pv. fuscans (Xcf). An effective method for managing this disease is the use of plant genetic resistance. However, it is not known whether the same or overlapping sets of genes are associated with resistance to both pathogens. This study aimed to identify a repertoire of genes potentially associated with resistance to Xpp and compare it with that previously reported for Xcf. Eighty carioca and black common bean cultivars that had previously been challenged with Xcf were inoculated with a strain of Xpp, and a genome‐wide association study (GWAS) using single‐nucleotide polymorphisms (SNPs) and disease severity data was conducted. Three carioca and three black bean cultivars exhibited high levels of resistance to Xpp. Five SNPs with the highest −log ₁₀ ( p ) values unveiled genes coding for diverse putative biochemical functions, including a light‐regulated Lir1 protein, a proton‐dependent oligopeptide transporter family protein, a metallo‐dependent phosphatase‐like protein, a WPP domain‐interacting tail‐anchored protein 2 and a pectin lyase‐like superfamily protein. No overlap between this repertoire of genes with that reported for Xcf was found. These findings provide important insights into genes potentially involved in the P . vulgaris resistance to Xpp and the complexity of the resistance response to CBB.

Outbreaks of bacterial leaf blight (BLB) frequently affect eucalypt plants under nursery and field conditions in several countries. Although research has been conducted to unveil the causal agent, different bacterial species have been associated with similar disease symptoms in different countries. In order to determine the causal agent of BLB in Brazil, a survey was conducted in nine states to recover bacterial isolates from eucalypt plants exhibiting typical BLB symptoms. A total of 41 yellow-colony isolates with varying aggressiveness towards a susceptible eucalypt clone were obtained, with 16S rDNA sequences indicating that they belong to the Xanthomonas genus. Rep-PCR analysis separated the Xanthomonas population affecting eucalypt into six distinct groups revealing its high genetic diversity. The same population formed three clusters together with reference strains of X. citri, X. euvesicatoria and X. phaseoli in a phylogenetic tree constructed with partial dnaK, fyuA, gyrB and rpoD gene sequences. Clustering in the phylogenetic tree was clearly related to grouping based on rep-PCR. Genome sequence comparisons of representative eucalypt isolates with type strains of validly published Xanthomonas species confirmed that the population consisted of X. citri, X. euvesicatoria and X. phaseoli. Inoculation of tomato, common bean, castor bean and eucalypt plants showed that the representative eucalypt isolates can cause disease in these plant species. Based on the results, the transfer of Xanthomonas axonopodis pv. eucalyptorum to Xanthomonas citri is proposed. These results are relevant for eucalypt BLB management under nursery and field conditions, including selection and deployment of effective plant resistance.