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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 −log10(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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Solubilization of plant nutrients from silicate rocks, using acids produced by microorganisms has emerged as both an environmentally friendly and an economically viable process for fertilizer production. In this work, biogenic acid was produced using Acidithiobacillus thiooxidans and elemental sulfur, and used it to solubilize K from verdete (Ve) and phonolite (Fo) rocks, comparing its solubilization efficiency to that of commercial sulfuric acid at 1 : 2 and 1 : 5 rock : acid ratios. After acid solubilization, the Ve and Fo rocks were chemically and morphologically characterized using several techniques. Agronomic performances of biogenic K-fertilizers derived from Ve and Fo were evaluated in a sequential corn–soybean–millet cropping system. Acid type and rock : acid ratio influenced the solubilization of K species from the rocks. Overall, biogenic acid led to a higher solubilization of K species in water and in citric acid than commercial sulfuric acid. The amount of solubilized K was higher at a 1 : 5 rock : acid ratio. Total dry matter yield and total K uptake by the crops increased as K rates increased and varied among K sources. Ve and Fo biogenic K-fertilizers provided higher amounts of available K to the crops than their in natura forms (rocks). The effect of acid solubilization was more notorious for Ve rock, significantly increasing the value of its acidified product as a fertilizer. Thus, our data demonstrate that biogenic acid produced by A. thiooxidans using elemental sulfur is a promising alternative to leach out K from silicate rocks. [ABSTRACT FROM AUTHOR]

Erwinia psidii (Eps) is the causal agent of emerging diseases of eucalypt and guava; however, the mechanisms underlying its pathogenicity are not fully understood. Here, we predicted factors involved in the ability of Eps to cause disease on its host plants. For that, the genomes of four Eps strains exhibiting different virulence on eucalypt were sequenced, and hrp/hrc genes coding for the type III secretion system (T3SS), effectors injected into the plant cell cytoplasm through the T3SS (T3SEs) and their plant subcellular localizations, as well as proteins deployed to the host apoplast, were predicted. It was found that Eps possesses a complete hrp/hrc gene cluster based on comparison with Erwinia amylovora. A total of 18 T3SEs were predicted, 11 of which were shared among all strains, none were exclusive to any strain and seven were absent in at least one strain. No sequence variation among strains was found for five T3SE candidates whereas extensive variation was found for six, suggesting the latter may be determinants of virulence differences. The T3SE candidates are predicted to target the plant cell nucleus, cytoplasm, mitochondrion, chloroplast and peroxisome. The predicted apoplastic effector repertoire common to all four strains was over‐represented in proteins of unknown functions or predicted to possess enzymatic activities, among which the most abundant were oxidoreductases and peptidases. Proteins with lytic transglycosylase activity were predicted in strain‐specific apoplastic effector repertoires. These results provide an important framework for future research aimed at uncovering the factors underlying Eps pathogenicity. [ABSTRACT FROM AUTHOR]

Foliar spots caused by Pseudomonas coronafaciens pv. garcae (Pcg), Pseudomonas amygdali pv. tabaci (Pat) and Pseudomonas cichorii (Pch) are major bacterial diseases that can reduce coffee production. However, little is known about the genetic diversity and molecular mechanisms underlying the pathogenicity to coffee plants of these bacteria. In this study, genome sequences of Pcg, Pat and Pch strains isolated from coffee plants in Minas Gerais state, Brazil, were used to assess their variability and plasticity, and compare their type III secretion system (T3SS) and apoplastic effector repertoires as well as tabtoxin biosynthetic/detoxification genes. Genomic diversity was found for all three phytopathogens, among which Pch possesses the highest number of exclusive proteins. The Pcg genome is the most stable whereas that of Pch is the most plastic, which is related to their host ranges. When compared with those of Pseudomonas syringae pv. tomato DC3000, hrp/hrc gene sequences are more conserved in Pcg and Pat than in Pch, which also possesses the smallest T3SS and the largest apoplastic effector repertoires. The only T3SS effector family common to all three pathogens is AvrE, suggesting that, as for other plant–Pseudomonas interactions, it may play a crucial role for pathogenicity towards coffee plants. Apoplastic proteins associated with maintaining the redox balance and degrading proteins/peptides not previously described as important in plant–bacteria interactions were found. Gain/loss of the tabtoxin biosynthetic cluster with retention of the antitoxin gene was observed, indicating that tabtoxin production is not a limiting factor for the occurrence of mixed infections. [ABSTRACT FROM AUTHOR]

Soybean bacterial pustule is caused by the gram‐negative bacterium Xanthonomas citri pv. glycines. The identification of sources of resistance for use in molecular breeding is a challenge due to the existence of complex interactions between pathogenic strains and soybean cultivars. This study aimed to evaluate the reaction of 118 soybean cultivars to inoculation with strains 2440P and 2447 of X. citri pv. glycines and to identify molecular markers associated with the resistance. The genome‐wide association study approach was used to identify association between the phenotype and the single nucleotide polymorphisms (SNP) markers. The positions of significant SNPs were mapped to the soybean Williams 82 genome, and protein‐coding genes near them were identified. One and 116 cultivars were resistant to strains 2440P and 2447, respectively. Eleven SNPs were significantly associated with resistance to strain 2440P and five to 2447. Two significant SNPs are predicted to result in amino acid changes in benzyl alcohol O‐benzoyltransferase‐like and MAIN‐LIKE 1‐like proteins, which after confirmation, could be used in marker‐assisted selection in order to increase the frequency of resistant alleles in new cultivars. [ABSTRACT FROM AUTHOR]

The Pucciniomycete fungus Hemileia vastatrix causes leaf rust on coffee trees. The pathogen is responsible for considerable yield losses in susceptible coffee cultivars if appropriate management strategies are not implemented. Rapid spread and epidemics of rust fungi are usually associated with the emergence of new races of the pathogen that overcome resistance or with the emergence of more aggressive populations of the pathogen. In Brazil, coffee production is dominated by susceptible cultivars of Coffea arabica and Coffea canephora. We assessed aggressiveness in 46 populations of H. vastatrix from Minas Gerais and Espírito Santo, two of the most important coffee-producing states in Brazil. We observed a significant difference in the incubation period between the populations from Minas Gerais and Espírito Santo when 183 single-pustule isolates were inoculated onto Catuaí Vermelho IAC 44, a susceptible C. arabica cultivar. Variation in aggressiveness components was observed between and within localities. Isolates with longer incubation periods also tended to have longer latent periods, although there was only a low correlation between these two aggressiveness components ( r2 = 0.34, P = 2.2 × 10−16). Low-sporulating isolates also had significantly longer incubation and latent periods. The H. vastatrix population from Minas Gerais and Espírito Santo is structured by the formation of groups of individuals with differential level of aggressiveness. Our results indicate that the variation in aggressiveness of the Brazilian H. vastatrix population may be associated with the geographic coffee-producing areas. [ABSTRACT FROM AUTHOR]

Common bean (Phaseolus vulgaris) is one of the most consumed agricultural products in the world. Its production is affected by common bacterial blight (CBB) caused by Xanthomonas citri pv. fuscans and X. phaseoli pv. phaseoli. In this work, we investigated the spectrum, genetics, and inheritance of common bean resistance to X. citri pv. fuscans. Inoculation of nine selected cultivars with an X. citri pv. fuscans strain showed that BRS Radiante and IAPAR 16 were resistant. These two cultivars were also resistant to six X. phaseoli pv. phaseoli strains of different geographic origins, demonstrating their broad-spectrum resistances. BRS Radiante sustained smaller X. citri pv. fuscans populations than two susceptible cultivars. Stomatal densities of IAPAR 16 and BRS Radiante were significantly higher than or not different from susceptible cultivars. BRS Radiante showed the lowest general combining ability values and the combination BRS Radiante x Carioca MG the lowest specific combining ability (SCA) values, revealing the capacity of BRS Radiante to increase resistance to X. citri pv. fuscans. Positive and negative parental SCA values indicated dominant and recessive genes involved in X. citri pv. fuscans resistance. Resistance of the BRS Radiante x Carioca MG cross segregated in a 9:7 ratio in the Ft population, indicating that it is governed by two complementary dominant genes. Maximum likelihood analysis showed that the resistance of BRS Radiante to X. citri pv. fuscans is conferred by a gene of major effect with contribution of additional polygenes. This study contributes with important knowledge on the resistance against CBB in Brazilian common bean cultivars as well as with molecular tools for confirmation of common bean hybrids. [ABSTRACT FROM AUTHOR]