The fungus Rhizoctonia solani anastomosis group (AG)-1 IA emerged in the early 1990s as an important pathogen causing foliar blight and collar rot on pastures of the genus Urochloa (signalgrass) in South America. We tested the hypothesis that this pathogen emerged following a host shift or jump as a result of geographical overlapping of host species. The genetic structure of host and regional populations of R. solani AG-1 IA infecting signalgrass, rice, and soybean in Colombia and Brazil was analyzed using nine microsatellite loci in 350 isolates to measure population differentiation and infer the pathogen reproductive system. Phylogeographical analyses based on the microsatellite loci and on three DNA sequence loci were used to infer historical migration patterns and test hypotheses about the origin of the current pathogen populations. Cross pathogenicity assays were conducted to measure the degree of host specialization in populations sampled from different hosts. The combined analyses indicate that the pathogen populations currently infecting Urochloa in Colombia and Brazil most likely originated from a population that originally infected rice. R. solani AG-1 IA populations infecting Urochloa exhibit a mixed reproductive system including both sexual reproduction and long-distance dispersal of adapted clones, most likely on infected seed. The pathogen population on Urochloa has a genetic structure consistent with a high evolutionary potential and showed evidence for host specialization.

The fungus Rhizoctonia oryzae-sativae is an important pathogen that causes the aggregated sheath spot disease on rice. In this study, we investigated the genetic structure of rice-adapted populations of R. oryzae-sativae sampled from traditional rice-cropping areas from the Paraíba Valley, São Paulo, Brazil, and from Meta, in the Colombian Llanos, in South America. We used five microsatellite loci to measure population differentiation and infer the pathogen's reproductive system. Gene flow was detected among the three populations of R. oryzae-sativae from lowland rice in Brazil and Colombia. In contrast, a lack of gene flow was observed between the lowland and the upland rice populations of the pathogen. Evidence of sexual reproduction including low clonality, Hardy-Weinberg equilibrium within loci and gametic equilibrium between loci, indicated the predominance of a mixed reproductive system in all populations. In addition, we assessed the adaptive potential of the Brazilian populations of R. oryzae-sativae to emerge as a pathogen to Urochloa spp. (signalgrass) based on greenhouse aggressiveness assays. The Brazilian populations of R. oryzae-sativae were probably only incipiently adapted as a pathogen to Urochloa spp. Comparison between R and Q showed the predominance of diversifying selection in the divergence between the two populations of R. oryzae-sativae from Brazil.

Leaf blight, sheath blight, and web blight are major diseases caused by Rhizoctonia species on both Fabaceae and Poaceae plant hosts in the Brazilian Amazon agroecosystem. To determine the diversity of Rhizoctonia species associated with foliar diseases on fabaceous (cowpea and soybean) and poaceous (rice and signal grass [Urochloa brizantha]) hosts, a broad survey was conducted in Pará, Rondônia, Roraima, and Mato Grosso, in the Amazon, from 2012 to 2013. We extended our survey to Cerrado areas of Mato Grosso, and the lowlands of Paraíba Valley, in São Paulo, where these Rhizoctonia foliar diseases have not been reported so far. Our findings revealed that these diseases are caused by a diversity of Rhizoctonia solani AG‐1 complex. We detected that R. solani AG‐1 IA (sexual phase Thanatephorus cucumeris) was the predominant pathogen associated with signal grass leaf blight and collar rot diseases in the Amazon, especially in Rondônia and northern Mato Grosso. In addition, a subgroup of R. solani (AG‐1 IF), not previously reported in Brazil, was associated with leaf blight on cowpea and soybean, in Roraima. Another subgroup (AG‐1 ID) was also detected in Roraima. In Mato Grosso Cerrados we did not find any of the major Rhizoctonia foliar pathogens. Instead, R. oryzae (Waitea circinata) was the predominant species associated with a collar rot on U. brizantha. In the lowlands of São Paulo, R. oryzae‐sativae (Ceratobasidium oryzae‐sativae) was the predominant pathogen detected causing the rice sheath spot disease.

Foliar blight and death of signalgrass (Urochloa spp.) pastures are caused by the Rhizoctonia solani fungus. This study aimed at determining which pathogens from the Rhizoctonia species complex are associated with leaf and sheath blight in Urochloa and rice, in the Colombian Llanos. Sympatric areas of Urochloa pastures adjacent to rice cropping areas were sampled using a linear transect system. The pathogens were identified using morphological traits, molecular detection based on specific primers and sequencing of the ITS-5.8S rDNA region. R. solani AG-1 IA predominated as the pathogen associated with foliar blight in all samples from U. brizantha cv. 'Toledo' and hybrid Urochloa cv. 'Mulato'. Besides R. solani AG-1 IA (18 % of the samples), Rhizoctonia oryzae-sativae (71 %) and Sclerotium hydrophilum (11 %) were also detected. In the cross-pathogenicity test, the R. solani AG-1 IA fungus was the most aggressive to Urochloa, while R. oryzae-sativae produced very mild infection symptoms. This is the first report of R. oryzae-sativae and S. hydrophilum associated with the complex of rice sheath blight diseases in Colombia.

RESUMO O fungo Rhizoctonia solani grupo de anastomose AG-1 IA emergiu como patógeno importante associado à queima foliar, podridão do coleto e morte de pastagens do gênero Urochloa (braquiária) na América do Sul. Neste estudo objetivou-se determinar se a adaptação de R. solani AG-1 IA à Urochloa spp. na Colômbia promoveu diferenças fenotípicas de agressividade a hospedeiros distintos. Testou-se a hipótese de que as populações do patógeno adaptadas à Urochloa não são hospedeiro-especializadas e, desta forma, não estão geneticamente isoladas, mantendo assim ampla gama de hospedeiros, incluindo as fabáceas feijão caupi e soja. Determinou-se, também, se dois grupos de isolados obtidos de populações de R. solani AG-1 IA amostradas de Urochloa na Colômbia tinham potencial adaptativo para emergir como patógeno do milho. Além do nível de agressividade da doença em diferentes hospedeiros, determinou-se os componentes de evolutibilidade como o coeficiente de variância genotípica (IG), de variância ambiental (IE) e a herdabilidade (h2). Concluiu-se que: i) A adaptação de R. solani AG-1 IA à Urochloa spp. não promoveu diferenças fenotípicas de agressividade em hospedeiros distintos e, desta forma, o patógeno mantêm ampla gama de hospedeiros; ii) A população de R. solani AG-1 IA de Urochloa híbrido Mulato da Colômbia tem potencial adaptativo para emergir como patógeno do milho.

No abstract

White Band Disease (WBD) is one of the most harmful coral syndromes in the Caribbean, de t eri ora tin g t he structure of many corals during the eighties and nineties. Since its e tiology is not entirely known, the use of techniques aimed at ide ntifying the associated agents could provide an approach to the composition of the populations involved in the deterioration of A. cervicornis. Therefore, this research's objective was to isolate and characterize bacteria associated with WBD in A. cervicornis from hanging nurseries of Rosario and San Bernardo Corals National Natural Park, Colombia, using MALDI-TO F MS and PCR. The re sults showed the presence of Bacillus cereus bacteria in individuals with bleaching signs from nurseries and transplant are as on Isla Tesoro and Isla Ceiner. O ne of these strains se quenced and phylogenetically analyzed was closely related to Bacillus thuringiensis, with similarities of up to 99%. The presence of B. cereus could indicate a special relationship be tween this microorganism and WBD. However, it is imperative to carry out more studies on identifying the bacteria a ss ocia ted wi t h t h is dise ase to support these findings.

In this work, we recognized cassava diseases and pests, by means of convolutional neural networks, as a way to avoid the spread of pathogens, prevent economic losses, and favor decision-making for a proper disease management. For the development of this system, VGG16, ResNet50 and Xception models were chosen for having displayed good performance in previous researches of disease classification in plants, which we considered very similar to our case of study. For the training procedure, a transfer learning technique was implemented, employing a database categorized by cassava diseases (bacterial blight, brown streak, green mite, mosaic disease), as well as healthy leaves. This database was balanced and refined manually, selecting the images that represented characteristics of each category, according to the description found in the existing literature. Finally, the best model was chosen taking into account its performance measured through the Accuracy metric. The best model obtained, which we propose in this work, was Xception, and was trained during a period of 35 epochs with 6120 images of cassava leaves, achieving an accuracy of 94.56% . This model provides an option to detect cassava leaf diseases early, reliably and cost-effectively.