Resistance of the wild tomato Solanum habrochaites to Phytophthora infestans is governed by a major gene and polygenes.

This work aimed to study the inheritance of resistance to Phytophthora infestans in tomato plants, using the maximum likelihood estimation function. The susceptible cultivar Santa Clara (Solanum lycopersicum) was used as the female genitor and the P. infestans resistant S. habrochaites f. glabratum accession (BGH 6902) as the male genitor. F1 plants from the crossing were self-pollinated to produce F2 progenies, and also backcrossed with PR and PS to produce BC1:R and BC1:S generations, respectively. The tomato plants were inoculated 50 days after transplanting. Disease severity was evaluated via a diagrammatic scale. Comparison of the genetic models created using the maximum likelihood function revealed that the inheritance of resistance to P. infestans in S. habrochaites is conferred by a major gene with additive and dominance effects, polygenes with additive effects, plus the environmental effect. Vertical resistance can be explored using genes with major effects. Programs of recurrent and maker-assisted selection are considered efficient strategies with which to select genotypes that hold P. infestans resistance conferred by polygenes.

Determining Whether Geographic Origin and Potato Genotypes Shape the Population Structure of Phytophthora infestans in the Central Region of Colombia.

Pathogen variation plays an important role in the dynamics of infectious diseases. In this study, the genetic variation of 279 Phytophthora infestans isolates was assessed using a combination of 12 microsatellite simple-sequence repeat markers. Isolates were collected from 11 different potato cultivars in 11 different geographic localities of the central region of Colombia. The objective of this study was to determine whether populations were differentiated by host genotype or geographic origin. Within a single clonal lineage, EC-1, 76 genotypes were detected. An analysis of molecular variance attributed most of the variation to differences within host genotypes rather than among the host genotypes, suggesting that host cultivars do not structure the populations of the pathogen. Furthermore, the lack of a genetic population structure according to the host cultivar was confirmed by all of the analyses, including the Bayesian clustering analysis and the minimum spanning network that used the Bruvo genetic distance, which suggested that there are no significant barriers to gene flow for P. infestans among potato cultivars. According to the geographic origin, the populations of P. infestans were also not structured, and most of the variation among the isolates was attributed to differences within localities. Only some but not all localities in the north and west of the central region of Colombia showed some genetic differentiation from the other regions. The absence of sexual reproduction of this pathogen in Colombia was also demonstrated. Important insights are discussed regarding the genetic population dynamics of the P. infestans populations of the central region of Colombia that were provided by the results. In Colombia, there is a high genetic variation within the EC-1 clonal lineage with closely related genotypes, none dominant, that coexist in a wide geographic area and on several potato cultivars.

Potato NPH3/RPT2-Like Protein StNRL1, Targeted by a Phytophthora infestans RXLR Effector, Is a Susceptibility Factor.

Plant pathogens deliver effectors to manipulate host processes. We know little about how fungal and oomycete effectors target host proteins to promote susceptibility, yet such knowledge is vital to understand crop disease. We show that either transient expression in Nicotiana benthamiana, or stable transgenic expression in potato (Solanum tuberosum), of the Phytophthora infestans RXLR effector Pi02860 enhances leaf colonization by the pathogen. Expression of Pi02860 also attenuates cell death triggered by the P. infestans microbe-associated molecular pattern INF1, indicating that the effector suppresses pattern-triggered immunity. However, the effector does not attenuate cell death triggered by Cf4/Avr4 coexpression, showing that it does not suppress all cell death activated by cell surface receptors. Pi02860 interacts in yeast two-hybrid assays with potato NPH3/RPT2-LIKE1 (NRL1), a predicted CULLIN3-associated ubiquitin E3 ligase. Interaction of Pi02860 in planta was confirmed by coimmunoprecipitation and bimolecular fluorescence complementation assays. Virus-induced gene silencing of NRL1 in N. benthamiana resulted in reduced P. infestans colonization and accelerated INF1-mediated cell death, indicating that this host protein acts as a negative regulator of immunity. Moreover, whereas NRL1 virus-induced gene silencing had no effect on the ability of the P. infestans effector Avr3a to suppress INF1-mediated cell death, such suppression by Pi02860 was significantly attenuated, indicating that this activity of Pi02860 is mediated by NRL1. Transient overexpression of NRL1 resulted in the suppression of INF1-mediated cell death and enhanced P. infestans leaf colonization, demonstrating that NRL1 acts as a susceptibility factor to promote late blight disease.

Effect of simulated rain on the efficiency of fungicides in potato late blight and early blight control / Efeito de chuva simulada sobre a eficiência de fungicidas no controle da requeima e pinta preta da batata

Rainfastness of fungicides used in the control of late blight (Phytophthora infestans) and early blight (Alternaria solani) of potato was evaluated under green house and laboratory conditions. ‘Agata and ‘Monalisa plants treated with fungicides against both diseases were subjected to 20 mm controlled rain simulation for 6 min at 30 min, 1, 2, and 4 h after application. Once all leaves had dried, foliar discs were transferred to Petri dishes and inoculated with the respective pathogens. The plates were then incubated in a BOD chamber for a 12-h photoperiod at 18°C and 25°C, respectively. Disease severity was evaluated by determining the area (%) of the foliar discs affected by disease on 5 and 7 days post-inoculation. The results suggest that systemic or inherent tenacity fungicides were less influenced by the simulated rain as compared to contact fungicides. An increase in drying time promoted higher control levels of both diseases, indicating a better retention and absorption of the tested fungicides.(AU)

A resistência de fungicidas à chuva no controle da requeima (Phytophthora infestans) e pinta preta (Alternaria solani) da batata foi avaliada em condições de casa-se vegetação e laboratório. Plantas de batata das cultivares Agata e Monalisa tratadas com fungicidas indicados para as duas doenças foram submetidas à chuva controlada de 20 mm durante 6 minutos aos 30 minutos, 1, 2 e 4 horas após a pulverização. Após a secagem das plantas, discos foliares foram coletados e transferidos para placas de Petri e inoculados com os patógenos. Em seguida as placas foram incubadas em câmara BOD a 18° C para P. infestans e 25 ° C para A. solani, sob fotoperíodo de 12 horas. A severidade foi avaliada através da porcentagem da área do disco afetada pelas doenças aos 5 e 7 dias após a inoculação, respectivamente. Os resultados obtidos permitiram concluir que os fungicidas sistêmicos, translaminares ou com tenacidade inerente foram menos afetados pela chuva simulada quando comparados aos fungicidas de contato. O aumento do tempo de secagem promoveu maiores níveis de controle da requeima e pinta preta, evidenciando uma maior retenção ou absorção dos produtos testados.(AU)

De novo pyrimidine biosynthesis in the oomycete plant pathogen Phytophthora infestans.

The oomycete Phytophthora infestans, causal agent of the tomato and potato late blight, generates important economic and environmental losses worldwide. As current control strategies are becoming less effective, there is a need for studies on oomycete metabolism to help identify promising and more effective targets for chemical control. The pyrimidine pathways are attractive metabolic targets to combat tumors, virus and parasitic diseases but have not yet been studied in Phytophthora. Pyrimidines are involved in several critical cellular processes and play structural, metabolic and regulatory functions. Here, we used genomic and transcriptomic information to survey the pyrimidine metabolism during the P. infestans life cycle. After assessing the putative gene machinery for pyrimidine salvage and de novo synthesis, we inferred genealogies for each enzymatic domain in the latter pathway, which displayed a mosaic origin. The last two enzymes of the pathway, orotate phosphoribosyltransferase and orotidine-5-monophosphate decarboxylase, are fused in a multi-domain enzyme and are duplicated in some P. infestans strains. Two splice variants of the third gene (dihydroorotase) were identified, one of them encoding a premature stop codon generating a non-functional truncated protein. Relative expression profiles of pyrimidine biosynthesis genes were evaluated by qRT-PCR during infection in Solanum phureja. The third and fifth genes involved in this pathway showed high up-regulation during biotrophic stages and down-regulation during necrotrophy, whereas the uracil phosphoribosyl transferase gene involved in pyrimidine salvage showed the inverse behavior. These findings suggest the importance of de novo pyrimidine biosynthesis during the fast replicative early infection stages and highlight the dynamics of the metabolism associated with the hemibiotrophic life style of pathogen.

Effect of simulated rain on the efficiency of fungicides in potato late blight and early blight control / Efeito de chuva simulada sobre a eficiência de fungicidas no controle da requeima e pinta preta da batata

Rainfastness of fungicides used in the control of late blight (Phytophthora infestans) and early blight (Alternaria solani) of potato was evaluated under green house and laboratory conditions. ‘Agata’ and ‘Monalisa’ plants treated with fungicides against both diseases were subjected to 20 mm controlled rain simulation for 6 min at 30 min, 1, 2, and 4 h after application. Once all leaves had dried, foliar discs were transferred to Petri dishes and inoculated with the respective pathogens. The plates were then incubated in a BOD chamber for a 12-h photoperiod at 18°C and 25°C, respectively. Disease severity was evaluated by determining the area (%) of the foliar discs affected by disease on 5 and 7 days post-inoculation. The results suggest that systemic or inherent tenacity fungicides were less influenced by the simulated rain as compared to contact fungicides. An increase in drying time promoted higher control levels of both diseases, indicating a better retention and absorption of the tested fungicides.

A resistência de fungicidas à chuva no controle da requeima (Phytophthora infestans) e pinta preta (Alternaria solani) da batata foi avaliada em condições de casa-se vegetação e laboratório. Plantas de batata das cultivares Agata e Monalisa tratadas com fungicidas indicados para as duas doenças foram submetidas à chuva controlada de 20 mm durante 6 minutos aos 30 minutos, 1, 2 e 4 horas após a pulverização. Após a secagem das plantas, discos foliares foram coletados e transferidos para placas de Petri e inoculados com os patógenos. Em seguida as placas foram incubadas em câmara BOD a 18° C para P. infestans e 25 ° C para A. solani, sob fotoperíodo de 12 horas. A severidade foi avaliada através da porcentagem da área do disco afetada pelas doenças aos 5 e 7 dias após a inoculação, respectivamente. Os resultados obtidos permitiram concluir que os fungicidas sistêmicos, translaminares ou com tenacidade inerente foram menos afetados pela chuva simulada quando comparados aos fungicidas de contato. O aumento do tempo de secagem promoveu maiores níveis de controle da requeima e pinta preta, evidenciando uma maior retenção ou absorção dos produtos testados.

Physiological and molecular characterization of Phytophthora infestans isolates from the Central Colombian Andean Region.

BACKGROUND: Late blight, caused by Phytophthora infestans, is one of the most devastating diseases found in potato and tomato crops worldwide. In Colombia it also attacks other important crops: cape gooseberry and tree tomato. The knowledge of the pathogen population is determinant to effectively design control strategies. AIMS: To determine the physiological and molecular characteristics of a set of Colombian P. infestans isolates. METHODS: Strains isolated from Cundinamarca and Boyacá were examined for the level of resistance to mefenoxam and cymoxanil. Virulence was tested for all strains and crosses between A1 mating type, from different hosts, and the Colombian A2 mating type were tested for the production and viability of oospores in different substrates. Additionally, the molecular diversity of the avirulence gene Avr3a, the ß-tubulin gene, and two single copy genes showing RxLR motif, was assessed. RESULTS: We found all levels of mefenoxam sensitivity, with 48% of the strains resistant. A high diversity of races was detected and the population was genetically clonal. Colombian strains had the possibility of sexual reproduction. CONCLUSIONS: These results will help in optimizing the use of fungicides and deployment of resistance as control strategies and will contribute to broader studies on diversity of this pathogen.

Targeted metabolic reconstruction: a novel approach for the characterization of plant-pathogen interactions.

Genome-scale metabolic reconstruction (GEMR), along with flux balance analysis, has been widely used to study complex metabolic networks in several microbial organisms. This approach is of particular applicability in biological systems where the lack of kinetics data is typical. This is the case of plant-pathogen interactions, where these methods open the possibility of studying host metabolic network phenotype during the interaction with pathogens. Since GEMRs are based on sequenced genomes, its applicability to organisms where genomic information is lacking is limited. Here we describe an alternative approach to GEMR: targeted metabolic reconstruction, where network reconstruction is guided by transcriptomic data instead of genomic information. This approach is being applied successfully in our laboratory for the Phytophthora infestans--Solanum tuberosum pathosystem.