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BACKGROUND: Corn is one of the main crops grown globally to produce food for human consumption and animal feed, including raw materials for bioenergy. Effective pest management is critical for the economic viability of corn production. The leafhopper Dalbulus maidis and the diseases transmitted by it have become relevant to corn production. Our study aimed to determine environmental parameters that affect D. maidis populations and the impacts of pathogen dispersion on corn productivity under different rotation systems and sowing seasons. RESULTS: The population density of leafhoppers found in the studied crops was low but capable of establishing the diseases and spreading them widely in the crops. The leafhopper's highest occurrence was in the corn vegetative development stage, and its population peaks were earlier in the corn off-season. The incidence of maize rayado fino virus and maize bushy stunt phytoplasma were higher in corn off-season than in the growing season. The incidence of diseases was higher in the final stages of the cultivation cycle. Yield losses were significantly higher for maize bushy stunt phytoplasma and not significant for maize rayado fino virus. CONCLUSION: Our study observed that corn's physiological stage was the main factor influencing D. maidis dynamics. The occurrence of D. maidis at low densities was sufficient to ensure the efficient transmission and dissemination of maize rayado fino virus and maize bushy stunt phytoplasma, which had a higher incidence in the reproductive stage and the corn sowed off-season. © 2023 Society of Chemical Industry.

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The infection of Capsicum annuum cv. mirasol by Candidatus Phytoplasma trifolii (16SrVI) causes devastating crop losses in northern Mexico. This study addresses the metabolomics profiling of mirasol chili peppers (Capsicum annuum cv. mirasol) infected by Candidatus Phytoplasma trifolii. For this study, 25 diseased fruits and 25 healthy fruits were used. Principal component analysis (PCA) and orthogonal projections to latent structures discriminant analysis (OPLS-DA) revealed dramatic changes in the content of 42 metabolites which were identified in diseased and healthy mirasol chili peppers. The endogenous levels of fructose, glucose and formic acid were substantially decreased in the diseased chili peppers. In the same group of samples, high concentrations of alanine, asparagine, fumaric acid, sucrose and threonine were observed. The content of Choline didnt present a significant difference. This evidence supports the fact that Candidatus Phytoplasma trifolii infection reduces de CO2 fixation into carbohydrates, decreases invertase activity, and inhibits glycolysis in the diseased plant tissues. The levels of ascorbic acid, capsaicin and dihydrocapsaicinin in diseased fruits were dramatically decreased, suggesting that Candidatus Phytoplasma trifolii can reduce the pungency and the nutraceutical value of mirasol chili peppers.

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Biological invasions of vectorborne diseases can be devastating. Bioclimatic modeling provides an opportunity to assess and predict areas at risk from complex multitrophic interactions of pathogens, highlighting areas in need of increased monitoring effort. Here, we model the distribution of an economically critical vectorborne plant pathogen 'Candidatus Phytoplasma aurantifolia', the etiological agent of Witches' Broom Disease of Lime. This disease is a significant limiting factor on acid lime production (Citrus aurantifolia, Swingle) in the Middle East and threatens its production globally. We found that temperature, humidity, and the vector populations significantly determine disease distribution. Following this, we used bioclimatic modeling to predict potential novel sites of infections. The model outputs identified potential novel sites of infection in the citrus producing regions of Brazil and China. We also used our model to explore sites in Oman where the pathogen may not be infectious, and suggest nurseries be established there. Recent major turbulence in the citrus agricultural economy has highlighted the importance of this work and the need for appropriate and targeted monitoring programs to safeguard lime production.

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Background and Aims: Maize bushy stunt phytoplasma (MBSP) is a bacterial pathogen of maize ( Zea mays L.) across Latin America. MBSP belongs to the 16SrI-B sub-group within the genus ' Candidatus Phytoplasma'. MBSP and its insect vector Dalbulus maidis (Hemiptera: Cicadellidae) are restricted to maize; both are thought to have coevolved with maize during its domestication from a teosinte-like ancestor. MBSP-infected maize plants show a diversity of symptoms. and it is likely that MBSP is under strong selection for increased virulence and insect transmission on maize hybrids that are widely grown in Brazil. In this study it was investigated whether the differences in genome sequences of MBSP isolates from two maize-growing regions in South-east Brazil explain variations in symptom severity of the MBSP isolates on various maize genotypes. Methods: MBSP isolates were collected from maize production fields in Guaíra and Piracicaba in South-east Brazil for infection assays. One representative isolate was chosen for de novo whole-genome assembly and for the alignment of sequence reads from the genomes of other phytoplasma isolates to detect polymorphisms. Statistical methods were applied to investigate the correlation between variations in disease symptoms of infected maize plants and MBSP sequence polymorphisms. Key Results: MBSP isolates contributed consistently to organ proliferation symptoms and maize genotype to leaf necrosis, reddening and yellowing of infected maize plants. The symptom differences are associated with polymorphisms in a phase-variable lipoprotein, which is a candidate effector, and an ATP-dependent lipoprotein ABC export protein, whereas no polymorphisms were observed in other candidate effector genes. Lipoproteins and ABC export proteins activate host defence responses, regulate pathogen attachment to host cells and activate effector secretion systems in other pathogens. Conclusions: Polymorphisms in two putative virulence genes among MBSP isolates from maize-growing regions in South-east Brazil are associated with variations in organ proliferation symptoms of MBSP-infected maize plants.

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BACKGROUND: Witches' broom disease of Mexican lime (Citrus aurantifolia L.), which is associated to the phytoplasma 'Candidatus Phytoplasma aurantifolia', is a devastating disease that results in significant economic losses. Plants adapt to biotic stresses by regulating gene expression at the transcriptional and post-transcriptional levels. MicroRNAs (miRNAs) are a recently identified family of molecules that regulate plant responses to environmental stresses through post-transcriptional gene silencing. METHODS: Using a high-throughput approach to sequence small RNAs, we compared the expression profiles of miRNAs in healthy Mexican lime trees and in plants infected with 'Ca. P. aurantifolia'. RESULTS: Our results demonstrated the involvement of different miRNAs in the response of Mexican lime trees to infection by 'Ca. P. aurantifolia'. We identified miRNA families that are expressed differentially upon infection with phytoplasmas. Most of the miRNAs had variants with small sequence variations (isomiRs), which are expressed differentially in response to pathogen infection. CONCLUSIONS: It is likely that the miRNAs that are expressed differentially in healthy and phytoplasma-infected Mexican lime trees are involved in coordinating the regulation of hormonal, nutritional, and stress signalling pathways, and the complex interactions between them. Future research to elucidate the roles of these miRNAs should improve our understanding of the level of diversity of specific plant responses to phytoplasmas.

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Huanglongbing (HLB) is a severe citrus (Citrus spp.) disease associated with the bacteria genus Candidatus Liberibacter, detected in Brazil in 2004. Another bacterium was found in association with HLB symptoms and characterized as a phytoplasma belonging to the 16SrIX group. The objectives of this study were to identify potential leafhopper vectors of the HLB-associated phytoplasma and their host plants. Leafhoppers were sampled every other week for 12 mo with sticky yellow cards placed at two heights (0.3 and 1.5 m) in the citrus tree canopy and by using a sweep net in the ground vegetation of two sweet orange, Citrus sinensis (L.) Osbeck, groves infected by the HLB-phytoplasma in São Paulo state. Faunistic analyses indicated one Agalliinae (Agallia albidula Uhler) and three Deltocephalinae [Balclutha hebe (Kirkaldy), Planicephalus flavicosta (Stål), and Scaphytopius (Convelinus) marginelineatus (Stål)] species, as the most abundant and frequent leafhoppers (Hemiptera: Cicadellidae). Visual observations indicated an association of leafhopper species with some weeds and the influence of weed species composition on leafhopper abundance in low-lying vegetation. S. marginelineatus and P. flavicosta were more frequent on Sida rhombifolia L. and Althernantera tenella Colla, respectively, whereas A. albidula was observed more often on Conyza bonariensis (L.) Cronq. and B. hebe only occurred on grasses. DNA samples of field-collected S. marginelineatus were positive by polymerase chain reaction and sequencing tests for the presence of the HLB-phytoplasma group, indicating it as a potential vector. The association of leafhoppers with their hosts may be used in deciding which management strategies to adopt against weeds and diseases in citrus orchards.

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"Candidatus Phytoplasma aurantifolia" is the causative agent of witches' broom disease in the Mexican lime tree (Citrus aurantifolia L.), and is responsible for major tree losses in Southern Iran and Oman. The pathogen is strictly biotrophic, and, therefore, completely dependent on living host cells for its survival. The molecular basis of compatibility and disease development in this system is poorly understood. We applied a proteomics approach to analyse gene expression in Mexican limes infected with "Ca. Phytoplasma aurantifolia". Leaf samples were collected from healthy and infected plants and were analysed using 2-DE coupled with MS. Among 800 leaf proteins that were detected reproducibly in eight biological replicates of healthy and eight biological replicates of infected plants, 55 showed a significant response to the disease. MS resulted in identification of 39 regulated proteins, which included proteins that were involved in oxidative stress defence, photosynthesis, metabolism, and the stress response. Our results provide the first proteomic view of the molecular basis of the infection process and identify genes that could help inhibit the effects of the pathogen.

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Color sticky traps are one of the main alternatives to collect insect vectors, as they are easy to handle and are inexpensive. We aimed to compare the effect of color and height of the traps on the attractiveness to potential cicadellids vectors of plant pathogens. Yellow and green colored stick traps were placed at two different heights in plant of Gaultheria phillyreifolia. Seventeen leafhopper species were identified, with Ribautiana tenerrima Herrich-Shãffer (49 percent), Carelmapu ramosi Linnavuori & DeLong (33 percent), Carelmapu aurionitens Linnavuori (5 percent) and Atanus sp. (6 percent) being the most common. All these species were significantly attracted by yellow sticky traps. Ribautiana tenerrima was the only species affected by the height of the sticky traps. However, this was also dependent on the sampling season. The phytoplasma vector candidate, C. ramosi, showed two population peaks in early and late summer, which may indicate two different generations. Males of this species were more abundant than females on sticky traps, but were both similarly attracted to yellow sticky traps. No differences were detected in the capture efficiency of both sexes at any height of the traps. The high proportion of C. ramosi captured suggests that the yellow sticky traps can be an important element for monitoring this species.

Las trampas pegajosas de colores son una de las principales alternativas en la captura de insectos vectores, debido a su bajo costo y su fácil implementación. El objetivo fue comparar las preferencias a los colores y la altura de colocación de trampas para los posibles cicadélidos vectores de fitopatógenos. Trampas pegajosas amarillas y verdes fueron colocadas en plantas de Gaultheria phillyreifolia a dos distintas alturas. Se diferenciaron 17 especies de cicadélidos, siendo Ribautiana tenerrima Herrich-Shãffer (49 por ciento), Carelmapu ramosi Linnavuori & DeLong, Carelmapu aureonitens Linnavuori (33 y 5 por ciento), Atanus sp. (6 por ciento) las especies más comunes. Todas estas especies se vieron significativamente atraídas por trampas de color amarillo. Ribautiana tenerrima fue la única especie afectada por la altura de las trampas pegajosas, aunque este efecto fue influenciado por la temporada de colecta. La especie candidato a vector, C. ramosi, presentó dos curvas de crecimiento al inicio y finales del verano, lo cual puede representar la emergencia de dos generaciones distintas. Machos de esta especie fueron más abundantes que las hembras en las trampas pegajosas, pero ambos con una similar preferencia hacia el color amarillo. Además, no se detectaron diferencias en la posición de las trampas en la captura de ambos sexos. La alta proporción capturada de C. ramosi, sugiere que trampas de color amarillo pueden ser um elemento importante en el monitoreo de esta especie.

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Color sticky traps are one of the main alternatives to collect insect vectors, as they are easy to handle and are inexpensive. We aimed to compare the effect of color and height of the traps on the attractiveness to potential cicadellids vectors of plant pathogens. Yellow and green colored stick traps were placed at two different heights in plant of Gaultheria phillyreifolia. Seventeen leafhopper species were identified, with Ribautiana tenerrima Herrich-Shäffer (49%), Carelmapu ramosi Linnavuori & DeLong (33%), Carelmapu aurionitens Linnavuori (5%) and Atanus sp. (6%) being the most common. All these species were significantly attracted by yellow sticky traps. Ribautiana tenerrima was the only species affected by the height of the sticky traps. However, this was also dependent on the sampling season. The phytoplasma vector candidate, C. ramosi, showed two population peaks in early and late summer, which may indicate two different generations. Males of this species were more abundant than females on sticky traps, but were both similarly attracted to yellow sticky traps. No differences were detected in the capture efficiency of both sexes at any height of the traps. The high proportion of C. ramosi captured suggests that the yellow sticky traps can be an important element for monitoring this species.

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