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Although 'Candidatus Liberibacter asiaticus' (Las) is a major pathogen associated with citrus huanglongbing (HLB), some characteristics of transmission by the psyllid vector Diaphorina citri are not fully understood. We examined the latent period and persistence of transmission of Las by D. citri in a series of experiments at 25°C, in which third-instar psyllid nymphs and 1-week-old adults were confined on infected citrus for an acquisition access period (AAP), and submitted to sequential inoculation access periods (IAPs) on healthy citrus seedlings. The median latent period (LP, i.e., acquisition time after which 50% of the individuals can inoculate) of 16.8 and 17.8 days for psyllids that acquired Las as nymphs and adults, respectively, was determined by transferring single individuals in 48-h IAPs. Inoculation events were intermittent and randomly distributed over the IAPs, but were more frequent after acquisition by nymphs. A minimum latent period of 7 to 10 days was observed by transferring groups of 10 psyllids in 48-h IAPs, after a 96-h AAP by nymphs. Psyllids transmitted for up to 5 weeks, when submitted to sequential 1-week IAPs after a 14-day AAP as nymphs. The long latent period and persistence of transmission are indirect evidences of circulative propagation of Las in D. citri.

Phytoplasmas are insect-transmitted bacterial pathogens that colonize a wide range of plant species, including vegetable and cereal crops, and herbaceous and woody ornamentals. Phytoplasma-infected plants often show dramatic symptoms, including proliferation of shoots (witch’s brooms), changes in leaf shapes and production of green sterile flowers (phyllody). Aster Yellows phytoplasma Witches’ Broom (AY-WB) infects dicots and its effector, secreted AYWB protein 11 (SAP11), was shown to be responsible for the induction of shoot proliferation and leaf shape changes of plants. SAP11 acts by destabilizing TEOSINTE BRANCHED 1-CYCLOIDEA-PROLIFERATING CELL FACTOR (TCP) transcription factors, particularly the class II TCPs of the CYCLOIDEA/TEOSINTE BRANCHED 1 (CYC/TB1) and CINCINNATA (CIN)-TCP clades. SAP11 homologs are also present in phytoplasmas that cause economic yield losses in monocot crops, such as maize, wheat and coconut. Here we show that a SAP11 homolog of Maize Bushy Stunt Phytoplasma (MBSP), which has a range primarily restricted to maize, destabilizes specifically TB1/CYC TCPs. SAP11MBSP and SAP11AYWB both induce axillary branching and SAP11AYWB also alters leaf development of Arabidopsis thaliana and maize. However, only in maize, SAP11MBSP prevents female inflorescence development, phenocopying maize tb1 lines, whereas SAP11AYWB prevents male inflorescence development and induces feminization of tassels. SAP11AYWB promotes fecundity of the AY-WB leafhopper vector on A. thaliana and modulates the expression of A. thaliana leaf defence response genes that are induced by this leafhopper, in contrast to SAP11MBSP. Neither of the SAP11 effectors promote fecundity of AY-WB and MBSP leafhopper vectors on maize. These data provide evidence that class II TCPs have overlapping but also distinct roles in regulating development and defence in a dicot and a monocot plant species that is likely to shape SAP11 effector evolution depending on the phytoplasma host range.

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.

“Candidatus Sulcia muelleri” is a symbiont of sap-feeding insects in the suborder Auchenorrhyncha. The strain “Ca. Sulcia muelleri” ML is associated with the maize leafhopper (Dalbulus maidis), collected in Brazil, which is a disease vector that affects corn production. Here, we report the complete genome sequence of this bacterium.

Since 2007, a new disease in broccoli (Brassica oleracea var. italica Plenck) has been observed in the São Paulo state, Brazil. The characteristic symptoms of the disease are plant stunting, inflorescence malformation, reddening of the leaves and phloem necrosis. Nested polymerase chain reaction with P1/Tint and F2n/R2 primer pairs revealed the presence of phytoplasmas in diseased broccoli plants. Restriction fragment length polymorphism and phylogenetic analysis of the 16S rDNA gene showed that phytoplasmas belonging to 16SrI, III and XIII groups were associated with the plants. To the best of our knowledge, this is the first report of phytoplasmas in this Brassica species in Brazil, as well the first time phytoplasmas of 16SrIII and XIII groups have been associated with broccoli plants.

28 Phytoplasmas are insect-transmitted bacterial pathogens that colonize a wide range of plant 29 species, including vegetable and cereal crops, and herbaceous and woody ornamentals.30 Phytoplasma-infected plants often show dramatic symptoms, including proliferation of shoots 31 (witch's brooms), changes in leaf shapes and production of green sterile flowers (phyllody). 32 Aster Yellows phytoplasma Witches' Broom (AY-WB) infects dicots and its effector, 33 secreted AYWB protein 11 (SAP11), was shown to be responsible for the induction of shoot 34 proliferation and leaf shape changes of plants. SAP11 acts by destabilizing TEOSINTE 35 BRANCHED 1-CYCLOIDEA-PROLIFERATING CELL FACTOR (TCP) transcription 36 factors, particularly the class II TCPs of the CYCLOIDEA/TEOSINTE BRANCHED 1 37 (CYC/TB1) and CINCINNATA (CIN)-TCP clades. SAP11 homologs are also present in 38 phytoplasmas that cause economic yield losses in monocot crops, such as maize, wheat and 39 coconut. Here we show that a SAP11 homolog of Maize Bushy Stunt Phytoplasma (MBSP), 40 which has a range primarily restricted to maize, destabilizes only TB1/CYC TCPs. 41 SAP11 MBSP and SAP11 AYWB both induce axillary branching and SAP11 AYWB also alters leaf 42 development of Arabidopsis thaliana and maize. However, only in maize, SAP11 MBSP 43 prevents female inflorescence development, phenocopying maize tb1 lines, whereas 44 SAP11 AYWB prevents male inflorescence development and induces feminization of tassels. 45 SAP11 AYWB promotes fecundity of the AY-WB leafhopper vector on A. thaliana and 46 modulates the expression of A. thaliana leaf defence response genes that are induced by this 47 leafhopper, in contrast to SAP11 MBSP . Neither of the SAP11 effectors promote fecundity of 48 AY-WB and MBSP leafhopper vectors on maize. These data provide evidence that class II 49 TCPs have overlapping but also distinct roles in regulating development and defence in a 50 dicot and a monocot plant species that is likely to shape SAP11 effector evolution depending 51 on the phytoplasma host range. 3 52 53 Author summary 57 Phytoplasmas are parasites of a wide range of plant species and are transmitted by sap-58 feeding insects, such as leafhoppers. Phytoplasma-infected plants are often easily recognized 59 because of their dramatic symptoms, including shoot proliferations (witch's brooms) and60 altered leaf shapes, leading to severe economic losses of crops, ornamentals and trees 61 worldwide. We previously found that the virulence protein SAP11 of aster yellows witches' 62 broom phytoplasma (AY-WB) interferes with a specific group of plant transcription factors, 63 named TCPs, leading to witches' brooms and leaf shape changes of the model plant 64 Arabidopsis thaliana. SAP11 has been characterized in a number of other phytoplasmas. 65 However, it is not known how phytoplasmas and their SAP11 proteins modulate processes in 66 crops, including cereals such as maize. We identified a SAP11 homolog in Maize bushy stunt 67 phytoplasma (MBSP), a pathogen that can cause severe yield l...

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