Maria Cristina Canale

Molecular identification of a 16SrIII-B phytoplasma associated with cassava witches’ broom disease

Cassava plants displaying typical symptoms commonly associated with phytoplasmas, such as witches’ broom, general stunt, leaves with chlorosis, deformation, and reduced size, were observed in fields located in the state of São Paulo, Brazil. Molecular analysis using specific primers evidenced that the phytoplasma found in all positive samples was affiliated with group 16SrIII (X-disease group). Based on the virtual RFLP patterns and similarity coefficient calculations, the phytoplasma was classified as a member of the group 16SrIII, subgroup B (16SrIII-B). Phylogenetic analysis showed this phytoplasma as closely related to the reference strain for the subgroup 16SrIII-B. Representatives of 16SrIII-B have been described in several cultivated species in Brazil and cassava is an additional host species for this phytoplasma.

A few sequence polymorphisms among isolates of Maize bushy stunt phytoplasma associate with organ proliferation symptoms of infected maize plants

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.

Complete Genome Sequence of “Candidatus Sulcia muelleri” ML, an Obligate Nutritional Symbiont of Maize Leafhopper (Dalbulus maidis)

ABSTRACT “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.