Phytoplasma Infections and Potential Vector Associations in Wheat and Maize in Poland

The production and quality of wheat and maize grain can be significantly affected by various pests and pathogens, with phytoplasmas posing a particular threat due to their rapid spread and potential to cause severe damage to cultivated crops. The objective of this investigation was to evaluate the risk associated with these wall-less bacteria in wheat and maize crops. To achieve this, a survey was conducted in commercial fields located in southwestern Poland. Samples of winter wheat and fodder maize were collected at two distinct developmental stages, including both symptomatic and asymptomatic plants. Symptoms observed in wheat included yellowing, stunting, and excessive tillering, while maize plants showed yellow leaf striping, red discoloration, and stunted growth. Polymerase chain reaction (PCR) assays using phytoplasma-specific primers, followed by Sanger sequencing and sequence analysis, confirmed phytoplasma infections in 2% of wheat and 1.5% of maize samples. Virtual restriction fragment length polymorphism (RFLP) analysis identified the wheat-infecting phytoplasmas as belonging to subgroup 16SrI-C (‘Candidatus Phytoplasma tritici’-related strain)—a pathogen of major concern for wheat, while maize-infecting phytoplasmas were classified into subgroups 16SrI-B and 16SrV-C. Additionally, wheat plants collected during the early elongation phase were tested for Mastrevirus hordei (former wheat dwarf virus, WDV) using double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA), which confirmed the presence of WDV in all tested samples. Preliminary screening of field-collected leafhoppers revealed that 7.5% of Psammotettix alienus, the predominant species in wheat fields, carried 16SrI-C phytoplasmas. In maize fields, Zyginidia scutellaris was the most prevalent species, with 1.7% of individuals carrying 16SrV-C phytoplasma. These findings suggest that these insect species may contribute to the transmission of phytoplasmas in wheat and maize. This study provides the first documented evidence of 16SrI-C phytoplasma infecting wheat in Poland, and of 16SrV-C and 16SrI-B phytoplasmas infecting maize, expanding the known host range of these subgroups in the country and highlighting their potential phytosanitary importance.