Spatiotemporal Detection of 'Candidatus Phytoplasma vaccinium sp. witches' broom', the Causal Agent of Cranberry False Blossom Disease.

Abstract

Infection of cranberry by the 16SrIII-Y group phytoplasma responsible for cranberry false blossom disease results in floral disfigurement, fruit abortion, and phyllody, ultimately sterilizing infected plants. The pathogen almost devastated the cranberry industry in the 1930s, until control measures involving resistant cultivars and insect vector management were implemented. Recent discoveries of the pathogen and its vector in Wisconsin have renewed interest in exploring the pathosystem to gain deeper insights into host-pathogen interactions. A qPCR assay was used to detect phytoplasma infection, both spatially and temporally, in both symptomatic and asymptomatic cranberry plants. Dissection of infected vines by tissue type allowed detection of the phytoplasma throughout the entirety of the plant, revealing the systemic nature of the infection in cranberry vines. Furthermore, sampling throughout the growing season demonstrated that phytoplasma detection is possible at multiple time points, suggesting that diagnosis may be feasible even in the absence of clear symptoms like flower abnormalities, thereby enhancing diagnostic capabilities. Additionally, the qPCR method proved effective in detecting the causal agent within the insect vector, the blunt-nosed leafhopper. Phytoplasma acquisition occurs during feeding, colonizes various organs of the insect, and ultimately infect salivary glands making transmission possible. While the rate of colonization of both the plant and insect hosts is unknown, these findings provide valuable insights in industry decision-making for control and detection, as well as expanding understanding of a returning threat.