Exploring the Spatiotemporal Dynamics and Phenology of the Cranberry False Blossom Phytoplasma and its Leafhopper Vector, Limotettix vaccinii

Abstract

Cranberry false blossom disease (CFBD), caused by a phytoplasma, and its insect vector the blunt-nosed leafhopper (BNLH), Limmotettix vaccinii, are a re-emerging threat in the Wisconsin cranberry, Vacciniium macrocarpon, industry. The aim of this research was to explore the status of CFBD in Wisconsin at the few field sites that have reported its presence, while characterizing the seasonal phenology and the impact of feeding by L. vaccinii. Chapter I covers the historical significance of this pathogen-vector pair over 100 years ago and its re-emergence in modern cranberry. Chapter II details the testing of symptomatic and asymptomatic cranberry uprights from fields with confirmed CFBD presence for DNA molecular analysis and symptom documentation. Advanced qPCR diagnostic techniques were utilized for detection, and it was found that infection was systemic with cranberry plants. Chapter III characterizes the seasonal phenology of L. vaccinii throughout the 2021-2023 growing seasons, to include first incidence of juveniles, first incidence of adults, and last incidence of adults, from late May through mid- August. All adult specimens collected to were identified to morphospecies to determine leafhopper species composition and found that L. vaccinii was the predominant species present in Wisconsin cranberry. The potential for an edge effect on L. vaccinii location within the bed was considered but found no significant result suggesting locational preference. A greenhouse feeding assay utilizing varying densities of nymph and adult L. vaccinii that were allowed to feed on cranberry uprights for two weeks. Uprights were then observed for feeding injury manifestation for three weeks following insect removal. The mean amount of feeding injury was dependent on density of nymph L. vaccinii at each week of observation, but only at the initial observation of adult L. vaccinii feeding. The results of these studies altogether suggest that current pruning techniques for CFBD control are ineffective, as infected root stock may grow back. Additionally,

current recommendations for CFBD prevention via control of L. vaccinii nymphs prevents both population persistence and pathogen transmission by adults but may allow for transmission by L. vaccinii nymphs.