Vector‐pathogen‐host plant relationships of chrysanthemum yellows (CY) phytoplasma and the vector leafhoppers Macrosteles quadripunctulatus and Euscelidius variegatus

Abstract

AbstractChrysanthemum yellows (CY) phytoplasma is a plant‐pathogenic mollicutes belonging to the 16Sr‐IB genetic group which infects a variety of dicotyledonous plants and is transmitted in nature by some species of Cicadellidae Deltocephalinae. The transmission characteristics of CY and the factors influencing the vector efficiencies of the leafhoppers Macrosteles quadripunctulatus Kirschbaum and Euscelidius variegatus Kirschbaum are described in the present study using transmission experiments and phytoplasma‐specific polymerase chain reaction (PCR) assays. Vector insects were allowed to acquire CY under different experimental conditions and then transferred to healthy test plants for inoculation and/or sampled for DNA extraction and amplification. The transmission efficiency of CY was very high and almost all the leafhoppers became infective following acquisition on CY‐infected daisies. The latent period in the vector ranged from 16 to 20 days after the start of the acquisition and infectivity lasted, in general, for life. The PCR assay was successful in detecting CY phytoplasmas in the insects well before they became infective (5 versus 16–18 days) and was used to estimate the proportion of infective insects. When analysed for CY presence by PCR, all the leafhoppers fed for 7–18 days on source daisy reacted positively while, following one day of acquisition, some insects failed to provide amplification. Host‐plant species influenced CY acquisition, and daisy appeared a more efficient source for both leafhoppers compared to periwinkle. Life stage did not appear to be critical for CY acquisition, although newly‐hatched nymphs of E. variegatus acquired CY less efficiently than fifth instar nymphs.