Characterisation of the tolerance to the beet leafhopper transmitted virescence agent phytoplasma in the PI128655 accession of Solanum peruvianum

In 1992, Thomas and Hassan reported an apparent immunity and tolerance to the beet leafhopper transmitted virescence agent (BLTVA) phytoplasma in the PI128655 accession of Solanum peruvianum (Plant Disease 76:139). We revisited this interaction in an effort to better characterize the bases of plant resistance and tolerance to phytoplasmas. After challenge with a BLTVA strain, plants of the PI128655 accession fell into two distinct symptom‐based groups, termed class I and class II. Class II plants displayed symptoms on the vegetative parts and phloem hyperplasia, whereas class I plants showed symptoms only on the inflorescence parts, and no phloem hyperplasia. Plants of both classes hosted similar titres of BLTVA, demonstrating that the lower symptom severity in class I plants was due to tolerance rather than resistance. However, this tolerance was not effective against all phytoplasmas, as both classes of plants were equally susceptible to a stolbur phytoplasma strain. A genetic analysis suggested that the BLTVA tolerance of class I plants was monogenic. Finally, a reciprocal graft experiment showed that the virulence of the BLTVA strain seemed to increase after propagation through class II plants. These results provide valuable insights on the tolerance of plants to phytoplasma diseases, and highlight the usefulness of the S. peruvianum/BLTVA experimental pathosystem.