TRANSMISSION OF CHRYSANTHEMUM YELLOWS, A SUBGROUP 16SrI-B PHYTOPLASMA, TO GRAPEVINE BY FOUR LEAFHOPPER SPECIES

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SUMMARY Chrysanthemum yellows phytoplasma (CY), subgroup 16SrI-B, was experimentally transmitted to seedlings of grapevine (Vitis vinifera), cv. ‘Barbera’ and ‘White Muscat’ with four leafhopper species: Euscelidius variegatus, Euscelis incisus, Macrosteles quadripunctulatus and Scaphoideus titanus. Acquisition was accomplished in three days by 3 rd instar nymphs on CY-infected marguerites (Chrysanthemum carinatum). After three weeks, insects were moved to new test plants of the same species and allowed to feed for seven days. They were then transferred to grapevine seedlings for another seven-day-period, and so on as long as they survived. The four leafhopper species transmitted CY to both marguerite and grapevine with the following respective rates: M. quadripunctulatus, 100 (25/25) and 33.3 (9/27); E. variegatus , 59.6 (31/52) and 47.5 (28/59); E. incisus, 95.6 (22/23) and 33.3 (6/18); S. titanus 12.5 (7/56) and 17.0% (8/47). Symptoms on C. carinatum were typical of those already described, while on V. vinifera they consisted of growth reduction and abnormal production of axillary shoots bearing small chlorotic leaves. Downward rolling and reddening of basal leaves was occasionally observed on cv. ‘Barbera’. RFLP analysis of ribosomal DNA amplified in direct and/or nested PCRs driven by universal or 16SrI group-specific primers confirmed that the phytoplasma present in symptomatic plants, either used as inoculum or obtained by transmission, and in inoculative S. titanus did belong to subgroup 16SrI-B and was identical to the CY reference isolate.