Etiology of lettuce yellows in Italy: genetic characterization of associated mycoplasmalike organisms

• Published in: Phytopathologia mediterranea Vol. 33; no. 3; pp. 179 - 186
• Main Authors: Vibio, M., Bertaccini, A., Lee, I.-M., Davis, R.E., Minucci, C., Milne, R.G.
• Format: Journal Article
• Language: English
• Published: Unione Fitopatologica Mediterranea 01-12-1994
• Subjects: Catharanthus roseus; DNA; DNA probes; Lactuca sativa; Lettuce; Medical genetics; Phytopathology; Plant diseases; Plants; Polymerase chain reaction; Ribosomal DNA; Symptoms; Italy
• ISSN: 0031-9465; 1593-2095

Mycoplasmalike organisms (MLOs) associated with lettuce yellows disease in Northern Italy were experimentally transmitted from infected lettuce to healthy periwinkle (Catharanthus roseus) plants by leafhoppers (Macrosteles quadripunctulatus) under greenhouse conditions. Because of symptom variability in the infected periwinkles, the MLOs in five plants with different symptoms were propagated separately and examined for genetic variability. Dot hybridization assays using cloned MLO DNA probes, and polymerase chain reaction (PCR) assays using primer pairs specific to the aster yellows (AY) MLO strain cluster, indicated that the naturally infected lettuce and all five isolates contained MLOs belonging to the AY strain cluster. Restriction fragment length polymorphism (RFLP) analyses of DNA using several well characterized probes, showed that all samples contained MLOs belonging to the type II, subcluster of the AY cluster. RFLP analyses of PCR-amplified 16S rDNA sequences confirmed the close relationship of all isolates and of MLO infecting lettuce to this subcluster. Only one isolate in periwinkle showed genetic differences that were associated with differences in symptoms.