PHYTOPLASMA INFECTION IN ASCLEPIAS PHYSOCARPA
Asclepias physocarpa (sin. Gomphocarpus physocarpus; Asclepiadaceae) is a perennial ornamental plant, mainly distributed in tropical and subtropical areas and it is reported to be infected by a few viruses, such as tobacco streak and tomato spotted wilt viruses. In August 2002, plants one and two years old showing severe stunting, associated with rosette-like symptoms were observed; in other plants symptoms of yellows and vein yellowing were also present. High percentages (up to 30-40%) of diseased plants were present in many fields in Imperia area (Liguria, North-Western Italy). Mechanical inoculations on herbaceous plants, leaf-dip preparations for electron microscopy, and DAS-ELISA tests gave negative results for virus presence. Molecular analyses (PCR/RFLP) were performed on nucleic acid extracted from phloem tissue collected from symptomatic and asymptomatic plants in November, and provided evidence of phytoplasma presence in the majority of samples examined. RFLP on 16S ribosomal gene indicated that 16SrI-B (aster yellows), sometimes in mixed infection with 16SrXII-A (stolbur) phytoplasmas, and 16SrIII-B (clover yellow edge) phytoplasmas were present in symptomatic material; in asymptomatic plants stolbur phytoplasmas were identified. This disease is seriously affecting A. physocarpa cultivations and it is likely that the plants become infected during cultivation cycles since leafhopper presence was quite spread in all the fields examined. It was not possible to attribute a certain phytoplasma or mixture of phytoplasmas to the different symptoms observed, except for stolbur phytoplasmas detected in single infection only in asymptomatic plants. Probably, the type of symptoms could be influenced by the plant stage at the moment of infection: i.e., infected young plants show stunting and rosetting, while those infected at older stages (2 years) only react with yellows to the presence of the same pathogen/s.
Bertaccini, A., Bellardi, M.G., Botti, S., Paltrinieri, S. and Restuccia, P. (2006). PHYTOPLASMA INFECTION IN ASCLEPIAS PHYSOCARPA. Acta Hortic. 722, 349-354
Asclepias physocarpa, stunting, yellows, PCR, RFLP