Group 16SrV Research Articles

Transmission of 16SrV phytoplasmas by Scaphoi-deus titanus Ball in northern Italy

Flavescence dorée (FD) has been defined as the disease that is caused by a phytoplasmas belonging to group 16SrV (elm yellows) and transmitted to plants by the insect Scaphoideus titanus Ball. We investigated transmission of FD agent by S. titanus in a vineyard located in Veneto region to determine which phytoplasma(s) may be transmitted in this region. Group 16SrV-C phytoplasma was detected and identified in field-collected S. titanus adults, in plant of grapevine (Vitis vinifera L. cv. Gamay) and broadbean (Vicia faba cv. Arlŕ) that had been fed upon by the insects. No evidence of experimental transmission of phytoplasma belonging to 16SrI-B subgroup phytoplasma by S. titanus has been observed.

Phytoplasmas Associated with Elm Yellows: Molecular Variability and Differentiation from Related Organisms.

Restriction fragment length polymorphism (RFLP) analyses were performed on polymerase chain reaction (PCR) amplimers of phytoplasmal DNA from eight samples obtained from Ulmus spp. (elms) affected by elm yellows (EY) in Italy and the United States, from Catharanthus roseus infected with strain EY1, and from five other plant species infected with phytoplasmas of the EY group sensu lato (group 16SrV). RFLP profiles obtained with restriction enzyme TaqI from ribosomal DNA amplified with primer pair P1/P7 differentiated elm-associated phytoplasmas from strains originally detected in Apocynum cannabinum, Prunus spp., Rubus fruticosus, Vitis vinifera, and Ziziphus jujuba. RFLP profiles obtained similarly with BfaI differentiated strains from A. cannabinum and V. vinifera from other phytoplasmas of group 16SrV. Elm-associated strains from within the United States had two RFLP patterns in ribosomal DNA based on presence or absence of an RsaI site in the 16S-23S spacer. Elm-associated phytoplasma strains from Italy were distinguished from those of American origin by RFLPs obtained with MseI in the same fragment of non-ribosomal DNA. Strain HD1, which was discovered in A. cannabinum associated with EY-diseased elms in New York State, was unique among the strains studied.

Identification and Epidemic Distribution of Two Flavescence Dorée-Related Phytoplasmas in Veneto (Italy).

Grapevine yellows associated with phytoplasmas of the elm yellows group (16SrV), better known as flavescence dorée (FD), is a serious quarantine problem in some important grapevine growing regions in the European Union. A survey was carried out in 1997 to 1998 in Veneto region (Italy) where a serious outbreak of FD was in progress. Phytoplasma identification by nested polymerase chain reaction (PCR)/restriction fragment length polymorphism (RFLP) analyses on 275 grapevine samples and on batches of Scaphoideus titanus was carried out. RFLP analyses of the 16S rDNA/spacer region with TaqI detected the presence of two distinct elm yellows phytoplasma subgroups designated 16SrV-C and 16SrV-D in 77 FD-infected grapevine samples. Only phytoplasmas of the 16SrV-D subgroup were detected in S. titanus. In 1997, the two phytoplasma subgroups appeared to be located in two diverse geographic areas; but in 1998, the 16SrV-D type also was detected in the provinces where in 1997 only 16SrV-C type was identified. The sequencing of a 400-bp fragment at the 3' end of 16S rDNA plus spacer region allowed a specific primer construction that was successfully employed for detection of both FD types in grapevine by direct PCR.

Identification of phytoplasmas associated with a decline of European hackberry (Celtis australis)

SummaryThe presence of phytoplasmas in declining trees of European hackberry was demonstrated for the first time using polymerase chain reaction assays with primers amplifying phytoplasma 16S rDNA regions. Restriction fragment length polymorphism analysis of these DNA fragments together with PCR, employing primers specific for particular phylogenetic groups of phytoplasmas, made it possible to detect the presence of aster yellows group (16SrI) related phytoplasmas. These were classified into two different subgroups (I‐B and I‐C) and were present in both symptomatic and asymptomatic hackberry plants. Aster yellows‐related phytoplasmas were found in all the root samples collected during the winter. In addition, phytoplasmas from the peach X disease group (16SrIH) were found in four out of 10 root samples; in five root samples phytoplasmas of the elm yellows group (16SrV) were also present.

Mixed Infection of Grapevines in Northern Italy by Phytoplasmas Including 16S rRNA RFLP Subgroup 16SrI-B Strains Previously Unreported in This Host

Grapevine plants of cv. Chardonnay showing symptoms like those of flavescence doree disease in the field in Piemonte, Italy, contained phytoplasmas affiliated with two phylogenetically different 16S rRNA restriction fragment length polymorphism (RFLP) groups. These phytoplasmas were detected and identified by polymerase chain reaction (PCR) amplification of 16S rDNA and by RFLP analysis of amplified DNA as strains belonging to group 16SrI (aster yellows and related phytoplasmas) and group 16SrV (elm yellows and related phytoplasmas). Thirteen of 16 tested plants contained group l6SrI strains. Twelve contained strains belonging to subgroup 16SrI-G (Italian periwinkle virescence and related phytoplasmas), and one contained only a strain belonging to subgroup 16SrI-B (Maryland aster yellows and related phytoplasmas). One plant that contained a subgroup 16SrI-G phytoplasma strains also contained a strain belonging to group 16SrV. Three plants were doubly infected by subgroup 16SrI-G strains and strains belonging to subgroup 16SrI-B. These results indicate susceptibility of grapevines to infection by three distinct phytoplasmas, and reveal for the first time grapevine infection by subgroup 16SrI-B phytoplasmas and mixed infection of single grapevine plants by strains in two different subgroups in group 16SrI.