Cauliflower stunt associated with a phytoplasma of subgroup 16SrIII-J and the spatial pattern of disease

Since 2000, a disease has occurred with high levels of incidence in crops of cauliflower grown in the green belt area of the city of S?o Paulo, Brazil. The symptoms are characterized by stunting, malformation of the inflorescence, reddening leaves, and vascular necrosis, suggesting infection by phytoplasma. These symptoms are similar to those described in Brassicas species affected by the aster yellows (16SrI) group of phytoplasma. In the present study, a phytoplasma from the 16SrIII-J subgroup was identified in cauliflower plants based on actual and virtual RFLP patterns and phylogenetic analysis, and was distinct from the phytoplasmas frequently associated with aster yellows disease in Brassicas. Pathogenicity assays using dodder confirmed that the identified phytoplasma is the agent of the observed disease, which is here designated as cauliflower stunt. Consequently, this species of Brassica may be recognized as a new host for subgroup 16SrIII-J, which has frequently been found in diverse species cultivated in Brazil. The spatial pattern of diseased plants was determined in ten cauliflower plots of 300 to 728 plants each. All plants in these plots were evaluated by visual assessments, assigned as diseased or healthy and mapped. The dispersion index and Taylor’s power law were determined for various quadrat sizes and the results showed that the diseased plants were distributed in a random pattern in fields with a low disease incidence and in an aggregated pattern in fields with a disease incidence greater than 25?%. According to an isopath area analysis, diseased plants were predominantly present in the field borders, suggesting that the pathogen is possibly introduced by vector(s) from the external area.     

Identification and characterization of two phytoplasma subgroups (16SrXI-D and 16SrXIV-A) associated with lychee (Litchi chinensis Sonn) in India

Journal of Plant Diseases and Protection - Leaf rolling, necrosis and apical bud proliferation symptoms were recorded on lychee plants at Bhatpar Rani (Deoria district) and Gorakhpur (Gorakhpur...     

Nested PCR assay for detection of sugarcane grassy shoot phytoplasma in the leafhopper vector Deltocephalus vulgaris: a first report

Nymphs of Deltocephalus vulgaris , the leafhopper vector of sugarcane grassy shoot (SCGS) disease, fed on SCGS-infected and healthy sugarcane leaves, and SCGS-infected and healthy plant tissue of sugarcane cv. CoLk 8102, were examined by nested PCR using phytoplasma-specific rRNA operon primers for detection of the SCGS phytoplasma. Samples of SCGS-infected plants with symptoms and SCGS-exposed D. vulgaris nymphs yielded SCGS-exclusive DNA bands when nested PCR was performed. Negative results were obtained when symptomless plant host and unexposed insect vector samples devoid of phytoplasma DNA templates were used. Such a reliable molecular tool for the precise detection of SCGS phytoplasma in the D. vulgaris population would help forecast the potential of secondary spread of SCGS in a susceptible sugarcane variety, and may facilitate control of the disease.     

Detection and characterization of a phytoplasma associated with annual blue grass (Poa annua) white leaf disease in southern Italy

A phytoplasma was detected in annual blue grass (Poa annua L. Fienardo), exhibiting white leaf symptoms, that was grown in the fields near Caserta in southern Italy. Based on restriction fragment length polymorphism analysis of PCR-amplified 16S rDNA sequences, the phytoplasma associated with annual blue grass white leaf disease was identified as a new member of phytoplasma 16S rRNA group XI (16SrXI) (type strain, rice yellow dwarf phytoplasma). The annual blue grass white leaf phytoplasma is most closely related to Bermuda grass white leaf phytoplasma found in Asia. Annul blue grass white leaf and Bermuda grass white leaf phytoplasmas were designated as the third subgroup (16SrXI-C) of group XI. This is the first report that a plant pathogenic phytoplasma belonging to group 16SrXI is present on the European continent.     

A new disease of greenhouse tomatoes in Israel caused by a distinct strain ofTomato apical stunt viroid (TASVd)

Using the sequential PAGE method for detection of small circular RNA molecules we isolated a viroid from greenhouse-grown tomato plants exhibiting severe stunting in Israel. The viroid was transmitted to tomato and to several other solanaceous plants by graft and mechanical inoculation, but only tomato plants showed symptoms of disease. Cloning and sequencing revealed that the viroid RNA is composed of 363 nucleotides, has 92% identity with the type strain (Ivory Coast strain) ofTomato apical stunt viroid (TASVd) and 99% identity with the Indonesian strain of this viroid. The experimental host range of TASVd-Is differs significantly from that of the type strain of TASVd. The possible epidemiological consequences leading to TASVd spread in geographically distant areas are discussed. http://www.phytoparasitica.org posting Sept. 18, 2002. Corresponding author