Grapevine virus A variants of group II associated with Shiraz disease in South Africa are present in plants affected by Australian Shiraz disease,and have also been detected in the USA

Primers were designed for RT‐nested PCR amplification of the highly variable 293‐nt fragment from the 5′ terminal part of the Grapevine virus A (GVA) replicase gene, specific to South African variants of molecular groups I and II. This new technique, along with RT‐PCR for simultaneous amplification of variants of groups I, II and III, as well as cloning of amplicons, single‐strand conformation polymorphism (SSCP) analysis of clones and sequencing, were used to investigate the populations of variants infecting 16 local Shiraz grapevines with different Shiraz disease (SD) status. The techniques were also used to study variants in GVA‐infected grapevines from Australia and the USA. The Australian grapevines included seven plants of cvs Shiraz and Merlot affected by Australian Shiraz disease (AuSD), and one plant of cv. Crimson Seedless with unknown AuSD status. Grapevines from the USA included plants of cvs Chardonnay, Thompson Seedless and an unknown cultivar. The results confirmed the association of certain genetic variants of group II with SD and showed the common presence of these variants in AuSD‐affected grapevines from Australia. Interestingly, a variant of this group was also detected in grapevine cv. Chardonnay from the USA, although the disease has not yet been reported from that country. The study also supports an earlier observation that members of group II, closely related to variant GTR1‐2, are not associated with the disease. The variants were found only in SD‐free grapevines. Results show that variants of the most divergent group III, which are common in South Africa, are also present in Australia and the USA. These variants are not associated with SD, but frequently occur in mixed infections with members of group II in plants affected by this disease in South Africa.     

Electron microscopy and molecular identification of phytoplasmas associated with strawberry green petals in the Czech Republic

The presence of phytoplasma inFragaria ananassa x Duch cv Senga Sengana showing strawberry green petals symptoms was observed by electron microscopy of phloem tissue. No phytoplasmas were found in asymptomatic strawberry plants used as controls. Nucleic acids extracted from these plants were used in nested-PCR assays with primers amplifying 16S rRNA sequences specifie for phytoplasmas. Bands of 1.2 kb were obtained and the subsequent nested-PCR with specific primers and RFLP analyses allowed to classify the detected phytoplasmas in the aster yellows group (16SrI). They belonged to the subgroup I-C of which type strain is clover phyllody phytoplasma.     

Suppression of Rhizoctonia root-rot of tomato by Glomus mossae BEG12 and Pseudomonas fluorescens A6RI is associated with their effect on the pathogen growth and on the root morphogenesis

Rhizoctonia solani root-rot is a major soilborne disease causing growth and yield depression. The ability of Glomus mosseae BEG12 and Pseudomonas fluorescens A6RI to suppress this soilborne disease in tomato was assessed by comparing the shoot and root growth of plants infested with R. solani 1556 when protected or not by these beneficial strains. The epiphytic and parasitic growth of the pathogenic R. solani 1556 was compared in the presence and absence of the biocontrol agents by microscopical observations allowing the quantification of roots with hyphae appressed to epidermal cells (epiphytic growth) and of roots with intraradical infection (parasitic growth). The root architecture of the tomato plants under the different experimental conditions was further characterized by measuring total root length, mean root diameter, number of root tips and by calculating degree of root branching. G. mosseae BEG12 and P. fluorescens A6RI fully overcame the growth depression caused by R. solani 1556. This disease suppression was associated with a significant decrease of the epiphytic and parasitic growth of the pathogen together with an increase of root length and of the number of root tips of inoculated tomato plants. The combined effects of G. mosseae BEG12 and P. fluorescens A6RI on pathogen growth and on root morphogenesis are suggested to be involved in the efficient disease suppression.