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Uitenhage, South Africa

Van Der Westhuizen L.,Plant Protection Research Institute
African Entomology | Year: 2011

Madeira vine, Anredera cordifolia (Ten.) Steenis subsp. cordifolia (Basellaceae), is native to South America but has become invasive and problematic in many countries, including South Africa. Weedy vines are notoriously difficult to control through conventional mechanical and chemical means, so biological control of A. cordifolia in South Africa was initiated in 2003. No agents have yet been released against this plant in South Africa but exploratory observations on the life-history and host-specificity of two leaf-feeding beetles, Phenrica sp. (Coleoptera: Chrysomelidae) from Brazil and Plectonycha correntina Lacordaire (Coleoptera: Chrysomelidae: Chrysomelinae) from Argentina and Brazil, are reviewed here. Adults and larvae of both chrysomelids feed extensively on leaves and new growth of A. cordifolia, resulting in leaf and above-ground biomass reductions. The laboratory host-ranges of these potential agents seem acceptably narrow, with normal development restricted to the host plant. Adult feeding was recorded on other non-indigenous species within the Basellaceae, Portulacaceae and Talinaceae. The Phenrica sp. colony, being reared in quarantine, died out and re-collection has not been possible. Host-specificity studies are continuing on P. correntina.

In 2008, a field survey was conducted in northern Argentina to collect natural enemies of Cestrum species (Solanaceae) for use as biological control agents in South Africa. The rust fungus Uromyces cestri Bertero ex Mont. (Pucciniales: Pucciniaceae) was found on Cestrum parqui L'Hr. and imported into quarantine facilities in South Africa. No damaging pathogens were found on Cestrum laevigatum Schltdl. Preliminary host-range studies showed that U. cestri was able to infect and cause disease on C. parqui and on Cestrum elegans (Brongn. ex Neumann) Schltdl. in South Africa, and could have potential for the biological control of these species. The rust did not infect any of the other Cestrum species tested, and neither did it infect C. laevigatum which is the most problematic Cestrum species in South Africa.

This catalogue provides a comprehensive record of the 284 entities of organisms (insect, mite and pathogen species, or biotypes thereof) that have featured in biological control of invasive alien plants (weeds) in South Africa, since 1913. Fourteen of these entities are native species, or foreign species that have, by some unknown means, entered the country, while the remainder were intentionally imported specifically for biological control. The majority (237 of 284, i.e. 83 %) are phytophagous insects, the balance being made up of five species of mites (Acari) and 42 entities of plant-pathogens. The catalogue comprises the names of each of the target weeds, their origin, and an assessment of the degree of control that has been achieved with biological control, together with names and details (feeding guild, date released where applicable, current status and extent of damage inflicted) for each of the agents. Key references are provided. Of the 270 entities that were introduced into quarantine and tested for host specificity: 106 (39 %) were eventually released as biological control agents; 16 % are still under investigation; approximately 24 % were rejected by researchers because of doubts about their safety or efficacy; and 21 % have been shelved pending possible further study. Two of the pathogen species were developed as mycoherbicides. Seventy-five (71 %) of the 106 agents that were released in South Africa have become established on 48 invasive alien plant species, in 14 plant families. According to a rating system that has been widely adopted since 1999, and slightly amended in this account, approximately 21 % of the weed species on which biological control agents are established have been completely controlled, and another 38 % are under a substantial degree of control.

Analysis of two Grapevine virus B (GVB)-infected LN33 hybrid grapevines revealed that a plant exhibiting clear symptoms of corky bark (CB) disease was infected with two molecular variants of the virus, whereas a plant exhibiting no disease symptoms was infected with only one variant. Sequence results indicated that the single variant in the CB-negative grapevine was also one of the two present in the CB-affected hybrid. Plant extracts from these two grapevines were used to successfully transmit the virus to N. benthamiana. After further cloning and sequencing, two clearly divergent variants were identified. Comparative molecular analysis of the variants, named here GVB 953-1 and GVB-H1, respectively, transmitted from CB-affected and consistently CB-negative plants, revealed short genomic regions, most of them highly divergent, that encoded amino acid sequences, containing significant amino acid substitutions altering the net charges of their respective proteins. Interestingly, a comparison of these variants to genome sequence data of GVB variants GVB Italy and GVB 94/971 available from the GenBank, revealed that these significant amino acid substitutions were the same for, and unique to, the variant pairs GVB 953-1/GVB Italy and GVB-H1/GVB 94/971. This despite the variants of each pair being otherwise clearly different at nucleotide and amino acid levels. In addition, both sets of variants differed substantially in their respective 3'-non-translated (3'NTR) regions. The relevance of these findings is discussed. © 2010 Springer Science+Business Media, LLC.

Goszczynski D.E.,Plant Protection Research Institute
Archives of Virology | Year: 2010

The presence of rugose-wood-associated viruses of the genera Foveavirus and Vitivirus in the family Betaflexiviridae was investigated in various clones of own-rooted and grafted Vitis vinifera cv. Shiraz that were affected, or not, by Shiraz decline, and in rootstocks. RT nested-PCR amplification of double-stranded RNA using degenerate primers for the simultaneous detection of foveaviruses and vitiviruses (Dovas CI, Katis NI in J Virol Meth 170:99-106, 2003), cloning of DNA amplicons, SSCP analysis of clones, sequencing and computer-assisted analysis of sequences was used to characterize viral genetic variability. A total of 1,137 clones were analysed by SSCP, and, of those, 371 clones were sequenced. The results revealed that variants of five molecular groups belonging to the species Grapevine rupestris stem pitting-associated virus (GRSPaV), including highly divergent variants related to strain SY (Lima MF et al. in Arch Virol 151:1889-1894, 2006) were present in plants of various clones of Shiraz regardless of their Shiraz decline status, and in rootstocks. Grapevine virus A (GVA) and grapevine virus B (GVB) were detected in a relatively small number of plants. This study suggested no involvement of GRSPaV, GVA or GVB in Shiraz decline. © 2010 Springer-Verlag.

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