F. Halleen

DNA phylogeny, morphology and pathogenicity of Botryosphaeria species on grapevines.

Several species of Botr yosphaeria are known to occur on grapevines, causing a wide range of disorders including bud mortality, dieback, brown wood streaking and bunch rot. In this study the 11 Botryosphaeria spp. associated with grapevines growing in various parts of the world, but primarily in South Africa, are distinguished based on morphology, DNA sequences (ITS-1, 5.8S, ITS-2 and EF1-α) and pathological data. Botryosphaeria australis, B. lutea, B. obtusa, B. parva, B. rhodina and a Diplodia sp. are confirmed from grapevines in South Africa, while Diplodia porosum, Fusicoccum viticlavatum and F. vitifusiforme are described as new. Although isolates of B. dothidea and B. stevensii are confirmed from grapevines in Portugal, neither of these species occurred in South Africa, nor were any isolates of B. ribis confirmed from grapevines. All grapevine isolates from Portugal, formerly presumed to be B. ribis, are identified as B. parva based on their EF1-α equence data. From artificial inoculations on grapevine shoots, we conclude that B. australis, B. parva, B. ribis and B. stevensii are more virulent than the other species studied. The Diplodia sp. collected from grapevine canes is morphologically similar but phylogenetically distinct from D. sarmentorum. Diplodia sarmentorum is confirmed as anamorph of Otthia spiraeae, the type species of the genus Otthia (Botryosphaeriaceae). A culture identified as O. spiraeae clustered within Botryosphaeria and thus is regarded as probable synonym. These findings confirm earlier suggestions that the generic concept of Botryosphaeria should be expanded to include genera with septate ascospores and Diplodia anamorphs.

Fungi associated with healthy grapevine cuttings in nurseries, with special reference to pathogens involved in the decline of young vines

Little information is presently available on the disease aetiology and epidemiology of the fungi involved in the decline of young vines. To address this question, four rootstock-scion combinations, originating from three commercial nurseries in the Wellington area of the Western Cape Province of South Africa were investigated during the 1999/2000 season. The first isolations were made in September from callused cuttings prior to planting in nurseries. After planting, asymptomatic rooted cuttings were selected from nurseries after 3, 6 and 9 months. Isolations were made from the roots, rootstock, grafting union and scion. Isolations from callused cuttings prior to planting clearly demonstrated that primary pathogens associated with Petri disease, such as Phaeomoniella chlamydospora and Phaeoacremonium spp. were already present in the apparently healthy rootstock propagation material as endophytes. However, Cylindrocarpon spp., which cause black foot disease, rarely occurred in propagation material at this time. Species of this genus were isolated at higher percentages later during the season. Less than 1% of the plants were infected with Cylindrocarpon spp. before planting in the nursery (October), whereas 50% or more of the plants were infected at the end of the season (June). These findings suggest that the low percentage survival of vine plants observed in recent years is partly due to infected propagation material, and to new infections established in nurseries.

Reassessment of Phomopsis species on grapevines

Ten species of Phomopsis have previously been identified from grapevines. Of these, P. viticola, the causal agent of Phomopsis cane and leaf spot, and P. vitimegaspora, the causal agent of swelling arm of grapevines, have been confirmed as severe pathogens of this host. Earlier taxonomic treatments of Phomopsis species chiefly distinguished taxa based on host specificity, cultural characteristics and morphology. More recent studies have indicated, however, that these characteristics can no longer be used to distinguish species of Phomopsis due to the wide host ranges of some species, and the morphological plasticity of others. Using morphology, DNA sequences (ITS-1, 5.8S, ITS-2) and pathogenicity data, 15 Phomopsis spp. were distinguished from grapevines in the present study. Diaporthe helianthi, a known pathogen of sunflowers, is for the first time reported from grapevines. A further six, presently unknown species of Phomopsis, are also distinguished from grapevines. A phylogenetic analysis of ITS data generated in this study distinguished three clades containing isolates previously identified as D. perjuncta. Based on type studies, the name D. viticola can be applied to collections from Portugal and Germany. A new species, D. australafricana, is proposed for South African and Australian isolates formerly treated as D. perjuncta or D. viticola. A description for D. perjuncta is provided based on newly designated lectotype and epitype specimens. D. perjuncta is distinguished from D. viticola and D. australafricana based on morphology and DNA phylogeny. Artificial inoculations of green grapevine shoots indicated that, of the species tested, P. amygdali, a known pathogen of peaches in the USA, and P. viticola were the most virulent.

Proactive Control of Petri Disease of Grapevine Through Treatment of Propagation Material

Petri disease is a vascular disease associated with decline and dieback of young grapevines. A major means of spread of the causal organisms, Phaeomoniella chlamydospora and Phaeoacremonium spp., is via infected propagation material. Since no curative control measures are known, proactive measures must be taken in grapevine nurseries to manage this disease. To study this aspect, semicommercial trials with naturally infected rootstock material were performed in grapevine nurseries in South Africa. Prior to grafting, rootstocks were treated as follows: 1-h drench in suspensions of benomyl, phosphoric acid, different bacterial and Trichoderma formulations, water, or hot water treated (HWT; 30 min at 50°C). Grafted cuttings were planted and grown in a greenhouse and two commercial field nurseries and uprooted 8 months later. In instances where rootstocks were treated with benomyl or Trichoderma formulations, the incidences of Phaeomoniella and Phaeoacremonium in grafted cuttings and uprooted nursery vines were significantly lower than that of the water treatment. However, the reduction was most consistent and noteworthy in vines on rootstocks that received HWT prior to grafting. HWT of dormant nursery vines effected a similar reduction in Phaeomoniella and Phaeoacremonium incidence. Root-stock drenches in benomyl and/or Trichoderma formulations could thus be integrated with HWT for the proactive management of Petri disease in grapevine nurseries.

Occurrence of grapevine trunk disease pathogens in rootstock mother plants in South Africa

The incidence of grapevine trunk disease pathogens in grapevine rootstock mother plants from different cultivars, ages and growing areas in South Africa was determined by means of isolations from the basal and pruning wound end s of 2-year-old stubs. Phaeoacremonium spp. and Cylindrocarpon spp. occurred at very low incidences (average 0.12% and 0.17%, respectively). Phaeomoniella chlamydospora was most frequently isolated and significantly more from cvv. 101–14 Mgt and Ramsey than cvv. 99 Richter and 110 Richter mother plants. It was not evident whether Pa. chlamydospora invaded the mother plants via pruning wounds. However, it appeared as if Botryosphaeria and Phomopsis species invaded rootstock mother plants through unprotected pruning wounds. Results from this survey suggest the presence of latent infections of trunk disease pathogens in rootstock mother plants and highlight the need for pruning wound protection to prevent the se infections.

Investigation on the occurrence of Phaeomoniella chlamydospora in canes of rootstock mother vines

The presence of Phaeomoniella chlamydospora and Phaeoacremonium spp., the causal organisms of Petri disease of grapevine, in canes of rootstock vines in four mother blocks was determined monthly by means of isolations from the basal and fourth internodes. The canes were generally free from fungal, yeast and bacterial infection with only 2.4% of the total number of isolated xylem segments colonised. Basal internodes exhibited three-fold higher levels of infestation. The incidence of Pa. chlamydospora and Phaeoacremonium spp. was extremely low (< 0.2%) in the symptomless canes sampled from these rootstock mother vines. This emphasises the need for more sensitive detection techniques to be used for phytosanitary evaluation and research.

A review of black foot disease of grapevine

Summary. Black foot disease of grapevine is a relatively new, and as yet poorly known disease affecting vines in various countries where grapevines are cultivated. The causal organisms, their distribution, associated symptoms, known epidemiology and possible management strategies are discussed. Specific attention is also given to the taxonomy of the fungi involved, and the detection methods being developed to facilitate rapid identification of these pathogens.

Pathogenicity testing of lesser-known vascular fungi of grapevines

Several hyphomycetes were recently isolated from asymptomatic or symptomatic vascular tissues of grapevines showing Petri disease symptoms in South Africa. In most cases, their status as pathogens was unknown and pathogenicity studies were, therefore, conducted to determine their potential as decline pathogens. The fungi included Acremonium cf. charticola, Acremonium cf. ochraceum, Cadophora luteo-olivacea, Phialemonium cf. curvatum, Pleurostomophora richardsiae, Phaeoacremonium (Pm.) krajdenii, Pm. parasiticum, Pm. subulatum, Pm. venezuelense and Pm. viticola. Of these, Pm. parasiticum and Pm. viticola have been associated with Petri disease symptoms, although their pathogenicity has not been tested. Phaeomoniella (Pa.) chlamydospora and Pm. aleophilum, known to be involved in Petri disease and esca, were included as positive controls. Pathogenicity studies were conducted in glasshouse experiments where grapevine rootstocks were artificially inoculated, as well as in the field. Data obtained after 3 months from a glasshouse trial were difficult to interpret, due to the small lesions and similarity in disease expression among different species. However, Pa. chlamydospora produced the largest lesions and was by far the most aggressive pathogen. To supplement the glasshouse trial, grapevine trunks and pruning wounds of Vitis vinifera cv. Periquita were artificially inoculated in the field. Field trials, rated after 14 months, confirmed Pa. chlamydospora to be the most aggressive pathogen, since it produced the largest trunk and pruning wound lesions. Furthermore, it was re-isolated more frequently than any of the other fungi, especially from the pruning wounds. All the fungi were able to infect, colonise and produce lesions statistically different to those caused by the water control and the non-pathogen in the field trial.

A review of Phaeoacremonium species involved in Petri disease and esca of grapevines

Summary. The current status of Phaeoacremonium species involved in Petri disease and esca is reviewed. The taxonomical position and classification of Phaeoacremonium as well as its teleomorph, Togninia, are discussed. The review also provides the currently known distribution and host range of Phaeoacremonium species. The epidemiology of Phaeoacremonium species together with the more commonly isolated Phaeomoniella chlamydospora, is also treated. An overview is given of the molecular methods that have been used thus far to identify and detect the fungi involved in Petri disease. The role that Phaeoacremonium species, and the morphologically closely related pathogen Pa. chlamydospora, play in disease development and the results obtained with pathogenicity trials are also discussed. Lastly, an overview is given of the effect of management strategies on the Phaeoacremonium species associated with Petri disease and esca.

Cylindrocarpon pauciseptatum sp. nov., with notes on Cylindrocarpon species with wide, predominantly 3-septate macroconidia

A Cylindrocarpon species with up to 10 microm wide, straight and predominantly 3-septate macroconidia, subglobose to ovoidal microconidia and chlamydospores, is described as Cyl. pauciseptatum. It is most similar to Cyl. austrodestructans but no chlamydospores and microconidia are formed in the latter. Similar macroconidia also occur in Cyl. theobromicola, which forms oval to ellipsoidal microconidia at least sparsely and has slightly curved macroconidia, and Cyl. destructans var. crassum, which forms abundant 1-celled microconidia. DNA sequence data of the internal transcribed spacer regions 1 and 2 plus the 5.8S rDNA and the partial beta-tubulin gene were used for phylogenetic inferences. Cylindrocarpon pauciseptatum and Cyl. macrodidymum are monophyletic and are closely related to other species of Cylindrocarpon sensu stricto including members of the Cyl. destructans (teleomorph, Neonectria radicicola) species complex, which accommodates Cyl. liriodendri (teleomorph, Neon. liriodendri), Cyl. destructans var. crassum and Cyl. austrodestructans (teleomorph, Neonectria austroradicicola comb. nov.). Cylindrocarpon theobromicola is distantly related to species of Cylindrocarpon sensu stricto or Neonectria sensu stricto. It clustered among cylindrocarpon-like species with curved macroconidia, of which some belong to the Neon. mammoidea group. Relatively voluminous cells in sporodochial conidiophores of Cyl. theobromicola resembled those described for Campylocarpon, which is closely related to members of the Neon. mammoidea group including Cyl. theobromicola. Cylindrocarpon pauciseptatum has been isolated from roots of Vitis spp. in South-eastern Europe (Slovenia) as well as New Zealand, where it also occurs on roots of Erica melanthera.