Paul H. Fourie

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.

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.

Botryosphaeria spp. as grapevine trunk disease pathogens

Summary. Several species of Botryosphaeria, including Botryosphaeria dothidea, B. obtusa, B. parva and B. australis, were isolated and/or described from declining grapevines in association with a wide range of decline and dieback symptoms. Internal wood symptoms most commonly included black streaking, wedge-shaped necrosis and brown internal necrosis. Several diseases under names such as excoriose, grapevine decline syndrome and black dead arm have been described for decline and dieback symptoms associated with Botryosphaeria. This has led to the confusing situation where the same symptoms and causal species are often associated with more than one disease. This review summarises the research on Botryosphaeria on grapevine by focusing on the causal species, their associated symptoms, known epidemiology and possible effective control and management strategies.

Novel Phaeoacremonium species associated with necrotic wood of Prunus trees

The genus Phaeoacremonium is associated with opportunistic human infections, as well as stunted growth and die-back of various woody hosts, especially grapevines. In this study, Phaeoacremonium species were isolated from necrotic woody tissue of Prunus spp. (plum, peach, nectarine and apricot) from different stone fruit growing areas in South Africa. Morphological and cultural characteristics as well as DNA sequence data (5.8S rDNA, ITS1, ITS2, β-tubulin, actin and 18S rDNA) were used to identify known, and describe novel species. From the total number of wood samples collected (257), 42 Phaeoacremonium isolates were obtained, from which 14 species were identified. Phaeoacremonium scolyti was most frequently isolated, and present on all Prunus species sampled, followed by Togninia minima (anamorph: Pm. aleophilum) and Pm. australiense. Almost all taxa isolated represent new records on Prunus. Furthermore, Pm. australiense, Pm. iranianum, T. fraxinopennsylvanica and Pm. griseorubrum represent new records for South Africa, while Pm. griseorubrum, hitherto only known from humans, is newly reported from a plant host. Five species are newly described, two of which produce a Togninia sexual state. Togninia africana, T. griseo-olivacea and Pm. pallidum are newly described from Prunus armeniaca, while Pm. prunicolum and Pm. fuscum are described from Prunus salicina.

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.

Coniochaeta (Lecythophora), Collophora gen. nov. and Phaeomoniella species associated with wood necroses of Prunus trees

Species of the genus Coniochaeta (anamorph: Lecythophora) are known as pathogens of woody hosts, but can also cause opportunistic human infections. Several fungi with conidial stages resembling Lecythophora were isolated from necrotic wood samples of Prunus trees in South Africa. In order to reveal their phylogenetic relationships, these fungi were studied on a morphological and molecular (5.8S nrDNA, ITS-1, ITS-2, GAPDH, EF-1α, 28S nrDNA, 18S nrDNA) basis. Some of the isolates were identified as Coniochaeta (Sordariomycetes), including C. velutina and two new species, C. africana and C. prunicola. The majority of the isolates, however, formed pycnidial or pseudopycnidial synanamorphs and were not closely related to Coniochaeta. According to their 28S nrDNA phylogeny, they formed two distinct groups, one of which was closely related to Helotiales (Leotiomycetes). The new genus Collophora is proposed, comprising five species that frequently occur in necrotic peach and nectarine wood, namely Co. africana, Co. capensis, Co. paarla, Co. pallida and Co. rubra. The second group was closely related to Phaeomoniella chlamydospora (Eurotiomycetes), occurring mainly in plum wood. Besides P. zymoides occurring on Prunus salicina, four new species are described, namely P. dura, P. effusa, P. prunicola and P. tardicola. In a preliminary inoculation study, pathogenicity was confirmed for some of the new species on apricot, peach or plum wood.

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.

Novel Paraconiothyrium species on stone fruit trees and other woody hosts

Coniothyrium-like fungi are common wood and soil inhabitants and hyperparasites on other fungi. They belong to different fungal genera within the Pleosporales. Several isolates were obtained on wood of different Prunus species (plum, peach and nectarine) from South Africa, on Actinidia species from Italy and on Laurus nobilis from Turkey. Morphological and cultural characteristics as well as DNA sequence data (5.8S nrDNA, ITS1, ITS2, partial SSU nrDNA) were used to characterise them. The isolates belonged to three species of the recently established genus Paraconiothyrium. This is the first report of Paraconiothyrium brasiliense on Prunus spp. from South Africa. Two new species are described, namely Paraconiothyrium variabile sp. nov. on Prunus persica and Prunus salicina from South Africa, on Actinidia spp. from Italy and on Laurus nobilis from Turkey, and Paraconiothyrium africanum sp. nov. on Prunus persica from South Africa. Although other known species of Paraconiothyrium commonly produce aseptate conidia, those of P. africanum and P. hawaiiense comb. nov. are predominantly two-celled.