Characterisation of pathogens associated with trunk diseases of grapevines

[摘要] ENGLISH ABSTRACT: In an attempt to combat some of the pathogens that are associated with trunk diseases anddisorders of grapevines, research in this thesis focused on the taxonomy and pathological aspectsof Coniellai/Pilidiella, Botryosphaeria and Phomopsis spp.Previously, conidial pigmentation was used to separate Pilidiella from Coniella.Recently, however, the two genera have been regarded as synonymous, with the older name,Coniella, having priority. The most important species in the Coniellai/Pilidiella complex ofgrapevines is C. diplodiella (Speg.) Petr. & Syd., the causal organism of white rot of grapevines.Previous studies found it difficult to distinguish between C. diplodiella and C. fragariae(Oudem.) B. Sutton, which is known to occur in soil and caused leaf diseases of Fragaria andEucalyptus. Both these species have previously been reported from South Africa. None of thereports on C. diplodiella could be scientifically substantiated; therefore it is still a quarantineorganism. However, this status has been questioned. Based on sequence analyses of the internaltranscribed spacer region (ITS 1, ITS 2), 5.8S gene, large subunit (LSU) and elongation factor 1-α gene (EF l- α) from the type species of Pilidiella and Coniella, Coniella was separated fromPilidiella, with the majority of taxa residing in Pilidiella. Pilidiella is characterised by specieswith hyaline to pale brown conidia (avg. length: width >1.5), with Coniella having dark brownconidia (avg. length: width ≤1.5). Pilidiella diplodiella, previously C. diplodiella, causalorganism of white rot of grapevines, was shown to be an older name for C. petrakii. This fungusis present in South Africa and is therefore no longer of quarantine importance. Based onanalyses of the histone (H3) gene sequences of isolates in the P. diplodiella species complex, P.diplodiella was separated from a newly described species, P. diplodiopsis. A new species, P.eucalyptorum, is proposed for isolates formerly treated as C. fragariae, associated with leafspots of Eucalyptus spp. This species clustered basal to Pilidiella, and may represent yet a thirdgenus within this complex. Pilidiella destruens was newly described as anamorph ofSchizoparme destruens, which is associated with twig dieback of Eucalyptus spp. in Hawaii.The genus Botryosphaeria Ces. & De Not. are known to be cosmopolitan, with broad hostranges and geographical distributions. Several saprotrophic species have been reported fromgrapevines, while others are severe pathogens of this host. These species include B. dothidea(Moug.: Fr.) Ces. & De Not., B. parva Pennycook & Samuels, B. obtusa (Schwein.) Shoemaker,B. stevensii Shoemaker, B. lutea A.J.L. Phillips and B. ribis Grossenb. & Duggar. Speciesreported from South Africa as grapevine pathogens are B. obtusa, B. dothidea, B. ribis and B.vitis (Schulzer) Sacco.In the present study, morphological, DNA sequence data (ITS 1, 5.8S, ITS2 and EFI-α) and pathological data were used to distinguish 11 Botryosphaeria spp. associatedwith grapevines from South Africa and other parts of the world. Botryosphaeria australis, B.lutea, B. obtusa, B. parva, B. rhodina and a Diplodia sp. were confirmed from grapevines inSouth Africa, while Diplodia porosum, Fusicoccum viticlavatum and F. vitifusiforme weredescribed as new species. Although isolates of B. dothidea and B. stevensii were confirmed fromgrapevines in Portugal, neither of these species, nor B. ribis, were isolated in this study. Allgrapevine isolates from Portugal, formerly presumed to be B. rib is, are identified as B. parvabased on EF1-α sequence data. Artificial inoculations on grapevine shoots showed that B.australis, B. parva, B. ribis and B. stevensii are more virulent than the other species studied. TheDiplodia sp. collected from grapevine canes was identified as morphologically similar, butphylogenetically distinct from D. sarmentorum, while D. sarmentorum was confirmed asanamorph of Otthia spiraeae, the type species of the genus Otthia (Botryosphaeriaceae). Aculture identified as O. spiraeae clustered within Botryosphaeria, and is thus regarded as aprobable synonym. These findings confirm earlier suggestions that the generic concept ofBotryosphaeria should be expanded to include genera with septate ascospores and Diplodiaanamorphs.The genus Phomopsis (Sacc.) Bubak contains many species that are plant pathogenic orsaprotrophic. Ten species are known from grapevines. However, only two have been confirmedas being pathogenic, namely P. viticola (Sacc.) Sacc., causal organism of Phomopsis cane andleaf spot and P. vitimegaspora Kuo & Leu (teleomorph Diaporthe kyushuensis Kajitani &Kanem.), causal organism of swelling arm disease of grapevines. P. amygdali (Delacr.) 1.1.Tuset & M.T. Portilla, a known pathogen from Prunus sp., was shown to be a possible pathogenof grapevines in a previous study. D. perjuncta Niessl. causes bleaching of dormant canes onlyand is therefore of little importance as a grapevine pathogen. Recently a number of Phomopsisisolates were obtained from grapevines in the Western Cape province of South Africa. Isolationswere made from Phomopsis-like symptoms, pruning wounds and asymptomatic nursery plants.These isolates showed great variation in morphology and cultural characteristics. Earliertaxonomic treatments of Phomopsis, based species identification on host specificity, culturalcharacteristics and morphology. Recent studies have indicated that these characteristics can nolonger be used to distinguish species of Phomopsis due to wide host ranges and morphologicalplasticity of some species. The use of anamorph/teleomorph relationships in speciesidentification is also untenable, since Diaporthe teleomorphs have only been described forapproximately 20% of the known Phomopsis species. In this study morphological data, DNAsequences (ITS-I, 5.8S, ITS-2) and pathogenicity data were combined to distinguish Phomopsisspp. from grapevines. Fifteen species of Phomopsis were delineated by phylogenetic analysis ofITS sequence data. Diaporthe helianthi, a sunflower pathogen, was reported from grapevines forthe first time, with a further six, unknown species also distinguished. Three different cladescontained isolates previously identified as D. perjuncta. Based on type studies, it appeared thatthe name D. viticola was available for collections from Portugal and Germany, a new species, D.australafricana, was proposed for South African and Australian isolates, formerly treated as D.perjuncta or D. viticola. An epitype specimen and culture were designated for D. perjuncta.This species was distinguished from D. viticola and D. australafricana based on morphology andDNA phylogeny. Artificial inoculations of green grapevine shoots indicated that, of the speciestested, P. amygdali, a known pathogen of peaches in the USA, and P. viticola were the mostvirulent.

[发布机构] Stellenbosch University