The characterization and control of Phomopsis cane and leaf spot on vine

[摘要] ENGLISH ABSTRACT: Phomopsis cane and leaf spot disease of grapevine is an economically important diseasein many of the vine-growing areas of the world. Four different Phomopsis spp. havepreviously been associated with this disease. The present study investigates thetaxonomic significance of the different taxa found on grapevines in South Africa, as wellas the endophytic growth and fungicide sensitivity of Phomopsis viticola isolates. Thethesis is compiled of several different parts, which deal with specific, but related topics,and hence some duplication has been unavoidable.Understanding the epidemiology of a disease is important for the correct timing ofdisease control. To investigate the endophytic growth of P. viticola, asymptomaticshoots were collected at eight different growth stages. Nodes, internodes, leaf petioles,leaves, tendrils and bunch peduncles were investigated. Two Phomopsis spp., taxon 1 and2 were identified in this study. The Phomopsis viticola-complex had a relativeimportance of 9% and accounted for 3% of the isolations. P. viticola (taxon 2) is mainlyisolated from the nodes and internodes. Inoculations of healthy, young vine tissueconfirmed taxon 2 to be a virulent pathogen, suggesting that it is a latent pathogen ratherthan an endophyte. In contrast, taxon 1 appeared to be a true endophyte, and did notseem to be an important pathogen on vines.The true identity of the causal organism of Phomopsis cane and leaf spot diseasewas investigated by collecting samples from 58 different vineyards in the grapevinegrowing areas of the Western Cape. P. viiicola occurred in grapevine material collectedfrom Lutzville to Swellendam, but was not found in the Oudtshoorn and Orange Rivergrapevine areas. Diaporthe perjuncta (taxon 1), P. vutcola (taxon 2), taxon 3 and aPhomopsis species commonly associated with shoot blight of peaches in the U.S.A., P.amygdali, were identified among the South African grapevine isolates. Examination ofthe Australian culture designated as taxon 4 found it to be a species of Libertella, thusexcluding it from the P. viticola-complex. An Italian isolate was found to represent aspecies of Phomopsis not previously known from grapevines, and this was subsequentlydescribed as taxon 5. Species delimitation was based on morphological and culturalcharacteristics, stem inoculations and the formation of the teleomorph in vitro. Theidentity of each morphological taxon was confirmed by means of phylogenetic analysesof the nuclear ribosomal DNA internal transcribed spacers (ITS 1 and ITS2) and the 5'end partial sequence of the mitochondrial small subunit (mtSSU). P. amygdali,associated with peach shoot blight in the U.S.A., was isolated once only and appeared tobe of lesser importance in this disease complex. Furthermore, taxa 1 (Diaportheperjuncta) and 3 were also rarely encountered and proved to be non-pathogenic,indicating their non-functional role in Phomopsis cane and leaf spot disease. Taxon 2(Phomopsis viticolas was common and widely distributed in diseased vineyards. Thistaxon was associated with the typical disease symptoms and proved to be pathogenic.Morphologically taxon 2 corresponded best with P. viticola, which was also neotypifiedin this study. Taxon 2 was mostly isolated from buds and nodes, indicating that these areimportant sites in which the fungus survives during winter. Molecular data indicated thattaxon 3 and P. amygdali were not host specific to grapevine.The currently used foliar fungicides were compared to the new strobilurinfungicides. The effects of nine fungicides (azoxystrobin, flusilazole, folpet, fosetyl-Al+mancozeb, kresoxim-methyl, mancozeb, penconazole, spiroxamine andtrifloxystrobin) were tested in vitro on inhibition of mycelial growth. The following EC50(ug/ml) values were obtained: azoxystrobin (0.350), flusilazole (0.007), folpet (4.489),fosetyl-Al+mancozeb (3.925), kresoxim-methyl (1.665), mancozeb (2.891), penconazole(0.023), spiroxamine (0.321) and trifloxystrobin (0.051). Additionally, azoxystrobin,folpet, kresoxim-methyl, mancozeb, propineb and trifloxystrobin were tested for theirability to inhibit spore germination in vitro. The subsequent EC50 (ug/ml) values wereobtained: azoxystrobin 0.123), folpet (0.510), kresoxim-methyl (0.0037), mancozeb(0.250), propineb (0.156) and trifloxystrobin (0.003). The results reported in part 4showed that the strobilurin fungicides inhibited the mycelial growth and sporegermination of P. viticola. However, further trials need to be conducted to verify thesefindings under field conditions. In the present study taxa 1, 3 and P. amygdali wereinfrequently isolated, suggesting that they played a less prominent role in the P. viticolacomplex.

[发布机构] Stellenbosch University