Browsing by Author "Halleen, F."

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    Cleistothecia and flag shoots : sources of primary inoculum for grape powdery mildew in the Western Cape Province, South Africa
    (South African Society for Enology and Viticulture, 2000) Halleen, F.; Holz, G.
    Little is known about the mode of survival and sources of primary inoculum of Uncinula necator, the causal pathogen of grapevine powdery mildew, in vineyards in the Western Cape province. A study was therefore undertaken to determine whether cleistothecia and flag shoots are formed on vines in local vineyards. Flag shoots were found shortly after budbreak in September 1997 in a Carignane vineyard near Somerset West. Cleistothecia were first observed during April to May 1996 on severely infected leaves from three vineyards in the main grapegrowing areas of Stellenbosch. This was the first report of cleistothecia and flag shoot formation in vineyards in the Western Cape province. Cleistothecia occurred in small numbers on leaves (1 - 10 per leaf) and all were immature. Cleistothecia were dispersed by late summer and autumn rains from leaves to bark of grapevines, where they overwinter. No conclusion could be made regarding the viability of cleistothecia. However, the characteristics of the first symptoms that developed on leaves, namely separate, individual lesions formed at random on first-formed leaves growing in close proximity to the bark, provided circumstantial evidence that cleistothecia are dispersed to the bark. Weather conditions suitable for release of ascospores from overwintered cleistothecia occurred frequently between budbreak and bloom in all the areas.
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    Genera of phytopathogenic fungi : GOPHY 2
    (Elsevier, 2019) Marin-Felix, Y.; Hern andez-Restrepo, M.; Wingfield, M. J.; Akulov, A.; Carnegie, A. J.; Cheewangkoon, R.; Gramaje, D.; Groenewald, J. Z.; Guarnaccia, V.; Halleen, F.; Lombard, L.; Luangsa-ard, J.; Marincowitz, S.; Moslemi, A.; Mostert, L.; Quaedvlieg, W.; Schumacher, R. K.; Spies, C. F. J.; Thangavel, R.; Taylor, P. W. J.; Wilson, A. M.; Wingfield, B. D.; Wood, A. R.; Crous, P. W.
    This paper represents the second contribution in the Genera of Phytopathogenic Fungi (GOPHY) series. The series provides morphological descriptions and information regarding the pathology, distribution, hosts and disease symptoms for the treated genera. In addition, primary and secondary DNA barcodes for the currently accepted species are included. This second paper in the GOPHY series treats 20 genera of phytopathogenic fungi and their relatives including: Allantophomopsiella, Apoharknessia, Cylindrocladiella, Diaporthe, Dichotomophthora, Gaeumannomyces, Harknessia, Huntiella, Macgarvieomyces, Metulocladosporiella, Microdochium, Oculimacula, Paraphoma, Phaeoacremonium, Phyllosticta, Proxypiricularia, Pyricularia, Stenocarpella, Utrechtiana and Wojnowiciella. This study includes the new genus Pyriculariomyces, 20 new species, five new combinations, and six typifications for older names.
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    Genetic diversity among isolates of Phaeomoniella chlamydospora on grapevines
    (2006) Mostert, L.; Abeln, E. C. A.; Halleen, F.; Crous, P. W.
    Phaeomoniella chlamydospora is one of the main causal agents of Petri disease and esca of grapevines. Although it is known to have a coelomycete synanamorph, no teleomorph has thus far been reported for P. chlamydospora, and its disease cycle remains largely unknown. The present study compared the genetic diversity of P. chlamydospora isolates from different grapevine-growing countries using amplified fragment length polymorphisms. Sixty-three isolates from South Africa and 25 from grapevine regions in Australia, France, Iran, Italy, New Zealand, Slovenia and the USA were studied. Two primer combinations were used producing 138 scorable markers, of which 33% were polymorphic. An unweighted paired group method of arithmetic averages analysis showed a high similarity (≥94.5%) among the different isolates. The overall low level of genetic variation confirmed asexual reproduction to be dominant in the field. Different genotypes were found among isolates of P. chlamydospora within the same grapevine, suggesting multiple infections from different inoculum sources. Isolates from different production areas and countries had a high percentage of similarity and clustered together, indicating the absence of genotype-geographic structure. The presence of the same genotype in different vineyards and production areas suggests that long-range dispersal through aerial inoculum or infected plant material play an important role in genotype distribution. © Australasian Plant Pathology Society 2006.
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    An integrated strategy for the proactive management of grapevine trunk disease pathogen infections in grapevine nurseries
    (South African Society for Enology and Viticulture, 2016) Halleen, F.; Fourie, P. H.
    The aim of this study was to compare 11 treatment regimes (TR) in grapevine nurseries in order to eradicate trunk pathogens. Grapevine propagation material was subjected to treatments before cold storage, before and after grafting, before planting and after uprooting. Isolations were made from roots, rootstocks and graft unions of uprooted vines. None of the treatments consistently affected the number of certifiable vines produced. TR 1 (benomyl), TR 3 (Sporekill) and TR 4 (Trichoflow) increased root mass. Phaeomoniella chlamydospora was the most frequently isolated pathogen from all plant parts. In general, TR 2, 7, 9 and 11 caused the lowest occurrence of Phaeomoniella. TR 9 consistently reduced the incidence of Phaeoacremonium. Pleurostomophora richardsiae occurred most frequently in graft unions, but treatments were too inconsistent to draw meaningful conclusions. TR 7 (hot water treatment (HWT) of uprooted grapevines) consistently reduced incidences of black foot disease (BFD) pathogens. The highest incidence of Botryosphaeriaceae occurred in graft unions, but all treatments significantly reduced infections. The colonisation of rootstocks and graft unions by Trichoderma was significantly better with TR 4 (Trichoflow). The other Trichoderma treatments (TR 9, 10 and 11) differed from the control treatment only in the graft unions. This is a first report of an integrated strategy covering all the phases of the propagation process, from the moment the nursery receives the propagation material until the dormant vines are removed. TR 9 is recommended for use in nurseries, although HWT of dormant vines is recommended to eradicate BFD pathogens. Benomyl can be replaced by carbendazim when benomyl is no longer available.
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    An overview of the biology, epidemiology and control of uncinula necator (powdery mildew) on grapevine, with reference to South Africa
    (South African Society for Enology and Viticulture, 2001) Halleen, F.; Holz, G.
    Grape powdery mildew, caused by Uncinula necator, is the most widespread and destructive disease of grapevine. The disease can be found in most grape-growing areas of the world, including the tropics. In South Africa, grape powdery mildew was first reported in 1880, and since then has become the most important disease of grapevine. The disease can effect all phases of plant growth, and without necessarily causing obvious symptoms, may have a harmful effect on the vine and its products. The pathogen follows a specific pattern in each part of the world to create an epidemic. This pattern is determined by biological characteristics of the organism, climatic factors, cultivation practices and cultivar choices. Increased world-wide emphasis on the production of disease-free grapes with minimal fungicide input provides a sound reason for exploring more efficient disease management strategies through a better understanding of U. necator epidemiology and population genetics. Knowledge of these aspects is available for various parts of the world, but little is known about its relevance to South African vineyards. In this article a South African perspective of the pathogen and its control is outlined, based on recent local findings, and considered in the light of knowledge available in other parts of the world.
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    Resistance in uncinula necator to triazole fungicides in South African grapevines
    (South African Society for Enology and Viticulture, 2000) Halleen, F.; Holz, G.; Pringle, K. L.
    The distribution of Uncinula necator variants resistant to triadimenol, penconazole and flusilazole were determined in vineyards with suspected resistance in the regions Tulbagh, Franschhoek, Stellenbosch, De Dooms, Riebeeck Kasteel and Paarl. The regional subpopulations had all been exposed to triadimefon or triadimenol prior to 1989, when these fungicides were phased out and other demethylation-inhibiting fungicides (DMls) were applied. The occurrence of resistant variants in the subpopulations was compared with those in a vineyard in the Ceres Karoo region, which was isolated by two mountain ranges from the viticultural regions and where triadimefon was used prior to 1989, then abandoned. No other DMls were applied. A discriminatory germ tube length was used as a criterion to distinguish between sensitive and tolerant conidia at a discriminatory fungicide dose of 0.3 μg/mL. All the populations showed reduced sensitivity to triadimenol. This finding indicated an earlier shift in triadimenol sensitivity in the subpopulations and showed that resistant variants are sufficiently competitive to become established in vineyards. Cross-resistance between the triazoles was indicated by the frequency at which resistant variants occurred in subpopulations. The Ceres Karoo population was at baseline sensitivity level for penconazole and flusilazole. However, the four populations (De Dooms, Franschhoek, Riebeeck Kasteel and Stellenbosch) which showed the highest shifts in sensitivity to triadimenol, also displayed a high level of reduced sensitivity to flusilazole. This was in spite of the fact that only the Stellenbosch population was regularly treated with flusilazole. The other three populations were predominantly exposed to penconazole. Reduced sensitivity to penconazole was furthermore most prevalent in the Paarl K, Paarl I, Riebeeck Kasteel and De Dooms populations. Of these populations, Paarl K and Paarl I received predominantly penconazole, whereas the other two populations were treated with a range of DMis. Penconazole EDso values for the Paarl K, Paarl I, Riebeeck Kasteel and De Dooms pathogen populations (which showed the highest shifts in sensitivity to this fungicide) were 0.908, 1.022, 1.253 and 1.942 μg/mL, respectively. In these populations, 53%, 38%, 71 % and 91 % of the conidia respectively belonged to the 1.0-3.0 μg/mL and higher resistant classes. Reduced sensitivity to flusilazole was most prevalent in the Stellenbosch, De Doorns, Riebeeck Kasteel and Franschhoek populations. Flusilazole EDso values for these populations were 1.580, 1.813, 2.143, 3.885 μg/mL, respectively, whereas 83%, 82%, 96% and 79% of the conidia respectively belonged to the 1.0-3.0 μg/mL and higher resistant classes. These findings suggest a differing sensitivity of the pathogen to the three triazole fungicides which indicate that resistance to DMis is a multigenic trait in U. necator.