SUNScholar - Browsing by Author "Fourie, P. H."

Browsing by Author "Fourie, P. H."

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Effect of fungicide spray cover on botrytis cinerea infection in grape bunches
(South African Society for Enology and Viticulture, 2006) Brink, J. C.; Holz, G.; Fourie, P. H.
The effect of fungicide spray cover on Botrytis cinerea infection in grape bunches was determined. Bunches were sprayed at pea size and bunch closure with different volumes of a mixture of fenhexamid and a yellow fluorescent pigment, and the percentage fluorescent pigment coverage on pedicels was determined. Bunches were subsequently dusted with dry airborne conidia of B. cinerea in a settling tower and incubated for 24 h at high relative humidity (98%). Infection was determined by estimating the amount of B. cinerea infections on susceptible bunch parts (pedicel, receptacle and rachis) with isolations onto paraquat (herbicide) and Kerssies (B. cinerea selective) mediums. Linear regressions for the part × stage combinations of percentage B. cinerea incidence on different bunch parts were fitted on mean coverage levels. An increase in spray cover caused linear reductions in levels of B. cinerea on bunch parts. Higher B. cinerea incidences were recorded at pea size. Furthermore, higher B. cinerea incidences were found on paraquat medium for both stages, than on Kerssies medium. The information gathered from this study will be used to facilitate future determination of minimum effective coverage levels for effective B. cinerea control in grape bunches.
First report of Phyllosticta citricarpa and description of two new species, P. paracapitalensis and P. paracitricarpa, from citrus in Europe
(Elsevier, 2017) Guarnaccia, V.; Groenewald, J. Z.; Li, H.; Glienke, C.; Carstens, E.; Hattingh, V.; Fourie, P. H.; Crous, P. W.
The genus Phyllosticta occurs worldwide, and contains numerous plant pathogenic, endophytic and saprobic species. Phyllosticta citricarpa is the causal agent of Citrus Black Spot disease (CBS), affecting fruits and leaves of several citrus hosts (Rutaceae), and can also be isolated from asymptomatic citrus tissues. Citrus Black Spot occurs in citrus-growing regions with warm summer rainfall climates, but is absent in countries of the European Union (EU). Phyllosticta capitalensis is morphologically similar to P. citricarpa, but is a non-pathogenic endophyte, commonly isolated from citrus leaves and fruits and a wide range of other hosts, and is known to occur in Europe. To determine which Phyllosticta spp. occur within citrus growing regions of EU countries, several surveys were conducted (2015–2017) in the major citrus production areas of Greece, Italy, Malta, Portugal and Spain to collect both living plant material and leaf litter in commercial nurseries, orchards, gardens, backyards and plant collections. A total of 64 Phyllosticta isolates were obtained from citrus in Europe, of which 52 were included in a multi-locus (ITS, actA, tef1, gapdh, LSU and rpb2 genes) DNA dataset. Two isolates from Florida (USA), three isolates from China, and several reference strains from Australia, South Africa and South America were included in the overall 99 isolate dataset. Based on the data obtained, two known species were identified, namely P. capitalensis (from asymptomatic living leaves of Citrus spp.) in Greece, Italy, Malta, Portugal and Spain, and P. citricarpa (from leaf litter of C. sinensis and C. limon) in Italy, Malta and Portugal. Moreover, two new species were described, namely P. paracapitalensis (from asymptomatic living leaves of Citrus spp.) in Italy and Spain, and P. paracitricarpa (from leaf litter of C. limon) in Greece. On a genotypic level, isolates of P. citricarpa populations from Italy and Malta (MAT1-2-1) represented a single clone, and those from Portugal (MAT1-1- 1) another. Isolates of P. citricarpa and P. paracitricarpa were able to induce atypical lesions (necrosis) in artificially inoculated mature sweet orange fruit, while P. capitalensis and P. paracapitalensis induced no lesions. The Phyllosticta species recovered were not found to be widespread, and were not associated with disease symptoms, indicating that the fungi persisted over time, but did not cause disease.
Fitness on grape berries of botrytis cinerea isolates belonging to different dicarboximide sensitivity classes
(South African Society for Enology and Viticulture, 2003) Fourie, P. H.; Holz, G.
Seasonal fluctuations in the frequency of dicarboximide-resistant Botrytis cinerea isolates in Western Cape vineyards suggest a reduced fitness of these isolates. In this study fitness of sensitive, ultra-low-level and low-level dicarboximide-resistant isolates of B. cinerea were compared on grape berries. Conidia were dispersed as single cells on berry surfaces from airborne inoculum in a settling tower or deposited as clusters in water droplets. Investigations were conducted at two potential infection courts on dicarboximide treated and untreated berries, namely the intact cuticle and wounds. Surface sterilisation, isolation and freezing techniques were used to determine surface colonisation and penetration by airborne inoculum. Decay incidence, severity and sporulation incidence were determined following inoculation with conidial clusters. The different tests indicated that germlings of dicarboximide-sensitive and -resistant isolates had similar surface-colonising abilities of dicarboximide-free berries. However, sensitive strains penetrated significantly more often. Fitness decreased with an increase in the level of dicarboximide resistance. Iprodione caused a drastic disturbance in the ratio of different dicarboximide sensitivity classes that occupied the berry surface and allowed the development of germlings of predominantly resistant isolates, but with few successful infections. Significantly higher levels of infection and proliferation of dicarboximide-resistant isolates on sprayed or unsprayed berries were facilitated by wounding or the termination of host resistance (freezing). According to these findings, these modes of infection should not contribute to a gradual build-up of inoculum of either dicarboximide-sensitive or -resistant isolates. Trends by airborne conidia described here suggest that another primary infection event in the vineyard, most likely floral infection and subsequent debris colonisation, should largely regulate the dynamics between dicarboximide-sensitive and -resistant isolates in B. cinerea populations on grapevine.
Frequency of dicarboximide resistant strains of botrytis cinerea in South African table grape vineyards and influence of spray schedules on resistant sub-populations
(South African Society for Enology and Viticulture, 1998) Fourie, P. H.; Holz, G.
Between 1993 and 1995, 1139 isolates of Botrytis cinerea were collected from table grape vineyards in the Western and Northern Cape provinces and tested for sensitivity to dicarboximides (vinclozolin) and benzimidazoles (carbendazim). Overall the frequency of resistance to vinclozolin and carbendazim averaged 9,4 and 11,9%, respectively. Ninety-seven percent of the vinclozolin-resistant isolates were dual resistant to carbendazim. Fifty-nine percent of the isolates were from the Hexriver region; of these 7,7% were vinclozolin, and 12,6% carbendazim resistant. The Paarl region had the highest resistance incidence (37,7% vinclozolin and 41,5% carbendazim resistant). Only two of the 191 isolates tested from the Orange River region were vinclozolin resistant. ED50 values of ultra-low-level and low-level dicarboximide-resistant isolates ranged from 0,843 to 1,834 and 2,053 to 5,129 μg vinclozolin/ml, respectively. Vinclozolin-resistant strains were not abnormally osmotically sensitive. Monitoring of changes in the frequency of resistance in 10 commercial vineyards under high-, medium- and low-schedule dicarboximide programmes from 1993-1995 showed that the resistance frequency fluctuated from low (average 12,7% ) during the winter to high (average 55,8 % ) during the growing season. Maximum levels of dicarboximide resistance were recorded during bunch closure. Distinct differences were, however, observed in the resistance frequency in individual vineyards. In four high-schedule dicarboximide vineyards resistance frequencies increased early in the season, prior to any dicarboximide applications. This finding suggests dual resistance between broad-spectrum fungicides and dicarboximides.
Incomplete cross-resistance to folpet and iprodione in botrytis cinerea from grapevine in South Africa
(South African Society for Enology and Viticulture, 2001) Fourie, P. H.; Holz, G.
The sensitivity to folpet of Botrytis cinerea isolates obtained from table grape vineyards in the Western Cape province of South Africa with a known history of dicarboximide (DC) resistance and high-schedule DC and folpet programmes was investigated. In the Simondium vineyards, 61 % of the B. cinerea isolates from Dan-hen-Hannah and 20% of the isolates from Waltham Cross were resistant to iprodione. In the Northern Paarl vineyards, 95% of the isolates from Dan-hen-Hannah and 95% of the isolates from Waltham Cross were designated resistant. In the case of the iprodione-sensitive isolates from vineyards in Simondium, folpet ECso values ranged from 4.9 to 29.1 μg/mL for the Dan-hen-Hannah and 15.0 to 43.5 μg/mL for the Waltham Cross sub-populations, respectively. Folpet ECso values of the iprodione-resistant isolates, on the other hand, ranged from 19.7 to above 100 μg/mL for the Dan-hen-Hannah subpopulation. In the Northern Paarl subpopulations, where the isolates were predominantly iprodione-resistant, folpet ECso values of the latter isolates ranged from 21.5 to above 100 μg/mL. Similar shifts in folpet sensitivity were displayed by ultra-low- and low-level DC-resistant B. cinerea isolates obtained from other regional subpopulations. The results indicated incomplete cross-resistance between iprodione and folpet. This finding suggests that early increases in DC resistance frequencies in B. cinerea, observed prior to DC application in vineyards under the high-schedule DC and folpet programmes, can be attributed to incomplete cross-resistance to these fungicides in sub-populations of the pathogen.
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.
A protocol for molecular detection of Phaeomoniella chlamydospora in grapevine wood
(Academy of Science for South Africa, 2005) Retief, E.; Damm, U.; Van Niekerk, J. M.; McLeod, A.; Fourie, P. H.
PETRI DISEASE IS A SERIOUS DECLINE AND dieback disease of young grapevines. The principal causal organism, Phaeomoniella chlamydospora, is distributed mainly by infected propagation material. Pathogen detection and accurate diagnosis are currently based on fungal isolation in artificial growth media. The fungus is extremely slow-growing, however, and cultures are often overgrown by co-isolated fungi before it can be identified. To avoid this problem, we have developed and validated an efficient and cost-effective protocol for the molecular detection of Pa. chlamydospora in grapevine wood. This novel molecular technique, using a species-specific PCR, detected as little as 1 pg of genomic Pa. chlamydospora DNA. The protocol was validated with grafted grapevines from different nurseries, including grapevines that were first treated with hot water. The basal end of the rootstock was analysed for Pa. chlamydospora by means of both isolations in artificial medium and molecular detection. The latter was found to be considerably more sensitive than isolations, and detected Pa. chlamydospora in samples that recorded both positive and negative in isolations. The identity of PCR products obtained from a subset of samples that tested positive only for Pa. chlamydospora, based on molecular detection, was confirmed to be Pa. chlamydospora-specific through restriction digestion with AatII. The pathogen was not isolated from samples treated in hot water. However, as expected, Pa. chlamydospora DNA was detected in samples exposed to hot water at rates similar to those detected in material not immersed in hot water.
Spray deposition and control of botrytis cinerea on grape leaves and bunches : part 1 (table grapes)
(South African Society for Enology and Viticulture, 2016) Brink, J. C.; Calitz, F. J.; Fourie, P. H.
Insufficient quantity but also quality of spray deposition on susceptible grapevine tissue (i.e. target sites) and favourable conditions for pathogens could lead to control failure during high disease pressure situations. To determine deposition quantity and quality benchmarks for biologically effective spray deposits, bunches and leaves of table grapes (Waltham Cross) were sprayed at various growth stages, using different application volumes of a mixture of fenhexamid and a fluorescent tracer pigment and subsequently dusted with dry conidia of Botrytis cinerea where after infection levels on pedicels, receptacles and leaves were determined. Pigment deposition quantity and quality were determined from photos of sprayed parts taken with a digital camera under a stereo microscope and black light illumination at ×30 or ×10 magnifications and assessed with digital image and Hoerl regression analyses. The deposition quantity resulting in 75% control of B. cinerea infection (FPC75 values) was calculated from biological efficacy curves (sigmoidal regression analyses) for leaves and for each growth stage, for pedicels and receptacles. Deposition quantity and quality measurements correlated favourably with Botrytis infection. An optimal deposition value for the control of B. cinerea was determined by increasing spray volume, however by increasing spray volume and deposition quantity or quality levels past this optimum will not significantly improve disease control further. It was indicated that efficacy of agricultural chemicals could be influenced by improving both deposition quantity and quality, quantifiable by digital image analyses of fluorescent pigment deposition. FPC75 values obtained in this study can be used as benchmarks to evaluate future spray application in vineyards.
Spray deposition and control of botrytis cinerea on grape leaves and bunches : part 2 (wine grapes)
(South African Society for Enology and Viticulture, 2016) Brink, J. C.; Calitz, F. J.; Fourie, P. H.
Poor control of fruit and foliar diseases in vineyards is often attributed to insufficient spray deposition of susceptible tissue. To optimise spray deposition, a deposition assessment protocol using fluorometry, photomicrography and digital image analyses was developed to determine minimum spray deposition quantity and quality levels needed for effective B. cinerea control in wine grapes (Chenin blanc). Leaves and bunches were sprayed at different growth stages with different volumes of a mixture of fenhexamid and fluorescent pigment. Pigment deposition quantity and quality were determined from photos of pedicels and leaves taken with a digital camera under a stereo microscope and black light illumination at ×30 and ×10 magnification, respectively. After inoculation with dry airborne conidia of B. cinerea infection levels on pedicels, receptacles and leaves were determined and infection levels and deposition data were subjected to sigmoidal and Hoerl regression analyses, respectively. From these biological efficacy curves the deposition levels that affected 75% control of B. cinerea infection (FPC75 values) were calculated for leaves and for each growth stage for pedicels and receptacles. Deposition measurements on sprayed leaves and bunch parts correlated favourably with Botrytis infection levels. An increase in spray volume resulted in higher deposition quantity and improved quality values with a reduction of B. cinerea infections. However, at a certain point, deposition quality remained constant and infection levels did not decrease significantly with increasing spray volume. Susceptibility of pedicels and receptacles to B. cinerea decreased with maturity. FPC75 values can be used as benchmarks to evaluate spray application in wine grape vineyards.

Browsing by Author "Fourie, P. H."

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