Browsing by Author "Langenhoven, Shaun"

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    Dectection and quantification of soilborne pathogens in grapevine nurseries
    (Stellenbosch : Stellenbosch University, 2017-12) Langenhoven, Shaun; Mostert, Lizel; Halleen, Francois; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH ABSTRACT: Black-foot disease (BFD) and crown and root rot (CRR) are important decline diseases of grapevines, worldwide. These diseases occur in both nurseries and vineyards. Black-foot disease is caused by species in the genera: Dactylonectria, Ilyonectria, Campylocarpon, Cylindrocladiella and Thelonectria, whereas CRR is caused by Phytophthora, Pythium and Phytopythium species. Plant stress, caused by improper planting holes, waterlogging, drought, nutrient deficiencies and high temperatures, is a major predisposing factor for BFD and CRR. The symptoms of these two diseases are similar and include necrotic root lesions, reduced root biomass, leaf chlorosis and ultimately, plant death. The first aim of this study was to conduct a survey of BFD and CRR pathogens in nursery grafted plants over a 3 year period (2013-2015) as well as from weeds and rotation crops in the alternate season (2014). Furthermore, pathogen detection using quantitative realtime polymerase chain reaction (qPCR) was conducted on soil samples which were collected in close proximity to the sampled grapevine plants, weeds and rotation crops. Soil was collected up to a depth of 30 cm and 60 cm. The decline pathogens that were quantified in the soil with qPCR were Dactylonectria and Ilyonectria genera, Phytophthora species and Pythium irregulare. The predominant BFD pathogens isolated from grapevines were Dactylonectria macrodidyma, Campylocarpon pseudofaciculare and Ca. fasciculare. The predominant CRR pathogens were Pythium irregulare followed by Phytopythium vexans. Furthermore, Dactylonectria macrodidyma, D. novozelandica, D. pauciseptata, Py. irregulare, Py. ultimum and Py. heterothallicum were isolated from Triticale roots. Dactylonectria was also isolated from the weed corn spurry, while Py. irregulare and Py. ultimum were isolated from numerous weeds and rotation crops. Dactylonectria, Ilyonectria, Phytophthora and Py. irregulare DNA was detected in all nurseries across all years at varying concentrations with Nursery E having the lowest concentrations. Ilyonectria and Dactylonectria mean soil DNA concentrations ranged from 0.04 pg.µL-1 to 37.14 pg.µL-1, while the Py. irregulare mean soil DNA concentrations ranged from 0.01 pg.µL-1 to 3.77 pg.µL-1. The Phytophthora mean soil DNA concentrations ranged from 0.01 pg.µL-1 to 33.48 pg.µL-1. This study successfully used existing SYBR green I qPCR assays to quantify BFD and CRR pathogens in grapevine nursery soil. During this study nursery soils were confirmed as a sources of infection for BFD and CRR pathogens, and that weeds may serve as alternative hosts to these pathogens. This is also the first report of D. alcacerensis and D. pauciseptata in South African nurseries. The second aim was to describe a putative new Phytopythium species which was isolated from nursery grapevine roots and to determine if it is a pathogenic species. Six isolates of an unknown Phytopythium species were isolated from the roots of an asymptomatic plant. Morphological observations and phylogenetic analyses, based on the ITS rDNA and cytochrome oxidase subunit 1 gene regions, proved that it was indeed a novel species. Together with an undescribed Japanese isolate, the six South African isolates were named Phytopythium paucipapillatum and displayed occasionally papillate, direct sporangial germination as well as sporangia which proliferates internally. The sporangia were globose, subglobose, ovoid, obovoid, limoniform to ellipsoid or distorted. The oogonia were small, globose, with some oogonia also displaying short papillae protruding from the surface. This putative new species was also insensitive to the isoxazole fungicide, hymexazol. A pathogenicity trial, on the rootstock 110-Richter, revealed that Pp. paucipapillatum was not pathogenic towards grapevines. In accordance with other studies regarding Phytopythium species, Pp. paucipapillatum may be a soil inhabitant.
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    Detection and quantification of black foot and crown and root rot pathogens in grapevine nursery soils in the Western Cape of South Africa
    (Firenze University Press, 2018) Langenhoven, Shaun; Halleen, Francois; Spies, Christoffel F. J.; Stempien, Elodie; Mostert, Lizel
    Black foot disease (BFD) and crown and root rot (CRR) are important soilborne diseases that affect young grapevines in nurseries and vineyards. A 3-year survey (2013–2015) of five open-field grapevine nurseries was conducted in the Western Cape Province of South Africa. The survey involved the isolation of BFD and CRR pathogens from grafted rootstocks (ten plants per nursery, per year) that were rooted in soil for 1 year. In 2013 and 2015, grapevines were sampled, while in 2014, sampling was focused on rotation crops and weeds (ten plants each). The rotation crops included white mustard, lupins, canola, triticale and forage radish. The weed species sampled included Johnson grass, ryegrass, winter grass, Cape marigold and corn spurry. Soil samples from ten sites per nursery were also collected in close proximity to the sampled plants, at depths of 0–30 cm and 30–60 cm (ten samples per depth). Isolations were made from the grapevines, rotation crops and weeds. Pathogen detection and quantification in the soil were determined using quantitative real-time polymerase chain reaction technology. The predominant BFD pathogens isolated from grapevines were Campylocarpon fasciculare, Ca. pseudofasciculare and Dactylonectria macrodidyma. The predominant CRR pathogens were Pythium irregulare and Phytopythium vexans. Dactylonectria macrodidyma, D. novozelandica, D. pauciseptata, Py. irregulare, Py. ultimum var. ultimum and Py. heterothallicum were isolated from triticale roots. Dactylonectria spp. were also isolated from corn spurry, while Py. irregulare and Py. ultimum var. ultimum were isolated from numerous weeds and rotation crops. Mean soil DNA concentrations of Ilyonectria and Dactylonectria were from 0.04 to 37.14 pg μL-1, and for Py. irregulare were between 0.01 and 3.77 pg μL-1. The Phytophthora mean soil DNA concentrations ranged from 0.01 to 33.48 pg μL-1. The qPCR protocols successfully detected and quantified BFD and CRR pathogens in grapevine nursery soil. This is the first report of D. pauciseptata and D. alcacerensis in South African grapevine nurseries.