J.E. Van der Waals

J.E. Van der Waals
University of Pretoria | UP · Department of Plant and Soil Sciences

PhD Plant Pathology

About

71
Publications
36,700
Reads
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1,252
Citations
Additional affiliations
January 2000 - January 2015
University of Pretoria
Position
  • Professor (Associate)

Publications

Publications (71)
Article
Ralstonia spp., the causal agents of bacterial wilt, cause severe yield losses of Solanaceous crops, including tomato. The disease is difficult to control due to the pathogen's ability to survive in soil and to cause latent infections. Therefore, characterizing Ralstonia strains is important in developing effective strategies for diagnoses , quaran...
Chapter
Dic.key'a. N.L. fem. n. Dickeya, after the American phytopathologist Robert S. Dickey, for his contribution to research on the Erwinia chrysanthemi complex. Proteobacteria / Gammaproteobacteria / Enterobacterales / Erwiniaceae / Dickeya Cells of the genus Dickeya are Gram-negative rods with rounded ends, which mostly occur alone or in pairs and som...
Chapter
Pec.to.bac.te'ri.u,m. N.L. suff. pecto-, pertaining to pectin; from Gr. adj. pêktos, curdled, congealed; N.L. neut. n. bacterium, a small rod; N.L. neut. n. Pectobacterium, a pectolytic bacterium. Proteobacteria / Gammaproteobacteria / Enterobacterales / Pectobacteriaceae / Pectobacterium Cells of the genus Pectobacterium are Gram-negative rods, 0....
Conference Paper
Full-text available
The biotrophic protozoan Spongospora subterranea f. sp. subterranea (Sss) causes powdery scab, root infection and root galling diseases on potato. The susceptibility of 10 potato cultivars commonly grown in South Africa to Sss diseases was assessed in pot trials in a greenhouse. Disease severity of root gall formation and root infection was determi...
Article
Charcoal rot, caused by Macrophomina phaseolina, is an important disease in tropical and subtropical regions which affects a broad range of host plants, including potato (Solanum tuberosum L.). In this crop, charcoal rot can reduce the marketable quality of tubers (Arora 2012) and cause yield losses up to 88% (Somani 2007). During a survey of a pot...
Chapter
Full-text available
Management of soft rot Pectobacteriaceae (SRP) is a challenge as there are no control agents available and no effective resistance present in commercial cultivars. In addition, many species of SRP have a broad host range and spread via rotten plant material takes place readily. In this chapter, the possibilities for disease management are outlined....
Chapter
The soft rot Pectobacteriaceae (SRP) infect a wide range of plants worldwide and cause economic damage to crops and ornamentals but can also colonize other plants as part of their natural life cycle. They are found in a variety of environmental niches, including water, soil and insects, where they may spread to susceptible plants and cause disease....
Chapter
Soft rot Pectobacteriaceae (SRP) are ubiquitous on earth as there are records of findings from all continents where host plants are grown. This chapter describes information on soft rot diseases on these continents. For some countries, detailed information is provided by local experts on the SRP present, their economic damage, and the management st...
Article
Full-text available
Why this research Matters Plant–soil feedbacks (PSFs) give a mechanistic understanding on how soil properties established by previous plant species go on to influence the performance of the same or different species in monoculture, intercropping or crop rotation systems. We hypothesized that different dryland crops such as Zea mays L., Helianthus a...
Article
Full-text available
Potato is a staple crop that contributes to food security and poverty alleviation in developing nations. Despite this, yields in developing nations are often unsustainably low, due to various biotic and abiotic factors that negatively affect production. Some of the most important biotic constraints are pathogens, many of which are disseminated by s...
Article
Full-text available
Potato has increased in importance as a staple food in sub-Saharan Africa, where its production is faced with a multitude of challenges, including plant disease development and spread under changing climatic conditions. The economically most important plant viruses affecting potatoes globally are Potato virus Y (PVY) and Potato leafroll virus (PLRV...
Article
Pectobacterium brasiliense (Pb) is one of the causal agents of soft rot and blackleg diseases and has become a pathogen of economic importance in many potato production regions worldwide. Accurate, sensitive and timely identification of Pb is critical for improved management of the pathogen to mitigate yield losses. This study describes the develop...
Article
Full-text available
Potato (Solanum tuberosum L.) is considered as one of the most economically important non-sugar food crops in Mauritius, with annual production of over 14,000 tonnes (Statistics Mauritius 2018). In September 2019, in a seed potato field located in St Pierre, approximately 10% of tubers showed the presence of numerous irregular-shaped black scurf le...
Article
Full-text available
Plants defend themselves from pathogens by producing bioactive defense chemicals. The biochemical mechanisms relating to quantitative resistance of potato to root infection by Spongospora subterranea f. sp. subterranea (Sss) are, however, not understood, and are not efficiently utilized in potato breeding programs. Untargeted metabolomics using ult...
Article
Spongospora subterranea f. sp. subterranea (Sss) is an obligate parasite that can only multiply within the living tissues of a host plant. Greenhouse experiments were carried out to determine the host status of Sss in some crops and weeds commonly found in southern African fields. These experiments used both qPCR and light microscope examination to...
Article
Sclerotinia sclerotiorum (Lib.) de Barry, causal agent of Sclerotinia stem rot of soybeans, is one of the pathogens that could have a potentially devastating impact on the growth of the soybean industry in South Africa. Several quantitative trait loci (QTLs) that play a role in soybean resistance to Sclerotinia stem rot have been identifed and mapp...
Article
Spongospora subterranea f. sp. subterranea, causal agent of powdery scab and root galls of potatoes, occurs worldwide and is responsible for quality and yield losses in potato production in South Africa. Despite being one of the most important potato pathogens in South Africa, little information is available on the genetic structure and diversity o...
Article
Full-text available
Land-use change from natural to managed agricultural ecosystems significantly impacts soil bacterial diversity and function. The Eastern Free State (EFS) is one of the most productive agricultural regions in South Africa. However, no studies aiming to understand the changes in bacterial diversity, composition and function due to land-use change in...
Article
Full-text available
Powdery scab caused by Spongospora subterranea f. sp. subterranea (Sss) has recently become one of the most devastating potato diseases of economic importance in South Africa. The use of resistant cultivars has long been considered the most effective and sustainable strategy to manage the pathogen. However, little is known about the molecular mecha...
Article
Charcoal rot incidence in soybean and sunflower in South Africa is increasing. Irrigation as a means to manage charcoal rot is limited as water resources are decreasing and oil seed production is predominantly on dry land. The effect of reduced soil moisture on charcoal rot incidence, severity and colonization of host tissues, as well as subsequent...
Article
Soil fungal communities perform important ecological roles determining, at least in part, agricultural productivity. This study aimed at examining the fungal community dynamics in the potato rhizosphere across different development stages in two consecutive growing seasons (winter and summer). Microbial fingerprinting of rhizosphere soil samples co...
Article
Ralstonia spp., the causal agents of bacterial wilt, cause severe yield losses of Solanaceous crops, including tomato. The disease is difficult to control due to the pathogen's ability to survive in soil and to cause latent infections. Therefore, characterizing Ralstonia strains is important in developing effective strategies for diagnoses, quarant...
Article
Rhizoctonia is a major pathogen of potato causing substantial yield losses worldwide. Control of Rhizoctonia diseases is based predominantly on the application of fungicides. However, little is known about the fungicide response variability of different Rhizoctonia anastomosis groups associated with potato diseases in South Africa. A total of 131 R...
Article
Understanding the contribution of seed tuber- and soilborne inocula of Rhizoctonia solani AG 3-PT in causing potato disease epidemics is an important step in implementing effective management strategies for the pathogen. A 2-year study was conducted to evaluate the contribution of each source of inoculum using an integrative experimental approach c...
Article
Potato skin blemishes with known causes (typical blemishes) are manageable in contrast to those with unknown causes (atypical blemishes). This study investigated possible fungal causal agents of atypical tuber blemishes in South Africa and Zimbabwe through isolation and pathogenicity testing. Several fungal genera were isolated from elephant hide,...
Article
Powdery scab caused by Spongospora subterranea f. sp. subterranea (Sss) causes extensive losses in potato production systems globally. Two pot experiments were established in the greenhouse in summer 2013 and winter 2014 to evaluate the effectiveness of different soil chemicals, fumigant, amendments and biological control agents (BCAs) against Sss...
Article
Full-text available
Alternaria blight (AB) of sweet potato (Ipomoea batatas L.), caused by Alternaria spp., is a new disease recently reported in South Africa, but is common in southern and eastern Africa. Elsewhere in the world, AB is controlled primarily using resistant varieties. Twenty-five sweet potato varieties/breeding lines, from different origins were assesse...
Article
Full-text available
Cowpea (Vigna unguiculata) is susceptible to pathogens such as Rhizoctonia solani, Pythium ultimum and Fusarium solani, which cause seedling diseases in cowpea and result in low yields. Three commercial synthetic fungicides containing mefenoxam 350 g ai L−1, mefenoxam 240 g ai L−1 and fludioxonil 100 g ai L−1, respectively, were evaluated against t...
Article
Full-text available
Rhizoctonia solani AG 3-PT is an important potato pathogen causing significant yield and quality losses in potato production globally. However, little is known about the levels of genetic diversity and population structure of this pathogen in South Africa. A total of 114 R. solani AG 3-PT isolates collected from four geographic regions were analyze...
Article
Streptomyces scabiei is largely accepted as the causal organism of common scab on potato in South Africa, and other Streptomyces species associated with common scab are not often considered. This study therefore aims to determine the diversity and prevalence of Streptomycetes associated with common scab on potatoes in South Africa. Isolates from 11...
Article
Potato blackleg and soft rot cause major losses and are caused by two bacterial genera, Pectobacterium and Dickeya. Species affecting potatoes are Pectobacterium atrosepticum (Pba), Pectobacterium carotovorum subsp. carotovorum (Pcc), Pectobacterium carotovorum subsp. brasiliense (Pcb), Pectobacterium wasabiae (Pwa), Dickeya dadantii (Dda) and Dick...
Article
Full-text available
A survey of anastomosis groups (AGs) of Rhizoctonia species associated with potato diseases was conducted in South Africa. A total of 112 Rhizoctonia solani and 19 binucleate Rhizoctonia (BNR) isolates were recovered from diseased potato plants, characterized for AG and pathogenicity. The AG identity of the isolates was confirmed using phylogenetic...
Conference Paper
Full-text available
Powdery scab, caused by Spongospora subterranea f.sp. subterranea (Sss), is a devastating and economically important disease of potatoes. Sss is an obligate parasite for which no single control measure is effective, due to the ability of the cystorsori (sporeballs) to survive in soil for many years. Powdery scab regularly leads to extensive losses...
Conference Paper
Full-text available
A bioassay is a technique also known as 'baiting', which is used to detect a pathogen in soil for example. The bioassay technique for Spongospora subterranea f.sp. subterranea (Sss) was first developed using tomato seedlings and has since been used with potato seed tubers. This pathogen is able to cause lesions on the growing potato tuber as well a...
Article
Full-text available
Since the first report of brown spot of potatoes (Solanum tuberosum) caused by Alternaria alternata (Fr.) Keissl in South Africa (3), disease intensity has steadily increased. No fungicides are registered for control of brown spot of potatoes in South Africa but growers attempt to control the disease with products registered for early blight, which...
Conference Paper
Full-text available
Potato diseases caused by Rhizoctonia solani are a serious threat to potato commercial production globally, causing yield depression and reduced tuber quality. The aim of this study was to identify isolates of Rhizoctonia solani associated with potato diseases in South Africa. A total of 131 isolates were recovered from diseased potato plants, char...
Article
Full-text available
Nutrients such as boron, nitrogen and calcium stimulate the production of phenols. This research focuses on the role of calcium in increasing phenol metabolism in potato peels and the ensuing tuber resistance to soft rot pathogens was investigated. Two field experiments were conducted at the University of Zimbabwe campus plots in 2008 and 2009 summ...
Article
Full-text available
Rhizoctonia solani consists of 13 anastomosis groups (AGs) designated AG1 to 13. AG3-PT is considered the predominant AG in potatoes (4) and is associated with quantitative and qualitative yield losses. Qualitative losses are typically associated with the tuber blemish disease, black scurf. However, atypical tuber blemishes such as elephant hide co...
Article
Dwarf and common cashew (Anacardium occidentale) genotypes were screened separately for resistance against anthracnose (Colletotrichum gloeosporioides). Disease incidence was assessed on emerging leaves over three consecutive crop seasons in Mocuba, Meconta and Pebane districts of northern Mozambique. Evaluation the disease using leaf incidence is...
Article
Anthracnose of cashew (Anacardium occidentale) was studies on various genotypes and locations in Mozambique. Colletotrichum gloeosporioides was identified as the anthracnose causal agent using polymerase chain reaction. The relationships between incidence and severity of anthracnose on cashew genotypes were statistically analyzed by regression. Ant...
Article
Full-text available
A set of daily weather data simulations for 1961 to 2050 were used to calculate past and future trends in pest and disease pressure in potato cropping systems at three agro-ecologically distinct sites in South Africa: the Sandveld, the Eastern Free State and Limpopo. The diseases and pests modelled were late blight, early blight and brown spot, bla...
Article
Full-text available
Soft rot and blackleg can cause severe economic losses in potato production in South Africa and Zimbabwe depending on climatic conditions. The aim of the study was to identify the predominant bacteria causing potato soft rot and blackleg in these countries. Samples, comprising of stems and tubers from potato plants with blackleg and soft rot sympto...
Data
Phylogenetic tree based on recA gene sequence showing the phylogenetic relationship among Zimbabwean strains, D. dadantii subsp. dadantii and different Pectobacterium spp. The phylogram was produced by the neighbour-joining programme (Tamura et al. 2007). The numbers on the branches indicate bootstrap value support based on neighbour-joining analys...
Article
Full-text available
Soft-rot Enterobacteriaceae (SRE), which belong to the genera Pectobacterium and Dickeya, consist mainly of broad host-range pathogens that cause wilt, rot, and blackleg diseases on a wide range of plants. They are found in plants, insects, soil, and water in agricultural regions worldwide. SRE encode all six known protein secretion systems present...
Article
Full-text available
Powdery scab, a root and tuber disease caused by the pathogen Spongospora subterranea f.sp. subterranea (Sss), poses a major problem to potato producers worldwide because it affects potato quality. Inoculum can be seed-borne or originate from contaminated growing media or contaminated equipment. During 2006, a potato mini-tuber production facility...
Article
Powdery scab, a root and tuber disease caused by the pathogen Spongospora subterranea f.sp. subterranea (Sss), poses a major problem to potato producers worldwide because it affects potato quality. Inoculum can be seed-borne or originate from contaminated growing media or contaminated equipment. During 2006, a potato mini-tuber production facility...
Article
Full-text available
Ngadze, E., Icishahayo, D., Coutinho, T. A., and van der Waals, J. E. 2012. Role of polyphenol oxidase, peroxidase, phenylalanine ammonia lyase, chlorogenic acid, and total soluble phenols in resistance of potatoes to soft rot. Plant Dis. 96:186-192. Pectobacterium atrosepticum, P carotovorum subsp. brasiliensis, and Dickeya spp. cause soft rot of...
Article
Full-text available
Type IV pili are virulence factors in various bacteria. Several subclasses of type IV pili have been described according to the characteristics of the structural prepilin subunit. Although type IVa pili have been implicated in the virulence of Ralstonia solanacearum, type IVb pili have not previously been described in this plant pathogen. Here, we...
Article
Full-text available
A survey was carried out in the potato- (Solanum tuberosum L.) growing regions of Zimbabwe in April 2009 to assess the prevalence of bacterial soft rot. A total of 125 tubers with soft rot symptoms were collected. The disease caused severe economic losses ranging from 20 to 60% on tubers in the field and in storage. Affected tubers had symptoms tha...
Article
Full-text available
In South Africa during the 2006/2007 potato growing season, outbreaks of blackleg occurred, causing severe economic losses in commercial potato production fields. Symptoms were initially observed on only one stem per plant, on which the top leaves rolled upwards, wilted and became necrotic. As symptoms progressed to the lower leaves with subsequent...
Article
Full-text available
During recent growing seasons, a new leaf blight was observed on potatoes (Solanum tuberosum L.) in various production regions in South Africa. Symptoms were observed before early blight, from 50 to 60 days after emergence of the potato plants. Typical leaf symptoms were small, circular, brown lesions, first visible on the abaxial sides of leaves....
Article
Full-text available
Genetic diversity among isolates of Alternaria solani, the causal agent of early blight of potato, from various potato-growing regions in South Africa (SA), was determined using virulence assays, vegetative compatibility (VC) tests, and random amplified microsatellite (RAMS) primers. The virulence assays showed low virulence levels for the largest...
Article
Full-text available
Trends in weather variables and concentrations of airborne conidia of Alternaria solani were monitored in a potato field in South Africa during three potato-growing seasons in 2001 and 2002. Distinct seasonal variation was noted, with a drop in spore numbers during winter. Peaks in spore concentration coincided with periods favorable for spore form...
Article
Full-text available
Trends in weather variables and concentrations of airborne conidia ofAlternaria solani were monitored in a potato field in South Africa during three potato-growing seasons in 2001 and 2002. Distinct seasonal variation was noted, with a drop in spore numbers during winter. Peaks in spore concentration coincided with periods favorable for spore forma...
Article
Full-text available
Early blight is a major foliar disease of potatoes in most potato growing regions of the world. Numerous forecasting models have been developed and evaluated for the control of early blight on potatoes; however, prior to the development of the PLANT-Plus early blight forecaster none were applicable to South African conditions and cultivars. Field t...
Article
Full-text available
A survey of control practices and grower perceptions of early blight in South Africa was conducted from May 2001 — July 2002 using an informally structured questionnaire. Questionnaires were collected from the 10 largest of the 14 potato production regions in South Africa. The predominant control method for early blight was the use of fungicides wi...

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