SUNScholar - Browsing by Author "Viljoen, Altus"

Browsing by Author "Viljoen, Altus"

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Assessing genotype-by-environment interactions in aspergillus ear rot and pre-harvest aflatoxin accumulation in maize inbred lines
(MDPI, 2017) Okoth, Sheila; Rose, Lindy J.; Ouko, Abigael; Netshifhefhe, Nakisani E. I.; Sila, Henry; Viljoen, Altus
Aspergillus flavus, causal agent of the Aspergillus ear rot (AER) of maize, also produces aflatoxins that cause aflatoxicosis in humans and livestock. Ten maize inbred lines were evaluated in replicated trials in two aflatoxicosis outbreak hot spots in Kenya and in three maize-growing areas in South Africa for resistance to AER, A. flavus colonization, and pre-harvest aflatoxin accumulation during the 2012/13 growing season. AER severity was measured by visual assessment, while A. flavus colonization and aflatoxin content were quantified by real-time polymerase chain reaction (PCR) and liquid chromatography tandem mass spectrometry, respectively. Genotype by environment interaction (GEI) was determined using analysis of variance (ANOVA), additive main effects and multiplicative models (AMMI), and genotype plus by environment (GGE) biplot analyses. Stability of genotypes was evaluated using AMMI analysis. AER severity and fungal colonization significantly (p < 0.001) varied between genotypes. GEI influenced the severity of AER symptoms and aflatoxin accumulation significantly (p < 0.001), while fungal colonization was not affected. The inbred lines response was consistent for this trait in the test environments and was thus considered a desirable measure to indicate maize lines with a high risk of aflatoxin accumulation. CML495, CKL05019, LaPosta, and MIRTC5 were the least diseased lines, with the lowest aflatoxin contamination and a stable phenotypic response across the environments. Kiboko was determined as the ideal representative test environment, with discriminative ability of the genotypes for selection of the desired stable responses of the three traits.
Characterisation of South African isolates of Fusarium oxysporum f.sp. cubense from Cavendish bananas
(Academy of Science of South Africa (ASSAf), 2010-04) Visser, Marinda; Gordon, Tom; Fourie, Gerda; Viljoen, Altus
Fusarium wilt, caused by the soil-borne fungus Fusarium oxysporum f.sp. cubense (Foc), is a serious vascular disease of bananas in most subtropical and tropical regions of the world. Twenty-four vegetative compatibility groups (VCGs) and three pathogenic races have been identified in Foc, reflecting a relatively high genetic diversity for an asexual fungus. To characterise a South African population of Foc, a collection of 128 isolates from diverse geographic origins were isolated from diseased Cavendish bananas and subjected to VCG analysis and sequencing of the translation elongation factor 1-α (TEF) gene region. The presence of mating type genes was also determined using MAT-1 and MAT-2 specific primers. VCG 0120 was established as the only VCG of Foc present in the South African population studied. Only the MAT-2 idiomorph was present in all the local isolates of Foc. A phylogenetic analysis of DNA sequences of the TEF gene region revealed that the South African isolates grouped closely with VCG 0120 isolates from Australia and Asia. These results suggest that the South African population of Foc was most likely introduced in a limited number of events and that it had spread with infected planting material within the country. The presence of only one mating type and the limited diversity in this pathogen render it unlikely to rapidly overcome disease management strategies involving host resistance. © 2010. The Authors.
Contamination of bananas with beauvericin and fusaric acid produced by Fusarium oxysporum f. sp. cubense
(Public Library of Science, 2013) Li, Chunyu; Zuo, Cunwu; Deng, Guiming; Kuang, Ruibin; Yang, Qiaosong; Hu, Chunhua; Sheng, Ou; Zhang, Sheng; Ma, Lijun; Wei, Yuerong; Yang, Jing; Liu, Siwen; Biswas, Manosh Kumar; Viljoen, Altus; Yi, Ganjun
Background Fusarium wilt, caused by the fungal pathogen Fusarium oxysporum f. sp. cubense (Foc), is one of the most destructive diseases of banana. Toxins produced by Foc have been proposed to play an important role during the pathogenic process. The objectives of this study were to investigate the contamination of banana with toxins produced by Foc, and to elucidate their role in pathogenesis. Methodology/Principal Findings Twenty isolates of Foc representing races 1 and 4 were isolated from diseased bananas in five Chinese provinces. Two toxins were consistently associated with Foc, fusaric acid (FA) and beauvericin (BEA). Cytotoxicity of the two toxins on banana protoplast was determined using the Alamar Blue assay. The virulence of 20 Foc isolates was further tested by inoculating tissue culture banana plantlets, and the contents of toxins determined in banana roots, pseudostems and leaves. Virulence of Foc isolates correlated well with toxin deposition in the host plant. To determine the natural occurrence of the two toxins in banana plants with Fusarium wilt symptoms, samples were collected before harvest from the pseudostems, fruit and leaves from 10 Pisang Awak ‘Guangfen #1’ and 10 Cavendish ‘Brazilian’ plants. Fusaric acid and BEA were detected in all the tissues, including the fruits. Conclusions/Signficance The current study provides the first investigation of toxins produced by Foc in banana. The toxins produced by Foc, and their levels of contamination of banana fruits, however, were too low to be of concern to human and animal health. Rather, these toxins appear to contribute to the pathogenicity of the fungus during infection of banana plants.
Development of a hydrolysis probe-based real-time assay for the detection of tropical strains of Fusarium oxysporum f. sp. cubense race 4
(Public Library of Science, 2017-02-08) Aguayo, Jaime; Mostert, Diane; Fourrier-Jeandel, Celine; Cerf-Wendling, Isabelle; Hostachy, Bruno; Viljoen, Altus; Ioos, Renaud
Fusarium oxysporum f. sp. cubense (Foc) is one of the most important threats to global banana production. Strategies to control the pathogen are lacking, with plant resistance offering the only long-term solution, if sources of resistance are available. Prevention of introduction of Foc into disease-free areas thus remains a key strategy to continue sustainable banana production. In recent years, strains of Foc affecting Cavendish bananas have destroyed plantations in a number of countries in Asia and in the Middle East, and one African country. One vegetative compatibility group (VCG), 01213/16, is considered the major threat to bananas in tropical and subtropical climatic conditions. However, other genetically related VCGs, such as 0121, may potentially jeopardize banana cultures if they were introduced into disease-free areas. To prevent the introduction of these VCGs into disease-free Cavendish banana-growing countries, a real-time PCR test was developed to accurately detect both VCGs. A previously described putative virulence gene was used to develop a specific combination of hydrolysis probe/primers for the detection of tropical Foc race 4 strains. The real-time PCR parameters were optimized by following a statistical approach relying on orthogonal arrays and the Taguchi method in an attempt to enhance sensitivity and ensure high specificity of the assay. This study also assessed critical performance criteria, such as repeatability, reproducibility, robustness, and specificity, with a large including set of 136 F. oxysporum isolates, including 73 Foc pathogenic strains representing 24 VCGs. The validation data demonstrated that the new assay could be used for regulatory testing applications on banana plant material and can contribute to preventing the introduction and spread of Foc strains affecting Cavendish bananas in the tropics.
The distribution and host range of the banana fusarium wilt fungus, fusarium oxysporum f. sp. cubense , in Asia
(Public Library of Science, 2017) Mostert, Diane; Molina, Agustin B.; Daniells, Jeff; Fourie, Gerda; Hermanto, Catur; Chao, Chih- Ping; Fabregar, Emily; Sinohin, Vida G.; Masdek, Nik; Thangavelu, Raman; Li, Chunyu; Yi, Ganyun; Mostert, Lizel; Viljoen, Altus
Fusarium oxysporum formae specialis cubense (Foc) is a soil-borne fungus that causes Fusarium wilt, which is considered to be the most destructive disease of bananas. The fungus is believed to have evolved with its host in the Indo-Malayan region, and from there it was spread to other banana-growing areas with infected planting material. The diversity and distribution of Foc in Asia was investigated. A total of 594 F. oxysporum isolates collected in ten Asian countries were identified by vegetative compatibility groups (VCGs) analysis. To simplify the identification process, the isolates were first divided into DNA lineages using PCR-RFLP analysis. Six lineages and 14 VCGs, representing three Foc races, were identified in this study. The VCG complex 0124/5 was most common in the Indian subcontinent, Vietnam and Cambodia; whereas the VCG complex 01213/16 dominated in the rest of Asia. Sixty-nine F. oxysporum isolates in this study did not match any of the known VCG tester strains. In this study, Foc VCG diversity in Bangladesh, Cambodia and Sri Lanka was determined for the first time and VCGs 01221 and 01222 were first reported from Cambodia and Vietnam. New associations of Foc VCGs and banana cultivars were recorded in all the countries where the fungus was collected. Information obtained in this study could help Asian countries to develop and implement regulatory measures to prevent the incursion of Foc into areas where it does not yet occur. It could also facilitate the deployment of disease resistant banana varieties in infested areas.
Fusaric acid instigates the invasion of banana by Fusarium oxysporum f. sp. cubense TR4
(Wiley Online, 2019) Liu, Siwen; Li, Jian; Zhang, Yong; Liu, Na; Viljoen, Altus; Mostert, Diane; Zuo, Cunwu; Hu, Chunhua; Bi, Fangcheng; Gao, Huijun; Sheng, Ou; Deng, Guiming; Yang, Qiaosong; Dong, Tao; Dou, Tongxin; Yi, Ganjun; Ma, Li-Jun; Li, Chunyu
Fusaric acid (FSA) is a phytotoxin produced by several Fusarium species and has been associated with plant disease development, although its role is still not well understood. Mutation of key genes in the FSA biosynthetic gene (FUB) cluster in Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) reduced the FSA production, and resulted in decreased disease symptoms and reduced fungal biomass in the host banana plants. When pretreated with FSA, both banana leaves and pseudostems exhibited increased sensitivity to Foc TR4 invasion. Banana embryogenic cell suspensions (ECSs) treated with FSA exhibited a lower rate of O2 uptake, loss of mitochondrial membrane potential, increased reactive oxygen species (ROS) accumulation, and greater nuclear condensation and cell death. Consistently, transcriptomic analysis of FSA-treated ECSs showed that FSA may induce plant cell death through regulating the expression of genes involved in mitochondrial functions. The results herein demonstrated that the FSA from Foc TR4 functions as a positive virulence factor and acts at the early stage of the disease development before the appearance of the fungal hyphae in the infected tissues.
Fusarium spp. and levels of fumonisins in maize produced by subsistence farmers in South Africa
(Academy of Science of South Africa, 2011) Ncube, Edson; Flett, Bradley C.; Waalwijk, Cees; Viljoen, Altus
Fusarium spp. produce fumonisins – mycotoxins that are of importance to maize production in South Africa. Fumonisins have been associated with human oesophageal cancer and cause various diseases in animals that are of concern to the animal feed industry. Maize samples, collected from subsistence farm fields in the Eastern Cape, KwaZulu-Natal, Limpopo and Mpumalanga provinces of South Africa during the 2006 and 2007 growing seasons, were analysed for Fusarium spp. and contamination with fumonisins. Fusarium verticillioides was the most common Fusarium species in maize followed by F. subglutinans and F. proliferatum. Levels of contamination with fumonisins ranged from 0 μg/g to 21.8 μg/g, depending on the region where samples were collected. Levels of fumonisins were highest in northern KwaZulu-Natal (Zululand) where 52% and 17% of samples collected in 2006 and 2007, respectively, exceeded 2 μg/g. Regression analyses showed a positive correlation between fumonisin-producing Fusarium spp. determined by real-time polymerase chain reaction and concentration of fumonisins (r = 0.93). Many samples from Zululand, and some from Mokopane (Limpopo) and Lusikisiki (Eastern Cape), contained fumonisins at levels well above the maximum levels of 2 μg/g set by the Food and Drug Administration (USA) and therefore also the limit of 1 μg/g set by the European Union for food intended for direct human consumption. Regulations governing contamination of grain with fumonisins are not yet implemented in South Africa. The high incidence of fumonisins in subsistence farming systems indicates the need for awareness programmes and further research.
Mycotoxigenic Fusarium species associated with grain crops in South Africa – a review
(Academy of Science of South Africa, 2017) Beukes, Ilze; Rose, Lindy J.; Shephard, Gordon S.; Flett, Bradley C.; Viljoen, Altus
Cereal grains include some of the most important crops grown in South Africa and play a major role in the local economy. Maize, wheat and sorghum are extensively consumed by humans and farm animals, and are also utilised in industrial processes. Grain crops that are grown commercially contribute up to 33% of the country’s total gross agricultural production, whereas subsistence farmers grow grains mainly to sustain their families. In rural communities an average intake of maize grain of more than 300 g dry weight per person per day is not uncommon. The production of grains is often constrained by pests and diseases that may reduce their yields and quality. In South Africa, 33 mycotoxin-producing Fusarium species have been associated with grain crops. Mycotoxins, such as fumonisins and deoxynivalenol, have been found in levels exceeding the maximum levels imposed by the US Food and Drug Administration and the European Union and therefore pose a serious public health concern. We provide an extensive overview of mycotoxigenic Fusarium species associated with grain crops in South Africa, with particular reference to maize, wheat and sorghum.
Occurrence and spread of the banana fungus Fusarium oxysporum f. sp. cubense TR4 in Mozambique
(ASSAf, 2020-11-26) Viljoen, Altus; Mostert, Diane; Chiconela, Tomas; Beukes, Ilze; Fraser, Connie; Dwyer, Jack; Murray, Henry; Amisse, Jamisse; Matabuana, Elie L.; Tazan, Gladys; Amugoli, Otuba M.; Mondjana, Ana; Vaz, Antonia; Pretorius, Anria; Bothma, Sheryl; Rose, Lindy J.; Beed, Fenton; Dusunceli, Fazil; Chao, Chih-Ping; Molina, Agustin
Fusarium wilt, caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc), poses a major threat to banana production globally. A variant of Foc that originated in Southeast Asia, called tropical race 4 (TR4), was detected on a Cavendish banana export plantation (Metocheria) in northern Mozambique in 2013. Foc TR4 was rapidly disseminated on the farm, and affected approximately half a million plants within 3 years. The fungus was also detected on a second commercial property approximately 200 km away (Lurio farm) a year later, and on a small-grower’s property near Metocheria farm in 2015. Surveys in Mozambique showed that non-Cavendish banana varieties were only affected by Foc race 1 and race 2 strains. The testing of Cavendish banana somaclones in northern Mozambique revealed that GCTCV-119 was most resistant to Foc TR4, but that GCTCV-218 produced better bunches. The occurrence of Foc TR4 in northern Mozambique poses a potential threat to food security on the African continent, where banana is considered a staple food and source of income to millions of people. Cavendish somaclones can be used, in combination with integrated disease management practices, to replace susceptible Cavendish cultivars in southern Africa. The comprehensive testing of African cooking bananas for resistance to Foc TR4 is required, along with the improvement of biosecurity and preparedness of growers on the African continent.
Pathogenicity associated genes in Fusarium oxysporum f. sp. cubense race 4
(Academy of Science of South Africa, 2013) Sutherland, Rene; Viljoen, Altus; Myburg, Alexander A.; Van den Berg, Noelani
Fusarium oxysporum f. sp. cubense (Foc) is a fungus that infects banana roots and causes a destructive plant disease called Fusarium wilt. Foc consists of three pathogenic races (Foc races 1, 2 and 4), classified according to their selective impairment of banana cultivars. Foc race 4 is economically important as it comprises strains that infect Cavendish bananas, which are the most widely planted variety of bananas in the world, in both the tropics (Foc TR4) and subtropics (Foc STR4). The aim of this study was to investigate which genes are potentially involved in fungal pathogenicity by comparing transcript-derived cDNA fragments (TDFs) from Foc STR4 and TR4 to those from non-pathogenic F. oxysporum using cDNA-AFLP analysis. This comparison resulted in the identification of 229 unique gene fragments which include the putative pathogenicity-related TDFs encoding chitinase class V (chsV), GTPase activating protein, Major Facilitator Superfamily (MFS) multidrug transporter and serine/threonine protein kinase (ste12) genes. Quantitative analysis of transcript abundance showed a significant increase in expression of chsV, MFS multidrug transporter and ste12 genes in Foc STR4 and TR4 compared with the non-pathogenic F. oxysporum. These genes play a role in escaping host defence responses and in cell wall degradation. In addition, pathogenicity-related genes from other formae speciales of F. oxysporum, such as the sucrose non-fermenting, cytochrome P450 and F-box protein required for pathogenicity genes, were significantly up-regulated in Foc STR4 and TR4 but not in F. oxysporum isolates non-pathogenic to banana. This study provides the first in vitro comparative analysis of TDFs expressed in pathogenic Foc race 4 isolates and non-pathogenic F. oxysporum isolates from banana.
Tolerance to fusarium verticillioides infection and fumonisin accumulation in maize F1 hybrids and subsequent F2 populations
(Wiley Periodicals, 2020-04-24) Ouko, Abigael; Okoth, Sheila; Netshifhefhe, Nakisani E. l.; Viljoen, Altus; Rose, Lindy Joy
Fusarium verticillioides causes Fusarium ear rot (FER) in maize (Zea mays L.), thus reducing grain quality, yield, and contaminates grains with fumonisins. Grain infection by these fungi occurs before harvest and selection of parental lines resistant to fumonisin accumulation for breeding purposes is the most effective and environmentally friendly control strategy for F. verticillioides. This study intended to evaluate F1 hybrids and F2 breeding populations in Kenya for improved resistance to FER and fumonisin contamination. Trials were artificially inoculated and FER severity, F. verticillioides accumulation, and fumonisin contamination were determined. Inheritance of resistance was also determined in the F1 hybrids. CML444 × MIRTC5, R119W × CKL05015, and CML444 × CKL05015 exhibited little to no FER and had the least fungal and fumonisin contamination, respectively. Inbred lines CML495, CKL05015, and P502 had negative, significant general combining ability (GCA) estimates for F. verticillioides colonization and fumonisin contamination, but positive, significant GCA estimates for 1,000-kernel weight, respectively. The genotype × environment interaction was the main source of variation observed in the F2 populations with R119W × CKL05015 and CML444 × CKL05015 being the most tolerant to fungal and fumonisin contamination in Kiboko and MIRTC5 × CML495 the most tolerant in Katumani.
Transcriptome profiling of resistant and susceptible cavendish banana roots following inoculation with Fusarium oxysporum f. sp. cubense tropical race 4
(BioMed Central, 2012-08) Li, Chun-yu; Deng, Gui-ming; Yang, Jing; Viljoen, Altus; Jin, Yan; Kuang, Rui-bin; Zuo, Cun-wu; Lv, Zhi-cheng; Yang, Qiao-song; Sheng, Ou; Wei, Yue-rong; Hu, Chun-hua; Dong, Tao; Yi, Gan-jun
Abstract Background Fusarium wilt, caused by the fungal pathogen Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), is considered the most lethal disease of Cavendish bananas in the world. The disease can be managed in the field by planting resistant Cavendish plants generated by somaclonal variation. However, little information is available on the genetic basis of plant resistance to Foc TR4. To a better understand the defense response of resistant banana plants to the Fusarium wilt pathogen, the transcriptome profiles in roots of resistant and susceptible Cavendish banana challenged with Foc TR4 were compared. Results RNA-seq analysis generated more than 103 million 90-bp clean pair end (PE) reads, which were assembled into 88,161 unigenes (mean size = 554 bp). Based on sequence similarity searches, 61,706 (69.99%) genes were identified, among which 21,273 and 50,410 unigenes were assigned to gene ontology (GO) categories and clusters of orthologous groups (COG), respectively. Searches in the Kyoto Encyclopedia of Genes and Genomes Pathway database (KEGG) mapped 33,243 (37.71%) unigenes to 119 KEGG pathways. A total of 5,008 genes were assigned to plant-pathogen interactions, including disease defense and signal transduction. Digital gene expression (DGE) analysis revealed large differences in the transcriptome profiles of the Foc TR4-resistant somaclonal variant and its susceptible wild-type. Expression patterns of genes involved in pathogen-associated molecular pattern (PAMP) recognition, activation of effector-triggered immunity (ETI), ion influx, and biosynthesis of hormones as well as pathogenesis-related (PR) genes, transcription factors, signaling/regulatory genes, cell wall modification genes and genes with other functions were analyzed and compared. The results indicated that basal defense mechanisms are involved in the recognition of PAMPs, and that high levels of defense-related transcripts may contribute to Foc TR4 resistance in banana. Conclusions This study generated a substantial amount of banana transcript sequences and compared the defense responses against Foc TR4 between resistant and susceptible Cavendish bananas. The results contribute to the identification of candidate genes related to plant resistance in a non-model organism, banana, and help to improve the current understanding of host-pathogen interactions.

Browsing by Author "Viljoen, Altus"

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