Some of the most devastating plant diseases in South Africa are thus at the heart of these articles. One of the most neglected areas of plant pathology in South Africa is the systematic collection of information on disease outbreaks and effects.
These concepts of horizontal and vertical resistance have been discussed by many researchers in the field of plant pathology and plant breeding. It is also a fitting tribute to remember him in the International Year of Plant Health.
Acknowledgements
The greatest impact of the PSHB invasion observed to date has been in urban environments. Experience from California, Israel and South Africa indicates that managing the PSHB is particularly challenging.
Introduction
This review covers a period in the history of virus discovery in South Africa during which several plant viruses from commercial and smallholder farms were identified and characterized. This review provides a historical account of the discovery and characterization of several viral pathogens of important agricultural crops grown by smallholder and commercial farmers in South Africa.
A new green-sterile viral disease of guar in Mpumalanga
Several twin viruses have also been detected in South Africa and neighboring southern African countries causing severe yield reductions in cassava, maize, tomatoes, beans and sweet potatoes.15 Two unipartite begomovirus isolates, which either alone or in mixed infection in sweet potatoes (Ipomoea batatas) prevent. plants, was identified for the first time in South Africa in 2011 from samples near Louis Trichardt in the Limpopo Province.16 The complete genome sequence of one of the isolates corresponded to Potato mosaic-associated virus (SPMaV; SPMaV-[ZA:WP) :2011]), with which it shared 98.5% nucleotide identity. This review reports a number of new viruses or virus isolates that have been identified between the years 1985 to 2011 in various provinces in South Africa.
The challenge of routine avocado sunblotch viroid detection in avocado trees
An ssRNA shown to be 9.4 kb was isolated from purified GGSV virions, and Western blots showed the coat protein to be ~34 kD.20 The nucleotide sequence of the 3' terminal region (1359 nt) of GGSV and translated amino acid was determined. and compared to the latent seed-borne guar symptomless potyvirus in guar imported to the US from India.21 The presence of the amino acid triplet DAG in both GGSV and guar-US was consistent with aphid transmissibility. GGSV and guar-US formed a tight cluster most closely related to the BCMV subgroup of potyviruses based on the coat protein and 3'-UTR, strongly suggesting that GSV-US and GGSV are strains of BCMV-NL4.
First report, characterisation and phylogenetic justification of Ryegrass mosaic virus–South
Further studies of guar may demonstrate other potyvirus infections, and this may have a negative impact on the use of this valuable crop, not only in the food and livestock industry, but also in pharmacotherapy, where guar gum has recently been used in treatment. of intestinal disorders. While there have been no extensive studies on RGMV-SA in the years since its discovery and characterization, breeding of this important forage crop is ongoing.
Unravelling the disease aetiology of tobacco leaf curl disease in southern Africa: Tobacco
Discovery of Tobacco leaf curl Zimbabwe virus – a new distinct monopartite begomovirus
Although extensive research on RGMV-SA has not taken place in the years since its discovery and characterization, breeding of this important forage crop is ongoing. multiflorum breeding program at ARC-Cedara in KwaZulu-Natal province provides substantial evidence of the benefits of breeding to improve yields.38 Because ryegrass mosaic disease can affect yields, it is important that ryegrass growers are aware of a potential problem and stay vigilant. Paximadis and Rey50). e) Symptoms of leaf curl and mosaic on cassava cv.60444 agro-inoculated with dual South African cassava mosaic virus DNA A and B.
The elusive identification of South African cassava mosaic virus: A novel geminivirus
Evidence supports recombination events among begomoviruses in the islands of Africa, the Mediterranean, and the southwestern Indian Ocean.71 Recently, three additional cassava begomovirus species, Cassava mosaic virus–Madagascar, East African cassava mosaic virus–Kenya, and East African cassava mosaic virus–Zanzibar—have been discovered in cassava in sub-Saharan Africa. Two different species, Indian cassava mosaic virus and Sri Lankan cassava mosaic virus, have been described from the Asian subcontinent.58,72.
First report of Pepino mosaic virus infecting tomato in South Africa
With a growing human population and droughts associated with climate change predicted for the future, cassava could provide a solution for food security in South Africa and other countries in the SADC region. Because begomoviruses are a major threat, genetic engineering for virus resistance through RNA interference and gene editing may provide critical solutions for controlling viral diseases.
Concluding remarks
This review is an acknowledgment to all my Masters and PhD students who were involved in this period of virus discovery and the many who joined me in an old Datsun 'bakkie' around South Africa and the fields to hunt virus symptoms in plants. I thank the research collaborators who also participated in this adventure of virus discovery over the years: Brian Beck, Mbudzeni Sibara, Ed Rybicki, Hanu Pappu, Roy French, Judy Brown, Maureen Wolfson, Kenneth Palmer, Ken Mabasa, Guido Boccardo, Christian Potgieter, Schalk van Heerden, Henrietta van Heerden and Michele Cloete.
Competing interests
Evidence of synergism between African cassava mosaic virus and a new double recombinant geminivirus infecting cassava in Cameroon. Complete nucleotide sequence of South African cassava mosaic virus: Further evidence for recombination among begomoviruses.
Late blight
In this review we discuss five of the most important diseases on potatoes in southern Africa, namely Phytophthora, Bacterial Wilt, Soft Rot/Black Leg, Powdery Scab and Zebra Chip. Establishing and implementing seed certification systems in South African countries will increase potato yields and thus contribute to food security.
Bacterial wilt
Phytophthora control in developed countries is achieved through seed certification, integrated management, intensive fungicide spray programs, early planting dates, inoculum elimination, and planting-resistant cultivars.10,15 However, in developing countries, where systemic fungicides are not readily available or prohibitive, growers use often large amounts of low-cost contact fungicides of the dithiocarbamate type, especially mancozeb, which pose significant health risks to farm workers and their families.16 It has been suggested that late blight in developed countries could be controlled by phosphonate applications, as a safer alternative to the dangerous dithiocarbamate derivatives currently be used.16 However, additional research is needed to determine the optimal timing, rates of application, specific host responses, environmental effects, and interactions of phosphonates with other chemical compounds.16 The same level of control of the pathogen achieved by intensive spray programs involving both contact and systemic fungicides will not be achieved by phosphonate application alone. Host resistance may be the most effective way for poor growers to control Phytophthora.16,17 However, adoption of resistant cultivars in developing countries is often slow due to the scarcity of functional seed certification systems18 and because P.
Soft rot / blackleg disease complex
This practice results in changes in the composition of bacterial communities, allowing biocontrol organisms to become established in the soil.30 This practice may be a practical and affordable way for farmers in southern Africa to manage this devastating disease. It is vital that potato growers in Southern Africa implement as many of these practices as possible to avoid severe economic losses.
Powdery scab
The disease complex is a major problem for the potato industry worldwide and a major contributor to yield loss in southern Africa.44,45 This disease has increased in both severity and distribution, likely due to an increase in planting of susceptible cultivars, and effects of climate change. on the composition of the pathogen population causing soft rot and black leg in southern Africa.11 The majority of research into SRP in southern Africa has been conducted in South Africa and to a lesser extent in Zimbabwe.44-46. the most widespread pathogen causing soft rot and black leg in these countries is Pectobacterium brasiliense.44,45Pectobacterium brasiliense has been shown to grow at temperatures between 20 °C and 38 °C47, which are the prevailing temperatures during the main potato growing seasons in southern Africa. These practices have variable success rates due to latent infections of tubers, rapid reproduction of bacteria and subsequent disease development under favorable environmental conditions.37 Nevertheless, as with R.
Zebra chip disease
Discussion
One of the challenges encountered in gathering information for this review was the lack of published data on disease occurrence and epidemiology, the type of pathogen strains present, pathogen prevalence, or disease impact on potato production in southern Africa. Border porosity and the lack of plant quarantine enforcement by monitoring services in Africa result in the unhindered movement of pests and pathogens across regional and national borders on the continent27, and food security in southern Africa needs urgent attention.
Authors’ contributions
How big is the potato (Solanum tuberosum L.) yield gap in sub-Saharan Africa and why. Areas requiring further research to manage PVY and PLRV in sub-Saharan Africa are identified.
PVY and PLRV management
However, depending on the landscape, trap catches from 8-m traps may be representative of aphid flight activity over a radius of 30 km.69 South Africa has an extensive suction trap network and farmers receive weekly information on aphid numbers and vector pressure to alert producers about the risk of PVY and PLRV spread.30 The establishment and maintenance of aphid monitoring programs can be challenging, because of the costs involved and the difficulty of identifying aphid species, especially for small farmers. The longer transmission time of PLRV compared to PVY makes it easier to manage virus spread with chemical control because insecticides can affect aphid vectors before they can transmit the virus.44 Synthetic insecticides may not be effective in preventing PVY transmission, but can be effective to reduce aphids. populations49 and is one of the main methods for managing PVY and PLRV.
Conclusion
South Africa is an arid country and consequently has very limited natural forest resources in the western part of the country. This review does not aim to provide a detailed history of forest conservation in South Africa.
Pest and pathogens of native woody plants
There are various previous reviews dealing with the history of forest pathology and forest entomology in the country that treat the subject relatively comprehensively.5-9 Nor is it intended to address the finer details of the likely future of forest tree health in this country. This topic has also been discussed in detail in various recent reviews, particularly those relating to plantation forestry.10,11 In contrast, we attempt to briefly cover some of the key elements of the history of forest conservation in South Africa.
Pests and pathogens of plantation trees
2 (originally recorded as G. scutellatus)41 recorded in South Africa in 1916 (Figure 1), was the first serious non-native pest to affect non-native plantations in the country42,43. Non-native pests and pathogens entering South Africa may arrive from the native range of plantation trees.
Management of pests and pathogens
Host-specific insect pests and pathogens of species of Pinus, Eucalyptus and Acacia known to occur in the areas of origin of these trees have appeared with increasing frequency in South African plantations. Much like in the case of introduced insect pests, a large number of host-specific pathogens of Pinus, Eucalyptus and Acacia species have been recorded in South Africa.2,3,12 Many of these are relatively weak pathogens that have not caused serious damage. , while others are much more important.
Looking ahead
Intensive commercial forestry practices such as those used in South Africa can in themselves increase the threat of damage from insect pests and pathogens. At the same time, the ability to deal with pests and pathogens after their introduction must be strengthened.
Acknowlegements
Identification of the causal agent of Armillaria root rot of Pinus species in South Africa. Diversity of tree-infesting Botryosphaeriales on native and non-native trees in South Africa and Namibia.
Background
Rust diseases, although seasonal, have been serious limitations in wheat production in South Africa for almost 300 years. Collaboration between plant pathologists, geneticists and breeders has provided momentum in rust research and control in South Africa in recent years.
Rust surveillance and phenotypic analysis
Seedling infection types produced on World and European differential kits39,40, followed by an A+ or A suffix to describe virulence or avirulence for the YrA gene in Avocet R41, are used for Pst race designations in South Africa. It has been suggested that wheat grown at a higher altitude in Lesotho in the summer serves as a source of Pst inoculum for winter crops in South Africa.8 Although not usual, some hectares may also be sown to wheat in the Free State in the summer.
Genetic analysis of Puccinia isolates
However, it is not yet known whether Pst will successfully establish itself in Zimbabwe and migrate to South Africa as expected. However, the impact of these formal off-season productions on rust epidemiology has not been studied in detail.
Host resistance
Prins et al.62 assessed stem rust response in an African wheat collection and identified several marker-trait associations in a genome-wide study. Furthermore, Pretorius et al.71 demonstrated the use of remote sensing and the normalized vegetation index for difference in reliable phenotyping of wheat stripe rust response in the field.
Breeding and selection
Marker trait associations on chromosomes 6AS and 3BS and the Lr34/Yr18/Sr57 resistance locus were confirmed, along with stem rust resistance QTL not detected in the association study, including the significant QTL QSr.ufs-4D. The MAS program started in 2011 with the capacity to screen for 19 genes/QTL, 13 of which were associated with rust resistance.
Conclusions
A review of the context and scope of wheat (Triticum aestivum) research in South Africa from 1983 to 2008. First report of a novel wheat leaf rust variety (Puccinia triticina) with virulence for Lr12, 13 and 37 in South Africa.
Wheat production
Fusarium head blight (FHB), also known as head blight, is a devastating fungal disease that affects small grain cereal crops such as wheat (Triticum aestivum L.). In South Africa there are currently no registered fungicides or bio-fungicides, no resistant wheat cultivars and only limited control is achieved through cultural practices.
Epidemiology of F. graminearum
Disease cycle and symptom development
The authors further reported that trichothecene biosynthesis is not required for the formation of these structures or the initial infection of wheat tissue.36. Infected kernels may appear shriveled, shriveled, and discolored with a light brown or pinkish-white appearance.2 These Fusarium-damaged kernels (FDKs) are often associated with high mycotoxin concentrations, reduced seedling emergence, and reduced seedling vigor, rendering them unusable as food, fodder or seed.38,39.
Economic and social importance of FHB
Initial symptoms of the disease include water-soaked lesions on spikelets that later appear bleached or bleached. 11,37 Afterwards, white or pink mycelium (Fig. 3a) and pink or orange masses of spores (Fig. 3b) appear on the edge of the husks of the infected spikelets. .37,38 Small purple or black spherical structures (perithecia) are produced (Figure 3c)37,38 which then sporulate and further infect healthy host tissue2.
Management strategies
Several bacterial, fungal and yeast strains have been reported to provide effective reduction of FHB severity and/or DON concentrations in infected grains.15,63,64 These were reviewed by Legrand et al.65 and presented in the right tables. In a study by Pan et al.67, Bacillus megaterium reduced the incidence and severity of FHB and DON production under field conditions by 93%, 54%.
Way forward
Effect of Fusarium graminearum inoculum availability and fungicide application timing on Fusarium head blight in wheat. Integrated strategies to control Fusarium head blight and deoxynivalenol contamination in winter wheat.
Materials and methods
Weighing the costs associated with the use of fungicides against the benefit of natural resistance of NCLB-resistant varieties and the additional benefits of reduced ear rot infection potentially provided by NCLB-resistant varieties will be beneficial to growers, allowing for informed decisions regarding which varieties to plant. The current study reports the observed effect of corn blight severity on F.
Results
The onset of ascospore release was generally earlier in the northern parts of the country (Limpopo and Mpumalanga) compared to the east. There were many days of measurable rain before first ascospore release in the Eastern Cape (ranging from 31 to 54) compared to 0 to 19 for northern sites (Table 2).
Discussion and conclusions
After seed treatment, highly significant differences were observed in the colonization of the tissues (roots, stem and leaves) x B. Trials of biological control of the stem borer Chilo partellus Swinhoe (Lepidoptera: Pyralidae) in South Africa.
Results and discussion
Northern leaf blight was consistently one of the top two diseases in both the Eastern Cape and KwaZulu-Natal (Figure 2). Influence of agricultural practices on the population genetics of the maize pathogen Cercospora zeina in South Africa.
