Crops In South Africa Research Articles

Morphological and molecular identification of economically important Tortricidae (Lepidoptera) on deciduous fruit tree crops in South Africa

Four tortricid species are of major economic importance on deciduous fruit tree crops in South Africa. They are codling moth, Cydia pomonella, oriental fruit moth, Grapholita molesta, false codling moth, Thaumatotibia leucotreta, and carnation worm, Epichoristodes acerbella. Pest management and phytosanitary practices are often hampered by the inability to distinguish between the immature stages of these four species. To address this need, the final instar larvae and pupae of E. acerbella are described and illustrated. The morphology of these immature stages of E. acerbella is compared with those of the aforementioned tortricid species. Keys are included to distinguish between the four species. In addition, as an alternative method of identification of any life stage, a means of discriminating between the four species, based on analysis of nucleotide sequences of the mitochondrial cytochrome oxidase I gene, is described.

Agricultural impacts on water quality and implications for virtual water trading decisions

Research on the flow of virtual water associated with agricultural crop production and trade has focussed almost entirely on water quantity. It is pertinent to consider and quantify the opportunity costs in terms of reduced water quality associated with crop production. This paper investigates the impacts of water quality on virtual water trading by creating a proxy for water quality impacts by calculating the amount of water required to dilute nonpoint-source agrochemical inputs to relevant water quality guideline values. The quantity of water required for dilution of five agrochemicals (two nutrients; nitrogen and phosphorus and three insecticides; azinphos-methyl, chlorpyrifos and endosulfan) was estimated for five crops in South Africa (maize, wheat, sugar cane, citrus and cotton) and compared to consumption of irrigation water (blue water) and rainfall (green water) for the same crops. Results indicate that the volume of water required for dilution is similar to the total sum of green and blue water required for crop production, but significantly greater than blue water use (irrigation use). For all crops phosphorus losses require greater amounts of water for dilution than for nitrogen, while pesticides result in the greatest water quality use. Estimates of water quality use are based on assumptions for a number of input variables (i.e. fertilizer application rates, percentage loss of agrochemicals from cropped areas). A Monte Carlo analysis (5000 iterations) was run to randomly select input variables from within defined ranges. Water quality use was calculated and expressed as a factor of blue water use. For all crops the average factor indicated that the volume of water required for dilution of all agrochemicals was greater than that required for irrigation. The results of this study clearly indicate that the impacts of agriculture on water quality need to be considered in virtual water trading scenarios. The incorporation of a method to predict impacts on water quality provides a comparative tool which generates a more holistic frame of reference for decision making with regard to impacts on the water resource and virtual water trading.

Iris yellow spot virus in Onion Seed Crops in South Africa.

In December 2006, symptoms typical of iris yellow spot caused by Iris yellow spot virus (IYSV; genus Tospovirus, family Bunyaviridae) were observed on scapes (seed stalks) in an onion (Allium cepa L.) seed crop in the Klein Karoo of the Western Cape Province, South Africa. Symptoms included diamond-shaped chlorotic or necrotic lesions on the scapes, some of which had 'green-islands' with nested diamond-shaped lesions, as well as indistinct, circular to irregular, chlorotic or necrotic lesions of various sizes. At the time symptoms were observed, approximately 5% of the scapes had lodged as a result of extensive lesions resembling those caused by IYSV. The crop was 2 to 3 weeks from harvest. Symptomatic tissue from two plants (two samples from one plant and four samples from the other plant) was tested for IYSV by reverse-transcriptase (RT)-PCR. Total RNA was extracted from symptomatic scape tissue with the SV Total RNA Isolation System (Promega, Madison, WI) according to the manufacturer's instructions. First strand cDNA was synthesized with the RevertAid H Minus First Strand cDNA Synthesis kit (Fermentas Inc., Hanover, MD), followed by PCR amplification with primers IYSV-For (TGG YGG AGA TGY RGA TGT GGT) and IYSV-Rev (ATT YTT GGG TTT AGA AGA CTC ACC), which amplify the nucleocapsid (NP) gene of IYSV. An amplicon of expected size (approximately 750 bp) was observed for each of the symptomatic plants assayed and was sequenced. Comparison of the sequence (GenBank Accession No. EF579801) with GenBank sequences revealed 95% sequence identity with the NP gene of IYSV GenBank Accession No. EF419888, with eight amino acid differences. The known geographic distribution of IYSV in onion bulb or seed crops has increased rapidly in recent years in many areas of the world (1). To our knowledge, this is the first confirmation of IYSV in South Africa. Approximately 6,100 ha of onion bulb crops are grown annually in South Africa in the Western Cape, Kwazulu Natal, Limpopo, and Northern Cape provinces, and 600 ha of onion seed crops are grown primarily in the semi-arid regions of the Western Cape. Examination of an additional 10 onion seed crops in the Klein Karoo during January 2007 revealed the presence of iris yellow spot in three more crops at approximately 5% incidence in each crop. The four symptomatic crops had all been planted as bulb-to-seed crops, using vernalized bulbs produced on the same farm. This suggests that IYSV may have been disseminated into the seed crops on the vernalized bulbs, either as infected bulb tissue or in viruliferous thrips on the bulbs. Reference: (1) D. H. Gent et al. Plant Dis. 90:1468, 2006.

Measuring the Price Volatility of Certain Field Crops in South Africa using the ARCH/GARCH Approach

The conditional volatility in the daily spot prices of the crops traded on the South African Futures Exchange (yellow maize, white maize, wheat, sunflower seed and soybeans) is determined. The volatility in the prices of white maize, yellow maize and sunflower seed have been found to vary over time, suggesting the use of the GARCH approach in these cases. Using the GARCH approach, the conditional standard deviation is the measure of volatility, and distinguishes between the predictable and unpredictable elements in the price process. This leaves only the stochastic component and is hence a more accurate measure of the actual risk associated with the price of the crop. The volatility in the prices of wheat and soybeans was found to be constant over time; hence the standard error of the ARIMA process was used as the measure of volatility in the prices of these two crops. When comparing the medians of the conditional standard deviations in the prices of white maize, yellow maize and sunflower seed to the constant volatilities of wheat and soybeans, the price of white maize was found to be the most volatile, followed by yellow maize, sunflower seed, soybeans, and wheat respectively. These results suggest that the more risk-averse farmers will more likely produce wheat, sunflower seed and to a lesser extent soybeans, while maize producers are expected to utilise forward pricing methods, especially put options, at a high level to manage the higher volatility.

The incidence of fungi and mycotoxins in South African barley and barley products

Barley is grown as a crop in South Africa, mainly for use in the barley beer (lager) industry, particularly in the production of barley malt. This investigation was done to find out what fungal infection and mycotoxin contamination this barley and the malt contained. The survey, done in 2005, not only covered barley and malt but also the final product in the form of several brands of beer purchased from retail outlets. Analysis was done using a range of methodologies including chromatography, immunoaffinity/fluorimetry and cytotoxicity testing. The results show that barley, which also includes barley sold directly to the public, and malt, contain various fungi, sometimes at high incidence and also a range of mycotoxins which persisted through, although at low levels, to beer. The malt showed a different pattern of micro flora, as compared to the barley, which indicates infection during the malting process, which is not uncommon. Interestingly, fumonisin B1 was found in some of the samples, as well as the beer, although in the latter case these were at very low levels. Recent studies have shown that the immunoaffinity/fluorimetry method can give false positives for the fumonisins, so these results were confirmed by high performance liquid chromatography. As is the case with other cereals grown in South Africa, there is the concern that the public is exposed to mycotoxins on a regular basis through the consumption of products made from them.

Intermediate Agricultural Processing Technologies for Cereal Crops in South Africa

ABSTRACT A comparative evaluation of the performance of a tractorpowered maize sheller and shelling with tractor wheels, electrically and diesel-operated sorghum milling machines with traditional maize shelling and sorghum milling techniques was conducted at Vergelegen rural community in the Northern Province of South Africa. Maize shellers and the traditional shelling techniques were evaluated in terms of shelling efficiency, grain output and grain damage, while the sorghum milling machines and the traditional techniques were evaluated in terms of flour output, losses and quality of output. The performance of these intermediate processing technologies for shelling and milling operations were compared with traditional processing techniques. Shelling of maize with tractor wheels incurred the highest percentage of grain damage. The difference in shelling with intermediate technologies and traditional techniques has significant effects on grain damage, grain output and shelling efficiency. A higher flour output from sorghum was obtained with new milling technologies than with traditional milling technique. The different milling methods have significant effects on the degree of fineness of flour for particle size greater than 1000 micrometer and less than 150 micrometer.

Operational forecasting of South African sugarcane production: Part 1 – System description

Commercial sugarcane crops in South Africa are grown under a wide range of agronomic and socio-economic conditions. These factors, together with climatic variation have resulted in a 17% variation in sugarcane production and there is considerable scope to improve productivity through accurate and timeous forecasts. This paper reports on the development of an operational crop forecasting system based on a simulation model. The country’s entire area of sugar production was subdivided into homogeneous climate zones using a wide range of data and expert opinion. These zones serve as simulation units within the system and model input and area aggregation data were obtained for each climate zone. Irrigation is simulated according to typical, zone specific strategies taking into account water use restrictions. Simulations of crops growing in the current year are completed using 10 historic seasons to substitute the remainder of the season. The selection of these seasons is based on the climate outlook. Reports containing information for national, regional and site specific cane production are generated and distributed to industry stakeholders. To the authors’ knowledge, this is the first national scale model-based operational yield forecasting system for sugarcane. Possible future improvements to the system may include stochastic input variables, more representative irrigation simulations, quantifying forecast uncertainty and providing suitable reference crop yield. The system is evaluated in another paper.

Stakeholder attitudes towards the risks and benefits of genetically modified crops in South Africa

The attitudes and interests of stakeholders involved in national public debates on the risks and benefits of genetically modified crops are having a significant influence on public opinion as well as public policy outcomes related to the use of genetically modified organisms (GMOs) in agriculture in developed and developing countries. This article discusses the results of a perception survey conducted with South African stakeholders involved in the GMO debate in 2000 and uses them to explain GMO policy in South Africa in 2004. The results suggest that academia, government, producer and consumer organizations and industry in South Africa strongly believe in the benefits of GM crops, while non-governmental organizations and churches do not. Instead, the latter emphasize the potential risks that, they claim, the government does not address with its permissive policy toward GMOs. The paper concludes that South Africa has become an African leader in promoting as well as in opposing modern biotechnology in agriculture. At the same time, the domestic debate on GMOs continues to be very polarized. The South African government may reassume public leadership by designing a biotechnology policy that aims at minimizing the risks and maximizing the benefits of the technology not just in terms of economic growth but also environmental conservation and poverty alleviation.

Potential for cassava production in the Bathurst region of the Eastern Cape Province of South Africa

Cassava (Manihot esculenta) is a minor crop in South Africa that has had periodic rises in interest since it was first cultivated in the country. Interest in the crop has waned over the years, but the crop is now being used as a source of high quality starch, which has again stimulated interest in its use as a commercial crop. No cassava is cultivated in the Bathurst area despite the apparently suitable climatic conditions. This study was conducted in order to evaluate the potential of this area for dryland cassava production. Eight varieties (I92/0326, I90/00330, I93/0170, TMS60444, TMS90853, ThaiI, Aunty Alice and Tokunbo) were planted at a density of 8 300 plants ha-1 using tissue cultured plants. Harvesting took place at 6, 15 and 21 months after planting (MAP), with each harvest date being established as a separate block. Tuber yields 6 MAP ranged from 8 to 22 t ha-1, with I93/0170 producing the highest yield. After 15 months, the highest yield was around 34 t ha-1 produced by TMS90853, although no significant (P>0.05) differences were noted between varieties at this stage. TMS60444 produced a yield of 76 t ha-1 21 MAP. Only three varieties showed significant (P

Root Rot and Stunting of Hydroponically Grown Endive, Fennel, and Sorrel Caused by Pythium F-group in South Africa.

Specialized vegetable crops such as endive (Cichorium endiva), fennel (Foeniculum vulgare), and sorrel (Rumex spp.) are being cultivated hydroponically in South Africa to be marketed as admixtures in salads. Stunted growth accompanied by browning and rotting of the root tips has been observed at a commercial recirculating gravel bed hydroponic system near Pretoria during the warm summer months. Root segments excised from symptomatic plants were rinsed in sterile water and plated on Pythium selective medium (1). Pythium F-group, characterized by the production of noninflated filamentous sporangia and no oospores (2), was isolated from 40% of endive, 60% of fennel, and 7% of sorrel root segments. Koch's postulates were confirmed by inoculating 4-week-old seedlings of each crop in the greenhouse with a Pythium F-group isolate from the particular crop. Inoculations were performed by adding 3 ml of suspension (105 zoospores per ml) to each liter of aerated nutrient solution. Control plants received no inoculum, and the experiment was repeated once. After 4 weeks, inoculated plants showed stunting of the foliage and slight to moderate root rot. Pythium F-group could readily be reisolated from roots of inoculated plants. To our knowledge, this is the first report of Pythium F-group on these crops in South Africa.

DEVELOPMENT OF A NEW FLOWER BULB CROP IN SOUTH AFRICA

DEVELOPMENT OF A NEW FLOWER BULB CROP IN SOUTH AFRICA

LACHENALIA: DEVELOPMENT AND COMMERCIALIZATION OF A NEW FLOWER BULB CROP

LACHENALIA: DEVELOPMENT AND COMMERCIALIZATION OF A NEW FLOWER BULB CROP

The in vitro phytotoxicity of culture filtrates of Fusarium oxysporum to five genotypes of Amaranthus hybridus

Stem decay and root rot of Amaranthus hybridus, caused by Fusarium oxysporum is a serious threat to the commercial production of this crop in South Africa. Five Amaranthus hybridus varieties were examined in vitro for sensitivity to a culture filtrate of Fusarium oxysporum. The phytotoxicity of the culture filtrate was assessed for its inhibitory effect on callus and seeding root growth, as well as on the viability of callus cells. The five varieties exhibited a significant amount of variation in response to the culture filtrate of the pathogen. Variety 17 was the most sensitive variety in each bioassay, whereas variety 20 displayed least sensitivity to the culture filtrate. Callus of variety 20 grew well in the presence of concentrations of culture filtrate that were toxic to another four varieties and the percentage mortality of callus cells after exposure to the filtrate was also the lowest of the five varieties. Root growth of variety 20 was also least affected by exposure to the culture filtrate for up to 6 days. To our knowledge, the presence of resistance in germplasm of A. hybridus to culture filtrates of F. oxysporum has not been demonstrated before. The present study is therefore of significant value to breeding programs aimed at speedily finding amaranth cultivars that are resistant to this important pathogen.

ACREAGE RESPONSE TO RISK: THE CASE OF MAIZE AND WHEAT IN THE SOUTH AFRICA

Price and yield risk factors were incorporated into an econometric model to analyse area allocations to maize and wheat crops in South Africa under uncertainty. Results of this study suggest that maize and wheat producers are risk-averse and both price and yield risks are important determinants in farmers' area allocation decisions.

Prospects for biological control of Chilo partellus in grain crops in South Africa

Chilo partellus (Swinhoe) was first recorded in South Africa in 1958 and became a major pest of maize and grain sorghum. It has invaded the main maize producing areas in the Highveld Region, gradually competitively displacing the indigenous Busseola fusca (Fuller). Between 1980 and 1993 two egg, seven larval and two pupal parasitoids were introduced for biological control of Ch. partellus. Cotesia flavipes Cameron (Braconidae), Paratheresia claripalpis van der Wulp (Tachinidae), Tetrastichus howardi (Olliff) (Eulophidae) and Xanthopimpla stemmator Thunberg (Ichneumonidae) were released and recovered from the field. Recoveries were made up to a few weeks after releases but parasitoids failed to survive the winter and establish. The harsh winter conditions in the release sites, the long larval diapause period of Ch. partellus, lack of synchronisation between the development of the parasitoids and that of their host larvae, and absence of alternative host plants were identified as the main obstacles for the parasitoids establishment. It is concluded that the prospects of achieving any degree of biological control of stemborers in the Highveld Region with parasitoids from the tropics are poor. A parasitoid from a temperate zone of the USA, Macrocentrus grandii Goidanich (Braconidae), was introduced recently into South Africa and is currently reared on Ch. partellus in quarantine. Macrocentrus grandii stays dormant in its diapausing host, Ostrinia nubilalis (Hubner), during winter to emerge in spring. Because of its ability to diapause in winter it is hoped that after releases, M. grandii will establish on Ch. partellus in the Highveld Region of South Africa.

COMPARATIVE ADVANTAGE OF THE PRIMARY OILSEEDS INDUSTRY IN SOUTH AFRICA

Given South Africa's poor resource endowments coupled with the ongoing deregulation and liberalisation of agriculture, it is of the utmost importance that resources are used in the most optimal manner to ensure international competitiveness. Since oilseeds constitute one of the most important field crops in South Africa, the comparative economic advantages (CEA) of sunflower seeds, groundnuts and soya-beans were calculated for different regions classified as low yielding, high yielding and irrigation areas. The results show that (a) the extent of developing new cultivars with improved yield potential will largely determine the comparative advantage of oilseeds in areas where agro-ecological conditions are poor; (b) distortionary policies on the input side is one of the main factors influencing the comparative advantage of the primary oilseeds industry; (c) the introduction of a water rate will have serious implications for irrigated oilseeds; and (d) increased efficiency forms the basis for being competitiveness.

Potential yield losses caused by barley leaf rust and oat leaf and stem rust to South African barley and oat cultivars

Puccinia hordei (leaf rust) on barley as well as Puccinia coronata f. sp. avenae and Puccinia graminis f. sp. avenae (leaf/crown and stem rust) on oats are important diseases of these respective crops in South Africa. Notwithstanding the regular occurrence of epidemics, recent crop loss data for these diseases are not available. In this study epidemics were created artificially while control plots were sprayed with fungicide. In the oat trial, yield losses of as high as 85% were recorded for leaf (crown) and stem rust while in the case of barley leaf rust losses of as much as 58% were recorded. Not only were yields influenced by disease but also quality. Hectolitre mass was reduced by as much as 45% in oat, while kernel plumpness of barley was reduced by up to 65% and percentage siftings was increased by as much as 590%. This study emphasises the importance and destructive nature of rust diseases on both crops. It also emphasises the importance of ongoing research aimed at finding solutions to control these diseases.

Plant-parasitic nematodes in field crops in South Africa. 6. Soybean

AbstractTwelve plant-parasitic nematode genera and 25 species were identified in soil and root samples collected from 17 localities in the soybean production areas of South Africa during the 1995/96 season. Predominant endoparasites found included Meloidogyne incognita, M. javanica, M. hapla, M. ethiopica, Pratylenchus zeae and P. brachyurus. Meloidogyne species occurred in 91% of all root samples, P. zeae in 87% and P. brachyurus in 33%. The occurrence of the three predominant endoparasites was not restricted to sandy soil, but they were also prevalent in soils with high clay contents. Other endoparasitic nematode species were Pratylenchus crenatus, P. teres, P. neglectus, P. thornei, Rotylenchulus parvus and Ditylenchus africanus. Nematodes found in soil included Helicotylenchus dihystera and Scutellonema brachyurus, which occurred in 78 and 71%, respectively, of all soil samples. Other nematodes found in soil samples were Helicotylenchus pseudorobustus, H. digonicus, H. microcephalus, Scutellonema truncatum, Rotylenchus unisexus, Mesocriconema sphaerocephalum, Paratrichodorus minor, Longidorus pisi, Xiphinema vanderlindei, X. elongatum and Tylenchorhynchus goffarti. Highest prominence values (PV) for Meloidogyne species were recorded on cultivars Prima, Bakgat, Tamboti, Hutcheson and Knap and the lowest on cultivars PAN812, SCS1, Nyala, Gazelle and A7119. Eight nematode genera and 19 species extracted during this study are reported for the first time in association with soybean in South Africa.

The effect of Liriomyza trifolii (Burgess) (Dipt., Agromyzidae) on fruit production and growth of tomatoes, Lycopersicon esculentum (Mill) (Solanaceae)

Abstract: The serpentine leafminer, Liriomyza trifolii (Burgess) (Agromyzidae) has, during the past 8 years, become an increasingly important pest on tomatoes, the second most important vegetable crop in South Africa. In some areas where weekly chemical applications are made on the basis of a threshold level of 0.25 mines per plant, it is feared that this pest has become resistant. In the present study, examination of the effect of various levels of infestation on growth and yield of tomatoes showed that neither growth nor yield were negatively affected by infestation levels of up to 1092 and 468 mines per plant in a glasshouse and field trial, respectively. A comparison of yield on control plants with 1–50, 51–100 and > 100 mines per plant (field trial) indicated that low L. trifolii infestations of 1–50 mines/plant in fact increased the yield by c. 60%. The phenology of L. trifolii feeding (before or during and after flowering) had no effect on yield and the effect of herbivory by L. trifolii was not obscured by any relationship between fruit production and growth of the tomato plants. These results were confirmed by a field trial and it is thus clear that even the threshold level being applied in the USA (four mines per three terminal leaflets per plant) is unrealistically low. Low correlations between number of mines per plant and percentage of pinnae or leaves infected indicated that assessing levels of infection by counting mines could not be replaced by the easier counting of pinnae or leaves infected.

Purification and Identification of a South African Isolate of Watermelon Mosaic Virus – Morocco

AbstractCucurbit crops in South Africa are seriously affected by a flexuous rod‐shaped virus 706 to 770 nm long which causes the plant to be stunted, the leaves to display symptoms of chlorotic mosaic, dark green blisters and malformation, and fruit to be malformed. The virus was purified from infected Cucurbita pepo by extraction in 0.5 M borate buffer, pH 8, containing ethylenediaminotetra‐acetic acid and mercapto‐ethanol, clarification with chloroform, addition of Triton X‐100, sedimentation by ultracentrifugation for which a sucrose cushion was used and centrifugation in 10 to 40 % sucrose gradients. The virus was mechanically transmitted to a limited host range with Chenopodium album, C. amaranticolor, C. quinoa and Gomphrena globosa being the only hosts infected outside the Cucurbitaceae. Luffa cylindrica, Cucumis metuliferus, Coccinia sessilifolia and Citrullus ecirrhosus all members of the Cucurbitaceae, were not infected by the virus. The virus was non‐persistently transmitted by Myzus persicae, produced pinwheel and bundle inclusions in the plant cell cytoplasm and has a single coat protein with a molecular weight of 36,000 daltons and a degraded lighter component of 26,000 daltons. Serological comparisons with antiserum to watermelon mosaic virus 2, Papaya ringspot virus strain W and watermelon mosaic virus Morocco (WMV‐Mor.) identified the virus as an isolate of WMV‐Mor. It was found that WMV‐Mor. is the dominant virus in all the main cucurbit producing areas of South Africa which were surveyed.