| Isolation, identification and molecular characterisation of an isolate of Zucchini yellow mosaic virus occurring in KwaZulu-Natal, South Africa | Gubba, A | 2012 |
Keywordscucurbits, phylogenetic analysis, ZYMV AbstractAbstract Zucchini yellow mosaic virus (ZYMV) is an economically important virus infecting cucurbits and has a worldwide distribution. In the Republic of South Africa, ZYMV has been reported as a major limiting factor to cucurbit production. The aim of this study was to identify, isolate and partially characterise a ZYMV isolate from KwaZulu-Natal (KZN). On the basis of host reactions, electron microscopy, serology, and size of the coat protein, a potyvirus infecting cucumber, squash, pumpkin and melon samples collected from farms around KZN was positively identified as ZYMV. Mechanical inoculation of test plants showed that the virus host range was limited to the cucurbits. Mottling, vein banding and blistering of leaves, and distortion of fruit were the main symptoms observed on field and inoculated hosts. Flexuous virus particles, 720–780 nm long, were observed under the electron microscope from purified virus samples. In ultra-thin leaf sections, infected plant cells contained pinwheel and scroll-type inclusion bodies. An enzyme-linked immunosorbent assay test using antibodies specific to ZYMV following single-lesion virus isolation gave a positive reaction. The size of the potyvirus coat protein was shown to be about 35.7 kDa using sodium dodecyl sulphate–polyacrylamide gel electrophoresis. Nucleotide sequence analysis of the partial coat protein gene of the ZYMV isolate from KZN revealed 95–98% sequence identity with isolates occurring in central Europe and the Indian subcontinent, and 90–93% identity with isolates from Singapore and Taiwan. These high levels of sequence identity indicate that the KZN isolate is a variant of ZYMV. We propose the name ZYMV-KZN for the virus strain we have identified. AuthorsGubba, A, Usher, L and Sivparsad, B Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.701669 This article contributed by:
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| Component dry masses and carbohydrate contents in honeybush I: Cyclopia genistoides | Wooldridge, J | 2012 |
Keywordshoneybush tea, sprouter, starch reserves, thickened roots AbstractCyclopia (honeybush), a new and largely unstudied South African horticultural crop, was investigated by carrying out a reconnaissance-level survey of C. genistoides (Cg) populations. Four-year average total dry mass (DM) in plantation-grown Cg cuttings and seedlings, and wild (veld) plants were, respectively, 981, 1 261 and 269 g plant−1. Top growth, thick roots (≥5 mm diameter) and thin roots (<5 mm diameter) constituted 39%, 41% and 20% of total DM in the cuttings, 40%, 43% and 17% in the seedlings, and 51%, 36% and 13% in the wild plants. Total root starch content averaged 13 815 mg (cuttings), 26 771 mg (seedlings) and 5 085 mg (wild plants). Of this starch, 74–80% was located in the thick roots. Thick root:thin root starch content ratios averaged 1.95:1 in the plantations and 3.89:1 in the wild plants, whereas shoot DM:total root DM ratios averaged 0.66:1 in the plantations and 1.03:1 in the wild plants. Starch contents and concentrations were higher between January and March than May to July. To optimise yields and starch contents, Cg should be harvested in autumn rather than summer. Top growth yields per plant in Cg plantations, notably seedlings, exceed those from wild Cg plants. AuthorsWooldridge, J, Joubert, ME and Booyse, M Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.716456 This article contributed by:
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| Growth, yield and grain protein content of wheat (Triticum aestivum L.) in response to nitrogen fertiliser rates, crop rotation and soil tillage | Agenbag, GA | 2012 |
Keywordscropping systems, fertiliser applications, soil properties, soil tillage, Triticum aestivum AbstractSoil tillage affects both the profitability and sustainability of cropping systems. Minimum- and no-tillage systems are promoted because research has shown that these systems may reduce production costs and improve biological sustainability when compared to conventional systems, in which mouldboard and disc ploughs are used. However, responses to different tillage systems may differ for different crops as well as different soil and climatic conditions. This long-term study, conducted under a Mediterranean-type climate, showed that no-tillage systems can be used successfully to produce spring-type wheat crops in sustainable crop rotation systems under rain-fed conditions in the Swartland wheat-producing area of the Western Cape province of South Africa. Higher wheat yields when wheat is grown in a crop rotation system compared to a monoculture system can be ascribed to improved soil organic carbon and nitrogen (N) contents, which result in more plant-available mineral N and hence more vigorous crop growth. Grain yields of wheat responded positively to increased N application rates and the results suggest that application rates of more than 100 kg ha−1 should be considered where minimum and no-tillage are practised. Higher N application rates resulted in higher grain protein and hence improved bread-making quality of the wheat. AuthorsAgenbag, GA Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.716457 This article contributed by:
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| Component dry masses and carbohydrate contents in honeybush II: Cyclopia subternata | Wooldridge, J | 2012 |
Keywordshoneybush tea, seeder, starch reserves, yield AbstractA four-year reconnaissance-level survey was carried out in a honeybush (Cyclopia subternata; Cs) population to obtain information concerning this new South African horticultural crop. Average total dry mass (DM) in Cs cuttings under plantation conditions was 2 481 g plant−1, of which the harvestable top growth (shoots), non-harvestable top growth (stem) and roots constituted 17%, 59% and 24%, respectively. Starch reserves averaged 6 321 mg plant−1, (stem 62%, roots 38%). Corresponding values for Cs seedlings were 3 796 g plant−1 (13%, 62% and 25%) and 10 044 mg plant−1 (69% and 31%). Ratios of shoot DM to non-harvestable DM, and of stem to root starch content were, respectively, 1:4.799 and 1:0.620 in the cuttings, and 1:6.753 and 1:0.447 in the seedlings. Yields of dry shoots averaged 3.6 t ha−1 from the cuttings and 4.2 t ha−1 from the seedlings. Top growth DM and starch reserves were greatest in late summer to autumn. Autumn is therefore the best time to harvest. AuthorsWooldridge, J, Joubert, ME and Booyse, M Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.717111 This article contributed by:
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| Simultaneous selection for yield and ratooning ability in sugarcane genotypes using analysis of covariance | Zhou, MM | 2012 |
Keywordsratooning cycles, sugarcane breeding method, Saccharum officinarum L AbstractRatooning ability increases sugarcane production economics by reducing frequency of planting. During sugarcane breeding, indirect selection for pest resistance and direct selection for high ratoon yields increases ratooning ability. The objective of this study was to describe the simultaneous screening of genotypes for yield and ratooning ability in sugarcane breeding trials using analysis of covariance. Data for cane yield (tons ha−1) and stalk population (×103 ha−1) collected from five trials harvested from plant to fourth ratoon crops were analysed using the Statistical Analysis System (SAS). There were significant differences in parameters for yield (intercept) and ratooning ability (slope) among test genotypes indicating potential for simultaneous screening. Comparison of genotypes to a control with known ratooning ability identified higher yield and good ratooning genotypes. Graphical trends identified genotype differences in yield and ratooning ability. The economics of yield and ratooning ability of two varieties was compared providing a mechanism for variety choice at planting. The method described provided statistical tests that would increase genotype selection efficiency for ratooning ability. The decline in yield among genotypes is slowed by the increase in stalk population. AuthorsZhou, MM and Shoko, MD Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.717639 This article contributed by:
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| Hydrological classification of orthic A horizons in Weatherley, South Africa | van Huyssteen, CW | 2012 |
Keywordstopsoil, Weatherley, wetland, wetness class AbstractOrthic A horizons carry little interpretive, especially hydrological, value. This paper aims to elucidate the hydrological interpretation of orthic A horizons. Measured water contents in the orthic A horizons of 28 profiles in the Weatherley catchment of South Africa were used to classify the topsoils into wetness classes. The very transitory wetness class had no Fe mottles; overlaid red apedal B, yellow-brown apedal B, or neocutanic B horizons; and had >650 mm below the orthic A horizon to an impervious layer. The transitory wetness class had few Fe mottles and had < yellow-brown apedal B < yellow E < grey E < soft plinthic B < G. Depth to the impervious layer generally decreased in the same order. Authorsvan Huyssteen, CW Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.717640 This article contributed by:
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| Maize–planting date interaction and effect of Bt maize on European corn borer (Ostrinia nubilalis (Hubner) (Coleoptera: Crambidae) damage | Obopile, M | 2012 |
Keywordsdelayed planting, grain yield, hybrid maturity, stalk tunnelling, transgenic plants AbstractAbstract A study was conducted to determine the influence of planting date and transgenic maize on maize yield following stalk injury by European corn borer, Ostrinia nubilalis (Hubner). Transgenic and non-transgenic maize hybrids with short- and full-season maturity were planted in late April, mid-May and early June from 2006 to 2008 in Ohio, USA. Maize stem tunnelling was significantly higher on non-transgenic maize and increased with delayed planting. Significantly higher yields were obtained from full-season than short-season hybrids when maize was planted early. The results suggest that when planting is delayed and an European corn borer population is known to cause economic damage in an area, selection of short-season hybrids with the Bt gene can be beneficial in controlling damage and improving yield. AuthorsObopile, M, Hammond, RB and Thomison, PR Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.719040 This article contributed by:
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| Open-top chambers to study air pollution impacts in South Africa. Part I: microclimate in open-top chambers | Heyneke, E | 2012 |
Keywordsdata registration, design and aeration, microclimate and fumigation control, SO2 and O3 fumigation AbstractSouth Africa's large industrial growth has created an obvious need to extend, improve and evaluate air pollution impacts on plants in order to assess present-day and future impacts of air pollutants on crop yields. In order to provide guidelines for policy-making and the imposition of air quality guidelines, there is a need to quantify effects and to develop dose–response relationships for crops. Plant responses to define such exposure–response relationships could include physiological, biochemical, growth and yield parameters measured in plants grown under different pollutant levels using controlled fumigation techniques. The experimental tool that has been regarded as the most acceptable for dose–response research is open-top chambers (OTC). Open-top chambers provide a compromise between free air fumigation, which is generally regarded as expensive, and closed growth chambers, which are considered artificial. This paper reports on the design and operation of Africa's first OTC facility, which consists of 12 chambers, each having a volume of 5 m3. Evaluation of the OTC microclimate during the summer of 2007 revealed light transmission of more than 90% photosynthetically active radiation. Effective ventilation at about 2.5 air changes per minute limited the chamber temperature to a maximum temperature elevation of 4.2°C at 12:00 in summer, 1°C at night and a overall mean increases of 2.3°C. The relative humidity in the OTCs showed a 20% decrease at 12:00. The SO2 and O3 concentrations could be controlled accurately in the ppb range as is often recorded near power stations in South Africa. AuthorsHeyneke, E, Smit, PR, van Rensburg, L and Krüger, GHJ Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.688372 This article contributed by:
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| Open-top chamber facility to study air pollution impacts in South Africa. Part II: SO2–drought interactions on yield, photosynthesis and symbiotic nitrogen fixation in soybean | Heyneke, E | 2012 |
Keywordsbiomass, chlorophyll fluorescence, CO2 response, JIP-test, Rubisco activity, SO2–drought interaction, ureide content AbstractSouth Africa has an extremely energy-intensive economy, resulting in substantial air pollution through its coal-fired power stations. Modelled sulphur dioxide (SO2) concentrations on the central Highveld mostly range between 10 and 50 ppb, exceeding 50 ppb in source areas. Well-watered and drought-stressed soybean (Glycine max) plants were exposed to different SO2 concentrations in open-top chambers to study the physiology of SO2 injury by measuring in parallel growth, biomass accumulation, photosynthetic gas exchange (as a function of internal CO2 concentration and photon flux density), chlorophyll a fluorescence, in vitro Rubisco activity and symbiotic nitrogen fixation. A strong concentration-dependent SO2-induced inhibition was displayed in all variables. After fumigation for only 7 d, photosynthesis was reduced without any accompanying visual injury symptoms, even at the 50 ppb treatment level. Exposure to SO2 also resulted in large decreases in biomass accumulation of both well-watered and drought stressed plants. Seed yield reduction of up to 57% occurred in plants exposed to the highest SO2 concentration and simultaneously subjected to drought stress. Root nodule ureide content was lowered at all treatment levels, but was lowered more in the SO2-treated plants subjected to drought stress. The photosynthetic gas exchange data showed a severe decrease in carboxylation and quantum efficiency pointing at increasing mesophyll limitation. The chlorophyll a fluorescence data, pointing at impaired electron transport and formation of end electron acceptors as well as the in vitro activity of Rubisco, supported the gas exchange data. Inhibition of photosynthesis proved to be the main constraint imposed by SO2. SO2 stress was aggravated by simultaneous drought stress. AuthorsHeyneke, E, Krüger, GHJ, Strauss, AJ and Strasser, RJ Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.688373 This article contributed by:
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| Hypersensitivity of rust resistance in lentil | Negussie, TG | 2012 |
Keywordshistology, hypersensitivity, Lens culinaris, resistance, Uromyces viciae-fabae AbstractCharacterising resistance at different levels of expression is important in understanding host defence mechanisms and the improvement of durable disease resistance in crop plants. Histological reactions of the lentil cultivars EL-142 (susceptible) and Gudo (resistant) to infection by Uromyces viciae-fabae, were investigated by means of fluorescence and confocal laser microscopy. Components of resistance included the proportion of successful penetrations, early abortion, host cell necrosis and colony size. The percentage of germinated urediniospores that had not penetrated was significantly higher for Gudo than for EL-142. Furthermore, Gudo had a higher percentage of early aborted colonies, frequently associated with host cell necrosis, than the susceptible cultivar. The host cell necrosis index for Gudo was 1.13, indicating an excessive hypersensitive response to lentil rust. At the macroscopic level, rust pustules on Gudo were surrounded by chlorotic and necrotic flecks. Results indicated that the resistance to lentil rust in Gudo is the result of prehaustorial and posthaustorial mechanisms. However, resistance to rust may not be durable because of its hypersensitive nature. AuthorsNegussie, TG, Bender, CM, van Wyk, PWJ and Pretorius, ZA Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.688377 This article contributed by:
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