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Slabbert R.M.,Vegetable and Ornamental Plant Institute | Kruger G.H.J.,North West University South Africa
Plant Physiology and Biochemistry | Year: 2011

The present study describes the behaviour of photosystem II (PSII) in Amaranthus hypochondriacus and Amaranthus hybridus under water stress conditions, assessed by the analyses of the polyphasic rise in chlorophyll a fluorescence (O-J-I-P). We determined the adaptive behaviour in relation to the regulation of the different functional and structural parameters of PSII, which was a direct and rapid response due to changes in soil water status indicated by a decrease in leaf water potential and relative water content. It allows for the identification of specific key or limiting chlorophyll fluorescence parameters which could be used to identify traits conveying tolerance. For the above partial processes of PSII function studied, it seems that A. hybridus remained the more stable upon water stress (after 17 days of withholding water), concerning the specific energy fluxes of absorption/reaction centre (ABS/RC) apparent (antenna size) and trapping/reaction centre (TR/RC) (maximum trapping flux), as well as the density of the reaction centres/cross section (RC/CS) and the phenomenological trapping flux/cross section (TR o/CS). It was clear that amaranth adjusts the non-photochemical (k n) deactivation constant of PSII and to a less extend also the photochemical (k p) deactivation constant by means of photoregulation, which forms the basis of the quenching of chlorophyll a fluorescence. Although drought stress caused the deactivation of RCs leading to a decrease in the density of active RCs, the plants compensated by increasing the efficiency of the conversion of trapped excitation energy to electron transport beyond Q A (efficiency of exciton trapping/reaction centre: ET o/TR o). Subsequent damage to PSII might be the reason for the slow, or lack of recovery, for most of the parameters measured. © 2011 Elsevier Masson SAS.


Bihon W.,University of Pretoria | Bihon W.,Vegetable and Ornamental Plant Institute | Wingfield M.J.,Vegetable and Ornamental Plant Institute | Slippers B.,Vegetable and Ornamental Plant Institute | And 2 more authors.
Fungal Genetics and Biology | Year: 2014

Diplodia pinea (= Sphaeropsis sapinea) is a well-known and economically important latent pathogen of Pinus spp. in many parts of the world. Despite intensive scrutiny, its sexual state has never been observed and the fungus has thus been considered exclusively asexual. It was, therefore, surprising that a recent population genetics study showed high genotypic diversity and random association of alleles in a number of populations, suggesting that the pathogen has a cryptic sexual stage. Using the genome sequence of two individual D. pinea isolates, we interrogated the structure of the MAT locus in this fungus. The results suggested that D. pinea is heterothallic (self-sterile) with complete and apparently functional copies of the MAT genes containing the α-1 and HMG domains present in different isolates. In addition to the MAT1-2-1 and MAT1-1-1 genes, we found a MAT1-1-4 gene in the MAT1-1 idiomorph and a novel MAT1-2-5 gene in the MAT1-2 idiomorph. Importantly, the frequencies of occurrence of both idiomorphs in populations examined were not significantly different from a 1:1 ratio, which would be expected in sexually reproducing populations. Although the sexual state has never been observed, the results strongly suggest that D. pinea has a cryptic, heterothallic sexual cycle. © 2013 Elsevier Inc.


Mampholo B.M.,Tshwane University of Technology | Sivakumar D.,Tshwane University of Technology | Beukes M.,University of Pretoria | van Rensburg W.J.,Vegetable and Ornamental Plant Institute
Journal of the Science of Food and Agriculture | Year: 2013

BACKGROUND: The perishability of Brassica chinensis poses a major challenge to distribution and marketing. The aim of this work was to select a suitable modified atmosphere packaging to retain the overall quality and bioactive compounds during storage. RESULTS: Four types of biorientated polypropylene packaging (BOPP) - BOPP03, BOPP04, BOPP05 and BOPP06 - with different perforations were evaluated regarding the maintenance of quality parameters (weight loss, leaf yellowing, colour L*, C*, h°), decay, chlorophyll a, chlorophyll b, bioactive compounds (carotenoids, ascorbic acid, total phenolic compounds), antioxidant scavenging activity, overall appearance and odour evaluation, at 10°C at 2, 4, 6, 8 and 10 days. Leaves were packed in BOPP (two 2-mm holes) and packed and unpacked leaves were included for comparison. The modified atmosphere created (2% O2 and 7% CO2) inside the BOPP05 reduced leaf yellowing (higher h°), improved the overall appearance with acceptable odour, moderately maintained chlorophyll a and b, bioactive compounds and antioxidant scavenging activity, and remained marketable for up to 10 days at 10°C. Gas composition within the packages influenced the retention of bioactive compounds and overall quality. CONCLUSION: Application of BOPP05 is a promising method for extending the shelf life of B. chinensis leaves in order to promote its utilisation and commercialisation via urban fresh-produce markets. © 2012 Society of Chemical Industry.


Fessehazion M.K.,University of Pretoria | Fessehazion M.K.,Vegetable and Ornamental Plant Institute | Annandale J.G.,University of Pretoria | Everson C.S.,University of Pretoria | And 4 more authors.
Agricultural Water Management | Year: 2015

Poor management of irrigation water and nitrogen (N) fertiliser in ryegrass cropping systems reduces forage yield, and quality, N-use efficiency, and potentially leads to atmospheric and water pollution. The objective of this study was to calibrate and validate the soil water balance (SWB-Sci) model for annual ryegrass (. Lolium multiflorum) pasture and assess the impact of different irrigation strategies on forage yield, irrigation water use and N use efficiency. Field trials were conducted using annual ryegrass under a range of irrigation and N application strategies to calibrate and test the SWB-Sci model. Once calibrated and validated, the model was used to investigate and compare the impact of different irrigation strategies on forage yield, unproductive water loss due to drainage and runoff and N leaching. Using the moderate deficit (irrigating to 60-80% of the field capacity) irrigation strategy, reduced water loss due to drainage and runoff by 54-66%, irrigation water by 37-63%, and N leaching by 69-72% compared to the common farmers' practice of 25. mm irrigation per week, without significant forage yield reduction. The SWB-Sci model showed ways of improving water and N fertilisation use efficiency using moderate deficit irrigation approaches in high rainfall areas. © 2014 Elsevier B.V.


Maboko M.M.,Vegetable and Ornamental Plant Institute | Maboko M.M.,University of KwaZulu - Natal | Du Plooy C.P.,Vegetable and Ornamental Plant Institute | Bertling I.,University of KwaZulu - Natal
South African Journal of Plant and Soil | Year: 2011

Cultivar selection for different hydroponic production systems is an important management decision, potentially impacting the tomato grower's profitability. Knowledge on the performance of tomato cultivars, in specific hydroponic systems (open-bag and closed system) under South African conditions, is still very limited. The performance of four cultivars was evaluated in an open and a closed hydroponic (gravel-film technique) system. The commonly grown cultivars evaluated in each of the two hydroponic systems were 'FA593', 'Malory', 'Miramar' and 'FiveOFive'. For each experiment a randomized complete block design was used with four replicates. Total, marketable and unmarketable yields, as well as internal fruit quality characteristics (total soluble solids (̊Brix) and pH) were determined. Although no significant differences in total yield could be established - neither in the open nor in the closed hydroponic system - differences in marketable yield were observed. 'Miramar' and 'FiveOFive' produced the highest marketable yield in the closed system; the high unmarketable yield of 'FA593' and 'Malory' in the closed hydroponic system could be attributed to the high number of cracked fruit due to their inherent larger fruit size. There were no significant differences in ̊Brix between cultivars in the closed system. Cultivar 'FiveOFive', 'FA593' and 'Miramar' produced higher marketable yields than cultivar 'Malory' when grown in the open-bag system. 'Malory' and 'FA593' produced the highest number of fruit exhibiting fruit cracking in the open bag system. In the open system, only cultivar 'Malory' had a higher ̊Brix than 'Miramar' and 'FiveOFive'. The most promising cultivars for local hydroponic tomato production, with regard to yield and quality, were identified as 'Miramar' and 'FiveOFive', with 'FA593' performing equally in the open system only. Further studies need to be undertaken on economical comparison of the two production systems.


Majola T.,Vegetable and Ornamental Plant Institute | Kelly J.,Plant Protection Research Institute
Journal of the Canadian Society of Forensic Science | Year: 2013

A preliminary study was conducted to investigate the effect of direct sunlight and shade on carcass decomposition and arthropod succession in the central region of South Africa. Three pig carcasses (Sus scrofa) were used in this study and were placed in full sunlight, partially in the shade, and in fully shaded conditions. This research was done during the spring season of 2003, from 23 September to 11 November. Internal carcass temperatures, as well as environmental temperatures, were recorded daily and the decomposition rates were compared between direct sunlight versus the partially and fully shaded carcasses. The carcass placed in direct sunlight attracted more arthropods and the decomposition rate was faster compared to those carcasses placed in the shade. Chrysomya chloropyga and Lucilia spp. were the most dominant species on these carcasses. Dermestes maculatus De Geer (Coleoptera, Dermestidae), followed by Necrobia rufipes De Geer (Coleoptera, Cleridae), were present in high numbers during the active decay stage. This study illustrates that shade has an effect on physical decomposition stages. The preliminary results showed that shaded or partly shaded carcasses decompose slower than carcasses exposed to full sunlight. There was no effect on arthropod species succession or development, although the numbers of individuals varied.


Maboko M.M.,Vegetable and Ornamental Plant Institute | Du Plooy C.P.,Vegetable and Ornamental Plant Institute
HortScience | Year: 2015

A 2-year study (2012-13 and 2013-14) was conducted to evaluate the effect of plant growth regulator’s (PGRs) on plant growth, yield, and quality of hydroponically grown sweet peppers. In 2012-13, sweet pepper plants were subjected to two levels of gibberellic acid (GA3) (10 and 15 mg·L-1), two levels of naphthalene acetic acid (NAA) (15 and 30 mg·L-1), and four combinations of NAA and GA3 (10 mg·L-1GA3 + 15 mg·L-1NAA, 10 mg·L-1GA3+ 30 mg·L-1NAA, 15 mg·L-1GA3+ 15 mg·L-1NAA, and 15 mg·L-1GA3+ 30 mg·L-1NAA) applied to plants at flower initiation in a nontemperature-controlled tunnel. This PGR application was repeated 60 days after transplanting (DAT). In 2013-14, in addition to previously mentioned treatments, two levels of 4-chlorophenoxyacetic acid (4-CPA), at 30 and 45 mg·L-1, were applied at flower initiation followed by three additional applications of the latter treatments at 20-day intervals in a temperature-controlled tunnel. Marketable and total yield were markedly reduced by application of 4-CPA at 30 and 45 mg·L-1. Plant height was increased by application of GA3, and GA3in combination with NAA, compared with application of 4-CPA, 30 mg·L-1NAA, and the control. Results also showed that application of GA3at 10 and 15 mg·L-1or in combination with NAA increased plant fresh and dry mass as well; however, this had no beneficial effect on the yield of sweet pepper fruit. The application methods and concentrations of various PGRs needs further investigation under different growing conditions on sweet pepper cultivars. © 2015, American Society for Horticultural Science. All rights reserved.


Gerrano A.S.,Vegetable and Ornamental Plant Institute | Jansen Van Rensburg W.S.,Vegetable and Ornamental Plant Institute | Adebola P.O.,Vegetable and Ornamental Plant Institute
Acta Horticulturae | Year: 2014

Amaranthus is a genus of traditional leafy vegetables that can play a role in food security, poverty reduction, and alleviation of malnutrition at household level in South Africa. The crop is mostly wild harvested for home consumption, income generation, and nutritional supplement. Very little attention has been paid to Amaranthus by breeders in South Africa despite its food security implications among the rural poor. It is therefore important to characterize and evaluate available genotypes in order to select superior parental lines as a first step for the improvement of the species. This will ultimately benefit the small-scale farmers who are the major user of the crop in South Africa. To this end, a total of 32 genotypes were planted in the field in a randomized complete block design, with three replications. The analysis of variance showed highly significant (p≤0.01) differences among the Amaranthus species for all phenotypic traits, indicating the existence of high genetic variability. This information will assist in the selection of suitable parental lines for use in Amaranthus improvement programme in South Africa.


Veale M.A.,Vegetable and Ornamental Plant Institute | Slabbert M.M.,Tshwane University of Technology | Van Emmenes L.,Vegetable and Ornamental Plant Institute
South African Journal of Botany | Year: 2012

Potato tuber moth (Phthorimaea operculella) is a major insect pest of potatoes during field cultivation and post harvest storage, causing high annual losses in potato production areas. The Bacillus thuringiensis gene (cry1Ia1) was introduced into the South African potato cultivar Mnandi with Agrobacterium-mediated transformation. The Agrobacterium tumefaciens strain LBA4404 harbouring the binary vector pSPUD5 carrying the cry1Ia1 gene under the transcriptional control of the (ocs)3mas promoter and the nptII gene (as selectable marker) was used to transform in vitro potato explants. In vitro potato explants were infected with Agrobacterium LBA4404, cultured on the pre-culture medium with 50μM acetosyringone, co-cultivated on pre-culture media for two days, and then regenerated on medium containing MS basal medium, 0.27μM NAA, 0.58μM GA3, 9.12μM zeatin and 50mg l-1 kanamycin. The regeneration frequency of 15% obtained with the potato cultivar Mnandi was an indication that this cultivar is sensitive to transformation with Agrobacterium. Verification of stable integration of the cry1Ia1 gene was confirmed by PCR and Southern blot hybridization procedures. The level of resistance to the potato tuber moth was investigated using leaf and tuber bio-assays which involved feeding studies of potato tuber moth larvae on the leaves and tubers of putatively transformed plants. Seven transformed lines expressed potato tuber moth resistance during the leaf and tuber assays. The Southern blot hybridization analysis verified that one to three copies of the cry1Ia1 gene was integrated into the genome of five transformed lines. © 2012 South African Association of Botanists.


Mabhaudhi T.,University of KwaZulu - Natal | Modi A.T.,University of KwaZulu - Natal | Beletse Y.G.,Vegetable and Ornamental Plant Institute
Water SA | Year: 2013

Bambara groundnut is a protein-rich legume, with food-security potential. Effects of irrigation levels and seed coat colour on growth, development, yield and water-use efficiency of local bambara groundnut landrace selections were evaluated under a rain shelter. Emergence was slow, although variation was indicated between landraces. Limited water availability was shown to lower stomatal conductance, although chlorophyll content index was shown to be unaffected. Additionally, growth indices of plant height, leaf number and leaf area index were shown to be lower in response to decreasing water availability. Furthermore, landraces generally flowered and matured earlier while also demonstrating higher water-use efficiency at lower water availability. Seed yield was lower under limited water availability resulting from lower pod mass and pod number. Drought tolerance in bambara groundnut landraces was achieved by reduced canopy size, early flowering and maturity, and maintaining high water use efficiency under stress. 'Brown' and 'Red' landraces responded to water stress better than the 'Light-brown' landrace, suggesting an effect of seed colour on possible drought tolerance.

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