| Transmission and movement of potential Citrus Tristeza Virus cross-protection sources in four soft citrus cultivars under greenhouse conditions | Vuuren, S.P.
Van | 2011 |
KeywordsClementine, ELISA, mandarin, tangor, virus sources AbstractAbstract Citrus Tristeza Virus (CTV), a member of the Closteroviridae family, is a globally distributed pathogen and is responsible for serious losses in citriculture. Infection with certain strains of the virus is associated with economically important diseases such as stem pitting, decline and a reduction in fruit yield, fruit size and quality. In countries where the disease and its effective aphid vector are endemic, cross-protection by the deliberate infection of virus-free propagation material with mild strains of the virus is the only practical method that can be applied to reduce the severe effects of the virus. The transmission efficiency, movement and effect on growth of four potential CTV cross-protection sources were evaluated in four soft citrus cultivars in a glasshouse experiment. The CTV sources were derived from sweet orange (Citrus sinensis L. Osb.) (SM46, SM47, SM48, SM49). The cultivars used were ‘Clemenluz’ and ‘Esbal’ clementines (C. clementina Hort. Ex Tan.), ‘Valley Gold’ mandarin (C. reticulata blanco) and ‘Morr’ tangor (C. reticulata Blanco X C. sinensis L. Osb.). The effects of the four CTV sources were compared to that of LMS6 (previous pre-immunising CTV source) and GFMS12 (current pre-immunising source) in each cultivar. Control plants were not pre-immunised. The results showed that the LMS6 source moved slowly, if at all, and was only detected sporadically in some plants of the clementine cultivars but not at all in the mandarin and tangor cultivars at different times during a 28-week period. These results preclude LMS6 as a pre-immunising source for soft citrus. Virus-free soft citrus plants will not easily acquire and maintain this source. Virus movement for LMS6 was shown to be slow, which will likely result in new shoots being virus-free and vulnerable to re-infections by various strains of CTV introduced by aphids in the field. The SM49 source however, moved the fastest and was detectable in all the cultivars tested. GFMS12, the present pre-immunising source for soft citrus moved slower than SM49. This may again result in virus-free shoots during active growing periods of trees which will make the introduction of severe natural strains possible. GFMS12, and to a lesser extent SM49, reduced the growth of the ‘Morr’ cultivar significantly AuthorsVuuren, S.P.
Van and Breytenbach, J.H.J Year Published2011 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2011.10640011 This article contributed by:
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| Host suitability of selected South African maize genotypes to the root-knot nematode species Meloidogyne incognita race 2 and Meloidogyne javanica: A preliminary study | Ngobeni, G.L. | 2011 |
KeywordsHybrids, open-pollinated varieties, resistance, root-knot nematodes, Zea mays AbstractAbstract Thirty-one commercial maize (Zea mays L.) hybrids and open-pollinated varieties (OPV’s) were screened in separate greenhouse trials with a resistant inbred line MP712W as reference genotype for host suitability to Mel-oidogyne incognita race 2 and Meloidogyne javanica. Approximately 10 000 eggs and second-stage juveniles (J2) of the appropriate root-knot nematode species were inoculated on roots of each maize seedling 10 days after plant emergence. The numbers of eggs and J2 per root system were counted, while it was also calculated g- 1 root. In addition, percentage resistance in relation to the most susceptible genotype and nematode reproduction factors (Rf) were calculated for the maize genotypes screened. Substantial variation existed among the maize hybrids and OPV’s with regard to the nematode parameters evaluated. A number of genotypes could be regarded as highly resistant to M. incognita race 2 based on the fact that they supported less than 10% of the population of this root-knot nematode species, compared to that supported by the most susceptible genotype. Several hybrids and OPV’s were identified with Rf values less than one for M. incognita race 2 and M. javanica respectively, indicating antibiosis resistance to these parasites. Screenings of maize genotypes in this study have provided a clear indication of the genetic variability within the maize genome, also with regard to susceptibility of the crop to root-knot nematodes. This substantiates the fact that maize could not be regarded as a non-host to root-knot nematodes on a generic basis, particularly in terms of commercial hybrids. It is suggested that commercial maize hybrids are screened on a continuous basis against root-knot nematodes, which would facilitate selection of hybrids that are less susceptible to both nematode species but that would perform optimally in soils conducive to root-knot-nematode infestation. AuthorsNgobeni, G.L., Fourie, H., Donald, A.H.
Mc and Mashela, P.W. Year Published2011 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2011.10640012 This article contributed by:
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| Photosynthetic capacity and diurnal gas exchange of ‘Brookfield Gala’ apple leaves under three irrigation systems | Stassen, P.J.C. | 2011 |
KeywordsDaily drip irrigation, intrinsic photosynthetic water use efficiency, micro irrigation, photosynthesis, water potential AbstractAbstract Water and nutrient application using three irrigation systems, namely daily drip irrigation, pulsing drip irrigation and micro irrigation were studied with respect to photosynthetic efficiency, water use efficiency and leaf water relations in ‘Brookfield Gala’ apple trees during 2004/5 and 2005/6 in the Western Cape Province, South Africa. The amount of water used per irrigation strategy was 5254 m3 ha−1 yr−1 and 5661 m3 ha−1 yr−1 for the micro irrigation; 3429 m3 ha−1 yr−1 and 39260 m3 ha−1 yr−1 for the daily drip and 3429 m3 ha−1 yr−1 and 4047 m3 ha−1 yr−1 for the pulsing drip for 2004/5 and 2005/6 seasons respectively. Trees were budded on either M793 or M7 root-stocks and planted in blocks using a split-plot experimental design with irrigation as the main effect and root-stock as the sub-plot. Maximum light-saturated net CO2 assimilation rate (Amax) was consistently higher under pulsing drip irrigation (this system applies water several times during the day creating an even shorter frequency cycle than the normal daily drip) compared to micro irrigation (applies water once to twice a week and uses sprinklers that spray water in a circle resulting in wetting a continuous strip within the drip row) but, occasionally, significantly higher than daily drip irrigation (applies water on a daily basis creating a shorter cycle compared to micro sprinkler system). The maximum rate of electron transport (Jmax) showed similar trends to Amax during 2004/5, but not during 2005/6. Amax peaked during midmorning (10h00) with a steady decline thereafter in all treatments, but with significantly lower rates under micro irrigation. Stomatal conductance (gs) declined steadily throughout the morning, with higher gs under the drip based systems compared to the micro system. The implications are that, irrigation application should be given early in the morning to sustain stomatal conductance and maximise CO2 assimilation rates during the period between 08h00 to 12h00. Results indicate higher photosynthetic capacity and water use efficiency under both drip-based irrigation systems compared to micro irrigation. Differences in photosynthetic capacity were related to both stomatal and non-stomatal responses. AuthorsStassen, P.J.C., Lebese, T.C. and Midgley, S.J.E. Year Published2011 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2011.10640013 This article contributed by:
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| Involvement of reactive oxygen species generating enzymes and hydrogen peroxide in the rust resistance response of sunflower (Helianthus annuus L.) | Mohase, L. | 2011 |
KeywordsNADPH oxidase, peroxidase, Puccinia helianthi, reactive oxygen species, resistance AbstractAbstract Activities of potential reactive oxygen species generating enzymes and the subsequent production of H2O2, were investigated during the rust (Puccinia helianthi)—sunflower interaction using resistant (PhRR3) and susceptible (S37–388) lines. The resistance response was associated with induced activities of NADPH oxidase and peroxidase, and resultant high levels of hydrogen peroxide that peaked 9 h after inoculation. This was confirmed by a concomitant induction of superoxide dismutase, an antioxidative enzyme. The induced high levels of reactive oxygen species generating enzyme activities and hydrogen peroxide preceded the development of considerably less disease symptoms in resistant plants, suggesting possible early involvement of reactive oxygen species generation during the resistance response. AuthorsMohase, L., Westhuizen, A.J.
der and Pretorius, Z.A. Year Published2011 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2011.10640014 This article contributed by:
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| Field evaluation of maize inbred lines for resistance to Exserohilum turcicum | Craven, M. | 2011 |
KeywordsCanonical variate analysis, Cercospora maydis, northern corn leaf blight, sources of resistance, Zea mays AbstractAbstract Nine maize inbred lines with excellent grey leaf spot resistance and good combining ability were evaluated for their reaction to infection by Exserohilum turcicum. The lines were compared to a differential set consisting of Oh43 and B73 (susceptible controls) and Oh43Ht1B, Oh43Ht2, Oh43Ht3, B37HtN (containing resistant genes) in both growth chamber and field trials. All nine lines possessed seedling resistance to northern corn leaf blight (NCLB). Two field trials were planted over two growing seasons (2007/08 and 2008/09) as randomized complete block designs with three replicates. Trials were inoculated twice (at the 4–5 and 8–12 leaf stages) with NCLB and disease assessments made at growth stages R1, R2, R3, R4 and R5. Disease progress curves were created and total severity (yt ), diseased plant severity (ydp ) and AUDPC were determined for each replicate. Linearised forms of the exponential, logistic and Gompertz models were fitted to the disease-progress data and the best model selected for each trial. Rate of disease increase (r) and level of disease at the onset of the epidemic (y0 ; time=0) were obtained from which y0 * (back-transformed from y0 ) were determined. Canonical vari-ate analysis (CVA) indicated that yt, ydp , sAUDPC and y0 * were responsible for 73.68% of the variation observed between the lines, with r explaining 15.44% of the variation. Ranking of lines were based on their yt, ydp , sAU-DPC and y0 * performance. GLS resistant lines 185–2, 182–2, 72–2A and 182–1 demonstrated higher levels of resistance to NCLB than that of lines Oh43Ht1B, Oh43Ht2, Oh43Ht3 and B37HtN while 122–2, 578 and 72–3 showed higher levels of resistance than that of Oh43Ht2 and B37HtN. AuthorsCraven, M. and Fourie, A.P. Year Published2011 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2011.10640015 This article contributed by:
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| Underutilised indigenous and traditional crops: why is research on water use important for South Africa? | Backeberg, G.R. | 2010 |
KeywordsDrought stress, indigenous crops, research, traditional crops, water use AbstractThe answer to the question ‘why is research on water use important for South Africa?’ is quite straightforward: more research is needed because there is a major gap in knowledge on water use of indigenous crops. These indigenous edible plants have sustained rural populations in developing countries for many decades if not centuries. Traditional crops are native to specific localities, are therefore better adapted to the environmental conditions and can be cultivated without the need for expensive inputs such as irrigation water and agri-chemicals (Water Research Commission, 2008). This must be seen in the context of the fact that the biggest share of water is used for farming, while at least 15 million people in rural areas of South Africa live below the poverty line. In the Research and Development Strategy for Water Utilisation in Agriculture (Water Research Commission, 2008) it is therefore stated that two relevant objectives are to (1) increase biological, technical and economic efficiency of water use; and (2) reduce poverty through water-based agricultural activities. Although farming makes a relative small contribution (7 – 12%) to income for livelihoods of the rural poor population (Van Aver-beke, 2008), there are many unutilised opportunities for production and earning of income, particularly from indigenous crops. Agriculture (farming and agri-processing activities) is therefore the key to rural development, but this requires that water use and production must be analysed as a value adding process in the food value chain (Backeberg & Sanewe, 2006). AuthorsBackeberg, G.R. and Water, A.J.
Sanewe Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10639996 This article contributed by:
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| Fitting underutilised crops within research-poor environments: Lessons and approaches | Azam-Ali, S.N. | 2010 |
KeywordsBambara, biodiversity, transdisciplinary, underutilised AbstractUnderutilised crops, the cropping systems in which they are cultivated and the people who manage, protect and conserve them represent important elements of agricultural biodiversity. Each of these components and our knowledge of them is increasingly marginalised by the structures and rewards of modern agricultural research. The ‘silofication’ of research into rigid disciplines, the incentives for fundamental research on major crops and the preference for short-term research on simple cropping systems all mitigate against progress on agricultural biodiversity, in general, and underutilised crops, in particular. This paper considers the lessons that can be learned from current research projects on one underutilised crop – bambara groundnut – and argues that new ‘trans-disciplinary’ approaches are necessary for future progress. AuthorsAzam-Ali, S.N. Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10639997 This article contributed by:
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| Early establishment performance of local and hybrid maize under two water stress regimes | Mabhaudhi, T. | 2010 |
KeywordsConductivity, emergence, germination, hybrids, landrace AbstractMaize (Zea mays L.) is the major grain crop in South Africa where most subsistence farmers still plant landraces. The objective of this study was to compare two landrace selections of maize with two hybrids popular among small-scale farmers in KwaZulu-Natal, for seed performance and water stress tolerance during seedling establishment. Two variations of a local landrace, white (Land A) and dark red (Land B), were compared to two hybrids, SC701 and SR52. Standard germination test and electrical conductivity were used to assess seed quality under laboratory conditions. Seedling emergence was performed in seedling trays using pine bark at 25% and 75% field capacity (FC), respectively, over a period of 21days. All seed types showed high germination capacity (>93%). There were highly significant differences (p5% in all varieties). Hybrids emerged faster than the landraces in both water regimes. Landraces performed better than hybrids under stress conditions. This study showed that landraces may have the same viability as hybrids and a better tolerance to stress during early establishment of the crop. AuthorsMabhaudhi, T. and Modi, A.T. Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10639998 This article contributed by:
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| Effect of pine bark goat manure medium on seedling growth and N, P, K concentration of various vegetables | Muchaonyerwa, P. | 2010 |
KeywordsCompost, growth medium, pine bark, slow release fertiliser, vegetable seedlings AbstractPine bark compost is the medium of choice for seedling growers in South Africa due to its availability, low cost and good physical properties. However, it is acidic, has low electrical conductivity (EC) and nutrient content such that fortification and liming is necessary. In a bid to improve the properties of pine bark compost, at a low cost, pine bark was co-composted with goat manure (PBG), and compared with commercial pine bark compost (PBCO) as a growing medium for vegetable amaranth, cabbage, tomato, and lettuce seedlings with and without Horticote (a slow release fertiliser). The water holding capacities of both PBCO and PBG media were higher than the minimum required but their air filled porosities were below optimum. Neither medium nor fertiliser levels had an effect on emergence of all the test crops. The different vegetable seedlings grew better in PBG than the PBCO medium. Addition of the slow-release fertiliser had similar positive effects on growth of seedlings grown on both media. Significant interactions between fertiliser and growing medium were observed in fresh weights of shoots for all the seedling crops evaluated. Results of this study revealed that PBG medium supported good seedling growth and could thus be a good substitute for PBCO as a growing medium. Use of a slow release fertiliser is highly encouraged as this can lower both nutrient losses through leaching and production costs. AuthorsMuchaonyerwa, P., Mupondi, L.T. and Mnkeni, P.N.S. Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10639999 This article contributed by:
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| Preliminary assessment of bambara groundnut (Vigna subterranea L.) landraces for temperature and water stress tolerance under field conditions in Botswana | Sesay, A. | 2010 |
KeywordsChlorophyll fluorescence, crop performance, electrolyte leakage, stress tolerance AbstractField experiments were conducted in 2006/07 and 2007/08 in Botswana to study the response of bambara groundnut to heat stress (2006/07 season) and to heat stress and soil moisture deficit stress (2007/08 season). In both seasons selected bambara groundnut landraces were grown at different sowing dates to provide a range of field environmental conditions. While the effects of water stress were mitigated by irrigation throughout the growing season in the 2006/07 season, in the 2007/08 season plants were grown under two irrigation regimes: a control that was irrigated throughout and a rain-fed treatment, with irrigation withheld at 30 days after sowing (DAS). Owing to significant and above average rainfall in the 2007/08 season no significant (p=0.05) differences in soil moisture content were obtained between the irrigated and rain-fed treatments. The highest average maximum temperatures of 34.1 and 29.2°C achieved in the December sowings in the 2006/07 and 2007/08 cropping seasons, respectively, did not impact any of the parameters measured, including leaf tissue electrolyte leakage, light adapted chlorophyll fluorescence, crop growth and yield. However, there was a highly significant (p<0.001) decline in crop performance with decline in temperature associated with delay in sowing after December. The results obtained suggest a sensitivity of bambara groundnut landraces to both low temperatures and photope-riod under field conditions in a semi-arid environment. AuthorsSesay, A., Mpuisang, T., Morake, T.S., Al-Shareef, I., Chepete, H.J. and Moseki, B. Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10640000 This article contributed by:
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