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Marais A.,Institute for Plant Production | Hardy M.B.,Institute for Plant Production | Morris C.D.,University of KwaZulu - Natal | Botha A.,Stellenbosch University
South African Journal of Plant and Soil | Year: 2010

Crop management practices, Including the addition of fertilisers, often lead to different microbial communities in agricultural soils. Soil dilution plates were used to enumerate yeasts, basldiomycetous fungi, general heterotrophic microbes, as well as actinomycetes in soils sampled at three times (winter, spring, early summer) within and between rows of plots planted to a wheat monoculture and wheat-legume rotation. An adapted version of the buried slide technique was used to measure the numbers of filamentous microbes in the soil. Seasonal changes (July- November) were evident in all measured microbial populations in both plots sampled. Whereas most microbe populations showed similar or declining numbers from winter (July) to spring (September), general heterotrophic counts increased slightly in the monoculture plot, while filamentous growth increased within crop rows in the monoculture plot. Biolog EcoPlates™ were used to give an indication of spatio-temporal changes In the soil bacterial metabolic profile. A seasonal shift occurred in the ability of the bacterial community to assimilate carbon sources with more organic acids utilised in November than in July. Fungi, capable of anaerobic growth, occurred more abundantly In the soil of the monoculture plot. This study Indicated the efficacy of using simple culture methods, in combination with the buried slide method, to detect fine-scale and short-term temporal changes in the abundance and metabolic activity of important microbial populations in soils subjected to different agronomic practices.

Tolmay J.P.C.,ARC Small Grain Institute | Tolmay J.P.C.,Stellenbosch University | Agenbag G.A.,Stellenbosch University | Hardy M.B.,Institute for Plant Production
South African Journal of Plant and Soil | Year: 2010

Low rainfall during the wheat growing season in Mediterranean climates leads to variation in growth period and this may constrain yield. Low seedling survival is among the factors that can limit yield in the Western Cape. Seedling survival rates of 50-70% are expected with conventional tillage, necessitating high sowing rates. Conservation tillage practices which can help to improve seedling survival have been readily adopted in the Winter Rainfall production region of South Africa, but require wider row widths than previously used in conventional tillage and seeding systems to facilitate stubble handling. Replicated, factorial experiments with split-split plot arrangements were established in commercial wheat fields during the 2005 and 2006 seasons at five localities. Treatments included three cultivars, split into row widths (250-350 mm) which were split into different planting densities. Seedling counts (3-4 weeks after planting) were used to determine seedling emergence and survival rates. Results indicated that seedling establishment was significantly reduced by increasing row widths (RW), higher planting densities (PD) and in PD × RW interactions in some trials, but that seedling survival of more than 80% were obtained when planting conditions were favourable. The lowest seedling survival of 63% occurred when dry conditions prevailed after planting at one locality in 2005. Anecdotally the no-till planting method as used in this region, can improve on the 50-70% seedling survival of previously used conventional planting methods.

Boutigny A.-L.,Stellenbosch University | Ward T.J.,Bacterial Foodborne Pathogens and Mycology Research Unit | Van Coller G.J.,Stellenbosch University | Van Coller G.J.,Institute for Plant Production | And 4 more authors.
Fungal Genetics and Biology | Year: 2011

Species identity and trichothecene toxin potential of 560 members of the Fusarium graminearum species complex (FGSC) collected from diseased wheat, barley and maize in South Africa was determined using a microsphere-based multilocus genotyping assay. Although three trichothecene types (3-ADON, 15-ADON and NIV) were represented among these isolates, strains with the 15-ADON type predominated on all three hosts. A significant difference, however, was identified in the composition of FGSC pathogens associated with Gibberella ear rot (GER) of maize as compared to Fusarium head blight (FHB) of wheat or barley (P<. 0.001). F. graminearum accounted for more than 85% of the FGSC isolates associated with FHB of wheat and barley (N= 425), and was also the dominant species among isolates from maize roots (N= 35). However, with the exception of a single isolate identified as an interspecific hybrid between Fusarium boothii and F. graminearum, GER of maize (N= 100) was exclusively associated with F. boothii. The predominance of F. graminearum among FHB isolates, and the near exclusivity of F. boothiii among GER isolates, was observed across all cultivars, collection dates, and provinces sampled. Because these results suggest a difference in host preference among species of the FGSC, we hypothesize that F. graminearum may be less well adapted to infect maize ears than other members of the FGSC. © 2011 Elsevier Inc.

Marais A.,Institute for Plant Production | Hardy M.,Institute for Plant Production | Booyse M.,Biometry Unit | Botha A.,Stellenbosch University
Applied and Environmental Soil Science | Year: 2012

Different plants are known to have different soil microbial communities associated with them. Agricultural management practices such as fertiliser and pesticide addition, crop rotation, and grazing animals can lead to different microbial communities in the associated agricultural soils. Soil dilution plates, most-probable-number (MPN), community level physiological profiling (CLPP), and buried slide technique as well as some measured soil physicochemical parameters were used to determine changes during the growing season in the ecosystem profile in wheat fields subjected to wheat monoculture or wheat in annual rotation with medic/clover pasture. Statistical analyses showed that soil moisture had an over-riding effect on seasonal fluctuations in soil physicochemical and microbial populations. While within season soil microbial activity could be differentiated between wheat fields under rotational and monoculture management, these differences were not significant. © 2012 A. Marais et al.

Broggini G.A.L.,ETH Zurich | Kost T.,ETH Zurich | Fahrentrapp J.,ETH Zurich | Fahrentrapp J.,ZHAW Zurich University of Applied Sciences | And 6 more authors.
Acta Horticulturae | Year: 2014

To date the use of natural resistance to manage fire blight epidemics in apple orchards has been limited by the reduced availability of such traits in commercial varieties as well as the very poor fruit quality of resistant wild apple genotypes. Such natural resistance offers great environmental advantages compared to any other disease control methods i.e. less treatments with chemicals and less tractor rides. We undertook the positional cloning of the fire blight resistance gene located on the linkage group 3 of Malus x robusta 5 (Mr5), a wild apple genotype immune to European strains of Erwinia amylovora. A single candidate gene (FB-MR5) was identified and validated by a transgenic approach, transforming the fire blight susceptible cultivar 'Gala'. This represents an unprecedented opportunity to deploy Malus-own resistance by cisgenics, similarly to what we recently reported for the scab resistance gene Rvi6, showing that such GM product may represent an effective and sustainable approach in fire blight management. Current state of the research will be presented. © 2014, International Society for Horticultural Science. All rights reserved.

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