The Use of Combining Ability Analysis to Identify Elite Parents for Artemisia annua F1 Hybrid Production

Artemisia annua is an important medicinal crop used for the production of the anti-malarial compound artemisinin. In order to assist in the production of affordable high quality artemisinin we have carried out an A. annua breeding programme aimed at improving artemisinin concentration and biomass. Here we report on a combining ability analysis of a diallel cross to identify robust parental lines for hybrid breeding. The parental lines were selected based on a range of phenotypic traits to encourage heterosis. The general combining ability (GCA) values for the diallel parental lines correlated to the positive alleles of quantitative trait loci (QTL) in the same parents indicating the presence of beneficial alleles that contribute to parental performance. Hybrids generated from crossing specific parental lines with good GCA were identified as having an increase in both artemisinin concentration and biomass when grown either in glasshouse or experimental field trials and compared to controls. This study demonstrates that combining ability as determined by a diallel cross can be used to identify elite parents for the production of improved A. annua hybrids. Furthermore, the selection of material for breeding using this approach was found to be consistent with our QTL-based molecular breeding approach.     

Macroinvertebrates as unreliable indicators of human disturbance in temporary depression wetlands of the south-western Cape, South Africa

Macroinvertebrates have a successful history of use as indicators of human impact in lotic environments. More recently, macroinvertebrate indices have been recommended for use in certain wetland types. Yet some authors do not recommend macroinvertebrates indices of wetland condition in areas with pronounced natural environmental heterogeneity. Our study provides a preliminary assessment of the feasibility of using macroinvertebrates for bioassessment of temporary isolated depression wetlands in the south-western Cape region of South Africa. We expected natural environmental heterogeneity among wetlands to exert a stronger influence on macroinvertebrates than human disturbance factors. Partitioning of the variation in macroinvertebrate assemblage composition that could be attributed to human disturbance factors (within and adjacent to wetlands), environmental variables and spatio-temporal factors indicated that environmental and spatio-temporal factors independent of human disturbances largely determined assemblage composition, whilst human disturbance played a relatively minor role. Linear regressions of taxon richness/diversity measures, individual families and a collation of metrics against measures of habitat transformation around wetlands and scores from a rapid assessment index of human disturbance revealed poor relationships. The univariate and multivariate patterns observed in this study do not lend themselves to the creation of a macroinvertebrate index of human disturbance for temporary wetlands in the region.     

Hydrologic and mechanical control for an invasive wetland plant, <Emphasis Type="Italic">Juncus ingens</Emphasis>, and implications for rehabilitating and managing Murray River floodplain wetlands,Australia

Wetlands are prone to increased invasion by plant species following changes in hydrologic regime, leading to shifts in plant community composition and potentially ecosystem function and health. In this paper, the ecology and potential control of Juncus ingens, a native wetland plant in the Murray-Darling Basin of south-eastern Australia, is investigated. J. ingens has benefited from altered Murray River hydrologic conditions by expanding its range and invading seasonally-flooded grassland and riparian habitats along the Murray River. Here results of complementary glasshouse and field research of seedling and mature J. ingens growth and resilience as influenced by hydrologic regime (moist, saturated, partial inundation and when possible, complete inundation) and mechanical control (i.e., clipping) are presented. A moist hydrologic regime (soil held at field capacity) resulted in the most vigorous seedlings (13.9–73.0% more total biomass), while saturated conditions (flooding maintained level with the soil surface) resulted in the most vigorous mature J. ingens (14.1–98.4% more total biomass). Seedling mortality was greatest under complete and prolonged inundation (60% fatal with remaining 40% showing severe stress), conditions suspected to have limited prior invasion but which currently occur infrequently as a result of reduced flooding magnitude. Clipping was fatal for nearly all seedlings regardless of hydrologic regime but was only fatal for mature plants if coupled with prolonged inundation. Coupling ground-level clipping with strategic flooding may be the most effective means for controlling current populations of J. ingens and limiting further invasion, promoting re-colonisation by displaced species and rehabilitating the health of Barmah Forest and similar Murray River floodplain wetlands.     

Influence of Colophospermum mopane canopy cover on litter decomposition and nutrient dynamics in a semi‐arid African savannah

The objective of this study was to investigate the influence of mopane canopy cover on litter decomposition in a semi‐arid African savannah. We used a randomized block design with five blocks of 100 × 100 m demarcated in a 10‐ha pocket of open mopane woodland. Litterbags were placed beneath large (8.3 m crown diameter) and small mopane trees (2.7 m crown diameter) and in the intercanopy area. Decomposition was fastest in the intercanopy area exposed to solar radiation (k = 0.35 year^?1), intermediate beneath small trees (k = 0.28 year^?1) and slowest beneath large trees (k = 0.23 year^?1). Soil temperatures beneath small and large trees were 3–5 and 6–9°C lower than in the intercanopy area, respectively. Bacterial and fungal counts were significantly higher (P < 0.05) beneath large than small trees and in the intercanopy area. The amount of N and P released did not vary significantly among sampling sites. Soil moisture in the dry season was similar among sampling sites but rainy‐season soil moisture was significantly greater (P < 0.05) beneath large than small trees and in the intecanopy area. Mopane canopy cover retarded litter decomposition suggesting that photodegradation could be an important factor controlling carbon turnover in semi‐arid African savannahs.     

Risk Assessment of Transgenic Virus-resistant White Clover: Non-target Plant Community Characterisation and Implications for Field Trial Design

One of the most difficult elements of the ecological risk assessment of transgenic plants is investigation of their potential impact on biodiversity in complex non-target communities. This problem is particularly acute for pasture plants, since many have a track record of invasiveness. In this paper we develop an understanding of some aspects of the ecology of Trifolium repens L. (white clover) in montane vegetation communities in southeastern Australia as part of a larger project investigating potential ecological risks associated with commercial release of newly-developed transgenic virus-resistant T. repens cultivars. We use a combination of floristic surveys and biomass sampling to determine the habitat affinity of T. repens, the structure and composition of associated communities, and the scale at which different abiotic and biotic factors correlate with T. repens abundance. We also compare the abundance of native and exotic species within specific morpho-functional groups and use this to determine the relative significance of T. repens as a community constituent, and to identify native species that would be most at risk by expanding populations of T. repens. We found that T. repens comprises a relatively small component of the total community cover and biomass, but is one of the most abundant herbaceous species in mesic Poa – dominated grasslands and Poa-Eucalyptus woodlands in the study area, and that T. repens abundance is correlated at the within-community scale primarily with soil moisture and fertility. At smaller scales T. repens is limited by the hierarchical dominance of native graminoids and we conclude that competition for inter-tussock space in mesic communities is the most likely mechanism by which expanding populations of T. repens would influence populations of associated native species. These results have significant implications for the manner in which future analysis and risk quantification stages of the risk assessment of virus-resistant T.␣repens and other transgenic pasture plants in complex plant communities are performed.     

Metal accumulation in two contiguous eutrophic peri-urban lakes,Chivero and Manyame,Zimbabwe

Concentrations of aluminium, cadmium, chromium, cobalt, copper, iron, lead, nickel and zinc were determined in surface water, benthic sediments, and the gills, liver and stomach muscle tissues of Oreochromis niloticus and Clarias gariepinus in peri-urban lakes Chivero and Manyame, Zimbabwe. Five sites were sampled in each lake once per month in November 2015, February, May, August and November 2016. Pollution load index detected no metal contamination, whereas the geo-accumulation index reflected heavy to extreme sediment pollution, with Fe, Cd, Zn, Cr, Ni and Cu present in both lakes. Significant spatial temporal variations were detected for Al, Cr, Cu and Pb across sites within and between the two lakes. High Fe, Al and Cr concentrations in water and sediments in lakes Chivero and Manyame derive from geogenic background sources in addition to anthropogenic loads and intensity. Elevated concentrations of Al, Pb, Cu, Cd, Fe and Zn detected in gills, liver and stomach tissue of catfish corroborate concentrations in water and sediments, and pose the highest ecological and health risk for hydrobionts in lakes Chivero and Manyame. Contiguity of peri-urban lakes exposes them to similar threats, necessitating creative water management strategies, which ensure ecological continuity.     

Chemical composition and in vitro ruminal fermentation of common tree forages in the semi-arid rangelands of Swaziland

Browse plants play an important role in providing feed for livestock in semi-arid rangelands of Africa. Chemical composition and in vitro ruminal fermentation of leaves collected from Acacia burkei, Acacia tortilis, Acacia nilotica, Dichrostachys cinerea and Ehretia obtusifolia in communal grazing lands in the lowveld of Swaziland is presented. Leaves were collected from trees located on two soil types (i.e., lithosol and vertisol) in the communal land but it had no effect on the chemical composition of tree leaves. The NDFom and ADFom content were highest in D. cinerea and A. burkei and lowest in E. obtusifolia and A. nilotica. Crude protein (CP) contents ranged between 108 g/kg and 122 g/kg DM. D. cinerea had the highest Ca and Mg content, while A. tortilis had the lowest. There were marked variations in K level amongst browse species, with A. tortilis (9.1 g/kg DM) having the highest value. The P, Zn and Fe did not differ between browse species. Soil type and tree species interaction impacted in vitro fermentation parameters. Extent of fermentation, as measured by 48 h cumulative gas production, and organic matter degradability was highest in E. obtusifolia leaves and lowest in D. cinerea leaves within soil type. Fermentation efficiency, as measured by partitioning factors, was highest in A. nilotica leaves. Leaves of E. obtusifolia could be a valuable supplementary feedstuff for ruminant livestock due to its in vitro fermentation characteristics as well as low fibre and moderate CP levels.     

The influence of mistletoes on nutrient cycling in a semi-arid savanna, southwest Zimbabwe

Parasitic plants are increasingly becoming the focus of research in many ecosystems. They have been shown to alter litterfall properties and decomposition rates in environments where they occur. Despite this recognition, the role of mistletoes in nutrient cycling in semi-arid savanna remains poorly understood. We investigated the litter input, element returns, and associated below-canopy soil nutrient concentrations of three mistletoe species (Erianthemum ngamicum, Plicosepalus kalachariensis, and Viscum verrucosum) that parasitize Acacia karroo trees in a semi-arid savanna, southwest Zimbabwe. Element concentrations in mistletoe leaf litter were enriched relative to the host. Litterfall from mistletoes significantly increased overall litterfall by up to 173 %, with E. ngamicum and P. kalachariensis having greater litterfall than their host trees. Associated with these changes in litterfall was an increase in element returns and the below-canopy soil nutrient concentrations. The increase in nutrient returns was due to both the effect of enriched mistletoe litter and increased volumes of litterfall beneath host trees. Litterfall, element returns, and the below-canopy soil nutrient concentrations were significantly influenced by mistletoe density, with higher values at high mistletoe density. Overall, E. ngamicum and P. kalachariensis had greater influence on litterfall, element returns, and soil nutrient concentrations than V. verrucosum. These findings are consistent with current understanding of enhanced nutrient cycling in the presence of parasitic plants particularly in nutrient-poor ecosystems. We conclude that the introduction of nutrients and associated increase in resource heterogeneity play an important role in determining ecosystem structure and function in semi-arid savannas.     

Wetland plant growth under contrasting water regimes associated with river regulation and drought: implications for environmental water management

An important characteristic of many wetland plants in semi-arid regions is their capacity to withstand fluctuations between extended dry phases and floods. However, anthropogenic river regulation can reduce natural flow variability in riverine wetlands, causing a decline in the frequency and duration of deep flooding as well as extended droughts, and an increase in shallow flooding and soil saturation. Our aim in this paper was to use an experimental approach to examine whether reductions in flooding and drought disadvantage species adapted to both these extremes, and favours those with water requirements that match the new regime of frequent low-level flooding. We compared the growth characteristics and biomass allocation of three native Australian aquatic macrophytes (Pseudoraphis spinescens, Juncus ingens and Typha domingensis), which co-occur at Barmah Forest, south-eastern Australia, under three water treatments: drought, soil saturation and deep flooding. The responses of species to the treatments largely reflected changes in their relative abundance at Barmah Forest since river regulation. Typha domingensis, which has remained uncommon, performed relatively poorly in all treatments, while J. ingens, which has increased its range, exhibited more vigorous growth under soil saturation. Pseudoraphis spinescens, which was once widespread but has declined markedly in its distribution, grew strongly under all water treatments. These findings suggest that a return to more natural, variable river flow regimes can potentially be an important conservation and restoration strategy in ecosystems characterised by species that have adaptations to extreme hydrological growing conditions.