Pectobacterium carotovorum ssp. brasiliense 1692 (Pcb1692) is an important emerging pathogen of potatoes causing blackleg in the field and soft rot during post-harvest storage. Blackleg diseases involve the bacterial colonization of vascular tissue and the formation of aggregates, also known as biofilms. To understand the role of quorum sensing in vascular colonization by Pcb1692, we generated a Pcb1692ΔexpI mutant strain. Inactivation of expI led to the reduced production of plant cell wall-degrading enzymes (PCWDEs), the inability to produce acyl homoserine lactone (AHL) and reduced virulence in potato tubers and stems. Complementation of the mutant strain with the wild-type expI gene in trans successfully restored AHL and PCWDE production as well as virulence. Transmission electron microscopy and in vitro motility assays demonstrated hyperpiliation and loss of flagella and swimming motility in the mutant strain compared with the wild-type Pcb1692. Furthermore, we noted that, in the early stages of infection, Pcb1692 wild-type cells had intact flagella which were shed at the later stages of infection. Confocal laser microscopy of PcbΔexpI-inoculated plants showed that the mutant strain tended to aggregate in intercellular spaces, but was unable to transit to xylem tissue. On the contrary, the wild-type strain was often observed forming aggregates within xylem tissue of potato stems. Gene expression analyses confirmed that flagella are part of the quorum sensing regulon, whereas fimbriae and pili appear to be negatively regulated by quorum sensing. The relative expression levels of other important putative virulence genes, such as those encoding different groups of PCWDEs, were down-regulated in the mutant compared with the wild-type strain.

BackgroundRelatively little has been researched or published on the importance of peri-urban domestic gardens as part of a household livelihood strategy in South Africa. Due to lack of comprehensive data on peri-urban domestic gardens, their potential value as luxury green space, provision of food, income and ecosystem services to the fast growing urban population in South Africa is not clearly known. The aim of this study was to document differences and similarities in plant use and diversity in domestic gardens of two peri-urban communities in the Limpopo Province that differ in proximity to an urban area.MethodsData on plant use categories of 62 domestic gardens in the peri-urban areas of the Limpopo Province were collected in Seshego and Lebowakgomo. Semi-structured interviews, observation and guided field walks with 62 participants were employed between May and October 2012.ResultsA total of 126 plant species were recorded for both Seshego and Lebowakgomo. Domestic gardens in the more remote areas of Lebowakgomo were characterized by higher percentage of food plants (47 species, 83.8% of the total food plants recorded) and medicinal plants (31 species, 83.7%). Lebowakgomo domestic gardens were also characterized by higher numbers of indigenous plants (76.7%) showing similarities to the natural surrounding vegetation in terms of plant species. On the contrary, domestic gardens of Seshego on the periphery of the city centre were characterized by higher percentage of exotic species (81.8%) and ornamental plants (73%), with food plants playing a supplementary role. Comparison of the two areas demonstrated a remarkable difference in plant use and composition.ConclusionsThis study revealed that there are differences in utilization of plant resources between households on the edge of an urban centre and those in the more remote areas. Food and medicinal plants play an important role in remote areas; while ornamental plants play an important role in urban domestic gardens. But the collective desire for food, medicinal and ornamental plants by both communities on the edge of an urban centre and those in the more remote areas highlight the importance of plant resources in domestic gardens.

The objective of this study was to document useful plants in urban domestic gardens in the Limpopo Province, South Africa. Data on plant use categories of urban domestic gardens in the under-developed areas of the Limpopo Province were collected by means of interviews and personal observations between May and October 2012.A total of 126 taxa belonging to 110 genera and 62 families were recorded from 62 urban domestic gardens. More than half of the species (52.4%) recorded in the surveyed domestic gardens are exotic to South Africa and 9.5 percent of the total garden flora are "indigenous cultivated", introduced in the Limpopo Province from other provinces of South Africa. The dominant plant use category in domestic gardens was ornamental, followed by fruit trees. The present study revealed that plants grown and maintained in urban domestic gardens play a vital role in the livelihoods of the people of Limpopo Province.

Leaf responses of a susceptible potato cultivar (S. tuberosum cv. Valor) were compared to those of a tolerant potato cultivar (S. tuberosum cv. BP1) following challenge by Pectobacterium carotovorum subsp. brasiliense 1692 (Pcb 1692). Leaves of the susceptible cultivar showed excessive maceration and water soaking symptoms as well as increased proliferation of the bacteria. In leaves of the tolerant cultivar, bacteria appeared to be restricted to the point of inoculation,subsequently; there was very little multiplication of bacterial cells. Furthermore we demonstrated that disease is associated with the extensive spread of cell death in S. tuberosum cv. Valor while in S. tuberosum cv. BP1 cell death was observed to be associated with lack of disease development. Another response associated with challenge by Pcb 1692 in the susceptible and tolerant potato cultivar leaf tissue was the oxidative burst. Generally, the accumulation of hydrogen peroxide and superoxide in leaf-tissue appeared to correlate with tolerance levels.

models of the area. Change analysis of the vertical stratification of the vegetation canopy revealed the location of biomass increases as almost solely attributable to the 1-3 m and 3-5 m height classes within the vertical vegetation structure. These changes are exacerbated by anthropogenic factors. The rangeland under the highest wood extraction pressure had the largest biomass increases, likely a strong regrowth response to excessive harvesting. Within rangelands, areas closest to roads and settlements experienced substantial biomass increases in 'hotspots' as a result of shrub level gains; the greater the wood extraction pressure on the rangeland, the greater the spatial coalescence of biomass 'hotspots'. This research shows a bush encroachment signal across the communal rangelands, likely an interactive combination of newly established woody encroachers and strong coppice regrowth in harvested species. The exacerbation of bush encroachment in natural resource-dependent communities has critical implications for ecosystem service provision.Kersting's groundnut (Macrotyloma geocarpum) is an under-exploited grain legume of West African origin. To meet future food demands, there is the need to diversify agriculture in order to harness the useful potentials of under-exploited crops such as the nitrate tolerant symbiosis and drought tolerance of Kersting's groundnut. This study was carried out to measure N 2 fixation and WUE of five Rhizobium-inoculated Kersting's groundnut landraces. The experiment involved five Rhizobium-inoculated and uninoculated Kersting's groundnut landraces (Puffeun, Dowie, Funsi, Sigiri and Boli) laid in randomized complete block design with four replications at two locations (Nyankpala and Savelugu) in the northern region of Ghana. At 90% flowering, five plants were dug up, separated into shoots, roots and nodules and oven-dried (65°C, 48 h) to determine nodule and shoot dry matter. Ground (0.85 mm sieve size) shoot samples were subjected to 15 N and 13 C isotopic analysis using mass spectrometer in order to measure N 2 fixation and WUE in the landraces. Data were subjected to ANOVA using Statistica software (version 10), and means separated using DMRT (p ≤ 0.05). The results of the study revealed that the Kersting's groundnut landraces were derived between 23.0 and 46.8% of their N requirements from atmospheric N 2 fixation (%Ndfa) and fixed 16.5-57.8 kg ha -1 N across the two locations. At Nyankpala, the landraces Puffeun and Funsi exhibited lower (p ≤ 0.05) δ 15 N values, resulting in higher %Ndfa by these landraces. At Savelugu, the landrace Funsi exhibited the least δ 15 N, higher %Ndfa and N-fixed. The Kersting's groundnut landraces exhibited contrasting responses to rhizobial inoculation between the two locations, suggesting possible differences in the efficiency of the indigenous rhizobia. The δ 13 C values revealed high WUE among Kersting's groundnut landraces. The grain yields of landraces (921-1556 kg ha − 1 ) in this study, indicates high yield potential of available Kersting's ...