Poorly crystalline iron and aluminium oxides contribute to the carbon saturation and sorption of dissolved organic carbon in the soil

Soil carbon (C) saturation implies an upper limit to a soil's capacity to store C depending on the contents of silt + clay and poorly crystalline Fe and Al oxides. We hypothesized that the poorly crystalline Fe and Al oxides in silt + clay fraction increased the C saturation and thus reduced the capacity of the soil to sorb additional C input. To test the hypothesis, we studied the sorption of dissolved organic carbon (DOC) on silt + clay fractions (<53 µm) of highly weathered oxic soils, collected from three different land uses (i.e., improved pasture, cropping and forest). Soils with high carbon saturation desorbed 38% more C than soils with low C saturation upon addition of DOC, whereas adsorption of DOC was only observed at higher concentration (>15 g kg^?1). While high Al oxide concentration significantly increased both the saturation and desorption of DOC, the high Fe oxide concentration significantly increased the desorption of DOC, supporting the proposition that both oxides have influence on the DOC sorption in soil. Our findings provide a new insight into the chemical control of stabilization and destabilization of DOC in soil.     

Competence of <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> from Cruciferous Weeds and Wallflower (<Emphasis Type="Italic">Erysimum cheiri</Emphasis>) to Induce Black Rot in Cabbage

Aphanomyces euteiches Drechsler is an oomycete pathogen of leguminous crops that causes root rot, a severe disease of pea (Pisum sativum L.) worldwide. An improved understanding of the genetic structure of A. euteiches populations would increase knowledge of pathogen evolution and assist in the design of strategies to develop pea cultivars and germplasm with stable disease resistance. Twenty six primers pairs were used to amplify Sequence Related Amplified Polymorphisms (SRAP) among 49 A. euteiches isolates sampled from pea. A total of 190 polymorphic SRAP bands were generated, of which 82 were polymorphic between all the A. euteiches isolates. The percentage of polymorphic bands per primer pair ranged from 22 to 75%. According to the PIC value estimated for each marker, 60% of the SRAP markers were highly to reasonably informative (PIC > 0.25). Genetic structure of A. euteiches populations sampled in different American and French locations showed low to high genetic diversity within populations. The largest variation occurred within countries, with a total estimated genetic diversity of 0.477 and 0.172 for American and French populations, respectively. This was particularly evident from a principal component analysis (PCA) and a Minimum Spanning Networks (MSN) based on genetic profiles of isolates, which generated two different clusters, one corresponding to the French isolates and four American isolates (MV1, MV5, MV7, Ath3), and the other to American isolates. A. euteiches populations from cultivated pea in France appeared as a single unstructured population, whereas American isolates of A. euteiches diverged into three different populations.     

Relationships between agroforestry and community development according to practitioners

Post-adoption studies are relatively uncommon in the agroforestry literature. Thus little is known about progress and permanence following adoption. To better understand the relationship between agroforestry implementation and community development, seventy-seven practitioners in Cameroon with three or more years of experience were surveyed about the relationships between agroforestry and community development. Hypotheses were that they have observed differences in the association between agroforestry and community capitals. They were also surveyed about their satisfaction with agroforestry. Hypotheses were that satisfaction is high and negatively skewed when compared to community capitals measurements. Game play was used to collect responses. Friedman’s two-way non-parametric statistic was used to test for inter-item differences within the community capitals and satisfaction response sets. Shapiro–Wilk statistic was used to test for normality in both response sets and a bootstrap procedure and t-tests were used to test for differences in data skewness and kurtosis. Natural capital scored highest but did not differ significantly from built, human, and social capitals. Financial capital was significantly lower than natural capital, but not built, human, or social capitals. Political and cultural capitals were significantly lower compared to all others. Satisfaction was significantly higher when compared to community capitals, but the data were also negatively skewed suggesting capitals are a more representative and useful metric for researchers and technical assistance professionals focused on long-term practitioner support.     

Risks for infection of strawberry plants with an aerosolized inoculum of <Emphasis Type="Italic">Xanthomonas fragariae</Emphasis>

Xanthomonas fragariae is the causative agent of angular leaf spot of strawberry, a quarantine organism in plant propagation material in the European Union. Field experiments were conducted to assess the risks for infection of strawberry plants through dispersal of an aerosolized inoculum. In practice, pathogen aerosols can be formed during mowing of an infected crop or by water splashing on symptomatic plants during overhead irrigation or rain. In our experiments, aerosols were generated by spraying suspensions of X. fragariae with a density of 10⁸ cfu ml^?1 or water under pressure vertically up into the air. In strawberry plants (cv Elsanta) placed at 1.3, 5 and 10 m distance downwind from the spray boom, infections were found, as evidenced with a combination of dilution–plating and molecular techniques, but more frequently in plants wetted prior to inoculation than in plants kept dry. A logarithmic decrease in infection incidence was found with the distance to the inoculum source. Symptomatic plants were found up to 5 m distance from the inoculum source. No infected plants were found in plants placed 4 m upwind or treated with water. In glasshouse studies, it was shown that under conditions favorable for disease development, spray-inoculation of strawberry plants with estimated densities of X. fragariae as low as 2000 cfu per plant were able to cause symptoms both in cv Elsanta and cv Sonata. Results indicate that there is a considerable risk on infections of strawberry plants exposed to aerosolized inoculum.     

Multilocus sequence analysis supports a low genetic diversity among ‘<Emphasis Type="Italic">Candidatus</Emphasis> Phytoplasma australasia’ related strains infecting vegetable crops and periwinkle in Egypt

‘Candidatus Phytoplasma australasia’ causes important damages to the Egyptian vegetable crop production. A prerequisite for controlling the different diseases it causes to eggplant, tomato and squash, is to trace its propagation pathways. To allow the differentiation of ‘Ca. P. australasia’ strains, a multilocus sequence analysis protocol was developed. Four conserved phytoplama genes namely tuf, secY, dnaK and dppA, were selected among the CDS of a ‘Ca. P. aurantifolia’ genome draft. The corresponding genes were PCR amplified from tomato, eggplant and squash collected in 2010 from the governorates Sharkia, Elmynia and Beni sueif, as well as from Catharanthus roseus periwinkles collected in 2013 from Kafrelsheikh governorate. Sequence comparisons showed no diversity among the Egyptian isolates of ‘Ca. P. australasia’ that also constitute a distinct cluster within the 16SrII-D taxonomic subgroup. This low diversity supports a common epidemiology for the different diseases affecting vegetable crops and periwinkle in Egypt and suggests that future investigations on insect vector should focus on polyphagous leafhoppers.     

Site‐specific management is crucial to managing Mikania micrantha

Increasingly, weeds have been taking on global distributions. With the proliferation of invasive weeds has come the challenge of managing these species over broad geographical regions, with diverse habitats and political jurisdictions. Here, we review the management of Mikania micrantha Kunth (Asteraceae; mile‐a‐minute) throughout its invaded range, extending through most of the Pacific islands and southern and south‐east Asia. Context matters when determining the best course of action for managing M. micrantha, as it has invaded a large variety of agricultural and natural systems. In Queensland, Australia and Florida, USA, M. micrantha has been targeted in relatively successful eradication campaigns, highlighting the importance of early detection and rapid response methods, while elsewhere in its invaded range, populations are either still increasing or showing limited signs of decline. An inter‐regional approach to research and management should incorporate successful management strategies employed throughout the invaded range including, but not limited to, chemical and cultural control practices, manual and mechanical control, classical biological control using the rust fungus Puccinia spegazzinii, plant–plant competition and integrated approaches utilising two or more control methods concurrently. Additional knowledge of M. micrantha genetics is required to determine if management approaches could be fine‐tuned for particular populations. Countries bordering the Mekong River formed a network in 2011 to co‐ordinate the management of invasive species such as M. micrantha. Expanding such a collaborative approach to other regions could further reduce populations of M. micrantha and limit its spread.     

Could the Supply of Boron and Zinc Improve Resistance of Potato to Early Blight?

The adequate supply of boron (B) and zinc (Zn) can improve the structural integrity and permeability of cell membranes, which is a defence mechanism against fungi infection. A greenhouse experiment was conducted to investigate the effect of the application of B and Zn on plant growth and the incidence and severity of potato early blight, a destructive foliar disease of potato crop caused by Alternaria grandis E.G. Simmons. Potato plants (Solanum tuberosum L. cv. Ágata) were grown in 11-l pots filled with sandy soil, unfertilized or fertilized with 5 mg kg^?1 B and 5 mg kg^?1 Zn (either alone or in combination). Potato plants were inoculated with isolates of Alternaria grandis at 40 days after planting. Early blight incidence and severity were evaluated visually 7 days after inoculation with A. grandis isolates. Disease incidence ranged from 16 to 41% infected leaves, and was significantly highest in the treatment with the application of B, followed by the control, and lowest with application of Zn and B + Zn. Early blight severity ranged from 2.5 to 25%, and was significantly higher in the unfertilized treatment than in those fertilized with Zn either alone or in combination with B. These findings suggest that Zn plays a critical role in potato tolerance to early blight and should be considered as a preventive measure in the disease management plan, since application of zinc reduced the incidence and severity of potato early blight. However, the physiological basis of this remains unknown.