Factors influencing citrus fruit scarring caused by Pezothrips kellyanus

Kelly’s citrus thrips (KCT) Pezothrips kellyanus (Bagnall) (Thysanoptera: Thripidae) is a recently recorded cosmopolitan citrus pest, causing fruit scarring that results in downgrading of fruit. Due to the detrimental effects caused on fruits by KCT, we wanted to study some of the factors influencing fruit scarring. Specifically, the objectives were: (1) to determine the fruit development stage when citrus fruits are damaged by KCT and the population structure of KCT during this period, (2) to study the influence of temperature on intensity of damage, and finally, (3) to identify alternative host plants. KCT populations on flowers and fruitlets and alternate plant hosts were sampled in four citrus orchards from 2008 to 2010. The percentage of damaged fruits was also recorded. The exotic vine Araujia sericifera (Apocynaceae) was recorded as a new host for KCT. Thrips scarring started to increase at 350–650 degree-days (DD) above 10.2 °C, coinciding with a peak abundance of the second instar larval stages over all 3 years of the study. The maximum percentage of larval stages of KCT was observed in the 3 years at about 500 DD, a period which corresponds to the end of May or early June. Variation in the severity of fruit scarring appeared to be related to air temperature. Temperature likely affects the synchronisation between the peak in abundance of KCT larvae, and the period when fruitlets are susceptible to thrips damage. Temperature can also influence the survival and development of KCT populations in citrus and other host plants in the citrus agro-ecosystem.     

WaLIS—A simple model to simulate water partitioning in a crop association: The example of an intercropped vineyard

The introduction of cover crops in vineyards is being tested as it mitigates some undesirable environmental impacts of these cropping systems, such as surface runoff and soil erosion. In some cases, it could even reduce an excessive vegetative vigour of grapevine. However, most of time, wine growers are worried that severe competition for soil resources between the intercrop and grapevines could impair grape yield and quality. WaLIS (Water baLance for Intercropped Systems), a simple model simulating the water resource partitioning in such an association was designed to evaluate and optimize the water regime in intercropped systems.The model is presented and evaluated in this paper in three situations: the same grapevine cultivar (cv. Aranel) with either bare soil, or a temporary intercrop (barley) or a permanent intercrop (tall fescue). All three situations are located in the south of France. It is based on an existing model, designed to simulate the water regime of a bare soil vineyard, which was adapted to take into account the specific features of intercropped systems. Hence it includes a two-compartment representation of the soil particularly adapted to row crops. The simulation of a grass cover growth and its transpiration were added. Finally, particular importance was dedicated to the simulation of surface runoff which was the main source of the original model deviation during the winter period and made difficult multi-year simulations. Now, the model appears to be able to evaluate perennial cropping systems and provide decision support.The WaLIS model simulated the water available for both grapevine and intercrop well, and it proved to be efficient in most of the tested situations and years. The modelling of the water stress experienced by both crops was also generally good and all water fluxes simulated by the model were realistic. The main observed deviation in the simulation of the water soil content occurred during winter, i.e. outside the grapevine growth period. It was very likely due to the use of a constant parameter value for the surface runoff which did not take into account of changes in the soil surface and their effects on water infiltration.Finally, the analysis of sensitivity made on the WaLIS model showed that it is robust and sensitive to a few parameters, which drive the maximal grapevine transpiration and soil evaporation or are linked to the surface runoff simulation. The work also revealed how a good estimate of the total soil water available for each crop is crucial. This model, easy to use and parameterise, can provide sound management advice for designing valuable intercropped cropping systems.     

Land use change and soil carbon pools: evidence from a long-term silvopastoral experiment

Multi-functional silvopastoral systems provide a wide range of services to human society including the regulation of nutrients and water in soils and the sequestration of atmospheric carbon dioxide (CO₂). Although silvopastoral systems significantly contribute to enhance aboveground carbon (C) sequestration (e.g. C accumulation in woody plant biomass), their long-term effects on soil C pools are less clear. In this study we performed soil physical fractionation analyses to quantify the C pool of different aggregate fractions across three land use types including (1) silvopastoral system with ash trees (Fraxinus excelsior L.), (2) planted woodland with ash trees, and (3) permanent grassland, which were established in 1989 at Loughgall, Northern Ireland, UK. Our results show that 26 years after the conversion of permanent grassland to either silvopastoral or woodland systems, soil C (and N) stocks (0–20 cm depth) did not significantly change between the three land use types. We found, however, that permanent grassland soils were associated with significantly higher C pools (g C kg^?1 soil; P < 0.03) of the large macro-aggregate fraction (> 2 mm) whereas soil C pools of the micro-aggregate (53–250 μm) and silt and clay (< 53 μm) fractions were significantly higher in the silvopastoral and woodland systems (P < 0.05). A key finding of this study is that while tree planting on permanent grassland may not contribute to greater soil C stocks it may, in the long-term, increase the C pool of more stable (recalcitrant) soil micro-aggregate and silt and clay fractions, which could be more resilient to environmental change.     

Archaeal populations in biological soil crusts from arid lands in North America

Archaea are common and abundant members of biological soil crust communities across large-scale biogeographic provinces of arid North America. Regardless of microbial community development, archaeal populations averaged 2 × 10⁷ 16S rRNA gene copies per gram of soil, representing around 5% of the prokaryotic (total calculated bacterial and archaeal) numbers assessed by quantitative-PCR. In contrast, archaeal diversity, determined by denaturing gradient gel electrophoresis fingerprinting and clone libraries of 16S rRNA genes, was very restricted. Only six different phylotypes (all Crenarchaea) were detected, three of which were very dominant. Some phylotypes were widespread, while others were typical of Southern desert areas.     

ESBL- and plasmidic class C beta-lactamase-producing E. coli strains isolated from poultry, pig and rabbit farms

This study aims to determine the presence of extended-spectrum (ESBL) and plasmidic class C beta-lactamase-producing Enterobacteriaceae in poultry, pig and rabbit farms of Catalonia (Spain). PFGE typing showed a low clonal relationship among strains carrying these mechanisms of resistance. Ninety-three percent of them were resistant to two or more of the non-beta-lactam antimicrobials tested and harboured ESBL and plasmidic class C beta-lactamases. Greater diversity of these enzymes was found in strains from poultry farms, the CTX-M-9 family, especially CTX-M-14, with CMY-2 being the most frequent. The isolation of TEM-52 and SHV-2-producing Escherichia coli strains from these animal farms is noteworthy. In contrast, 73% of the strains from pig farms had CTX-M-1, and neither the CMY-type nor CTX-M-9 family enzyme was found. Likewise, it is the first time that CTX-M-1 and SHV-5 encoding strains have been isolated in pigs. On the other hand, in rabbit farms CTX-M-9 family was also the most frequent, being detected in three of a total of four strains. The last one showed a CMY-2, for the first time detected in these animals, too. In conclusion, commensal E. coli strains of food-producing animal farms are a reservoir of ESBL and plasmidic class C beta-lactamases.