Sequence-optimised E2 constructs from BVDV-1b and BVDV-2 for DNA immunisation in cattle

We report DNA immunisation experiments in cattle using plasmid constructs that encoded glycoprotein E2 from bovine viral diarrhoea virus (BVDV)-1 (E2.1) and BVDV-2 (E2.2). The coding sequences were optimised for efficient expression in mammalian cells. A modified leader peptide sequence from protein gD of BoHV1 was inserted upstream of the E2 coding sequences for efficient membrane export of the proteins. Recombinant E2 were efficiently expressed in COS7 cells and they presented the native viral epitopes as judged by differential recognition by antisera from cattle infected with BVDV-1 or BVDV-2. Inoculation of pooled plasmid DNA in young cattle elicited antibodies capable of neutralising viral strains representing the major circulating BVDV genotypes.     

Limits imposed by salt to the growth of the halophyte Sesuvium portulacastrum

The growth of the halophyte Sesuvium portulacastrum, commonly known as sea purslane, is impeded by NaCl only at high (600–1000 mM) concentration. Therefore, the goal of this investigation was to identify the mechanisms which set the limit of the salt resistance of S. portulacastrum. 21‐day‐old cuttings were grown for 45–50 d under split‐root conditions in which one half of the root system was immersed in complete nutrient solution supplemented with 800 mM NaCl, while the other half was immersed in a NaCl‐free medium, containing all nutrients or being deprived of potassium or calcium or nitrogen. Using this approach, we demonstrate that K⁺ and N uptake was impaired in roots exposed to NaCl. Concerning Ca²⁺, there was no indication of uptake inhibition by NaCl. However, restriction of K⁺ uptake by roots was compensated by an increase in the K⁺‐use efficiency, so that growth was not inhibited. Concerning N, our analysis shows that NO and/or NH uptake, but not their assimilation, was limited by salt treatment. Thus, we conclude that at high salinity levels, the growth of S. portulacastrum is limited by the restrictions imposed by NaCl on N uptake, perhaps in addition to inhibiting effects of excessive Na⁺ accumulation in shoot.     

The timing of inorganic fertilization of sunfish ponds

Fertilization with diammonium phosphate (20 kg/ha per application) was initiated at different dates in each of four treatments replicated three times in 0.04-ha ponds. Although there were some differences in averages of total and filtrable orthophosphate concentrations and phytoplankton abundance among treatments (P < 0.05), sunfish production was not influenced by the timing of fertilization (P > 0.05). Phytoplankton blooms did not develop in any of the treatments until late spring or early summer. The failure of phytoplankton to respond to fertilization in late winter and early spring was apparently related to low water temperature and competition by macrophytes. In larger, deeper ponds (> 0.5 ha), inorganic fertilization will cause phytoplankton blooms in early spring even when water temperatures are low.     

Experimental modification of reciprocal recurrent selection in oil palm breeding in Cameroon

Reciprocal recurrent selection (RRS) exploits the genetic complementarity of dura populations of palms with a small number of large bunches and tenera/pisifera group of palms with large number of small bunches. An extra phase was introduced to RRS just after the second cycle of selection where outstanding dura derived from (DA3D × DA5D) combinations of the second cycle were self-pollinated for seed production. Best palms based on the phenotype were selected and crossed with pisifera of second cycle offspring of LM2T. [(DA3D × DA5D) self-pollinated × LM2T self-pollinated] progenies were field tested at La Dibamba (Cameroun) from 1987 to 1997. They were precocious with regard to the three-first years’ bunch yields (13.16–15.77 t/ha). Homogeneity for all bunch yield components and homogeneity for vertical growth were illustrated by low values of the variation coefficient (5.75–7.75%). The oil yield was 107% of the control against 115% from [(DA3D × DA5D) × LM2T self-pollinated] progenies of the second cycle of RRS, mostly due to poor mesocarp to fruit and poor oil to mesocarp ratios which led to a low oil extraction rate. The extra selection phase led mainly to homogenisation of progenies but also reduced the fruit quality. However, three progenies whose average oil yield represented 115% of the control (4.87 t/ha) in addition to their precocity can be released to oil palm growers. The extension of RRS did not fully meet expectations and poses the problem of its reliability.     

Residual alkalinity as tracer to estimate the changes induced by forage cultivation in a non-saline irrigated sodic soil

Soil alkalinisation generally constitutes a major threat to irrigated agriculture in the semi-arid regions of west Africa. The improvement of sodic soils is generally difficult and expensive. However, a recent study in the Niger valley in Niger, reveals that a natural de-alkalinisation is possible under natural conditions in a semi-arid climate. Transformation of non-saline sodic soil into brown steppe soil type was recorded. On the same site, the cultivation of a Sahelian fodder grass, locally known as ‘Burgu’ was used on the sodic soil/brown steppe soil transition zone to accelerate this natural de-alkalinisation and characterise its mechanisms. The geochemical properties of both soil types were monitored before cultivation and 1 year after continuous crop cultivation. After cultivation and regular irrigation, the chemical properties of the former sodic soils were close to those of the surrounding brown steppe soils, which are better suited for agriculture. This modification of the sodic soil properties can be attributed to (i) the large amount of water supplied during cultivation that induced salt leaching. This is the main phenomenon responsible for the changes observed; (ii) the root activity that modified the acid–base equilibrium and consumes alkalinity.

The residual alkalinity (RA) concept was used to select chemical tracers of the concentration/dilution of the soil solution. Here, sodium amount and calcite+fluorite residual alkalinity (RA_{calcite+fluorite}) were the most adequate ones. These two tracers decreased proportionally under the influence of leaching, but the exchanges between cations and protons changed the RA_{calcite+fluorite}, without modifying the sodium amount. Their combined use allowed us to separate and quantify the uptake of the plant from the leaching in the de-alkalinisation process. This study highlighted that reclamation of this type of sodic soils is feasible. The use of the RA concept is advisable to design a sustainable management system for irrigated sodic or saline soils.     

Spatial analysis of soil surface hydraulic properties: Is infiltration method dependent?

The management of irrigated agricultural fields requires reliable information about soil hydraulic properties and their spatio-temporal variability. The spatial variability of saturated hydraulic conductivity, K_s and the alpha-parameter α_vG-2007 of the van Genuchten equation was reviewed on an agricultural loamy soil after a 17-year period of repeated conventional agricultural practices for tillage and planting. The Beerkan infiltration method and its algorithm BEST were used to characterize the soil through the van Genuchten and Brooks and Corey equations. Forty field measurements were made at each node of a 6 m × 7.5 m grid. The soil hydraulic properties and their spatial structure were compared to those recorded in 1990 on the same field soil, through the exponential form of the soil hydraulic conductivity given by the Gardner equation, using the Guelph Pressure Infiltrometer technique. No significant differences in the results obtained in 1990 and 2007 were observed for either particle-size distribution or dry bulk density. The mean value of α_vG-2007 was found to be identical to that of α_G-1990, while that of K_s-2007 was significantly smaller than that of K_s-1990. In contrast to the Gardner equation, the van Genuchten/Brooks and Corey expression was found to be more representative of a well-graded particle-size distribution of a loamy soil. The geostatistical analysis showed the two parameters, K_s and α_vG-2007, were autocorrelated up to about 30 and 21 m, respectively, as well as spatially positively correlated within a range of 30 m. Despite the difference in the mean values of K_s between the two studies, the spatial structures were similar to those found in the 1990 experiment except for the covariance sign. The similarity in autocorrelation ranges indicate that the spatial analysis of soil hydraulic properties is independent of the infiltration methods (i.e., measurement of an infiltration flux) used in the two studies, while the difference in the covariance sign may be linked to the use of two different techniques of soil hydraulic parameterization. The covariance values found in the 2007 campaign indicates a positive relationship between the two parameters, K_s and α_vG-2007. The spatial correlations of soil hydraulic parameters appear to be temporally stabilized, at least within the agro-pedo-climatic context of the study. This may be attributed to the soil textural properties which remain constant in time and to the structural properties which are constantly renewed by the cyclic agricultural practices. However, further experiments are needed to strengthen this result.     

Production of embryogenic tissues and regeneration of transgenic plants in cassava (Manihot esculenta Crantz)

Disorganised embryogenic tissues have been utilised as target tissues for transgene insertion and transgenic plant regeneration in cassava (Manihot esculenta). The production of friable embryogenic callus in fourteen geographically diverse cassava cultivars, from which eleven were established as embryogenic suspension cultures, is reported. Embryogenic tissues were similar in nature in all cultivars tested although there was variation in the time required to generate friable callus and the growth rates of suspension cultures. Regeneration of plants has been achieved from eight cultivars but varied significantly in efficiency, with cv. TMS 60444and Line 2 from Zimbabwe being the most responsive. Tissues from the remaining eight cultivars became arrested at globular and torpedo stages of regeneration indicating that they most likely process an inherent ability to produce plants but require further research to allow this to be realised. Significant numbers of transgenic plants containing transgenes for putative resistance to important viral diseases of cassava in addition to visual marker genes have been regenerated. Transgenic plants from three the cultivars TMS 60444, Bonoua Rouge and M.Col 1505 were recovered after particle bombardment of embryogenic suspension cultures. Correlation's have been made between abnormal leaf morphology and plant vigour with the use of embryogenic suspension cultures for transgene insertion. As an result friable embryogenic callus is now being successfully utilsed as the target tissue for genetic transformation and plant regeneration at ILTAB. This revised version was published online in July 2006 with corrections to the Cover Date.     

Double dose efficiency of the yellow rust resistance gene Yr17 in bread wheat lines

Yellow rust, caused by Puccinia striiformis f. sp. tritici, is one of the most severe wheat disease worldwide. Crop losses have ranged from 10% to 70% and up to 100% in extreme conditions. Eighty-two resistance genes, designated Yr, have been identified. Among them, Yr17 derived from Aegilops ventricosa and located on chromosome 2A has been widely used in wheat breeding. However, it had been overcome already. Through recombination of the Ae. ventricosa Yr17-carrying 6N^v chromosome with 2D of wheat, we introduced Yr17 onto chromosome 2D. Then, lines carrying Yr17 on both 2A and 2D were generated. Seedlings of the latter, as well as those carrying a single dose of Yr17 either on 2A or on 2D, were inoculated with virulent or avirulent strains on wheat seedlings. The different genotypes were fully susceptible for the two pathotypes that are virulent on Yr17. In the case of avirulent pathotypes, the Yr17 double dose lines were fully resistant, while those with the Yr17 gene only on either 2A or 2D had intermediate resistance reactions towards one or the other or both pathotypes.