Yield and nutritional requirements of cassava in response to potassium fertilizer in the second cycle

Potassium (K) is one of the most absorbed nutrients by cassava because it acts on the synthesis and starch accumulation in the storage roots. Here, we show that K application at the beginning of the second vegetative cycle of cassava submitted to shoot pruning increased the yield of roots and starch, and the nutrient demand of plants. Application of 45–89 kg ha^?1 dipotassium oxide (K₂O) in the second cycle increased the yield of storage roots and starch from 36–49% and K applied at this time had a greater effect on the synthesis and allocation of starch in the storage roots. K supply increased the accumulation of N and S by 2.0- to 3.0-fold and the accumulation of other nutrients by 1.4- to 1.7-fold. The removal of phosphorus (P), manganese (Mn), and zinc (Zn) by storage roots was not affected by K application, whereas the removal of other nutrients increased by 1.3- to 4.3-fold.     

Decontamination of synthetic solutions containing heavy metals using chemically modified sawdusts bearing polyacrylic acid chains

New materials containing carboxylate groups have been synthesized by grafting polyacrylic acid onto sawdust. These new adsorbents were subjected to continuous extraction of different metal ions using packed columns to determine their maximum binding capacities. They exhibit binding capacities 15–40 times higher than unmodified sawdusts for removal of Cu²⁺, Ni²⁺, and Cd²⁺ chosen as representative heavy metal ions. Cation desorption and adsorbent regeneration could be effected by elution with a diluted HCl solution; water as an eluent has no effect on metal desorption.     

Identification of <Emphasis Type="Italic">Ditylenchus</Emphasis> species associated with Fabaceae seeds based on a specific polymerase chain reaction of ribosomal DNA-ITS regions

A technique based on the use of specific primers for polymerase chain reaction (PCR) was developed for the identification of the stem and bulb nematode belonging to the Ditylenchus dipsaci species complex. The internal transcribed spacer region ITS1 and ITS2, the gene 5.8 S and part of genes 18 S and 26 S of twenty populations of the D. dipsaci species complex belonging to both D. dipsaci sensu stricto and Ditylenchus sp. B (corresponding to populations of giant individuals associated to Vicia faba) and three congeneric species were amplified with two universal ribosomal primers. PCR-amplified DNA samples were digested with five restriction enzymes in order to reveal some polymorphism allowing the identification of D. dipsaci populations associated with Fabaceae seeds. The polymorphism among species was confirmed by the sequencing of the PCR products. A primer (DdpS2) was designed in a region conserved in all populations of both D. dipsaci sensu stricto and D. sp. B studied in the present work. The other Anguinidae species (except a few species from Central Asia associated to Astereaceae and D. sp. G associated to Plantago maritima) differ in two to four nucleotides at the 3′ extremity of this region. This sequence portion coincides with a TspEI restriction site. In combination with a primer located in the ribosomal region, this first primer is a good candidate for identification by PCR of populations of the D. dipsaci species complex found in Fabaceae seeds. A second primer (DdpS1) was designed in a similar way and was specific to D. dipsaci sensu stricto. The utility of these two sets of primers is discussed against the background of quarantine regulation.     

Experimental study on the toxicity of imidacloprid given in syrup to honey bee (Apis mellifera) colonies

Two groups of eight honey bee colonies were fed with two different concentrations of imidacloprid in saccharose syrup during summer (each colony was given 1 litre of saccharose syrup containing 0.5 microg litre(-1) or 5 microg litre(-1) of imidacloprid on 13 occasions). Their development and survival were followed in parallel with control hives (unfed or fed with saccharose syrup) until the end of the following winter. The parameters followed were: adult bee activity (number of bee entering the hive and pollen carrying activity), adult bee population level, capped brood area, frequency of parasitic and other diseases, mortality, number of frames with brood after wintering and a global score of colonies after wintering. The only parameters linked to feeding with imidacloprid-supplemented saccharose syrup when compared with feeding with non-supplemented syrup were: a statistically non-significant higher activity index of adult bees, a significantly higher frequency of pollen carrying during the feeding period and a larger number of capped brood cells. When imidacloprid was no longer applied, activity and pollen carrying were re-established at a similar level for all groups. Repeated feeding with syrup supplemented with imidacloprid did not provoke any immediate or any delayed mortality before, during or following the next winter, whereas such severe effects are described by several French bee keepers as a consequence of imidacloprid use for seed dressing in neighbouring cultures. In any case, during the whole study, mortality was very low in all groups, with no difference between imidacloprid-fed and control colonies. Further research should now address several hypotheses: the troubles described by bee keepers have causes other than imidacloprid; if such troubles are really due to this insecticide, they may only be observed either when bees consume contaminated pollen, when no other sources of food are available, in the presence of synergic factors (that still need to be identified), with some particular races of bees or when colonies are not strong and healthy.     

Prediction and Mapping of the Impact of Winter Temperature on the Development of Phytophthora cinnamomi-Induced Cankers on Red and Pedunculate Oak in France

ABSTRACT Phytophthora cinnamomi is the causal agent of a perennial canker that develops on the lower bole on northern red oak and pedunculate oak. The disease has a limited range in Europe, being reported only in southwest France. This limited distribution is probably linked to the susceptibility of P. cinnamomi to frost. A model was developed in previous work to estimate the impact of temperatures of <0 degrees C on the winter survival of P. cinnamomi in trunk cortical tissues and on the subsequent development of cankers. In this article, we report the use of this model to simulate canker development in 503 locations across France during a 30-year period. The predicted canker extension decreased sharply when the median P. cinnamomi winter survival index decreased from 0.95 to 0.65, with cankers that poorly developed when the median survival index was lower than 0.5 to 0.6. The actual incidence of the disease in 192 stands located across southwest France was compared with that of the model outputs. Both presence of disease in stands and frequency of cankered trees in infected stands, but not canker size on infected trees, were strongly related to the median P. cinnamomi survival index. No disease was present in stands with median survival index lower than 0.65, and the frequency of cankered trees in infected stands remained very low in stands with a median survival index between 0.65 and 0.70. Aspect was an additional factor explaining disease incidence, while the effect of elevation was likely due to its effect on winter temperatures. Maps of winter suitability to P. cinnamomi-induced cankers on oaks in France are presented.     

Proteolytic Activity in California Halibut Larvae (Paralichthys californicus)

The digestive tract of many marine fish larvae undergoes numerous morphological and functional changes during ontogeny that can substantially influence larval survival under culture conditions. Increasing our knowledge of the digestive capacity and nutritional requirements of the larvae of new candidate species for aquaculture will aid in the development of optimal feeding protocols and greatly improve production under hatchery conditions. In this study, we assess the proteolytic capacity of California halibut (Paralichthys californicus) larvae using biochemical and histological analyses. Newly hatched larvae were reared in a semiclosed recirculating system and fed with highly unsaturated fatty acid (HUFA)–enriched rotifers from hatching until 19 d posthatch (dph) and HUFA‐enriched Artemia nauplii thereafter. Total and specific activity of trypsin and leucine‐aminopeptidase (LAP) and acid and alkaline protease activities were assessed throughout development using spectrophotometric techniques. Trypsin‐like activity and LAP and alkaline protease activities were detected shortly after hatching and before the opening of the mouth. Acid protease activity was not detected until 36–40 dph, concomitant with the development of the gastric glands. The specific activity of trypsin and LAP showed two distinct peaks at 8 and 20 dph. The second peak coincided with the shift from rotifers to Artemia. Hence, newly hatched California halibut larvae possess alkaline proteolytic activity before first feeding. Based on the digestive capacity evaluated in this study and the timing of the development of the functional stomach, we propose that California halibut can be adequately weaned to formulated microdiets around 36 dph.     

Variability of hydrolysis of β-, αs1-, and αs2-caseins by 10 strains of Streptococcus thermophilus and resulting bioactive peptides

Milk proteins contain numerous potential bioactive peptides, which may be released by digestive proteases or by the proteolytic system of lactic acid bacteria during food processing. The capacity of Streptococcus thermophilus to generate peptides, especially bioactive peptides, from bovine caseins was investigated. Strains expressing various levels of the cell envelope proteinase, PrtS, were incubated with α(s1)-, α(s2)-, or β-casein. Analysis of the supernatants by LC-ESI-MS/MS showed that the β-casein was preferentially hydrolyzed, followed by α(s2)-casein and then α(s1)-casein. Numbers and types of peptides released were strain-dependent. Hydrolysis appeared to be linked with the accessibility of different casein regions by protease. Analysis of bonds hydrolyzed in the region 1-23 of α(s1)-casein suggests that PrtS is at least in part responsible for the peptide production. Finally, among the generated peptides, 13 peptides from β-casein, 5 from α(s2)-casein, and 2 from α(s1)-casein have been reported as bioactive, 15 of them being angiotensin-converting enzyme inhibitors.     

Banning of methyl bromide for seed treatment: could Ditylenchus dipsaci again become a major threat to alfalfa production in Europe?

In Europe, the stem and bulb nematode Ditylenchus dipsaci has been listed as a quarantine pest by EPPO: without any control, it may cause complete failure of alfalfa crops. Movement of nematodes associated with seeds is considered to be the highest‐risk pathway for the spread of this pest. Since the 2010 official withdrawal of methyl bromide in Europe, and in the absence of any alternative chemical, fumigation of contaminated seed batches is no longer possible, which makes the production of nematode‐free alfalfa seeds difficult to achieve and leads to unmarketable seed batches. Thermotherapy is being considered as a realistic alternative strategy, but its efficiency still remains to be validated. The combination of the currently available methods (i.e. use of resistant cultivars, seed production according to a certification scheme, mechanical sieving, seed batch inspection) could significantly reduce the likelihood of seed contamination. However, it does not guarantee a total eradication of the nematode. Although it is already widely distributed all over Europe, reclassification of D. dipsaci as a regulated non‐quarantine pest to reduce the possibility of further introductions and the rate of spread of this pest appears to be a risky strategy because of the lack of up‐to‐date documented data to evaluate damage thresholds and determine acceptable tolerance levels. [[ArtCopyrightmsg]]