Contribution of Fish Production to Farmers’ Subjective Well‐being in Vietnam – A Logistic Model

There is a growing awareness of the importance of food fish production on human nutrition, employment, poverty, and recreation. However, the role of aquaculture in livelihoods of fish farmers has not been considered rigorously. With 120 farmers interviewed in a field survey and a cumulative logistic model, this study identifies some determinants of subjective well‐being of small‐scale fish farmers in Vietnam and examines the role of earnings from fish production in generating their happiness. The results confirm that the farmers receive satisfaction from their farm working. Subjective well‐being of the farmers increases with their job satisfaction and cash earnings from fish farming. A doubling in cash returns from fish culture relative to household income raises a farmer’s happiness probability by an estimated 10.6%. Education also affects farmers’ life satisfaction. For better educated farmers, when their satisfaction from fish culture increases by one level, happiness probability is estimated to increase by 0.23%. Wild fish plays an important role in Vietnamese farmers as a doubling in relative income from wild fish captures raises their estimated probability of happiness by 139%.     

Soil physicochemical properties in a high-quality tea production area of Thai Nguyen province in northern region,Vietnam

This study investigated general physicochemical properties of tea garden soils at the alluvial plain of Cong River in Tan Cuong commune, Vietnam. Four gardens were selected as study sites on three transect lines established perpendicularly to the river. Soil samples were collected from the surface (0–10 cm) and subsurface (20–30 cm). Soil texture classes varied from sandy loam to light clay, which was affected by different terrains along the transect lines as well as severe disturbance such as terracing and earth excavation. The levels of total C and total N were correlated with increasing garden age, suggesting the replenishment of soil organic matter pool by the addition of plant residue and manure. Meanwhile, the soils showed strongly acidic nature with the average pH(H₂O) of 3.7 at the surface and 3.9 at the subsurface. The effective cation exchange capacity (ECEC) was low at 4.7 and 4.9 cmol_c kg^?1, respectively, and dominated by exchangeable Al³⁺. Soil acidification was exacerbated with increasing garden age. However, a relatively large saturation of exchangeable calcium (Ca²⁺), potassium (K⁺), and magnesium (Mg²⁺) on the ECEC was found in the surface soils. The levels of available P were high, occasionally exceeding 1000 and 500 mg kg^?1 at the surface and subsurface, respectively. In spite of strongly acidic condition, ammonium (NH₄-N) applied as fertilizer was converted to nitrate (NO₃-N) to move down to deeper layers. The levels of the bases, P, and mineral N seem to be principally determined by management practices. Significant portion of these nutrients was likely to exist in water soluble forms without adsorption onto soils. It should be required to develop proper schemes and to educate the owners for adequate fertilizer managements.     

Resistance to Taiwanese race 1 strains of Ralstonia solanacearum in wild tomato germplasm

A total of 252 wild Solanum accessions and one population of 49 introgression lines of LA716 were screened for resistance to a race 1/biovar 4/phylotype I strain Pss186 of Ralstonia solanacearum. Most wild tomato accessions were highly susceptible. However, five accessions of S. pennellii, i.e. LA1943, LA716, LA1656, LA1732 and TL01845 were resistant to strain Pss186. These accessions were then challenged against two other race 1/phylotpye I strains Pss4 and Pss190, which were more aggressive. All the five S. pennellii accessions were susceptible to Pss4, but displayed high to moderate resistance to Pss190 with a percentage of wilted plants ranging from 0% to 60%. Pss190 is an aggressive strain that made a resistant tomato line Hawaii 7996 susceptible. Thus, the results found in this study provide evidence of the presence of strain-specific resistance. LA3501, which has an introgression segment on chromosome 6, was found to be resistant to Pss186 among the screened introgression lines. This confirms the importance of resistance trait loci on chromosome 6 that have been identified by other studies. This is the first report of S. pennellii being resistant to bacterial wilt. These new resistant sources will provide breeders with more resources to breed for stable resistance to bacterial wilt of tomato.     

Utilization of fermented soybean meal for fishmeal substitution in diets of Pacific white shrimp (Litopenaeus vannamei)

Two feeding experiments were carried out to evaluate the utilization of fermented soybean meal (FSBM) in diets for Pacific white shrimp (Litopenaeus vannamei). The digestibility experiment was assessed with four diets: a reference diet and three ingredient test diets containing FSBM, local and Chilean fishmeal. The growth experiment was conducted including four isonitrogenous and isocaloric diets formulated to contain the graded levels of dietary fishmeal (0 g/kg, 150 g/kg, 300 g/kg and 450 g/kg) substituted by FSBM. The results indicated that ADCs of crude protein in FSBM were high (888.4 g/kg) and equal in local fishmeal but little lower than Chilean fishmeal while without any significant differences observed in ADCs of crude lipid among the different test ingredients. After 75 days of growth trial, survival rates and feed conversion ratio were not significantly different among the experimental treatments. However, shrimp fed the diets with increasing inclusions of FSBM had a tendency to reduce weight gain and specific growth rate. Based on the correlation between weight gain and substituted fishmeal level analysed by broken‐line regression, the optimum level of fishmeal replaced by FSBM in diet was 253.6 g/kg without adverse effects on growth and feed utilization of Pacific white shrimp.     

Population dynamics and pathogenic races of rice blast fungus, <Emphasis Type="Italic">Magnaporthe oryzae</Emphasis> in the Mekong Delta in Vietnam

In a study of the population dynamics of Magnaporthe oryzae in the Mekong Delta in Vietnam, 226 isolates were collected from various sites in December 2001, September and December 2004. The pathogenic races of isolates were determined using international differential rice varieties. Isolates with the same race number were not found, not even in the same field or on the same seedling, suggesting that the fungus in the Mekong Delta was dynamically changing. But focusing on the known major resistance genes in the Japanese differential varieties, some isolates in the area were found to be the same race. Phylogenetic analyses based on the transposable elements Pot2 and MGR586 in the genomes supported that the pathogenic races were critically variable in comparison with the genomic diversity. Isolates with MAT1-1 predominated in the Mekong Delta, but in some provinces those with MAT1-2 coexisted at low frequency with MAT1-1. However, no isolates produced perithecia and ascospores. Isolates in the Mekong Delta probably had hot spots in their genomes that are easily altered and associated with some avirulence genes.     

Photoprotection for deltamethrin using chitosan-coated beeswax solid lipid nanoparticles

BACKGROUND: In the natural environment, photodegradation is one of the most common degradative processes of pesticides. In order to reduce the photodegradation of pesticides, and so increase their killing activity against target pests, chitosan‐coated beeswax solid lipid nanoparticles (CH‐BSLNs) were prepared by a combination of hot homogenization and sonication, with deltamethrin as an active ingredient. RESULTS: Under optimal conditions, the highest encapsulation efficiency (95%) and a high payload of deltamethrin (approximately 12.5%) were achieved. In direct photolysis, in the case of CH‐BSLNs after UV irradiation for 24 h, 37.3% of deltamethrin remained, as opposed to only 14.6% of the free‐form deltamethrin. In addition, in indirect photolysis, in the case of CH‐BSLNs after UV irradiation for 2 h in 2% acetone solution, approximately 74.5% of deltamethrin remained, as opposed to only 37.6% of the free‐form deltamethrin. CONCLUSION: CH‐BSLNs showed good protection for deltamethrin against photodegradation. This novel nanocarrier may be useful in crop protection as an economical strategy to enhance the effect of pesticides in the field and protect the environment as well. Copyright © 2012 Society of Chemical Industry     

Knowledge of Rabies Prevention in Vietnamese Public Health and Animal Health Workers

Rabies is an invariably fatal, but preventable zoonotic disease. Despite a national programme for its prevention and control, the number of rabies associated deaths in Vietnam has increased in recent years. A cross‐sectional survey was undertaken in 2012 to assess and compare the knowledge, awareness and practices of 189 public health workers (PHW) and animal health workers (AHW) attending a joint training course for professionals from provinces in northern Vietnam with the highest number of deaths from rabies. Questionnaires facilitating self‐evaluation were provided, and total knowledge scores were calculated (maximum 38 points) and categorized into: ‘high’ (>30 points), ‘moderate’ (21–30) and ‘low’ (<21). The response rate was 100%, and among the 189 participants, 56% were PHW compared to 44% who were AHW. Although most respondents knew rabies could be transmitted through the bite of an animal, most commonly a dog, and that rabies is a preventable disease, significant differences between groups were identified. Major areas included poor knowledge of common rabies reservoirs, wound management and guidance on post‐exposure prophylaxis. Overall, the total mean knowledge scores for PHW was significantly higher (P = 0.011) compared to those for AHW, but both scores fell within the ‘moderate’ knowledge range. However, proportionately more PHW than AHW achieved ‘high’ knowledge scores (P = 0.0098). To our knowledge this is the first published study to simultaneously assess the knowledge and awareness of animal health and public health professionals attending joint training activities aimed at strengthening rabies prevention and control. To ensure effective prevention and control of rabies requires that AHW and PHW not only coordinate and collaborate, but have a common knowledge and understanding of rabies prevention and control measures. This study provides important baseline data in a relatively unexplored area of research that can focus future interventions and research.     

Biostimulant effects of Bacillus strains on wheat from in vitro towards field conditions are modulated by nitrogen supply

Bacillus velezensis strains, belonging to plant growth‐promoting rhizobacteria (PGPR), are increasingly used as microbial biostimulant. However, their field application to winter wheat under temperate climate remains poorly documented. Therefore, three B. velezensis strains IT45, FZB24 and FZB42 were tested for their efficacy under these conditions. Two biological interaction systems were firstly developed under gnotobiotic and greenhouse conditions combined with sterile or non‐sterile soil, respectively, and finally assayed in the field during two years coupled with different N fertilization rates. Under gnotobiotic conditions, all three strains significantly increased root growth of 14 d‐old spring and winter wheat seedlings. In the greenhouse using non‐sterile soil, only FZB24 significantly increased root biomass of spring wheat (+31%). The three strains were able to improve nutrient uptake of the spring wheat grown in the greenhouse, particularly for the micronutrients Fe, Mn, Zn, and Cu, but the observed increases in nutrient uptake were dependent on the organs and the elements. The root biomass increases in inoculated plants coincided with lowered nutrient concentrations of P and K. In 2014, under field conditions and absence of any N fertilizer supply, FZB24 significantly increased grain yields by 983 kg ha^?1, or 14.9%, in relation to non‐inoculated controls. The three strains in the 2015 field trial failed to confirm the previous positive results, likely due to the low temperatures occurring during and after inoculations. The Zeleny sedimentation value, indicative of flour quality, was unaffected by the inoculants. The results are discussed in the perspective of bacterial application to wheat under temperate agricultural practices.     

Phosphite (phosphorous acid): Fungicide, fertilizer or bio-stimulator?

Phosphite (     ; Phi), a reduced form of phosphate (     ; Pi), is widely marketed as either a fungicide or fertilizer or sometimes as a biostimulant. This is confusing for both distributors and growers. The present paper explores data from various studies to clarify that Phi does not provide plant P nutrition and thus cannot complement or substitute Pi at any rate. In addition, Phi itself does not have any beneficial effect on the growth of healthy plants, regardless of whether it is applied alone or in combination with Pi at different ratios or different rates. The effect of Phi on plants is not consistent, but is strongly dependent on the Pi status of the plants. In most cases, the deleterious effect of Phi is evident in Pi-starved, but not Pi-sufficient, plants. Plants fertilized with Pi allowing for approximately 80–90% of its maximum growth might still be at risk of the effect. This negative effect becomes more pronounced under more seriously Pi-deficient conditions. Although a number of studies have shown positive crop responses to Phi, these responses are likely to be attributable to the suppression of plant diseases by Phi and/or to Pi formed from oxidation of Phi by microbes. In addition, indirectly providing P by Phi-to-Pi oxidation is not an effective means of supplying P to plants compared with Pi fertilizer. An understanding of these issues will aid the right selection of fertilizer as well as minimize the harmful effects of Phi use on crops.     

Combined effects of a simulated marine heatwave and an algal toxin on a tropical marine aquaculture fish cobia (Rachycentron canadum)

Ongoing global warming is one of the major challenges for the development of aquaculture in the tropical regions where species are already cultured in the water temperature close to their upper physiological thresholds. Furthermore, warming can trigger blooms of toxic algae, yet we do not know how extreme warming such as a marine heatwave (MHW) and algal toxins may affect marine aquaculture species. To address this issue, we investigated the effects of a simulated MHW in combination with exposure to trans‐4‐trans‐decadienal (PUA), a diatom‐derived toxin, on survival, growth, development and biochemical composition of cobia larvae and juveniles. Cobia larvae were exposed for 48 hr to one of two temperatures (29 vs. 34°C) and two PUA treatments (0 vs. 0.5 µM). Surviving larvae from each treatment were divided into two subsets: three replicates were used for the feeding test and five replicates were used for the recovery test in a non‐contaminated environment at the respective temperatures of 29 or 34°C. Survival of cobia larvae was reduced by 16% in either MHW or PUA, but it dropped by 60% when both stressors were present, indicating a synergistic effect. MHW, but not PUA, reduced the feeding of cobia larvae. PUA had no delayed effects on growth rate and biochemical composition of the fish. MHW strongly reduced specific growth rate, body protein and lipid contents in cobia. Our results provide the first empirical evidence of how MHW and toxic algae may interact and challenge cobia and marine aquaculture production in tropical countries.