Evaluation of egg quality in broodstock cobia Rachycentron canadum L.

Twenty egg batches spawned naturally from 17 different females over two spawning seasons were used to evaluate the egg quality of cobia Rachycentron canadum. A reduction in egg size was observed towards the end of the spawning season for both years. The proportion of floating eggs demonstrated a positive linear relationship with both yolk‐sac larval survival (r²=0.91, P<0.05) and batch larval production (r²=0.80, P<0.01). Viable egg batches (i.e. fertilization success >50%) were of higher batch fecundity, had larger eggs and a higher proportion of floating eggs than non‐viable batches (i.e. 0% fertilization success). Also, biochemical analyses revealed that these viable eggs had significantly higher protein and amino acid contents. A multiple regression model based on the proportion of floating eggs, batch fecundity and fertilization success provided the most accurate predictions of batch larval production (r²=0.95, P<0.001). Similarly, using the egg content of arginine/glycine and methionine significantly increased the correlation coefficient in the multiple regression model predicting larval deformity (r²=0.92, P=0.002). This study reveals that accurate determination of egg quality in cobia can be improved using a combination of several variables rather than a single variable.     

Inoculant plant growth-promoting microorganisms enhance utilisation of urea-N and grain yield of paddy rice in southern Vietnam

Field experiments were conducted during successive rainy seasons in 2006 in the Chau Thanh district of southern Vietnam to evaluate the effects of an inoculant plant growth promoter product called “BioGro” and N fertiliser rates on yield and N and P nutrition of rice. The results indicated that inoculation with BioGro, containing a pseudomonad, two bacilli and a soil yeast, significantly increased grain and straw yields and total N uptake in both seasons, as well as grain quality in terms of percentage N. Nitrogen fertilisation increased grain and straw yields as well as total N and P uptakes significantly in both cropping seasons. The estimated grain yield response to added N was quadratic in nature with and without added BioGro. In the first crop, BioGro out-yielded the control up to 90 kg urea N ha^?1 whilst in the second season the beneficial effect of BioGro was observed up to 120 kg urea N ha^?1, indicating either an interaction of the inoculant with higher yielding seasonal conditions or a cumulative effect of BioGro application. In the first season, the estimated N rate for maximum grain yield was 103 kg N ha^?1 with BioGro while it was 143 kg N ha^?1 without BioGro. The maximum estimated grain yields were 3.21 and 3.18 t ha^?1 with and without BioGro, respectively. This information indicates that BioGro was able to save 40 kg N ha^?1 with an additional rice yield of 30 kg ha^?1 in the season. In the second rainy season, the estimated N rates for maximum grain yields were 94 and 97 kg N ha^?1 with and without BioGro, respectively. The estimated maximum grain yields were 3.49 and 3.25 t ha^?1 with and without BioGro, respectively. The two seasons’ combined results indicate that application of BioGro improved the efficiency of N use by rice significantly, saving 43 kg N ha^?1 with an additional rice yield of 270 kg ha^?1 in two consecutive seasons at the experimental site. The extra efficiency was shown by the fact that the same yield of rice was obtained with about 40 and 60 kg less fertiliser-N that the maximum yields with urea alone in the two successive harvests on the same plots.     

A Natural Forest of Commercial Timber Species: Logging or Not Logging

Most tropical forests outside protected areas have been or will be selectively logged because the timber industry is a main income-generating resource for many developing countries. Therefore, understanding the composition of commercial timber species and logging types is key for sustainable forest management in countries like Vietnam as they move toward fulfilling Reducing Emissions from Deforestation and Forest Degradation (REDD+) agreements. Seven 1-ha plots were surveyed in the Central Highland of Vietnam, and 18 commercial tree species from these plots, whose timber is widely used by local people for housing and furniture making and timber is easily sold at local markets for high prices, were analyzed. In total, 151 tree species with a diameter at breast height (DBH) of ≥?10 cm were recorded. The 18 commercially valuable species assessed in this study accounted for 33.2% of all stems (total of 524 stems ha^?1 for all species), 47.1% of basal area (total of 34.35 m² ha^?1 for all species), and 50.8% of aboveground biomass/AGB (total of 262.68 Mg ha^?1 for all species). Practicing diameter-limit harvesting of all commercially valuable species with DBH of ≥?40 cm, which is widely performed in Vietnam, will reduce the number of stems by 7%, basal area by 31.6%, and AGB by 38.2%. Because such harvesting practices cause severe ecological impacts on the remaining forest, logged forests may require >?40 years to recover the structure status of a pre-logged forest. In addition, the recovery of the 18 commercially valuable species may require a much longer time because they comprised 33.2% of stems. Permission for logging natural forests should be given in Vietnam to sustain lives of local communities, where logging has been prohibited. However, alternative harvesting systems, such as reduced-impact logging systems, should be considered. The systems selected must simultaneously generate economic returns for local people and respect the REDD+ agreements with regard to protecting biodiversity and reducing carbon emissions.     

Assessment of enrichment planting of teak (Tectona grandis) in degraded dry deciduous dipterocarp forest in the Central Highlands,Vietnam

After years of unsustainable logging, dry deciduous dipterocarp forest (DDDF) has become poor in timber stocks and has been converted to industrial crops such as rubber. The objectives of this study were to assess teak (Tectona grandis L.f.) tree establishment under degraded DDDF conditions and to determine factors that influence the suitability of teak as a forest enrichment tree species. A set of 64 experimental plots of 4 900 m² each was set up and observed for 4–5 years for testing enrichment planting with teak under various combinations of two groups of factors: ecological conditions and forest status. Weighted, non-linear, multivariate regression models were used to detect key factors that influenced the suitability of teak. The results showed that at the age of 4 years the average dominant tree height (defined as 20% of the tallest trees in the experimental plot) reached 11.2, 7.8, 5.3 and 3.8 m for very good, good, average and poor suitability levels, respectively. Survival rates of planted teak from average to very good suitability levels were over 90%. Six key factors that affected the suitability of teak were waterlogging during the rainy season, altitude, stand volume of the degraded DDDF, soil type, percentage of sand and concentration of P₂O₅ in the soil. Under the extreme ecological and environmental conditions of the DDDF, enrichment planting with teak gave promising results.     

Infection process of Phoma koolunga on stem and leaf tissue of resistant and susceptible field pea (Pisum sativum)

This study investigates the infection process of Phoma koolunga on field pea (Pisum sativum) stems and leaves using different susceptible and resistant pea genotypes for each tissue, viz. 05P778‐BSR‐701 (resistant) and 06P830‐(F5)‐BSR‐5 (susceptible) for stems and ATC 866 (resistant) and ATC 5347 (susceptible) for leaves. On both resistant and susceptible genotypes, light and scanning electron microscopy showed P. koolunga conidia infect stem and leaf tissues directly via appressoria or stomatal penetration, but with more infections involving formation of appressoria on stems than on leaves. On leaves of the resistant genotype, at 72 h post‐inoculation, P. koolunga penetrated more frequently via stomata (5.2 conidia per 36 893 μm²) than by formation of appressoria (1.8 conidia); yet no such difference was observed on stems of the resistant genotype. In contrast, at the same time point, the number of conidia infecting the susceptible genotype by formation of appressoria on either stems (135 conidia) or leaves (11.3 conidia) was significantly greater than via stomata (8 and 7.3 conidia, stems and leaves, respectively). Mean germ tube length of germinating P. koolunga conidia on both stems (29.8 μm) and leaves (32.9 μm) of the resistant genotype was less than on the susceptible genotype (40.5 and 63.7 μm, stem and leaves, respectively). In addition, there were differences in the number of germ tubes emerging from conidia on resistant and susceptible genotypes. These are the first insights into the nature of leaf and stem resistance mechanisms operating in field pea against P. koolunga.     

High soil Mn and Al,as well as low leaf P concentration,may explain for low natural rubber productivity on a tropical acid soil in Vietnam

The aim of the current study was to identify major soil and leaf factors accounting for low natural rubber (NR, Hevea brasiliensis) productivity on tropical acid Acrisols in Vietnam. Twenty NR plots were measured with NR productivity, leaf factors (N, P, K, Ca, Mg, Mn, Cu, Fe, and Zn), soil factors (pH, particle size distribution, total C, N, P, K, exchangeable K, Ca, Mg, Al, Mn, Fe, Zn, available P). Cluster analysis showed that NR productivity could be separated into three clusters with low (23.2), medium (38.2), and high (61.3 g tree^?1 harvest^?1) yield. High-yield cluster had higher leaf P concentration and soil pH, while low-yield cluster had higher leaf Mn, soil exchangeable Al, and Mn concentration. Simple and multiple linear regression analysis applied with backward elimination procedure suggested that leaf and soil toxic concentration may be responsible for low NR productivity in the study soil.     

Land-use impacts on surface runoff and soil detachment within agricultural sloping lands in Northern Vietnam

Two consecutive years of investigation on soil surface features, surface runoff and soil detachment within 1-m² microplots on 40% slope highlighted the effects of land-use change, vegetation cover and biological activity on the water pathways in Northern Vietnam. Three replicate plots were set up on each of five land-uses: cassava (CAS), grass fodder of Bracharia ruziziensis (BRA), a 3-year old fallow (FAL), tree stands of Acacia mangium and Venicia montana (FOR), and a fallow with regrowth of Eucalyptus regularly cut (EUC). The second year, two of the microplots under FAL and EUC were treated with herbicide (FALh, EUCh), one of them was burnt (FALh+b, EUCh+b). The highest yearly surface runoff coefficient of 16%, and soil detachment rate of 700 g m^− 2 yr^− 1 in average with a maximum of 1305 g m^− 2 yr^− 1 have been recorded under CAS. On FALh and FALh+b, runoff ratios were 8.7 and 13.5%, respectively and detachment rates were 86 and 389 g m^− 2. On FAL and BRA the yearly runoff ratio varied from 5.9 to 9.8% but the detachment rate was limited at 24 to 35 g m^− 2. FOR and EUC annual runoff was ≤ 3.1% and annual soil detachment ≤ 71 g m^− 2. These values were very low compared to the values reported on steep slopes in Laos within similar climate and vegetation cover.The runoff and detachment rates underlined the importance of rainfall intensities, soil physical properties, soil surface features, soil vegetation cover and biological activity. The annual surface runoff was highly correlated to the soil surface crusting. CAS and BRA plots were prone to crusting especially after weeding at the onset of the rainy season, when the soil surface was still uncovered. Soil bioturbation (earthworm casting activity) was the second factor that explains local variation of surface runoff and soil detachment. The continuous production of earthworms casts on soil surface, especially on FOR and EUC microplots, induced a marked surface roughness and reduced the surface runoff. The production of casts was very limited in FAL and completely absent in CAS microplots. So it is evident that our results confirm the deleterious effects of cassava on soil and water conservation.     

Incorporation of rice straw mitigates CH4 and N2O emissions in water saving paddy fields of Central Vietnam

This study evaluated the effects of rice straw and water regimes on CH₄ and N₂O emissions from paddy fields for two rice growing seasons (summer 2014 and spring 2015). Water regimes included alternating wet–dry irrigation (AWD) maintained at three levels (–5 cm, – 10 cm and –15 cm) in comparison to continuous flooding irrigation (CF). Rice straw (5 t ha^–1) was incorporated into the top soil (0 – 15 cm), distributed and burned in situ. Results showed that using burned in situ rice straw was found to reduce seasonal cumulative CH₄ emission (24–34% in summer; 18–28% in spring), N₂O emission (21–32% in summer; 22–29% in spring) and lower rice yield (8–9%) than rice straw incorporation into top soil. AWD methods reduced the amount of CH₄ production (22.6–41.5%) and increased N₂O emission (25–26%) without any decrease in rice yield. Rice straw incorporation into the top soil with AWD had higher water productivity (23–37%) than rice straw when burned in situ with CF. The results conclude that AWD and rice straw management can be employed as mitigation strategy for CH₄ and N₂O emissions from paddy fields in Central Vietnam.     

Detection of radiation-induced apoptosis using the comet assay

The electrophoresis pattern of apoptotic cells detected by the comet assay has a characteristic small head and spread tail. This image has been referred to as an apoptotic comet, but it has not been previously proven to be apoptotic cells by any direct method. In order to identify this image obtained by the comet assay as corresponding to an apoptotic cell, the frequency of appearance of apoptosis was examined using CHO-K1 and L5178Y cells which were exposed to gamma irradiation. As a method for detecting apoptosis, the terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay was used. When the frequency of appearance of apoptotic cells following gamma irradiation was observed over a period of time, there was a significant increase in appearance of apoptosis when using the TUNEL assay. However, there was only a slight increase when using the comet assay. In order to verify the low frequency of appearance of apoptosis when using the comet assay, we attempted to use the TUNEL assay to stain the apoptotic comets detected in the comet assay. The apoptotic comets were TUNEL positive and the normal comets were TUNEL negative. This indicates that the apoptotic comets were formed from DNA fragments with 3'-hydroxy ends that are generated as cells undergo apoptosis. Therefore, it was understood that the characteristic pattern of apoptotic comets detected by the comet assay corresponds to cells undergoing apoptosis.