A genome‐wide association study for partial resistance to southern corn rust in tropical maize

Southern corn rust (SCR) is a fungal disease found on corn in several countries worldwide. In Brazil, the disease can result in productivity losses of 65%, especially in areas with a history of the disease. In this study, the genetic architecture and identification of genomic regions associated with SCR resistance was investigated by performing a genome‐wide association study. Genotyping‐by‐sequencing was performed to carry out the association between single nucleotide polymorphism (SNP) markers and phenotypic data from two environments on a panel of 164 maize inbred lines. Eight SNPs were identified as significant for SCR resistance. These SNPs were colocalized with QTL regions, some of which underlie candidate resistance genes with functions that play an important role in the stress response during pathogen recognition. These candidate genes, involved in plant defense pathways, could be associated with partial resistance to SCR and provide a partial comprehensive insight into the genetic architecture of this trait. After validation of the SNPs, they will be useful for marker–assisted selection and for a better understanding of maize resistance to SCR.     

Advances in hatchery and grow-out technology of cobia Rachycentron canadum (Linnaeus)

This paper describes advances in hatchery and grow‐out technology of cobia (Rachycentron canadum, Linnaeus). In 2007, methods for capture, transport, acclimation, sampling, conditioned spawning, larval rearing, fingerling production, nursery, shipping and grow‐out have been perfected. Survival rates ranging from 17.5% to 35% were achieved from egg to shipping size fingerlings (1.0 g) in 2007 at the University of Miami Experimental Fish Hatchery, with production of approximately 20 000 fingerlings per 12 000 L tank. Wild and F1 broodstock cobia have been conditioned to spawn through temperature manipulation producing viable eggs for experimental and production level larval rearing trials in several hatcheries. Brood fish have also been induced to spawn using hormones. Cobia appear to be susceptible to infestations by parasitic protozoa such as Amyloodinium ocellatum and to infections caused by deleterious bacteria such as Photobacterium spp. and Vibrio spp. Prophylactic methods used to prevent and control epizootic diseases at the hatchery are summarized. Improved techniques for cage management were implemented, and both novel designs of submerged cages deployed in exposed areas and traditional gravity cages in protected areas have been used for commercial ongrowing of cobia in the Americas and the Caribbean region.     

Real‐time measurement of protein leaching from micro‐particulate larval fish feeds

The small size and high surface area to volume ratio of larval fish feed presents challenges for nutrient retention in micro‐particulate diets. A method for the accurate and rapid measurement of nutrient retention or loss from micro‐particulate feed in water is needed to help develop micro‐particulate feeds with good nutrient retention characteristics. The present study developed and validated an instrument method using fibre optic technology that measures protein leaching in real time. Larval fish feed particles of different sizes (100–500 μm) and formulations were measured. Under consistent experimental conditions, a feed could be assayed for the rate of mass loss and the half‐life or time of 50% total soluble mass loss. The results closely approximated natural decay models with coefficients of determination (r²) >0.95. The end result is a fast and accurate method to quantify and provide solid reference data for a feed formulation or particle size. Using this method allows different feeds to be compared and conclusions drawn for relative performance.     

Some effects of gas-supersaturated seawater on Spisula solidissima and Argopecten irradians

Two size classes of the surf clam, Spisula solidissima, and the bay scallop, Argopecten irradians, were exposed to different concentrations of gas-supersaturated seawater in a flowing seawater system. Both species tested experienced no mortality when held in the control treatment maintained at 96% oxygen and 109% nitrogen. Mortality, gill tissue damage, gas emboli, membranous tissue blisters, and abnormal secretion of shell material were induced experimentally at elevated levels of gas supersaturation. Results indicate significant mortalities of surf clams and scallops held at 114% O₂ and 195% N₂, and at higher levels of gas concentration. These values suggest a point of reference for the bivalve culturist in identifying potential problems which can be caused by gas-supersaturated seawater.     

Spontaneous Spawning of Captive Red Snapper, Lutjanus campechanus, and Dietary Lipid Effect on Reproductive Performance

Two experiments addressed the spontaneous spawning of red snapper, Lutjanus campechanus , under controlled temperatures and photoperiods and the effect of broodstock diets supplemented with oils rich in polyunsaturated fatty acids. In Experiment 1, broodfish were fed a standard diet (ST1) and one enriched with menhaden oil (ER1) over a 355-d period. ER1-influenced egg fatty acid profile, however, did not positively influence egg production. Both diets produced highly viable eggs and larvae but results varied within treatments. In Experiment 2, broodfish were fed either a standard diet (ST2) or one supplemented with oils (ER2) rich in docosahexaenoic and arachidonic acid using a 203-d cycle. Both treatments produced eggs but fertilization rates ranged 0–10%. There was no clear influence of the diets on egg fatty acid profiles. These results indicate that red snapper can spawn spontaneously in tanks under controlled environmental conditions and produce viable eggs and larvae when fed diets based on squid, shrimp, and fish. The fatty acid composition of the diets was reflected in the eggs to some degree, but the oil enrichments did not further enhance the reproductive performance and egg quality under the conditions of this study.     

Digestibility of Dry Matter, Protein, Lipid, and Organic Matter of Two Fish Meals, Two Poultry By-product Meals, Soybean Meal, and Distiller's Dried Grains with Solubles in Practical Diets for Sunshine Bass, Morone chrysops ×M. saxatilis

Limited information is available on digestibility of nutrients in various practical ingredients used in diets for commercially important finfish species, such as hybrid striped bass. This information is especially needed for sunshine bass, Morone chrysops × M. saxatilis , to improve least-cost diet formulations and to allow effective substitution of feedstuffs. A study was conducted with large (867 g) sunshine bass to determine the apparent digestibility coefficients (ADCs) for moisture, protein, lipid, and organic matter (OM) in a variety of ingredients in floating, extrusion-processed, diets. The practical ingredients tested were menhaden (MEN) fish meal (FM), anchovy (ANCH) FM, pet-food grade poultry by-product meal, feed-grade poultry by-product meal, dehulled soybean meal (SBM), and distiller's dried grains with solubles (DDGS). Test diets consisted of a 70:30 mixture of reference diet to test ingredient with chromic oxide (1.0%) as the inert marker. Reference and test diet ingredients were mixed and extruded on a Wenger X85 single-screw extruder to produce floating pellets. The digestibility trials were conducted in twelve 1200-L circular tanks. Diets were randomly assigned to tanks of 30 sunshine bass and were fed once daily to satiation. Protein digestibility coefficients were significantly ( P  < 0.05) different among test ingredients and ranged from 86.42% for MEN to 64.94% for DDGS. Lipid ADCs were significantly different ( P  < 0.05) among test ingredients and ranged from 92.14% for MEN to 57.11% for SBM. OM ADCs were significantly different ( P  < 0.05) among test ingredients and ranged from 89.41% for MEN to 16.94% for DDGS. This information will assist in the formulation of more efficient, economical diets for sunshine bass.     

Nitrous oxide emissions from the wheat-growing season in eighteen Chinese paddy soils: an outdoor pot experiment

To identify the key soil parameters influencing N₂O emission from the wheat-growing season, an outdoor pot experiment with a total of 18 fertilized Chinese soils planted with wheat was conducted in Nanjing, China during the 2000/2001 wheat-growing season. Average seasonal N₂O-N emission for all 18 soils was 610 mg m^-2, ranging from 193 to 1,204 mg m^-2, approximately a 6.2-fold difference between the maximum and the minimum. Correlation analysis indicated that the seasonal N₂O emission was negatively correlated with soil organic C (r²=0.5567, P<0.001), soil total N (r²=0.4684, P<0.01) and the C:N ratio (r²=0.4530, P<0.01), respectively. A positive dependence of N₂O emission on the soil pH (r²=0.3525, P<0.01) was also observed. No clear relationships existed between N₂O emission and soil texture, soil trace elements of Fe, Cu and Mg, and above-ground biomass of the wheat crop at harvest. A further investigation suggested that the seasonal N₂O-N emission (E, mg m^-2) can be quantitatively explained by E=1005-34.2SOC+4.1S_a (R²=0.7703, n=18, P=0.0000). SOC and S_a represent the soil organic C (g kg^-1) and available S (mg kg^-1), respectively.