Effect of Density at Harvest on the Growth Performance and Profitability of Hatchery‐reared Spotted Rose Snapper,Lutjanus guttatus,Cultured in Floating Net Cages

This study evaluated the effect of the density at harvest on the performance and profitability of hatchery‐reared spotted rose snapper cultured in cages. The fish were stocked at harvest densities of 15, 20, and 22 kg/m³ in cages of 222 and 286 m³. More than 39,000 snapper fingerlings with an initial weight of 14 g were stocked. The fish were fed an extruded diet and cultured over a 360 d period. The thermal growth coefficient ranged from 0.04 to 0.05 and survival was 95% for all treatments, with the highest final weight (436.8 g) observed for fish reared at a density of 20 kg/m³. The allometric value b indicated that hatchery‐raised, cage‐cultured snapper were heavier than their wild counterparts. The major costs were feed (ranging from 44.7–45.9%), labor (22.4–32.6%), and seed costs (20.2–26.1%). The total production cost ranged from US$ 6.5 to US$ 7.5/kg. The baseline scenario was not economically feasible. However, a 10% increase in the sales price resulted in increases in the internal rate of return (183%) and net present value (US$ 97,628.9). These results suggest that L. guttatus has the potential for commercial production in cages.     

Using midday stem water potential for scheduling deficit irrigation in mid–late maturing peach trees under Mediterranean conditions

Irrigation techniques that reduce water applications are increasingly applied in areas with scarce water resources. In this study, the effect of two regulated deficit irrigation (RDI) strategies on peach [Prunus persica (L.) Batsch cv. “Catherine”] performance was studied over three growing seasons. The experimental site was located in Murcia (SE Spain), a Mediterranean region. Two RDI strategies (restricting water applications at stage II of fruit development and postharvest) based on stem water potential (Ψ_s) thresholds (?1.5 and ?1.8 MPa during fruit growth and ?1.5 and ?2.0 MPa during postharvest) were compared to a fully irrigated control. Soil water content (θ_v), Ψ_s, gas exchange parameters, vegetative growth, crop load, yield and fruit quality were determined. RDI treatments showed significantly lower values of θ_v and Ψ_s than control trees when irrigation water was restricted, causing reductions in stomatal conductance and photosynthesis rates. Vegetative growth was reduced by RDI, as lower shoot lengths and pruning weights were observed under those treatments when compared to control. However, fruit size and yield were unaffected, and fruit quality was slightly improved by RDI. Water savings from 43 to 65 % were achieved depending on the year and the RDI strategy, and no negative carryover effect was detected during the study period. In conclusion, RDI strategies using Ψ_s thresholds for scheduling irrigation in mid–late maturing peach trees under Mediterranean conditions are viable options to save water without compromising yield and even improving fruit quality.     

Parentage assignment in Haliotis midae L.: a precursor to future genetic enhancement programmes for South African abalone

The establishment and evaluation of family lines using pedigree information provides an advanced understanding of the variability that exists for complex, economically valuable traits and is a necessary step in the execution of an effective breeding programme. The aim of this study was to assign parentage to mass‐spawned Haliotis midae juveniles using species‐specific microsatellite markers. Screening of wild abalone individuals revealed that the nine loci selected complied with the minimum requirements for parentage analyses: a null allele frequency <5% as well as a high number and frequency of alleles per locus. A total of 598 individuals were genotyped (198 breeding individuals and 400 F1 progeny) from two farms, with parentage results yielding 91% and 90% successful assignment for Farms A and B respectively. This study, therefore, provided the necessary pedigree information required for controlled breeding of individual adult abalone and indicated the usefulness of the panel of microsatellite markers selected for parentage assignment.     

Insecticidal efficacy of beauveria bassiana,diatomaceous earth and fenitrothion against rhyzopertha dominica and tribolium castaneum on stored wheat

Bioassays were conducted in stored grains to evaluate the combined use of the entomopathogenic fungus Beauveria bassiana, diatomaceous earth (DE) and fenitrothion against adults of Rhyzopertha dominica and Tribolium castaneum. The insecticide agents were applied to wheat as follows: the fungus at 1 × 10⁸ conidia/kg of wheat, DE at 3 g/kg of wheat and fenitrothion at a rate of 0.15 ml/kg of wheat (25% of field dose rate). Surviving insects and progeny production were monitored at thirty-day intervals until four months. For both insect species, significantly less progeny was produced on wheat treated with fenitrothion and DE + B. bassiana formulations in comparison with controls. The effect of insecticides on the grain damage, germination power of wheat and bulk density was also evaluated. After four months, B. bassiana mixed with DE reduced the damaged insect grains by 50% in comparison with both fenitrothion and control treatments. Trials using DE caused a reduction in bulk density while there were no significant differences for germination testing between treatments.     

Analysis of tree interactions in a mixed Mediterranean pine stand using competition indices

Studying species interactions in mixed forests allows us to assess their potential benefits and adapt current silvicultural tools developed in monospecific stands to multi-specific stands. We analyzed tree interactions in a Pinus halepensis Mill. and Pinus pinea L. mixed plantation using individual tree neighborhood models and competition indices that accounted for symmetric and asymmetric competition, to analyze whether the growth of each species was better explained by symmetric or asymmetric competition. We also split the competition indices into their intra- and interspecific forms, to test for competition effects on growth change based on competitor identity. Finally, we analyzed whether P. halepensis and P. pinea trees had different growth responses to competition. When calculating competition indices, we explored how spatial information and size of competitor trees contributed to the quantification of the process. Competition measurements were optimized to more precisely describe interactions. Results showed that the inclusion of competition indices generated important improvements in growth models. The main mode of competition was symmetric, which could be related to water restrictions typical of the Mediterranean climate. Considering competitor identity did not improve the growth models, while measurement without discriminating competitors by species generated more parsimonious models. P. halepensis and P. pinea trees had similar growth responses to competition, indicating that the two species cope with competition in similar ways. However, P. pinea showed lower average growth than P. halepensis in the period analyzed. Results suggest that preventing the onset of intense interspecific competition processes could help slow down the long-term replacement of P. pinea by P. halepensis and could have benefits for silvicultural management in systems with two species that share ecological niches but are capable of generating different goods and services.     

Evaluating the performance of xanthophyll,chlorophyll and structure-sensitive spectral indices to detect water stress in five fruit tree species

This study assessed the capability of several xanthophyll, chlorophyll and structure-sensitive spectral indices to detect water stress in a commercial farm consisting of five fruit tree crop species with contrasting phenology and canopy architecture. Plots irrigated and non-irrigated for eight days of each species were used to promote a range of plant water status. Multi-spectral and thermal images were acquired from an unmanned aerial system while concomitant measurements of stomatal conductance (g_s), stem water potential (Ψ_s) and photosynthesis were taken. The Normalized Difference Vegetation Index (NDVI), red-edge ratio (R₇₀₀/R₆₇₀), Transformed Chlorophyll Absorption in Reflectance Index normalized by the Optimized Soil Adjusted Vegetation Index (TCARI/OSAVI), the Photochemical Reflectance Index using reflectance at 530 (PRI) and 515 nm [PRI_(570–515)] and the normalized PRI (PRI_norm) were obtained from the narrow-band multi-spectral images and the relationship with the in-field measurements explored. Results showed that within the Prunus species, Ψ_s yielded the best correlations with PRI and PRI_(570–515) (r² = 0.53) in almond trees, with TCARI/OSAVI (r² = 0.88) in apricot trees and with PRI_norm, R₇₀₀/R₆₇₀ and NDVI (r² from 0.72 to 0.88) in peach trees. Weak or no correlations were found for the Citrus species due to the low level of water stress reached by the trees. Results from the sensitivity analysis pointed out the canopy temperature (T_c) and PRI_(570–515) as the first and second most sensitive indicators to the imposed water conditions in all the crops with the exception of apricot trees, in which Ψ_s was the most sensitive indicator at midday. PRI_norm was the least sensitive index among all the water stress indicators studied. When all the crops were analyzed together, PRI_(570–515) and NDVI were the indices that better correlations yielded with Crop Water Stress Index, g_s and, particularly, Ψ_s (r² = 0.61 and 0.65, respectively). This work demonstrated the feasibility of using narrow-band multispectral-derived indices to retrieve water status for a variety of crop species with contrasting phenology and canopy architecture.     

A comparison of indexes to estimate corn S uptake and S mineralization in the field

The development of simple predictors of sulfur (S) mineralization and its correlation with field-derived data may help improving corn S availability diagnosis. The objectives of this study were (1) to compare methods to estimate soil S mineralization, (2) to develop a model to predict soil S mineralization from S mineralization indexes and edaphic variables, and (3) to predict field-grown corn S uptake (S_uptake) and apparent S mineralization (S_min-app) from different S mineralization indexes and edaphic-climatic variables. We evaluated 26 experimental sites where we measured edaphic variables as soil organic C (SOC), organic C in the particulate fraction (C-PF), S mineralization potential (S_min-10wk), S mineralized during a short-term (7 days) aerobic incubation + initial inorganic S (S_min-7d?+?S_inorg), and N mineralized during a short-term (7 days) anaerobic incubation (N_an). Additionally, 18 field experiments were carried out to quantify S_uptake and S_min-app. The C-PF, S_min-7d?+?S_inorg, N_an, and SOC were variables significantly correlated with S_min-10wk (r?=?0.89, 0.89, 0.88, and 0.85, respectively). We developed a simple model to predict S_min-10wk from selected edaphic variables (S_min-10wk?=?0.038*N_an?+?0.106*SOC?+?0.74; R_a² =?0.87). The S_min-10wk, C-PF, and S_min-7d?+?S_inorg showed a liner-plateau association with S_uptake (R²?=?0.73, 0.53, and 0.48, respectively). We modified the method to estimate S_min-app to account for S losses (S_{min-app (modified)}) and developed a model to predict S_{min-app (modified)} from C-PF (S_{min-app (modified)}?=?4.65*C-PF?+?9.86; R²?=?0.62) or S_min-10wk (S_{min-app (modified)}?=?3.0*S_min-10wk?+?7.4; R²?=?0.54). Our results demonstrate that S mineralization indexes can be used to predict corn S availability under field conditions.