Integrated Management Approach to Citrus Fungal Diseases by Optimizing Cocoa-Based Agroforests Structural Characteristics

The health and productivity of citrus are generally jeopardized by a host of diseases, for which the environmental conditions of the cropping system are critical drivers. Several studies conducted on various diseases of perennial crops have shown the involvement of the structural futures of the cocoa-based agroforestry system (CBAFS) in the spread of pathogens and the epidemics development. This chapter highlights the effect of the CBAFS’s structural characteristics on the intensity of three citrus diseases in the humid forest zones of Cameroon. The involvement of CBAFS structural characteristics in diseases regulation is demonstrated. In particular, the spatial structure of citrus in agroforests shows an effect on the spread of diseases. Moreover, distribution of citrus in the CBAFS, with minimum spacing of 12 m between citrus trees, limits the damage caused by Pseudocercospora leaf and fruit spot disease (PLFSD) and citrus diseases caused by Phytophthora (CDP). Dense shading helps to minimize the intensity of diseases such as CDP and PLFSD and Citrus scab disease. This work may make it possible to contribute to the development of an integrated management tool for citrus diseases in an associated crop context.

Estimation of soil properties with mid-infrared soil spectroscopy across yam production landscapes in West Africa

Low soil fertility is challenging the sustainable production of yam and other staple crops in the yam belt of West Africa. Quantitative soil measures are needed to assess soil fertility decline and to improve crop nutrient supply in the region. We developed and tested a mid-infrared (mid-IR) soil spectral library to enable timely and cost-efficient assessments of soil properties. Our collection included 80 soil samples from four landscapes (10 km × 10 km) and 20 fields per landscape across a gradient from humid forest to savannah and 14 additional samples from one landscape that had been sampled within the Land Health Degradation Framework. We derived partial least squares regression models to spectrally estimate soil properties. The models produced accurate cross-validated estimates of total carbon, total nitrogen, total sulfur, total iron, total aluminum, total potassium, total calcium, exchangeable calcium, effective cation exchange capacity, and diethylenetriaminepentaacetic acid (DTPA)-extractable iron and clay content (R2>0.75). The estimates of total zinc, pH, exchangeable magnesium, bioavailable copper, and manganese were less predictable (R2>0.50). Our results confirm that mid-IR spectroscopy is a reliable and quick method to assess the regional-level variation of most soil properties, especially the ones closely associated with soil organic matter. Although the relatively small mid-IR library shows satisfactory performance, we expect that frequent but small model updates will be needed to adapt the library to the variation of soil quality within individual fields in the regions and their temporal fluctuations.

Seasonal Drought Induces Hydraulic Dysfunction, Not Carbohydrate Depletion, for Robinia Pseudoacacia in a Semi-humid Forest

BackgroundShifts in rainfall patterns that are associated with climate change are likely to cause widespread forest decline in regions where droughts are predicted to increase in duration and severity. However, causes of forest decline and their physiological mechanisms remain unclear, particularly the roles of carbon metabolism and xylem function. To explore the response of hydraulic architecture and non-structural carbohydrates (NSC) traits under seasonal drought, we conducted a manipulation experiment in a Robinia pseudoacacia plantation in 2015 and 2016 in Loess Plateau of China. Sap-flow, leaf area index, water potential, non-structural carbohydrate concentrations, and hydraulics in different organs were measured. ResultsThe mean pre-dawn and midday leaf water potential after two growing seasons of drought stress was significantly lower (-2.2 MPa and -2.7 MPa, respectively) than those of control trees (-1.5 MPa and -2.0 MPa, respectively). Drought stress accelerated the loss of conductivity, and promoted the formation of narrow hydraulic safety margins, which indicated that hydraulic failure could be a good predictor of “physiological drought” in trees when subjected to two growing seasons of drought. Both sugar and starch concentrations in stems and roots were similar in all trees throughout the drought period, which indicated that trees maintained good coordination between carbon supply and demand when confronted with two growing seasons of drought.ConclusionsOur results emphasized that hydraulic failure plays the predominant role in causing tree death during highly intense drought, while whether "carbon starvation" occurs during tree mortality remains to be tested in longer (multi-year) but less intense drought.

High species richness turnover of vascular epiphytes is associated with water availability along the elevation gradient of Volcán Maderas, Nicaragua

Research that has been conducted documenting species richness patterns on tropical mountains has resulted in conflicting observations: monotonic declines with increasing elevation, monotonic increase with increasing elevation, and a mid-elevation ‘bulge.’ Currently, it is unclear if these differences are due to environmental differences associated with the various study areas, the taxonomic groups or ecological groups (e.g., growth form) sampled, or the scale of the study area along an elevation gradient. Because of the difficulty in sampling and identifying canopy-dwelling plants, the number of inventories quantifying tropical epiphytes is relatively limited and recent. In this study, we provide a detailed qualitative and quantitative assessment of the vascular epiphyte flora and its spatial distribution on Volcán Maderas, Isla de Ometepe, Nicaragua, including weather and environmental measurements along the entire elevation gradient of the volcano. We sampled epiphytes in five distinct forest types associated with increasing elevation as follows: dry forest, humid forest, wet forest, cloud forest, and elfin forest Five weather stations were placed along the elevation gradient for us to relate observed patterns to environmental conditions. A hump-shaped species richness pattern was detected for all vascular epiphytes at approximately 1000 m in elevation (cloud forest), yet species abundance increased with increasing elevation. In total we obtained 206 unique species identifications of vascular epiphytes belonging to 26 families and 73 genera. The most species-rich family was the Orchidaceae with 55 species for the entire elevation gradient, followed by Bromeliaceae (29 species), Araceae (23), Polypodiaceae (25), Dryopteridaceae (16), and Piperaceae (11), with all other families respresented by fewer than 10 species each. We found that richness patterns differ phylogenetically within epiphytes, possibly due to different adaptive strategies, and species for the most part appear to be narrowly distributed within specific habitat zones along the elevation gradient.

Cuticular hydrocarbons from ants (Hymenoptera: Formicidae) Odontomachus bauri (Emery) from the tropical forest of Maranguape, Ceará, Brazil

Semiochemicals, 5-methyl-nonacosane, Alkanes, Chromatography.Ants are eusocial organisms with great relative abundance and species richness. Studies on these organisms are scarce, especially in the high altitude humid forest environments of the state of Ceará. In view of this condition, an evaluation of the chemical composition of cuticular hydrocarbons (CHCs) of the species Odontomachus bauri found and recorded for the first time in this study in the tropical forest of Maranguape was carried out, based on the hypothesis that different nests have different compositions of CHCs. For this purpose, collection incursions were carried out in the region to obtain individuals from three different nests. In the laboratory, the extraction of CHCs was performed by immersing the ants in hexane for 30 minutes. After removing the ants, the extracts were subjected to drying to assess the yield of the samples. Then, the extracts were subjected to a silica gel column, before performing an analysis by gas chromatography coupled with mass spectrometry. The chromatograms obtained were analyzed and demonstrated a great similarity, showing long-chain saturated hydrocarbons, mainly represented by alkanes and methyl-alkanes. 5-Methyl-nonacosane was the component with the highest relative abundance. Statistical analysis of similarity and correlation between samples was performed using non-parametric tests. These analyzes provided sufficient statistical evidence to confirm the existence of a strong positive correlation between the samples and also a significant difference in the composition of HCCs in two of the three paired analyzes performed, thus confirming the study hypothesis.