Oomycete species associated with Theobroma cacao crops in Colombia

The study of oomycetes associated with crops is highly important due to the economic losses they might cause. In cacao, the genus Phytophthora has been extensively studied, but little is known about other genera and species of oomycetes associated with this plant. This study aimed to determine the oomycetes’ diversity present in Colombian cacao crops. A total of 146 isolates were obtained from diseased plants and soil in 11 departments. Analysis of internal transcribed spacer (ITS) and cytochrome oxidase subunit I (coxI) sequences was performed along with the assessment of morphological characteristics. Nine species were identified, distributed in four genera: Phytophthora (P. palmivora, 54%; P. nicotianae, 1%), Phytopythium (Phy. chamaehyphon, 15%; Phy. cucurbitacearum, 9%; Phy. vexans, 7%; Phy. helicoides, 1%), Globisporangium (G. splendens, 3%), and Pythium (Py. delicense, 1%; Py. inflatum,1%). Additionally, an unidentified and possibly new species of Phytophthora (5%) and three unidentified species of Phytopythium (3%) were found. This is the first report of Globisporangium, Phytopythium, and Pythium in cacao crops of Colombia and the first report of the species Phy. chamaehyphon in the country. Interestingly, some isolates of Phytopythium spp. were isolated from necrotic leaves and vascular section of stems, which may suggest a role in cacao diseases traditionally associated with Phytophthora. Also, it is proposed that the new species of Phytophthora may be contributing significantly to black pod disease in Colombian cacao crops, and we highlight that the study of P. palmivora is urgent because of its distribution all over the country.     

Effect of annealing from traditional nixtamalisation process on the microstructural,thermal, and rheological properties of starch and quality of pozole

Eleven maize landraces were evaluated for pozole quality. The microstructural, thermal and rheological properties of annealed starch granules determine most of the quality of pozole. Annealed starch in traditional nixtamalisation has an important role in increasing gelatinisation onset (To), peak (Tp) and final (Tf) temperatures; peak, setback and final viscosity as well as the stability of the starch granule, all of which significantly affect pozole quality. Annealed starch in Cacahuacintle nixtamal (pozole end-use) increased temperatures To, Tp and Tf by >5.2, >3.8 and >4.1 °C respectively, and narrowed the range Tf − To from 13.78 to 12.62 °C. The enthalpy was reduced from 6.76 to 5.85 J/g, while the nixtamal starch in tortilla maize landraces presented fewer annealing effects. The annealing effect in nixtamal starch seems to stabilize the starch granules and avoid their collapse, compared to native starch, as shown by the X-ray diffraction peak intensity and pattern that is similar to unprocessed maize. Starch in nixtamal changes from Type A to Type V pattern in pozole. Kernel physical parameters, although important, affected the quality to a lesser extent, with the exception of the flotation index. Cacahuacintle maize landrace showed the best quality and yield as well as a short pozole cooking time.     

Soil Physicochemical Changes Following Buffelgrass Establishment in Mexico

Clearing brush from rangeland and seeding it to buffelgrass (Cenchrus ciliaris L.) is a popular range improvement practice in Mexico, but no data are available on the effects of these practices on soil properties. Twenty-nine study sites were randomly selected across 3 major climatic regions in Mexico: 13 in the northwest, 11 in the northeast, and 5 in the southeast. Soils under buffelgrass stands more than 10 years old and on adjacent virgin rangelands were sampled at 0-10, 10-20, and 20-30 cm depths to quantify sand, silt, clay, organic C, total N, pH, EC, CEC, available P, and exchangeable Ca2+, Mg2+, Na+, and K+.Because soil variables were not significantly (P 0.05) different among depths, only data from the surface horizon received further analysis. Soils in the northwest had higher (P 0.05) sand content and were particularly low in total N (0.08%), Ca2+, and K+, while soils of wetter and warmer southeast Mexico were significantly (P 0.05) higher than the other two regions in measures of soil fertility such as organic C (10 times higher), total N, and CEC (both at least 3 times higher). Long-term buffelgrass establishment had the most effect on soils in the southeast and no significant effect (P0.1) on soils of northeast Mexico. Soil organic C and total N both declined (P 0.025) by about 40% under buffelgrass pastures in the southeast; excgangeable Ca2+ decreased (P=0.027) by 21% in the same region, and Mg2+ declined (P=0.03) by 36% under buffelgrass in the northwest. Soil P did not respond to buffelgrass establishment. The findings of this study suggest that high forage yields following conversion of rangeland to buffelgrass pasture will be less sustainable in subtropical regions with high rainfall (mean of 1070 mm in this study) than in the semiarid zone with inherently poorer soils.     

Antibacterial activity of plant extracts obtained with alternative organics solvents against food-borne pathogen bacteria

The objectives of this study were: the chemical characterization of extracts from seven plants (Larrea tridentata, Flourensia cernua, Lippia graveolens, Agave lechuguilla, Yucca filifera, Opuntia ficus-indica, and Carya illinoensis) which are acclimated to the Mexican semi-desert. The extracts were obtained using Soxhlet method by water, ethanol and an infusion method using alternative organic solvents (lanolin and cocoa butter), in addition it was evaluated the antibacterial activity of semi-desert plant extracts against Enterobacter aerogenes, Escherichia coli, Salmonella typhi and Staphylococcus aureus. Chemical characterization of plant extracts showed that they are rich in secondary metabolites; cocoa butter was the non-conventional solvent which it was possible to obtain the highest content of total tannins. It was not possible to identify saponins in those extracts where non conventional solvents were used. While in extract where non conventional solvents were used, it was only possible to detect the presence of terpenes in creosote bush and prickly pear extracts. S. aureus was the bacterial strain that showed the highest growth inhibition as consequence of the plant extracts. The use of semi-desert plant extracts obtained using organic solvents are a good alternative for food-borne pathogen bacteria control because all the bacterial growth decreased with the tested extracts.     

Incorporation of dietary nitrogen from fish meal and pea meal (Pisum sativum) in muscle tissue of Pacific white shrimp (Litopenaeus vannamei) fed low protein compound diets

Stable isotope analyses were applied to explore the relative dietary nitrogen contributions from fish meal and pea meal (Pisum sativum) to muscle tissue of Pacific white shrimp postlarvae (141 ± 31 mg) fed low protein diets having different proportions of both ingredients as the sole dietary protein sources. A negative control diet was formulated to contain 100% pea meal and six more isoproteic diets to have decreasing levels of pea meal‐derived nitrogen: 95%, 85%, 70%, 55%, 40% and 0% of the initial level. Growth rates were negatively correlated to dietary pea protein inclusion due to progressive essential amino acid deficiencies (sulphur amino acids, threonine, lysine, histidine). The nitrogen turnover rate significantly increased in muscle tissue of shrimps fed diets having high levels of pea meal; however, contrary to observations from a previous study using soy protein, the relative contributions of dietary nitrogen from pea meal to shrimp muscle tissue were equal or higher than expected contributions established by the dietary formulations. Results highlight the effectiveness of stable isotope analysis in assessing the nutritional contributions of alternative ingredients for aquaculture feeds and the potential suitability of pea as a source of protein (provided the diets are nutritionally balanced).     

Effects of Mexican dwarf mistletoe (Arceuthobium vaginatum subsp. vaginatum) on the growth of Pinus cooperi in Durango,Mexico—A case study

Mexican dwarf mistletoe (Arceuthobium vaginatum subsp. vaginatum, Viscaceae) is the most widespread and damaging parasitic plant in Mexico. It parasitizes 10 species of pines (Pinus spp., Pinaceae) as principal hosts, including Pinus cooperi, one of the economically most important pines in the state of Durango. As a case study, we used stem analysis to estimate the effects of Mexican dwarf mistletoe on volume and height growth of dwarf mistletoe‐infected P. cooperi in western Durango (Ejido El Brillante, Municipality Pueblo Nuevo). This case study sampled a total of 48 trees, 12 in each of four infection classes estimated using the 6‐class dwarf mistletoe rating system (DMR): uninfected (DMR 0), lightly infected (DMR 1–2), moderately infected (DMR 3–4) and severely infected (DMR 5–6). Significant reductions in both volume and height growth were found for moderately and severely infected trees when compared to uninfected trees. On average, reductions in volume growth and height growth were as high as 50% and 17%, respectively. The largest growth reductions were for moderately infected trees, but large growth reductions also occurred for severely infected trees. Because of the reduced growth associated with moderate to severe infection, Mexican dwarf mistletoe‐infested pine forests in Durango, where timber production is a high priority, should be managed using harvesting practices that reduce dwarf mistletoe infection, and thereby, increase forest productivity.     

Succession and management of tropical dry forests in the Americas: Review and new perspectives

Understanding tropical forest succession is critical for the development of tropical forest conservation strategies worldwide, given that tropical secondary forests can be considered the forests of the future. Tropical dry forests (TDF) are among the most threatened tropical ecosystems, there are more secondary forests and forest restoration efforts that require a better understanding of successional processes. The main goal of this synthesis for this special issue on the ecology and management of tropical dry forests in the Americas is to present a summarized review of the current knowledge of the ecology and management implications associated to TDF succession. We explore specific issues associated to tropical dry forest succession with emphasis on the use of chronosequences, plant diversity and composition, plant phenology and remote sensing, pollination, and animal–plant interactions; all under the integrating umbrella of ecosystem succession. We also emphasize the need to conduct socio-ecological research to understand changes in land-use history and its effects on succession and forest regeneration of TDF. We close this paper with some thoughts and ideas associated with the strong need for an integrating dimension not considered until today: the role of cyberinfrastructure and eco-informatics as a tool to support sound conservation, management and understanding of TDF in the Americas.     

Can the Land Use Master Plan Control Urban Expansion and Protect Farmland in China? A Case Study of Nanjing

Urbanization represents a challenge for plans aimed at controlling urban expansion and protecting farmland, such as the land use master plan (LUMP) instituted by the Chinese national government. This paper studies the effectiveness of such top–down plans under the authoritarian regime through the case study of Nanjing. In contrast to previous studies that compare actual and planned land‐use maps, we compare actual and planned land‐use patterns. We use land‐use change data to examine spatio‐temporal land‐use change between the years 1997 and 2014. The results indicate that the actual amount of urban‐rural built‐up land exceeded planned regulatory amount by 50,185 ha and the total farmland was 70,541 ha less than the target outlined in the LUMP (1997–2010). Based on these results, and the fact that the allowed total urban‐rural built‐up land had already been surpassed in 2014, it is to be expected that the target of farmland protection outlined in the LUMP (2006–2020) will be broken, signaling the ineffectiveness of the plan to control urban expansion and protect farmland. Plan‐led developments (e.g., new towns, development zones) and market forces (e.g., housing market, foreign direct investment) explain these developments. This study indicates that when cities embrace “growth‐led” development and entrepreneurial governance, the ability of plans to control urban expansion and protect farmland is severely limited.     

Genomic prediction of the general combining ability of maize lines (Zea mays L.) and the performance of their single crosses

The objective of this study was to assess the effectiveness of genomic selection (GS) on predicting the general combining ability (GCA) of maize lines and the performance of their single crosses. Eight maize lines developed from the different self‐pollination generations of Chalqueño race, along with their 24 single crosses, were evaluated in the field during the years of 2011, 2012 and 2013. Genomic prediction results using genotyping‐by‐sequencing‐based single nucleotide polymorphisms showed that the GCA classification of the parental lines estimated from the SNP information was consistent with the phenotypic classification of the lines evaluated from the field trial data. The prediction accuracy values estimated from the cross‐validation method ranged from 0.49 to 0.61 in the different prediction models. Yield performance of the unevaluated single crosses was predicted based on their SNP information. The total genetic variance of the yield of the single crosses was most explained by the GCA effects. Compared with phenotyping method, GS is a more effective and efficient approach to predict the GCA of maize lines and their hybrid performance.