Water requirement of Aloe vera in a dry caribbean climate

Summary As hardly any data can be found on the water requirement and yield response to water of Aloe vera, an irrigation experiment on transplanted aloe poles was conducted on the Caribbean island of Aruba. Compared to non-irrigated treatments irrigation shows a positive influence on growth, number of developed leaves, raw gel figure and gel production per plant. The amount of irrigation water to apply can be best calculated based on crop coefficients (K_c) between 0.20 and 0.30. Treatment based on a K_c value higher than 0.30 did not further increase production. A lysimeter study conducted over a relatively short period revealed that the crop coefficient for Aloe vera varied between 0.25 and 0.40 which is characteristic of the so-called agave/pineapple group.     

Analysis of the uncertainty associated with the estimation of nitrogen losses from farming systems

This work describes the analysis of the uncertainty linked to the annual direct and indirect losses of different nitrogenous compounds at the scale of a group of farms. The nitrogen (N) forms taken into account are: ammonia (NH₃), nitric oxide (NO), nitrous oxide (N₂O), dinitrogen (N₂) and nitrate (NO₃). The gaseous N emissions for the different components of the farms are estimated with a selection of adapted emission factors. The NO₃ losses at the farm scale are calculated as the difference between the surplus of the farm-gate N balance and the gaseous N emissions.     

Diagnosis of regional evaporation by remote sensing to support irrigation performance assessment

The success of water management in large irrigation schemes with composites of soil, crop, wetness and micro-meteorological conditions is difficult to quantify. Performance assessment indicators, being among others a function of evaporation, are useful tools to evaluate the actual functioning of an irrigation system. The inevitable spatial variability of evaporation in large irrigation schemes makes its determination with conventional point measurements almost impossible. A new remote sensing evaporation parameterization algorithm has been tested with high resolution Landsat Thematic Mapper data for the Eastern Nile Delta, Egypt. Although the implementation of such an algorithm requires assumptions to be made, the current case study shows that these assumptions do not hamper the estimation of actual and potential evaporation at regional scale. The actual evaporation has been used to express the uniformity of crop water use which is related to the equity of irrigation water distribution. The coefficient of variance in actual evaporation between 53 differenent irrigation districts is 10% on average. The relative evaporation was considered to determine whether the crop was adequately irrigated. The relative evaporation was more than 75% for 48 out of 53 irrigation districts. It is concluded, that improved information on actual crop growth conditions through remote sensing provides an essential insight into the planning of real-time and seasonal irrigation water deliveries.     

Finding niches for whole-farm design models – contradictio in terminis?

Whole-farm design models quantitatively analyze the effects of a variety of potential changes at the farm system level. Science-driven technical information is confronted with value-driven objectives of farmers or other social groupings under explicit assumptions with respect to exogenous variables that are important drivers of agricultural systems (e.g., market conditions). Hence, farm design is an outcome of objective specification and the potential of a system. In recent publications, whole-farm design modelling has been proposed to enhance (farm) innovation processes. A number of operational modelling tools now offers the opportunity to assess the true potential of whole-farm design modelling to enhance innovation. In this paper, we demonstrate that it is not trivial to find niches for the application of goal-based farm models. Model outcomes appeared not to match questions of farm managers monitoring and learning from their own and other farmers’ practices. However, our research indicates that whole-farm design modelling possesses the capabilities to make a valuable contribution to reframing. Reframing is the phenomenon that people feel an urge to discuss and reconsider current objectives and perspectives on a problem. Reframing might take place in a situation (i) of mutually felt dependency between stakeholders, (ii) in which there is sufficient pressure and urgency for stakeholders to explore new problem definitions and make progress. Furthermore, our research suggests that the way the researcher enters a likely niche to introduce a model and/or his or her position in this niche may have significant implications for the potential of models to enhance an innovation process. Therefore, we hypothesize that the chances of capitalizing on modelling expertise are likely to be higher when researchers with such expertise are a logical and more or less permanent component of ongoing trajectories than when these researchers come from outside to purposefully search for a niche.     

Inflammation and wound healing in cats with chronic gingivitis/stomatitis after extraction of all premolars and molars were not affected by feeding of two diets with different omega‐6/omega‐3 polyunsaturated fatty acid ratios

Feline chronic gingivitis/stomatitis (FCGS) is a painful inflammatory disease in cats. Extraction of teeth, including all premolars and molars, has been shown to be the therapy of choice in cats not responding sufficiently to home care (e.g. tooth brushing) and/or medical treatment (corticosteroids and/or antibiotics). In this study, we hypothesize that a cat food with an omega‐6 polyunsaturated fatty acid (ω6 PUFA) to ω3 PUFA ratio of 10:1 reduces inflammation of the FCGS and accelerates soft tissue wound healing of the gingiva after dental extractions, compared to a cat food with a ω6:ω3 PUFA ratio of 40:1. The cats were fed diets with chicken fat and fish oil as sources of fatty acids. In one diet, part of the fish oil was replaced by safflower oil, resulting in two diets with ω6:ω3 PUFA ratios of 10:1 and 40:1. This double‐blinded study in two groups of seven cats revealed that dietary fatty acids influence the composition of plasma cholesteryl esters and plasma levels of inflammatory cytokines. The diet with the 10:1 ratio lowered PGD₂, PGE₂ and LTB₄ plasma levels significantly, compared to the diet with the 40:1 ratio (p = 0.05, p = 0.04, and p = 0.02 respectively). However, feeding diets with dietary ω6:ω3 PUFA ratios of 10:1 and 40:1, given to cats with FCGS for 4 weeks after extraction of all premolars and molars, did not alter the degree of inflammation or wound healing.     

Chemical disinfectants can reduce potato blackleg caused by ‘Dickeya solani’

Treatments of tubers with chemical disinfectants (70 % ethanol, 1 % sodium hypochlorite, 2 % copper sulphate, 5 % peracetic acid, 10 % hydrogen peroxide, 1 % MennoClean (benzoic acid), 5 % trisodium phosphate and 0.2 % caffeine) were evaluated for control of blackleg caused by ‘D. solani’. All disinfectants effectively killed bacteria in axenic cultures within 5 min and all, except hydrogen peroxide and trisodium phosphate, were able to kill ‘D. solani’ in spiked potato extracts. Treatments with all disinfectants except trisodium phosphate, reduced the pathogen populations on the periderm of tubers previously inoculated by dipping in a suspension of ‘D. solani’, when the disinfectant was applied for at least 15 min. However, in replicated greenhouse experiments, treatments with all disinfectants except hydrogen peroxide and caffeine resulted in phytotoxicity, reducing sprouting of tubers with 10 – 100 %. Sodium hypochlorite and MennoClean were selected for further studies. Treatments of inoculated tubers with these disinfectants prevented developing of soft rot symptoms on tubers when subjected to favourable rotting conditions. In replicated greenhouse experiments, inoculated tubers treated with sodium hypochlorite and MennoClean reduced the blackleg disease incidences from 50 % to 0 % and to 5 %, respectively, and symptomless infection of potato stems from 93 % to 0 % and to 5 %, respectively. A combination of both compounds was highly phytotoxic. The potential use of sodium hypochlorite and MennoClean in an integrated management strategy for potato blackleg is discussed.     

萤光假单胞细菌根部定殖对水培系统中香石竹镰刀菌枯萎病的作用

 本文报道萤光假单胞菌(fluorescent Pseudomas spp.) WCSX 13.WCS 417andWCS 358在水培系统中香石竹根部的定殖及其对香石竹镰刀菌枯萎病的抑制作用。细菌处理两周后,WCS 417在感病品种Lena和中抗品种Pallas根部的定殖分别为8.8×10²cfu/cm和9.8×10²cfu/cm,而WCS 358分别为0.9×10²cfu/cm和0.13×10²cfu/cm。在通气的三角瓶中水培的Pallas品种,人工接种病原菌香竹石尖镰孢Fusarium oxyspotum f.sp.dianthi (Prill.&Del.) Snyd.&Hans.(Fod)6周后,用WCSX·13和WCS 417根部处理的病指分别为0.19和0.31,未细菌处理的对照为0.58,细菌处理植株的根部及茎内组织的病原菌种群密度低于对照。营养膜技术(NFT)栽培的Lena品种,WCS 417细菌处理的发病率比对照减少13%。     

Seeds in a rainforest soil and their relation to shifting cultivation in the Ivory Coast

In the Taï region of the Ivory Coast, mature forest is felled and burned and a crop of rice is grown; forest is then allowed to regenerate for 20 or more years before being cropped again. The top 10 cm of soil beneath a 21-year-old forest prior to felling contained 2000 viable seeds m^?2 of mainly woody species of previous successional stages no longer represented in the vegetation. Seedling emergence was greater in full sunlight than under leaf canopy, especially for herbaceous species of open habitats. Burning destroyed almost half of the seeds, but overall germination of those that survived was advanced by about 2 weeks. Germination of some common pioneer species was enhanced by the fire. Provided that burning took place and the rice was planted immediately, vegetation arising from the seed bank did not present a problem. The density never exceeded 70 seedlings m^?2 and little or no weeding was required. Species present at densities greater than 1 seedling 10 m^?2 were all recorded in the seed bank.     

Growth of the mycoparasitic fungus Verticillium biguttatum from different geographical origins at near-minimum temperatures

Sclerotia ofRhizoctonia solani collected from potato tubers from different countries were assayed for the presence of mycoparasites. Among the mycoparasites observedVerticillium biguttatum predominated. Its geographical distribution was not restricted to certain latitudes or soil types;V. biguttatum occurred worldwide in potato fields.The minimum growth temperature of 57V. biguttatum isolates was found to be in the narrow range from 10 to 13°C, irrespective of their geographical origin. A non-linear logistic growth model was used to describe the radial growth onRhizoctonia mycelium and nutrient agar plates. At near-minimum temperature the maximum colony radii varied considerably; they were up to 3.8 times that of the reference isolate M73. Based on parameter values for logistic growth, fast-and slow-growing isolates could be distinguished. Although the growth properties ofV. biguttatum isolates from different locations varied, the presence of fast- and slow-growing isolates was not restricted to particular areas and both types could be found in the same field. However, bioassays with selected fast- and slow-growing isolates do not support the assumption that growth at near-minimum temperatures is a relevant criterion for screening isolates ofV. biguttatum in terms of effectiveness for biological control ofR. solani.     

New mite-borne virus isolates from rakkyo,shallot and wild leek species

Flexuous viruses were transmitted from rakkyo (Allium chinense) and wild leek species (especiallyA. commutatum) to plants of crow garlic (A. vineale), by transfer of dry bulb mites. By electron microscope decoration tests using three antisera and by inoculations onto test plants, it was concluded that from each of the two natural host species at least two viruses were isolated. The viruses from wild leeks are both pathogenic onAllium spp. and may be of economic importance. Decoration tests on a virus mixture from shallot obtained earlier, revealed another new mite-borne virus in this species. The mite-borne viruses ofAllium spp. appear to be very common; they are largely diverse and their identification remains difficult.