Modelling and measuring evapotranspiration in a daily drip irrigated cotton field

Summary An eddy correlation system (ECS) was used to estimate evapotranspiration (E) in a daily drip irrigated cotton field. Cotton yield, water use, and their ratio (Water use efficiency; WUE) were compared in four irrigation treatments. Three treatments were irrigated at levels of 85, 100, and 115% of E, while the fourth was irrigated according to grower's usual practice. E data were used to verify a one dimensional numerical model which simulates, in real time, the different energy fluxes existing in the soil-plant-atmosphere system. The model requires input of vegetation parameters (leaf area index, photometric properties, shading factor, root density distribution), soil parameters texture, hydraulic and photo-metric properties, temporal micrometeorological data (solar radiation, wind speed, air temperature and humidity) measured above the field, and irrigation quantities. The verification study was carried out during a cotton growing season in Hula Valley, Northern Israel. Results show that E rates are strongly affected by the intensity and arrival time of the inland penetrating Mediterranean sea breeze. WUE in the treatment which was irrigated according to the ECS was highest. Accurate estimations were also made by the model.     

Modeling the survival of two soilborne pathogens under dry structural solarization

ABSTRACT Structural (space) solarization of a closed, empty greenhouse for sanitation involves dry heating to 60 degrees C and higher and low relative humidity (RH), under a fluctuating temperature and RH regime. Survival of inocula of Fusarium oxysporum f. sp. radicis-lycopersici and Sclerotium rolfsii during structural solarization was studied for 4 years (total of 12 experiments) in an attempt to develop a dynamic model for expressing the thermal inactivation of the pathogens. After 20 days of exposure, the populations of F. oxysporum f. sp. radicis-lycopersici and S. rolfsii were reduced by 69 to 95% and by 47.5 to 100%, respectively. The Weibull distribution model was applied to describe pathogen survival. The Weibull rate parameter, b, was found to follow an exponential (for F. oxysporum f. sp. radicis-lycopersici) and the Fermi (for S. rolfsii) functions at constant temperatures. To improve the applicability of the model, fluctuating conditions of both temperature and RH were utilized. The Weibull distribution derivative, expressed as a function of temperature and moisture, was numerically integrated to estimate survival of inocula exposed to structural solarization. Deviations between experimental and calculated values derived from the model were quite small and the coefficient of determination (R (2)) values ranged from 0.83 to 0.99 in 9 of 12 experiments, indicating that ambient RH data should be considered. Structural solarization for sanitation could be a viable component in integrated pest management programs.     

Parasitism of <Emphasis Type="Italic">Trichoderma</Emphasis> on <Emphasis Type="Italic">Meloidogyne javanica</Emphasis> and role of the gelatinous matrix

Trichoderma (T. asperellum-203, 44 and GH11; T. atroviride-IMI 206040 and T. harzianum-248) parasitism on Meloidogyne javanica life stages was examined in vitro. Conidium attachment and parasitism differed beween the fungi. Egg masses, their derived eggs and second-stage juveniles (J2) were parasitized by Trichoderma asperellum-203, 44, and T. atroviride following conidium attachment. Trichoderma asperellum-GH11 attached to the nematodes but exhibited reduced penetration, whereas growth of T. harzianum-248 attached to egg masses was inhibited. Only a few conidia of the different fungi were attached to eggs and J2s without gelatinous matrix; the eggs were penetrated and parasitized by few hyphae, while J2s were rarely parasitized by the fungi. The gelatinous matrix specifically induced J2 immobilization by T. asperellum-203, 44 and T. atroviride metabolites that immobilized the J2s. A constitutive-GFP-expressing T. asperellum-203 construct was used to visualize fungal penetration of the nematodes. Scanning electron microscopy revealed the formation of coiling and appressorium-like structures upon attachment and parasitism by T. asperellum-203 and T. atroviride. Gelatinous matrix agglutinated T. asperellum-203 and T. atroviride conidia, a process that was Ca²⁺-dependent. Conidium agglutination was inhibited by carbohydrates, including fucose, as was conidium attachment to the nematodes. All but T. harzianum could grow on the gelatinous matrix, which enhanced conidium germination. A biomimetic system based on gelatinous-matrix-coated nylon fibers demonstrated the role of the matrix in parasitism: T. asperellum-203 and T. atroviride conidia attached specifically to the gelatinous-matrix-coated fibers and parasitic growth patterns, such as coiling, branching and appressoria-like structures, were induced in both fungi, similarly to those observed during nematode parasitism. All Trichoderma isolates exhibited nematode biocontrol activity in pot experiments with tomato plants. Parasitic interactions were demonstrated in planta: females and egg masses dissected from tomato roots grown in T. asperellum-203-treated soil were examined and found to be parasitized by the fungus. This study demonstrates biocontrol activities of Trichoderma isolates and their parasitic capabilities on M. javanica, elucidating the importance of the gelatinous matrix in the fungal parasitism.     

Evaluation of Trichoderma spp. as a Biocontrol Agent Against Soilborne Fungi and Plant-parasitic Nematodes in Israel

The optimal conditions required to market Trichoderma as a biocontrol agent against soilborne fungi and nematodes are discussed. These include a proper formulation, an efficient delivery system, and alternative methods for Trichoderma's application.The implementation of Trichoderma in integrated pest management (IPM) can be achieved using a soil treatment which combines reduced amounts of biocides/fungicides and the Trichoderma preparation. Biocontrol activity can be increased by combining two (or more) types of biocontrol agents. Moreover, the construction of a genetically modified Trichoderma can lead to the improvement of certain traits which are absent or not highly expressed in the native microorganism isolated from its natural habitat.Different Trichoderma harzianum and T. lignorum isolates were tested for their nematicidal activity against the root-knot nematode Meloidogyne javanica. In short-term experiments, improved growth of nematode-infected plants and decreases in the root-galling index and the number of eggs per gram of root were achieved when nematode-infested soils were pre- exposed to the T. harzianum preparations. A long-term experiment resulted in improved growth and higher yield of nematode-infected plants, but no significant change in the galling index, either by pre-exposure of the fungus to the soil or by enrichment in the root-ball.As biocontrol is an integral part of the IPM philosophy, judicious use of Trichoderma against soilborne pathogens, when demonstrated to be consistently effective, practical and economic, can serve as a model for the introduction and implementation of other biocontrol means into IPM.     

Methods for Determining Pythium Suppression In Container Media

Pythium damping-off and root-rot are among the most important soilborne diseases of greenhouse plants and seedlings grown in container media. It has been shown previously that composts may be conducive, suppressive or partially suppressive to Pythium diseases. The major goal of this work was to investigate rapid, practical and reliable methods for determining of the degree of suppressiveness of container media to Pythium damping-off. Several inoculation methods were tested in greenhouse bioassays, survival of propagules in suppressive versus conducive media was studied under laboratory conditions. Although both greenhouse and laboratory tests could indicate disease suppression, a bioassay with cucumber seedlings is suggested to be the most simple, effective and comprehensive method for testing suppression of Pythium diseases in compost amended container media.     

Nematicidal Activity of Chrysanthemum coronarium

Organic amendments and green manure are potential alternatives to the harmful chemical control means currently used against plant-parasitic nematodes. In this work, Chrysanthemum coronarium was applied to the soil as a green manure to control the root-knot nematodes Meloidogyne incognita and M. javanica. Chrysanthemum coronarium significantly reduced nematode infection of tomato roots and improved plant-top fresh weight, both in the greenhouse and in microplots. Other green manures, derived from Anthemis pseudocotula, wild chickpea (Cicer pinnatifidum), Geranium spp. and wheat, were not as effective as C. coronarium. Chrysanthemum coronarium, retained its nematicidal activity even when applied as a dried material. Only mature C. coronarium plants, in their flowering stage, exhibited nematode control activity, but the green plant parts were more effective than the flowers. An aqueous extract of C. coronarium exhibited in vitro, nematostatic activity towards M. incognita and M. javanica second-stage juveniles and inhibited their hatching from eggs and egg-masses; its nematostatic activity was expressed also against other phytonematode species such as Heterodera avenae and Pratylenchus mediterraneus, but did not affect the beneficial entomopathogenic nematode Steinernema feltiae.     

Improved attachment and parasitism of <Emphasis Type="Italic">Trichoderma</Emphasis> on <Emphasis Type="Italic">Meloidogyne javanica</Emphasis> in vitro

Monoclonal and polyclonal antibodies that bind to eggs and/or second-stage juveniles of the nematode Meloidogyne javanica were tested for their effects on the parasitic interactions between this nematode and the fungus Trichoderma. Parasitism of Trichoderma asperellum-203 and Trichoderma atroviride on nematode egg masses, eggs and juveniles was enhanced when antibodies were incorporated into in vitro parasitism bioassays. Parasitism on separated eggs (without gelatinous matrix) and their hatched juveniles was also improved, compared to controls without antibodies that did not attach fungal conidia. Improved parasitism could be due to bilateral binding of the antibodies to the nematodes and conidia, enabling better conidial attachment to the nematodes. Enhanced germination of antibody-bound conidia further improved parasitism. Differences were observed among antibodies in their effects on fungal parasitism and their interaction with Trichoderma species. We focused mainly on the egg- and juvenile-binding monoclonal antibody MISC that exhibited a stronger reaction with T. asperellum-203 than with T. atroviride. Pretreatment of this antibody with fucose inhibited its binding to nematodes and conidial attachment to nematodes, as well as conidial agglutination in the presence of the antibody. Antibody binding to juveniles affected their movement and viability, especially gelatinous matrix-originated juveniles. The fucose-specific lectin Ulex europaeus-I enhanced conidial attachment to nematode life-stages, and conidial agglutination occurred in its presence. These phenomena were inhibited by preincubating lectin with fucose. Our results suggest that carbohydrate residues, such as fucose, on the surface of the nematode and fungal conidia are involved in the antibody- and lectin-mediated improved parasitism.     

Effects of air temperature,relative humidity and canopy wetness on gray mold of cucumbers in unheated greenhouses

Microclimatic variables were monitored in cucumber crops grown in polyethylene-covered, unheated greenhouses in Israel during the winter of 1987/88. The winter was characterized by a relatively large number of rainy days. The relative humidity (RH) in the greenhouses was high (>97%) during most of the day, resulting in long periods of dew persistence. Dew point temperature and duration of dew deposition were calculated for the plant canopy. Disease incidence was monitored in 2-m-high plants, both on senescing female flowers (‘fruits’) and on stems. Multiple linear correlations were calculated for gray mold incidence and duration of air temperature and RH at specific ranges, and of leaf wetness (LW). Disease was characterized by two stages, according to the rate of its development and the microclimatic conditions influencing it. In the first phase of the epidemic a high correlation was found between infected fruits and air temperature in the range of 11–25°C, and RH in the range of 97–100% or LW. In the second phase, disease incidence was better correlated with air temperature in the range of 11–16°C and RH above 85% (R² = 0.681); there was no correlation between disease and LW at this stage. Development of stem infections was correlated with air temperature in the range of 11–16°C during the first phase of the epidemic. By contrast, the second phase was characterized by a close correlation between stem infections and RH in the range of 80–100% but also with air temperature in the range of 11–16°C, or with air temperature in the range of 11–25°C and RH 80–100%, and LW.     

Ventricular rate control using a novel vagus nerve stimulating system in a dog with chronic atrial fibrillation

A 4-year-old, intact male Dogue de Bordeaux dog with congenital valvular pulmonic stenosis, tricuspid valve dysplasia, and chronic atrial fibrillation underwent ultrasound-guided balloon valvuloplasty in addition to pharmacological treatment. Owner compliance to prescribed pharmacotherapy proved very poor, and concerns developed regarding the ability to successfully control heart rate and symptoms using drug therapy alone. These concerns were addressed by the implantation of a novel vagal stimulation system that was programmed to prevent a ventricular rate of >145 bpm. Consequently, post-operative ventricular response rate decreased from up to 250 to 140 bpm. Successful ventricular rate control was maintained for 291 days post-operatively, following which euthanasia was elected by the owner due to persistent right-sided congestive heart failure. To the authors' knowledge, this is the first report of successful continuous rate control using a vagal stimulating system in a closed-chest, client-owned dog with chronic atrial fibrillation secondary to spontaneously occurring organic heart disease.