Rootstock resistance to soil-borne phytopathogenic fungi, such as Phymatotrichum omnivorum (Shear) Duggar, is an important factor in disease control. Measurement of natural rootstock resistance is often based on plant survival/mortality percentage, and /or growth data. Fungal colonization of host roots in disease screening experiments may not be uniform for many reasons, causing variability in host response. Quantification of fungal colonization is needed in order to better understand rootstock performance. Ergosterol, a structural sterol in cell membranes of fungi, is not found in higher plants, and can thus be a measure of fungal colonization. Ergosterol was extracted from roots of pecan seedlings artificially inoculated with P. omnivorum and grown in an environmental growth chamber. Analysis of extracts with HPLC revealed that seedlings which were killed in screening, or had low root performance ratings, had increased levels of ergosterol. Non-inoculated controls also contained Ergosterol. indicating contamination and possible competition by other fungi.
Monte L. Nesbitt, J. Benton Storey, D. Lyda, and L.J. Grauke
Mario Orozco-Santos, Javier Farías-Larios, Jaime Molina-Ochoa, and José Gerardo López-Aguirre
Melon wilt (MW) is one of the main diseases affecting the cucurbitaceous crops in the Pacific Central region of Mexico. The use of resistant varieties is the most effective strategy to reduce the damage caused by MW; however, variety performance depends on the fungal race occurring in the field. The use of fungicides, such as benzimidazols and methyl bromide, is a common practice, but there are contamination concerns, and a search is on for alternatives to diminish the negative effects on the agro-ecosystem. The aim was to determine the effect of the application of soil amendments and mulching on the incidence of MW, and on melon yield. Soil amendments incorporated were: rice straw (3 t·ha-1); compost 1, prepared with chicken and bovine manure, and banana and orange wastes (5.7 t·ha-1); compost 2, prepared with bovine and horse manure, coconut wastes and grasses (8 t·ha-1), vermicompost (3 t·ha-1), and a control. All treatments were established using transparent mulching during 21 days. The number of MW propagules in amended soils were similar at 5, 10, and 20 cm deep, but the percentage of diseased plants was higher (4.5%) in the control, which could be caused by the incidence of other fungi propagules, perhaps antagonistic, that contributed in diminishing the MW when compared with the control. The fruit weights and fruit sizes were not different between treatments on small (21–30 sizes), medium (15–18 sizes), and large (9–12 sizes), but total fruit numbers were 1.15-, 1.07-, 0.99-, and 1.09-fold higher when compared with the control. The application of soil amendments affected the antagonistic fungal populations even when it did not affect the cantaloupe yield. We suggest that soil amendments will improve soil fertility and increase melon yields, and studies are currently running.
Orlando Javier Torres-Meza, Marcelino Bazan-Tene, Javier Farias-Larios, Jose Gerardo Lopez-Aguirre, and Jaime Molina-Ochoa
Low organic matter in soil is a large problem in crop production around the world because it affects physical, chemical, microbiological, and morphological properties. On the other hand, regions with agro-industry generally generate waste that can cause some level of contamination. Therefore, it is necessary to find some use for this kind of waste. This study was done to evaluate the effect of lemon industrial waste on tomato (Lycopersicum esculentum Mill.), growth in a saline soil. The experiment was conducted under greenhouse conditions. Soil samples were taken from 0- to 20-cm depths at the El Chococo ranch, located at 18°47'N and 103°55'W. Four treatments were imposed: 0 (0), 600 (1), 1200 (2), and 1800 (3) m3/ha. Soil in treatments was incubated at ambient temperature for 40 days. Tomato seeds were germinated for 30 days and later transplanted to plastic bags containing treatments. After transplant, tomato plants were grown during 40 days, after which was measured: high plant, dry and fresh weight, aerial, and radicular biomass and foliar area. Treatments were distributed under randomized design, and Tukey's (0.05) separation means was performed. Organic matter, pH, and CE in soil before treatment application was 1.01%, 8.5, and 7.6 dS/m respectively (in 1:5 soil: water ratio). After application, OM increased until 3.7% in treatment 3. pH and CE decreased to 5.5 in treatment 2, and 1.57 dS/m in treatment 0. All data measured in plants had the highest values in treatment 1, and all plants died in treatment 0. We believe that is necessary to do this experiment in the field to obtain additional data.
Alejandro Alarcon, Frederick T. Davies Jr., Robin L. Autenrieth, David Wm. Reed, and David A. Zuberer
A phytoremediation study in a 3 × 3 × 2 factorial experimental design was conducted to determine the effect of Glomus intraradices (AMF) inoculation and inorganic fertilization on the growth and development of Lolium multiflorum cv. Passarel Plus, and on the degradation of total petroleum hydrocarbons (TPH). The 80-day study was done with pots containing sandy soil. Seedlings of L. multiflorum were transplanted to uncontaminated or soil contaminated with Arabian crude oil (ACO) at concentrations of 3000 and 15,000 mg·kg-1. Half of the seedlings were inoculated with 500 spores of AMF. Plants were fertilized with Long Ashton Nutrient Solution (LANS) at 0.5×, 1.0×, or 2.0× strength, modified to supply 30 μg·mL-1 P to maximize the AMF establishment. Total plant dry weight and leaf antioxidant activity were reduced by ACO when compared to control plants. The LANS fertilization enhanced plant growth under ACO-contamination, and allowed similar antioxidant activity in plants exposed to 15,000 mg·kg-1. Soil rhizosphere respiration was increased by LANS, particularly with 15,000 mg·kg-1 ACO. AMF inoculation did not enhance plant growth, antioxidant activity, or microbial respiration. The average root colonization was around 30% in contaminated and uncontaminated rhizospheres, indicating that the tolerance of AMF symbiosis to ACO. Greater TPH degradation was achieved in non-AMF plants at 3000 mg·kg-1 ACO in combination with 0.5× LANS. LANS-fertilization with 1.0× or 2.0× did not enhance TPH-degradation when compared to 0.5× LANS.
Esmaeil Fallahi and John K. Fellman
Effects of three times and five rates of urea application on productivity, tree growth, soil nitrate movement, nutrient partitioning, and postharvest fruit quality of `Redspur Delicious' apple on M.7 rootstock over several years were studied. Time of application did not have significant effects on most fruit quality factors or yield. However, significant differences were observed for quality and yield measurements among different quantities of N. Fruit firmness decreased with every increment in N increase. Trees with N at 0.045 kg/tree had lower yield and higher fruit firmness than those with higher quantities of N. Fruit weight and color decreased with each increment increase in the quantity of N. Trees with N at 0.045 and 0.18 kg/tree had significantly better (more red) color and lower fruit N and leaf N than those with higher quantities of N. Bud tissue nutrients were affected by quantity of N application. Fruit from trees with N at <0.18 kg/tree had lower soluble solids. High N increased fruit ethylene and respiration. Nitrogen application affected 2-methyl butyl acetate of fruit. Monitoring nitrate movement through the soil showed that application of N at >0.45 kg/tree, particularly in fall resulted in excess levels of nitrate, increasing the possibility of underground water contamination. Applying N at ≤0.32 kg/tree did not result in excess soil nitrate at 1.52-m depth.
Hudson Minshew, John Selker, Delbert Hemphill, and Richard P. Dick
Predicting leaching of residual soil nitrate-nitrogen (NO3-N) in wet climates is important for reducing risks of groundwater contamination and conserving soil N. The goal of this research was to determine the potential to use easily measurable or readily available soilclimatic-plant data that could be put into simple computer models and used to predict NO3 leaching under various management systems. Two computer programs were compared for their potential to predict monthly NO3-N leaching losses in western Oregon vegetable systems with or without cover crops. The models were a statistical multiple linear regression (MLR) model and the commercially available Nitrate Leaching and Economical Analysis Package model (NLEAP 1.13). The best MLR model found using stepwise regression to predict annual leachate NO3-N had four independent variables (log transformed fall soil NO3-N, leachate volume, summer crop N uptake, and N fertilizer rate) (P < 0.001, R 2 = 0.57). Comparisons were made between NLEAP and field data for mass of NO3-N leached between the months of September and May from 1992 to 1997. Predictions with NLEAP showed greater correlation to observed data during high-rainfall years compared to dry or averagerainfall years. The model was found to be sensitive to yield estimates, but vegetation management choices were limiting for vegetable crops and for systems that included a cover crop.
Peggy G. Lemaux
The major challenge facing society in the 21st century is to feed and provide shelter for increasing numbers of people while protecting human health, our natural resource base, and the environment. To accomplish this, we must combine traditional technologies that stress conservation with modern technologies that rely heavily on biologically based solutions. Biotechnology, by its historical definition, has play an important role in environmental clean-up, but the contemporary practices of biotechnology will lead to more-sophisticated approaches. These technologies will allow clean-up of existing contamination and even prevention of contamination through more-sensitive and accurate monitoring systems. One of the most important advances is in bioremediation, in which microorganisms and plants remove contaminants from the soil or water and concentrate of volatilize them. In addition, plants are being modified through the changing of single genes so that they are less susceptible to pathogenic microorganisms, viruses, or insects, and more efficient in nitrogen utilization. The use of such modified plants, in concert with good agricultural practices, should lead to reductions in chemical inputs of pesticides and fertilizers. Strategies have also been developed that permit the “manufacture” in plant “pharms” of industrial products that are now produced through the use of nonrenewable resources. These biological approaches are part of the cadre of tools that we need to solve the problems of the next century. In addition, these tools will be instrumental in understanding the basic biological systems upon which the solutions to many of these challenges will come. Biotechnology is not a technological fix, but it should form part of the mind-set from which we design our strategies.
Nancy K. Todd and David Wm. Reed
Concerns over groundwater contamination due to greenhouse runoff have caused many growers to turn to subirrigation as an alternative watering method. One reported problem is the movement of salts to the top layer of the rootzone due to zero leaching. Many growers are faced with the added challenge of subirrigating plants with poor-quality water than contains a high salt content before the addition of fertilizer. An experiment was conducted to investigate the movement of salts in the root zone and the effects on root development and overall plant growth. Plants were grown using water treated with NaCl + CaCl2 (1:1 equivalent basis) at the following total concentrations: 0, 2, 4, 6, 8, 10, 14, and 18 mM. Treatment time was 10 weeks (marketable stage). At harvest, height was measured and plants were cut off at the soil line and divided into shoots (stems and leaves) and roots for fresh and dry weight. Leaf area was measured. The root zone was divided into three layers—top, middle, and bottom (≈3 cm each). Roots were separated from each soil layer and soil samples collected for measuring EC and pH using 1:2 dilution. Soil samples showed EC in the top layer of the root zone was much higher than the middle and bottom layers. Root weight also decreased substantially in the top layer of the root zone. Height, FW, DW, and leaf area of plants did decrease with increasing salt concentration, indicating that the detrimental effects of poor-quality water on subsequent plant growth, especially in a subirrigation system.
B. Bravdo and E.L. Proebsting
The use of drip irrigation in orchards is increasing worldwide. Water shortage, prevention of ground water contamination, and improved production are the main reasons for this increase. The combination of partial wetting of the soil and control of the water penetration depth considerably increases the efficiency of irrigation. Recent technological improvements permit maintenance of a constant volume of irrigated soil in which gradients of soil water matric potentials and mineral concentrations exist from the irrigation point to the margins of the wetted zone. Because water and mineral uptake is a function of soil matric potential and mineral concentration, respectively, optimal uptake rates by certain portions of the root system always exist along these gradients for any given environmental conditions. Gradients of air concentration act similarly and permit maintenance of high water availability without any interference with root aeration. Due to the relative ability of the roots to exchange water, minerals, and, possibly, oxygen, the entire root system functions more efficiently compared to root systems under conventional irrigation methods. Physiological root restriction effects induce the formation of a large number of small roots with frequent branching. Consequently, the relative surface area for water and mineral absorption is increased several-fold, and the increased number of root tips that are known to be involved in production of hormones (such as gibberelins and cytokinins) is significant. Evidence for enhanced fruit bud formation under conditions of root restriction is presented here. Water treatment and filtration technology has improved, and clogging of surface or buried drip systems now can be minimized, which also increases the suitable range of water quality for use in drip systems.
Jeffrey P. Mitchell*, Gene M. Miyao, Jim J. Jackson, Lee F. Jackson, Tom Lanini, Charlie G. Summers, and Jim J. Stapleton
Two field comparisons of conservation tillage tomato production alternatives following wheat were conducted in California's Central Valley. Both studies compared: 1) standard tillage; 2) bed disk or permanent bed minimum tillage; and 3) strip-tillage following winter wheat crops that were harvested the previous June. Processing tomatoes were produced at the site in Davis, Calif., and fresh market tomatoes were grown in Parlier, Calif. At both sites, establishing tomatoes using a commercial transplanter or a modified conservation tillage transplanter achieved adequate stands even in the minimally-tilled strip-till system. Timing of the strip till operation, however, is critical so that large chuncks of dry soil are not brought up and so that these do not create very rough bed surfaces that may cause harvest problems, particularly for processing tomatoes. Machine harvesting the crop at the Davis site did not seem to create any mechanical difficulties or generate additional trash going into the harvest trailer. This may have been due to the fact that by harvest time, the majority of the surface residue from the previous wheat crop had already been broken down or at least sufficiently worked into the soil to pose minimal mechanical harvester impedance or contamination. Tomato yields for the reduced till systems equalled yields of the standard till systems at both sites.