The following section of research provides a detailed overview of the interactive effects of biocontrol agents and environmental factors and how these affect both host plant and pathogen populations within hydroponic systems. A literature review gathered background information on the effects of biocontrol agents and environmental manipulations on plant growth and disease severity in hydroponic systems.
Trial 3 - The effect of Trichoderma (Eco-TID) in cucumber bag
Trial 1: Determining the optimum range of soil moisture for
Trial 2: Effects of Trichoderma inoculation under varying soil
The role of Trichoderma in N nutrition: Inconclusive
Trichoderma and nitrogen nutrition - effects on growth
In vitro screening of pH effects on Trichoderma conidial
Effects of pH and sugar availability on spore germination and
Interactions between Trichoderma and pH in the biological control of Pythium
Water temperature and form of nitrogen effects 143
Literature review
The effects of biological control agents on biotic a':ld abiotic interactions in hydroponic systems
Introduction
All of these fungi produce motile zoospores, are promoted by aquatic environments, and propagate in hydroponic systems by recirculating zoospore-infested nutrient solution. New features of hydroponic systems (including new pathogen problems) are highlighted, and both direct effects of biocontrol agents and interactive effects with controllable elements of the hydroponic environment are discussed in detail.
Novel features of hydroponic systems
If percolation past the root zone is properly managed, there is very little water loss and evaporation from the soil due to percolation and. Fertilizers Inefficient use due to Effective use of small amounts of spray applications that are evenly distributed, resulting in uneven action on all plants without distribution of leaching and leaching over the root zone more than 50% over the root zone.
Pythium spp. as major pathogens in hydroponics
Biocontrol in hydroponic systems
Biocontrol and Growth stimulation by Trichoderma
Antibiotic production or antibiosis refers to the ability of Trichoderma spp. to produce various antibiotic substances such as gliotoxin that inhibit plant pathogens. 1999) studied the ability of Trichoderma harzianum T-203 to induce plant defense responses in hydroponically grown cucumber seedlings.
Effects of biocontrol agents and soil moisture
The amount of air in a medium at container capacity is called the 'air-filled porosity' of the medium. Table ·1.4.B Summary of air-filled porosity requirements for plaQ!s in container growing media (From Handreck and Black, 1994).
Effects ofbiocontrol agents and root zone temperature
Resh (1995) provided a basic explanation of the effects of pH on the availability of various elements in plant nutrition. Harman and Taylor (1988) looked at the effects of pH in matrix priming with various biocontrol agents.
Effects of biocontrol agents and nutrition
The spread of stem rot was significantly lower in the case of the 4:1 KIN ratio. In the above case, the change of nutrient solutions was found to have direct effects on plant diseases.
Concluding Remarks
Mycorrhizal fungi are fungi that share a symbiotic association with the roots of a plant (Agrios, 1997). Haynes (1986) pointed out that mycorrhizal fungi are known to prefer NH4-N to N03-N and it seems possible that mycorrhizal fungi can act as biological control agents for nitrification under vegetated conditions.
1 .11 References
Effects of low and high levels of magnesium on the response of sunflower plants grown to ammonium and nitrate. Effects of pathogen species, inoculum concentration, temperature and soil moisture on bean root rot and plant growth.
Construction of Hydroponic Research Systems
- Introduction
- Greenhouse construction
- Verti-gro® system
- Horizontal mini troughs
- Temperature trials
- Bag culture trials
A flexible pipe was fitted to each pump to carry water from the tank to the top of the chimney, where it was connected to a specially designed irrigation ring. These rings ensured an even distribution of the nutrient solution to all parts of the upper pot at a rate of 2 elmin. Reservoirs with heaters for treatment with warm nutrient solution (24 °C or 30 °C) were placed at the ends of the respective troughs.
Dose effects of Trichoderma on Pythium disease severity and plant growth in Open and Closed Hydroponic Systems
Abstract
Introduction
Dose effects of Trichoderma on Pythium disease severity and plant growth in open and closed hydroponic systems. 1993) maintained, however, that direct stimulation of plant growth by Trichoderma cannot be ruled out. One possible explanation for this reduced plant growth is provided by Cutler et al. 1986) and Cutler and Jacyno (1991) who studied metabolites with phytotoxic activities produced by strains of Trichoderma.
Trial 1 - The effect of dosage rates of Eco-T®, in a recirculating (closed) hydroponics system, on Pythium control and plant growth
- Introduction
- Materials and methods
The seeds were then left to germinate in the pot for two days, as before. Instead, Trichoderma applied in the absence of the pathogen resulted in a decrease in yield at most doses. This would result in an abnormally high level of NH4-N in the root zone and could lead to ammonia toxicity.
Trial 2 - The effect of dosage rates of Eco-T® in cucumber bag culture (open system), on Pythium control and plant growth
- Results
At the end of the experiment, stems were cut at ground level and the total wet weight of shoots was recorded. No growth stimulation was recorded, all weights being below that of the uninoculated control. single application) and O.5g/Q Eco-~ (monthly application). Despite the statistical data, if one looks at the mean results (Fig. 3.3.3.A and B), many of the general trends are the same as observed in the salad experiment (Section 3.2).
Trial 3 - The effects of Trichoderma (Eco-~) in cucumber bag culture - some pitfalls overcome
- Introduction
- Materials and Methods
- Results
Rhizoctonia controls showed very low yields as some of the seedlings were killed and thus no growth was recorded. These results were to be expected because in open systems much of the Trichoderma inoculum can be leached from the system during subsequent irrigation cycles before the conidia can germinate. Other contributing factors included the biological characteristics of the Trichoderma strain used as well as the nature of the formulations.
Conclusions
The concentrations of the commercial products (CFU/g) varied by three orders of magnitude, contributing to the significant variations in efficacy. This is probably because Trichoderma conidia can be washed out of the reach of the root zone, while in closed systems they can be recirculated and have more opportunities to establish themselves in the root zone. A good understanding of the crop and the host-pathogen interactions is required to establish the correct method of data collection for such trials.
Management of soil moisture levels within artificial growth media can help control Pythium-induced reductions in yield. Similar trends were observed in strawberry trials although greater differences were recorded under optimal soil moisture conditions in terms of disease severity and growth stimulation. Biological control and growth stimulation activity was low in submerged plants and increased with increasing soil moisture.
Introduction
In this way, Trichoderma provides a buffer capacity against the direct and indirect negative effects of poor soil moisture management. There must therefore exist an optimal level of soil moisture between the two extremes, where optimal amounts of water and oxygen are supplied to the roots. The aim of these trials was to establish the optimum level of soil moisture and then to test the effects of Trichoderma on plant growth and the severity of Pythium disease under optimum as well as over- and under-watered conditions.
Trial 1: Determining the optimum range of soil moisture for hydroponically grown butter lettuce
- Results
A Soil moisture and air-filled porosity vary under optimal irrigation regimes in each medium. medium irrigation soil soil air filled air filled. When irrigation regimes resulted in soil moisture levels outside these limits (above or below), plant growth decreased. To test the interactive effects of soil moisture and Trichoderma on plant health, the optimal range identified in this initial trial was used as a baseline for future irrigation regimes.
Trial 2: Effects of Trichoderma inoculation under varying soil moisture conditions
- Introduction
- Materials and Methods
- Results
The same general trends were noted in the strawberry trial as in the lettuce trial. In the absence of the pathogen, high levels of growth stimulation resulted from Trichoderma treatments in both optimum and overwatered piles. However, in the submerged stacks, no significant growth stimulation was observed, even in the absence of the pathogen.
Conclusions
This occurs either through competitive exclusion of nitrifying bacteria in the root zone or through increased ammonium uptake facilitated by Trichoderma in a mycorrhizal type association. Trichoderma applications to soil in the absence of host plants still resulted in changes in the ammonium:nitrate ratio. The levels of NH4-N in the medium were shown to be inversely related to the population size of nitrifying bacteria.
Introduction
Inconclusive trials investigating the interactive effects of root zone temperature and Trichoderma application found that under conditions of high NH4-N and high temperatures, addition of Trichoderma could increase yield losses. It was concluded that when Trichoderma is added to artificially high population densities, it interferes with the normal process of nitrification. If Trichoderma is seen in this light, then the transition from growth promotion to growth inhibition with increasing application rate of Trichoderma is somewhat explained.
The role of Trichoderma in N nutrition: Inconclusive temperature trials reveal one of Trichoderma's secrets
- Introduction
- Materials and Methods
- Results
- Discussion
Similarly, significant biocontrol activity was recorded in the same temperature ranges (Fig. 5.3.3.8 and D and Table 5.3.3.A). This is in agreement with Kafkafi (2001) who found that the presence of ammonium in the nutrient solution is beneficial in a low root zone·. The large reduction in yield that occurred when Eco-~ was added at 24 °C and 30 °C can be explained in the same way.
Trichoderma and nitrogen nutrition - effects on growth promotion/inhibition
- Introduction
- Materials and Methods
- Results
- Discussion
A third plant was used to determine NH4-N in roots and NO3-N in shoots. At the same time, NO3-N levels in the uninoculated controls dropped to an average of only 104.3 mg/Q. Trichoderma apparently has some effect on NO3-N levels in the circulating nutrient solution seven days after Trichoderma treatment.
Trichoderma and N cycling
- Introduction
- Materials and Methods
- Discussion
This means that the proportion of NH4-N had increased from 4.9% to 7.5% after the addition of Trichoderma. Both the total bacterial population and nitrifying bacteria are seen to decrease with the addition of Trichoderma. The fact that bacterial populations appear to increase upon addition of Trichoderma at optimal rates (ie, 5x105 spores/ml) to pine bark medium is inexplicable.
Conclusions
Effect of biological strains of Trichoderma on plant growth, Pythium ultimum populations, soil microbial communities and soil enzyme activities. In liquid culture, conidial germination and subsequent root colonization were not observed at pH levels above 3.0.
Introduction
Trichoderma on the other hand favors more acidic pH levels with Harman and Taylor (1988) noting that Trichoderma species grew well at surrounding pH used these facts to improve the rh isosphere competence of Trichoderma harzianum to a practical level . Mycelial growth of Pythium ultimum was found to be strongly inhibited by Trichoderma harzianum under acidic conditions (pH 4.5 and 6) compared to pH 7.0 soils. In further experiments, hydrochloric acid (Hel) was added to the cucumber seed treatments to make the seed pH 3.7 or 3.1.
In .vitro screening of pH effects on Trichoderma conidial·
In the presence of a medium, Trichoderma is able to germinate and colonize roots at much higher pH levels. At pH 3.0, either the need for stimulants is negated, or the permeability of the conidial membranes is appropriately altered to make this possible. The observation that Trichoderma conidia germinate in nutrient solution in the absence of plant roots may suggest that the change in permeability of membranes at pH 3.0 may in itself enable increased metabolic pathways and consequent germination.
Effects of pH and sugar availability on spore germination and sporulation of Trichoderma
- Introduction
- Discussion
Media should be used to get a true reflection of pH responses with Trichoderma. The effect of pH on conidium germination is more pronounced under conditions of lack or very limited supply of sugar. Where a knowledge of the effects of pH can be applied is in the production of biocontrol agents.
Interactions between Trichoderma and pH in the biological control
- Introduction
- Materials and Methods
- Results
- Discussion
- Pythium control by Trichoderma under varying pHs
- Materials and Methods
- Results
- Conclusions
- References
Biocontrol activity of Eco--r In the research for this thesis, it was found that application rates differ between open and closed hydroponics systems. It was hypothesized that the addition of Trichoderma to a relatively sterile environment (provided by the Perlite medium) caused the Trichoderma to become established to the exclusion of nitrifying bacteria. In a separate experiment, an increase in the percentage of NH4-N was associated with a decrease in populations of nitrifying bacteria.
Thesis Overview
