EVALUATION OF BIOCONTROLS FOR THE CONTROL OF SEEDLINGS DISEASES OF SORGHUM AND TEF CAUSED BY RHIZOCTONIA AND PYTHIUMUNDER CONTROL. The main focus of the research was to screen and determine the effectiveness of potential biocontrol agents in the control of seedling diseases caused by Rhizoctonia solani and Pythium sp.
LITERATURE REVIEW ON BIOLOGICAL CONTROL OF SEEDLING AND ROOT DISEASES OF SORGHUM AND TEF
GENERAL INTRODUCTION
Successful development of BCAs is likely to depend on a thorough understanding of the biology and ecology of the pathogens and antagonists involved and their interactions with other soil inhabitants (Kerry, 1992) as well as the specific crop and husbandry of her (Berger et. al., 1996). The efficacy of biological control relies on the ability of the introduced antagonist to settle in the soil, which in turn is affected by the way it is formulated, stored and applied (Lewis and Papavizas, 1987).
SORGHUM [SORGHUM BICOLOR (L.) MOENCH] AND TEF [ERAGROSTIS TEF (ZUCC.) TROTTER]
Planting Practices: Sorghum is usually grown in rows 0.S-3.0 m apart with a sowing depth of 4-Scm depending on the cultivar's rotation habit (Martin et al., 1976). Fertilization must therefore be based on soil analysis and the requirements of a certain variety and its expected yield.
SEEDLING AND ROOT DISEASES
- Symptoms of seedling and root rot diseases of sorghum
In sorghum, the causal organisms for these diseases include Pythium spp. the main causative agent), Fusarium spp., Aspergillus spp., Rhizoctonia spp. In a study involving Pythium spp. caused severe seedling disease, Forbes et al. 1985) noted that some sorghum hybrids were able to resist the attack of this fungus.
BIOLOGICAL CONTROL
- Application of biocontrol agents
- Mechanisms of action of biocontrol agents
- Strategies for use of antagonists for biological control of plant diseases
Some of the most effective BCAs have been processed into commercially available products (Whipps and Lumsden, 2001). Knowledge of the crop: According to Cook and Baker (1983), the host plant plays a decisive role in the biological control of diseases.
Sivan, A., Elad, Y. and Chet, 1.1984. Biological control effects of a new isolate of Trichoderma harzianum on Pythiumaphanidermatum. Phytopathology 74,498-501. Control of cotton seedling damping off in the field by Burkholderia (Pseudomonas)cepacia. Plant disease.
ISOLATION AND IN VITRO SCREENING OF BACILLUS SPP
- INTRODUCTION
- MATERIALS AND METHODS
- Isolation of Bacillus spp
- Pathogenic fungi
- Dual culture test
- RESULTS
- DISCUSSION
- REFERENCES
The interaction between hyphae of pathogenic fungi and Bacillus isolates was evident on the second day of incubation, when both organisms grew towards each other. Plates A and B are examples of in vitro bioassay tests used in screening Bacillus isolates for their antifungal activities against R. After keeping the plates in the same medium for more than a week, the formation of dark rings at the edges and R.
In all antagonistic interactions between these two organisms, antibiosis appears to be the mechanism by which isolates of Bacillus inhibited the in vitro growth of the two pathogenic fungi. First, the screened biocontrol agents could inhibit the in vitro growth of the two target pathogenic fungi.
IN VITRO AND ULTRASTRUCTURE OF HYPHAL INTERACTIONS BETWEEN TRICHODERMA SPP. AND PYTHIUMSP
- INTRODUCTION
- MATERIALS AND METHODS
- Source of fungal isolates
- Dual culture tests
- Scanning electron microscopy studies
- RESULTS
- Fungal growth and interaction in dual cultures
- ESEM observations on hypha) interactions
- DISCUSSION
- REFERENCES
Individual culture tests, the contact between the hyphae of the antagonists and the pathogenic fungus began on the third day of incubation. In the interaction between SY3 and SY 4 and Pythium sp. the hyphae of the pathogen began to thicken at the point of contact and its further growth was inhibited (Figure 3.1, panels C and E). During the next few days of contact, the mycelium of the causative agent overgrew these.
In vitro results of the dual culture test revealed that the three isolates of Trichoderma were effective in inhibiting the growth of Pythium and completely outgrew the pathogen within 5-6 days of incubation. Interaction began when chemotrophic substances, released from the pathogen, stimulated the growth of the antagonist against the host (Thrane et al., 1997).
RHIZOCTONIA AND PYTHIUM UNDER CONTROLLED GREENHOUSE CONDITIONS
INTRODUCTION
However, none of these measures can prevent subsequent infections and the development of seedling diseases in the season (Kiewnick et al., 2001). Trichoderma (Hadar et al., 1984; Koch, 1999) and Bacillus (Handelsman et al., 1990; Berger et al., 1996) have been widely used as biocontrol agents against many soil-borne fungi, especially Pythium and Rhizoctonia. The introduction of Trichoderma (Elad et al., 1982) and Bacillus (Kim et al., 1997) into the soil in greenhouse trials has reduced the damping off caused by R.
Biocontrol strategy success depends on the appropriate application of one or more antagonists to the appropriate ecological niche at the right time (Harman, 1992; Lewis et al., 1995; Mao et al., 1998a). Several methods of application of biocontrol fungi (Bae and Knudsen, 2001) and bacteria (Mao et al., 1998b; Zaki et al., 1998) have been developed with the aim of increasing the spread and establishment of these agents.
MATERIALS AND METHODS .1 Source of materials
- Preparation of antagonistic bacteria and fungi
- Biological treatments
- Other treatments
- Artificial inoculation of the media with pathogens
- Variables of seedlings
- Statistical analysis
Speedling" 24 trays containing coated seeds were left in the seeding chamber overnight and watered only the next day to avoid dislodging germs prior to establishment. At the first sign of germination, Speedling'" 24 trays were transferred to a greenhouse that operated at a temperature of 26-28°C and a relative humidity of 75-85%. All Speedling'" 24 trays were left in the seeding chamber overnight and watered only the next day to allow germs to settle on the target seed.
At the first sign of germination, Speedling'" 24 trays were transferred to a greenhouse operating at temperatures of 26-28°C and a relative humidity of 75-85%. For the chemical treatments, untreated seeds were planted in Speedling'" 24 trays and roofed. with composted pine bark and watered with 3 ml Benlate®8 of 1.0 g I-I and Previcur®9 of 1.2 ml r' at planting to control R.
RESULTS
- Effects of treatments on damping-off caused by Rhizoctonia solani
- Effects of treatments on damping-off caused by Pythium sp
- Effects of season and application methods on biological control
Treatment effect was also statistically significant (P On both crops, the effects of season on the percentage emergence and final stand obtained by different treatments were not significant in controlling damping-off caused by R. so/ani or Pythium sp. In addition, there was a significant effect of season on plot weight of sorghum harvested from control treatments inoculated with R.so/ani (Tables 4.5-4.8). One of the possible reasons may be attributed to the timing of antagonistic activity in relation to infection. According to their investigations, the deleterious effects may be the result of antagonist self-inhibition or intrinsic pathogenicity. This means that no combination of BCAs and application is better or worse than the others. In contrast, beneficial substances applied to the sperm surface have the potential to be the first colonizers of the spermatosphere (Hadaret al., 1984; Chao et al., 1986). One of the likely disadvantages of a seed coating technique may be that seeds cannot be stored after treatment. Overall, the data obtained from this chapter indicate that control of damping off caused by R. Biological control of cucumber and sugar beet damping off caused by Pythium ultimum with bacterial and fungal antagonists. Development and benefits of rhizosphere-competent fungi for the biological control of plant pathogens.Journal of Plant Nutrition15,835-843. Integrated control of Rhizoctonia crown and root rot of sugar beets with fungicide and antagonistic bacteria. Seed treatment with a fungal or bacterial antagonist to reduce corn wilt caused by Pythium and Fusarium species. CHAPTERS FIELD EVALUATIONS OF BIOLOGICAL AND CHEMICAL TREATMENTS IN CONTROLLING DAMPING-OFF AND GROWTH Damping-off, caused by complex soil pathogens, is a common problem in almost all field and greenhouse crops (Bruehl, 1987; Georgakopoulos et al., 2002). Seed treatments with antagonistic microorganisms have been used successfully to eliminate or supplement the use of chemical fungicides to protect germinating embryos and seedlings from soil-borne diseases (Mao et al., 1998a; Nasby et al., 2000; Adekunle et al., 2001). ). Because protection of seeds or seedlings is required only a few days or weeks after planting, biological control of damping-off is relatively simple compared to other soil-borne diseases (Georgakopoulos et al., 2002). However, because of their variable responses, field use of biological control agents has been limited compared to fungicides (Berger et al., 1996). However, there is concern that some adhesives may have inhibitory effects on seed germination (El-Meligi, 1989), or may exacerbate seed infection by stimulating pathogen germination as they have a high nutritional value (Adekunle et al. , 2001). The flasks were inoculated with six mycelial agar plugs (diameter 8 mm, cut from the edge of a five-day-old mycelial mat on VS agar) of the pathogen. Data on precipitation at the experimental site for the period from January to July were obtained from Dr. Planting of the first trial was carried out on 26 February, and the crop was harvested on 4 (for tef) and 11 (for sorghum) April 2003. Harvested seedlings of the two crops were weighed immediately to obtain their total wet weight. After two days of drying in an oven at 70°C, the dry weights of the plant material were recorded. Significant variations due to the presence of the two pathogens were also observed on the plot weight of sorghum at P<0.05. On tef, reductions in plot weight of the control were <10% when plots containing clean seeds were infected with R. Effects of the sticker on seedling growth and disease severity relative to clean seeds are summarized in Tables 5.5 and 5.6. The effects of CMC on percent increase or reduction of seedling variables in plots were calculated by comparing the results of seeds coated only with CMC with the results of pure seeds. Effects of CMC on percent increase or decrease in plot weights were calculated by comparing the results of seeds coated only with CMC with the results of pure seeds. These two factors caused rapid drying of the soil less than one day after irrigation. Seed treatments with Bacillus or Trichoderma negatively affected seedling growth of the two crops. The main reason for the failure may have been linked to the lower germination and survival of seedlings on sorghum and relatively mild effects of the two pathogens on untreated plots. Despite the statistical information, the trends of Tables 5.5 and 5.6 show that the effects of the adhesive on the two crops were variable. No clear conclusions could therefore be drawn about the effects of the adhesive on growth and survival of seedlings as well as the severity of the disease. Therefore, repeated trials on a number of crops with larger plots with different adhesives at different concentration levels are necessary to determine the contribution of the adhesive to seedling growth and disease incidence. Effect of soil Pseudomonas isolates applied to maize, sorghum and wheat seeds on seedling growth and maize yield.Canadian Journal of PlantSciences 69,101-108. Integrated control of Rhizoctonia crown and root rot of sugar beet with fungicide and antagonistic bacteria. Plant disease. Seed treatment using pre-infiltration and biocontrol agents to reduce damping off of maize caused by species of Pythium and Fusarium. Effects of biocontrol strain of Trichoderma on plant growth, Pythium ultimum populations, soil microbial communities and soil enzyme activities. Different application methods may be preferred based on the ability of the antagonist to colonize a given area over a desired period of time, the biology of the target pathogen, and the amount of biocontrol agent to be applied. There is a need to develop an in vitro screening protocol that includes interactions of the pathogen, antagonist and the host;. In particular, the short- and long-term population dynamics of the antagonist and the pathogen;. Assessment of levels of pathogen inoculum and concentrations of the antagonist that should be used in the field to demonstrate efficacy for disease control is needed. Most of the antagonists used in various parts of this thesis appeared to have the potential biocontrol agents against attenuation induced by R.
DISCUSSION
STIMULATION OF SORGHUM AND TEF
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
GENERAL OVERVIEW
