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Assessment of Postharvest Soil Fungal Population with Special Reference to Trichoderma in Eggplants

A Shirin
Department of Plant Pathology, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

MD Hossain
Department of Plant Pathology, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

MH Ar Rashid
Department of Horticulture, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

MB Meah
Department of Plant Pathology, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

Abstract/ Executive Summary:

The research work was done to assess the postharvest soil fungal population and to find out the relation between population dynamics of Trichoderma and soil-borne disease of 41 eggplant cultivars. Soil samples collected from the IPM lab germplasm maintenance field at the post-harvest stage were analyzed for microbes in the dilution plate technique. Fungal colonies that appeared in each plate were counted and made their average. Incidence and severity of Fusarium wilt and Sclerotium collar rot in the plot of 41 eggplant varieties were recorded at the flowering-fruiting stage. The highest total soil fungal population was estimated from the plot soil of eggplant var. Singnath S (IPM- 42) that was 40.75×10⁴. The var. Bijoy had the lowest fungal population that was 7.5×10⁴. A comparison between Trichoderma population and other fungal populations was made. Different eggplant cultivars had variations in the population of two important soil fungi- Trichoderma and Fusarium. The total populations of Trichoderma and Fusarium in the plot soil of 41 eggplant varieties were 129.75 and 348.75 × 10⁴ per gram of soil, respectively. The average number of colonies of Trichoderma varied with the range (1-8.25) per plate. Fusarium varied with the range from (2-22.50). In 20 important eggplant varieties out of 41, both Fusarium wilt and Sclerotium collar rot incidence ranged between 0.00 to 40.00%. The variety Puta begun had the highest incidence of Fusarium wilt with the highest soil population of Fusarium oxysporum against the absence of Trichoderma harzianum. The disease incidence at the flowering-fruiting stage was negatively correlated with the population of Trichoderma. Disease severity decreased with the increase in Trichoderma population. An increase of Trichoderma population decreased the population of other fungi (Fusarium oxysporum and Sclerotium rolfsii). These results are clearly indicating that Trichoderma might have the antagonistic potential and might contribute to the reduction of incidence of soil-borne diseases.

Keywords: Soil fungal population, Trichoderma, Eggplant, Wilting, IPM

Location: Plant Diseases Diagnostic Clinic (PDDC), Department of Plant Pathology, Bangladesh Agricultural University, Mymensingh.

Start Date: 00-09-2010

End Date: 00-07-2011

Program Area: Pest Management

Commodity: Eggplant, Fungus

Objectives:

To determine the relationship between soil-borne pathogenic fungi, soil antagonist population, and soil-borne diseases and determine the post-harvest soil fungal population of eggplant, determine the varietal difference in harboring soil fungal population as well.

Methodology:

Experimental place: Field experiments were conducted at Plant Pathology Research Field from September 2010 to July 2011. The land of the experimental field was medium-high in topography and the soil belonged to the old Brahmaputra Flood Plain of the Agroecological zone (AEZ-9). It is characterized by a non-calcareous dark gray flood plain. The experimental field was located at 24^o 45` N latitude and 90^o 5` longitude at an altitude of 18m above the mean sea level (Karim 2003). The land type was medium-high with loamy soil texture near-neutral soil p^H range 5.5-6.8, low organic matter, and medium K status (Anonymous, 1997). Laboratory experiments were done at Plant Diseases Diagnostic Clinic (PDDC), Department of Plant Pathology, Bangladesh Agricultural University, Mymensingh. Eggplant varieties: Forty-one varieties of eggplant grown in the field for the maintenance of IPM lab Germplasm were used for this experiment. Collection and preparation of soil samples: The soil samples were collected from the IPM Lab germplasm maintenance field at the postharvest stages of the crop. Five soil samples were randomly collected from the plot of each eggplant variety. The five samples were mixed thoroughly to get composite samples which were used as working samples. Soil collection was made at a depth of 6 inches with the help of an auger. At the time of collection, the surface of the soil was scrapped to remove dry topsoil and other superficial plant debris. Each composite sample was kept in a cellophane bag with proper labeling. After collection, the bags were kept under shade. Design of experiment: The experiment was laid out in Completely Randomized Block Design (RCBD) with 4 replications. Isolation of soil fungi: Dilution Plate technique (Dhingra and Sinclair, 1985) was used for the isolation of soil microbes, and the following steps were followed. Preparation of working area: Since the bacteria and fungi are always present as contaminants in the soil, it is important to exclude them as much as possible from the surface of the working area and the equipment to be used. The surface of the working area was disinfected with cotton swabs (methylated spirit (70%). The hands were disinfected by the same. The glasswares (test tubes, Petri dishes, pipettes, beakers, etc.) were sterilized in a dry oven. Preparation of working sample: For every dilution of soil samples, the working sample was prepared from the composite sample that was made after the soil sample collection at the post-harvest stage of the eggplant field. One- gram soil sample was taken with the help of electric balance. Making soil suspension (soil dilution): One gram of soil was placed in the test tube containing 9 ml of sterile water and stirred thoroughly for few minutes in order to obtain a uniform 1:10 dilute soil suspension. This was used as a stock solution. One ml of that 1:10 stock suspension was transferred with the help of a sterile pipette into the 2^nd test tube containing 9 ml sterile water and shaken thoroughly thus resulting in 10^-1 dilution. Then 1 ml of 10^-1 dilution is transferred to 3^rd test tube containing 9 ml sterile water by sterile pipette thus making 10^-2 dilution. This way dilution was made up to 10^-4. Preparation of culture media: Potato Dextrose Agar (PDA) was used all through in the experiment for the culture of soil-borne microbes. The prepared standard PDA was poured in 500ml glass bottles and sterilized (121^oC, 121 psi for 15 min). The media were acidified with 30 drops of 50% lactic acid per 250 ml medium. The acid was added to avoid bacterial contamination if any. Isolation of micro-organisms (fungi) from soil: One ml of diluted soil sample was placed at the center of the PDA plate and spread with a spreader. Four Petri-dishes were inoculated for each sample with 1 ml of diluted soil sample. This is repeated with every soil sample. The inoculated PDA plates were then incubated for 7-10 days at room temperature (26±2^oC). The colonies that grew up in the Petri -plates were recorded after 3-7 days. The color and the colonies in different plates were counted for each eggplant variety. Subcultures were made by transferring a small colony to a new PDA plate on the basis of the color and morphology of the colony. Further transfers were made for the purification and identification of the microbe. During purification, the contaminated plates were discarded. Observations: The fungal colonies that emerged on PDA plates were observed for color, consistency, and shape. On the basis of the properties especially the color, the colonies in different plates were counted. Estimation of the fungal population in soil samples: The number of the colonies developed in each plate was counted and an average value was calculated for each sample. The number of colonies per ml of soil suspension was calculated by its colony forming units (CFU) (Islam, 2009). Data collected during the experimental period were tabulated and analyzed following MSTATC, a completely statistical method. Treatment means were compared with Duncan’s Multiple Range Test (DMRT) (Gomez and Gomez, 1984).

Source of Information: Progressive Agriculture 32 (1): 31-42, 2021

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Achievement/Findings:

It was observed that with the increase of Trichoderma population other soil-borne fungi including Sclerotium rolfsii and Fusarium oxysporum were decreased. Incidence of Fusarium wilt and Sclerotium collar rot were lower or absent in those eggplant varieties where the population of Trichoderma was higher. That means Trichoderma population in the soil can be helpful in reducing the population of other pathogenic soil fungi. So, the Trichoderma population in the soil can reduce other pathogenic soil-borne fungal populations, and can be used in controlling these soil pathogenic fungi. So IPM Lab Bio-pesticide may be used in the form of formulated Trichoderma. This will help the farmers to reduce the production cost avoiding haphazard and excess application of toxic chemicals which often have their residual effects in the soil, in plants, in fruits, and also in the farmers’ body.

Knowledge Management: Journal