The field experiment was conducted at the farm field of Sher-e-Bangla Agricultural University, and the laboratory experiment was conducted in the laboratory of the Department of Plant Pathology, Sher-e-Bangla Agricultural University, Dhaka-1207.

The experimental area was under the sub-tropical climate which, characterized by the comparatively low rainfall, low humidity, low temperature, relatively short-day during November to May, and high rainfall, high humidity, high temperature, and long-day period during April to September.

The annual precipitation and potential evapotranspiration of the site were 2152 mm and 1297 mm, respectively. The average maximum and minimum temperature was 30.34 0C and 21.21 0C, respectively, with a mean temperature of 25.17 0C. Temperature during the cropping period ranged from 12.2 0C to 31.2 0C. The humidity varied from 73.52% to 81.2%. The day length ranged from 10.5 to 11.0 hours only, and there was no rainfall during the experimental period. Temperature fluctuation plays a vital role in disease development.

The experimental site belonged to the Agro-EcologicalRegion of “Madhupur Tract” (AEZ No. 28). It was Deep Red Brown Terrace soil and belongs to “Nodda” cultivated series. The topsoil is slightly clay loam in texture. Organic matter content was very low (0.82%) and soil pH varied from 5.5-6The soil of experimental site was analyzed in Soil Resource Development Institute (SRDI), Dhaka and found as loamy soil which contains total Nitrogen 0.061(%), Phosphorus 35022 microgram per gram of soil, Sulphur 22.60 microgram per gram of soil, Potassium 0.030 miliequivalent per 100 gram soil and Calcium 2.67 miliequivalent per 100 gram soil.

The experimental plots were arranged in a Randomized Complete Block Design (RCBD) with three (3) replications. The total experimental area was 209m2 (19m×11m) and divided into three blocks, each comprising seven plots corresponding to seven treatments. The total number of plots was twenty-one. Each plot measured 2m × 3m (6m2) and planted thirty-six plants. The treatments were randomly assigned to plots within every block, with every treatment replicated once per block.

Six fungicides, namely Win 77 WP, Tilt 25 EC, Rovral 50 WP, Pipertax 50 WP, Mancozeb 80 WP, and Sazid 70 WP were collected from the local market.

Recommended doses of fungicidal solution were prepared by mixing thoroughly with the required quantity of fungicide and water. Win77 WP (1gm/L), Tilt 25 EC (1gm/L), Rovral 50 WP (1gm/L), Pipertax 50 WP (2gm/L), Mancozeb 80 WP (2gm/L), and Rovral 50 WP (1gm/L) for preparation of solution for recommended concentration.

Table 1: The Following Fungicidal Treatments Were Used For Spraying of Potato Seedlings

At recommended doses, suspensions/solutions of fungicides were prepared by mixing thoroughly with the requisite quantity of normal plain water. Spraying was started one month after transplanting. A total of 3 sprays were done with 15-day intervals with a hand sprayer. A control treatment was maintained in each block where spraying was done with plain water.

Collection of Diseased Samples

Diseased sample of BARI Potato-7 (Solanum tuberosum) and its leaves were collected from the Farm field of Sher-e-Bangla Agricultural University, Dhaka- 1207. Collected samples were put in polyethylene bags immediately after collection to protect from drying, as presented in Figure 1.

Diseased leaf samples were brought to the laboratory and washed thoroughly to clean different parts and cut into small pieces, by keeping infected and healthy tissues and sterilized by dipping in 0.1 % NaOCl solution for 30 seconds and rinsed three times with sterile water. Leaf samples were placed on moist blotter paper on Petri dish (Fig. 2), which was incubated at 20±2 ⁰C for 2 days in 12 hours with alternate light and darkness. potato leaves were incubated for 20 days at 20±2 ⁰C in the normal lab conditions. After incubation, when the whitish mycelium had grown a bit of mycelium was taken with the help of a sterilized needle and transferred onto sterile solid PDA plates and kept in an incubator at 25±1 ⁰C for growth. Temporary slides were prepared for identification under a compound microscope. No molecular characterization was conducted; only the morphological features of Alternaria Solani were observed in the experiment.

Disease incidence is the proportion of plant units diseased in relation to the total number of units examined. Plant units mean the leaves, stems, fruits, tubers, rhizomes, and bulbs, etc. that show any symptoms. In some cases, the plant unit represents the plant as a whole. Disease severity is the proportion of plant tissues infected in relation to the total amount of tissue examined. Ten plants per plot were randomly selected and marked with a red color tape for calculating the percentage Disease Incidence. In the case of percentage, the disease Severity from the selected plant’s leaf area was measured. The same selected plants were evaluated on each observation. One observer estimated the data.

Percent disease incidence and severity were calculated by using the following formula:

Disease Severity (%)

Disease Severity (%) = Area of tissues infected Total area of tissues inspected × 100

Disease Incidence (%)

Disease Incidence (%) = Number of plant units diseased Total number of plant units examined × 100

Leaf Area Diseased (LAD)/plant in different treatments

Leaf area diseased of the ten selected plants in each plot against each treatment was measured and recorded by eye estimation. The mean percentage of leaf area diseased was calculated by dividing the total number of observations.

The data of disease severity was assessed in a randomized complete block design with three replications by using the modified 0-5 disease rating scale of [20] for leaves, where-

The disease index (PDI) was expressed by using the formula suggested by [21]

PDI (%) = ∑ Disease Ratings ( Total Number of Observations × Maximum Disease Rating ) × 100

The recorded data were compiled, tabulated, and subject to statistical analysis. Analysis of variance was done with the help of the computer package program MSTAT-C with 5% level of significance. This experiment was two factorial designs. The mean differences were adjudged by Duncan’s New Multiple Range Test (DMRT) [22].

Spots appeared as small, dark, dry, papery flecks, which grew to become brown-black, circular to oval areas with concentric rings. The spots were often bordered by veins that made them angular.

Several temporary and semi-permanent slides were prepared to observe the microorganisms under the microscope. Infected leaves were collected from the field, then preserved for laboratory testing. Figure 2 shows the laboratory observations results. Observations of the fungus were recorded by adopting a slide culture. The fungus produced profuse mycelial growth on PDA. Initially, the mycelium was hyaline, which turned to grey-brownish. Fungus colonies were dark to grey-black, and conidiophores arising singly or in small groups produced spores in a chain. Conidia were large with longitudinal and transverse septa and a short beak, typical for Alternaria solani under the microscope.

Table 2: Efficacy of Different Fungicides on the Management of Plant Infection of Potato Against Early Blight Under Field Conditions

The treatments showed promising performance in reducing the disease incidence (plant infection) at different Days after planting (DAP). The application of different selected fungicides was observed and evaluated at regular intervals, at 60, 70, and 80 days after planting of potato tubers. At 60 DAP, the effect of different treatments was found to differ significantly in respect of plant infection. Among the fungicides, the lowest plant infection (17.65%) was recorded in the case of Mancozeb 80WP, followed by Rovral 50WP (18.70%). The highest plant infection (83.75%) was recorded in the control presented in Table 2. At 70 DAP, the highest plant infection (85.52%) was recorded in the control, and the lowest plant infection (14.32%) was recorded in the case of Mancozeb 80 WP, followed by Rovral 50 WP (14.75%). At 80 DAP, the lowest plant infection was also recorded in the case of Mancozeb 80 WP (13.05%) followed by Rovral 50 WP (14.55%). The application of different treatments was calculated based on the plant infection recorded at 80 DAP. Reduction of disease incidence at 80 DAP, 86.95% (plant infection) was recorded in the plot that was applied with Mancozeb 80WP. According to Table 1, at 60, 70, and 80 DAP, the treatments applied showed a similar trend of results in reducing the leaf infection. At 80 DAP, the lowest leaf infection was also recorded in the case of Mancozeb 80 WP (13.17%) followed by Rovral 50 WP (15.28%).

Table 3: Efficacy of Different Fungicides on the Management of Leaf Infection of Potato Against Early Blight Under Field Conditions

According to data in Table 3, at 60 DAP, among the fungicides, the lowest leaf infection (17.67%) was recorded in the case of Mancozeb 80WP, followed by Rovral 50WP (18.20%). At 70 DAP, the highest leaf infection (85.75%) was recorded in the control, and the lowest leaf infection (14.46%) was recorded in the case of Mancozeb 80 WP, followed by Rovral 50 WP (15.74%). At 80 DAP, the lowest leaf infection was also recorded in the case of Mancozeb 80 WP (13.17%) followed by Rovral 50 WP (15.28%). Reduction of disease incidence at 80 DAP 86.83% (leaf infection) was recorded I then which plot that was treated with Mancozeb 80 WP.

Table 4: Efficacy of Different Fungicides on the Management tf The Percent Disease Index (PDI) Of Potato Against Early Blight Under Field Conditions

The performances of the treatments on different days after planting (DAP), viz. 60 DAP, 70 DAP, and 80 DAP in reducing disease severity, showed a similar trend irrespective of different DAP. As per the last recording data at 80 DAP, the Mancozeb 80 WP showed the highest performance (86.70%) in the reduction of disease severity. The second highest reduction of disease severity was recorded in of Rovral 50 WP (85.92%) followed by Sazid 70 WP (84.72%), presented in Table 4.

Table 5: Efficacy Of Different Fungicides on the Yield of Potato Against Early Blight Under Field Conditions

The highest tuber yield (27.78 t ha-1) of potato was observed from the plot treated by Mancozeb 80WP, whereas a significantly similar yield (26.58 t ha-1) was harvested from the plot applied by Rovral 50 WP. The yields of potato 25.11 t ha-1, 22.77 t ha-1, 24.67 t ha-1, and 23.86 tha-1 were found from the plots treated with Sazid 70 WP, Tilt 25 EC, Win 77 WP, and Pipertax 50 WP, respectively. These results are shown in Table 4. At that time, the tuber yield (12.56 t ha- 1) of potato was observed from the control plot. The chemical fungicides also increased the yield considerably compared to the control. The highest increase in the percentage of yield was 121.18% when the field was applied by Mancozeb 80 WP.