Journal of Plant Pathology & Microbiology

Management of Powdery Scab (Spongospora subterranea) of Potato in Dailekh, Nepal

Roman Pandey^1*, Ritesh KumarYadav², Dipesh Giri¹, Bibek Budhathoki³, Ram Chandra Neupane¹ and Sudan Gautam^{1 1}Department of Agriculture, Agriculture and Forestry University, Rampur, Chitwan, Nepal
²Department of Plant Pathology, The Agriculture and Forestry University, Rampur, Chitwan, Nepal
³Department of Seed Science and Technology, Agriculture and Forestry University, Rampur, Chitwan, Nepal
^*Correspondence: Roman Pandey, Department of Agriculture, Agriculture and Forestry University, Rampur, Chitwan, Nepal, Email:

Received: 14-Jul-2022, Manuscript No. JPPM-22-17464; Editor assigned: 18-Jul-2022, Pre QC No. JPPM-22-17464 (PQ); Reviewed: 01-Aug-2022, QC No. JPPM-22-17464; Revised: 08-Aug-2022, Manuscript No. JPPM-22-17464 (R); Published: 16-Aug-2022, DOI: 10.35248/2157-7471.22.13.626

Introduction

In Nepal, potato powdery scab was first reported from a potatoes which grown about 3650 m above sea level in the Sherpa winter village, Jabluk near Beding in the Rolwaling valley in the North East. The development of disease in the tuber is either by planting disease free seed tubers in infested soil or infected seed tuber in non-infested soil. The disease is becoming a major constraint for profitable cultivation of potato under field conditions. Increasing concern regarding chemical residue, environment and health hazard, the impact of excessive pesticide usage on fragile Hilly ecosystem and mainstreaming of organic agriculture in Karnali Province at policy level demand alternative ecofriendly management method for powdery scab. Moreover, chemical treatments have been reported to provide limited control over disease [1].

The use of bio control agents and organic amendments has been suggested as an alternative to chemical for controlling plant disease. The recent study suggested that organic amendments have disease suppressing properties without chemical residue especially those caused by soil borne pathogen. The amendments commonly result in a highly metabolically active micro biota which can be antagonistic towards many pathogens. The mechanism of disease control for high nitrogen-containing amendments is the generation of ammonia and or nitrous acid following degradation of the amendments by microorganisms [2]. The formation of these products to concentrations lethal to pathogens is regulated by the soil pH, organic matter content, and nitrification rate, sand content and buffering capacity. Similarly, biological control agent, Trichoderma spp has potential to parasitize spore balls of Spongospora under controlled experimental growing conditions. Recent study has revealed the ability of endophytes to suppress this disease which includes Bacillus subtilis, Gliocladium catenulatum, Heteroconium chaetospira, Microbispora rosea sp., Streptomyces griseoruber, S. griseoviridis, Streptomyces lydicus, S. olivochromogenes, Trichoderma atroviride, T. harzianum and T. Viride.

Research and studies against management of potato powdery scab in Dailekh are limited. The main objectives of the research was to investigate the eco-friendly management options using bio-fungicide fortified organic amendments and safer chemicals for powdery scab disease of potato under field condition in Dailekh [3].

Materials and Methods

Experimental location

The experiment was carried out at Gurash Rural Municipality ward number 4, Dailekh district Nepal during 2020/2021. The study site is located at 28.74˚N latitude 81.65˚E longitudes with elevation of 1360 masl.

Experimental design

The experimental design details for this experimental trial are given in Table 1 [4].

Table 1: Details of experimental design used in study site at Rittha, Gurash Rural Municipality-04, Dailekh, Nepal, 2021.

Treatments details

The treatments used in the experiment along with application dosage and application method are given in Table 2.

Table 2: List of treatments, application dosage and application method.

Experiment details

Potato seed tubers were collected from Nepal potato seed production farmer group, Gurash-05, Dailekh. Also, the required treatments Trichoderma viride, Pseudomonas fluorescens, Bacillus subtillis, boric acid, Metalyxal+Mancozeb, Flusulfamide, well decomposed farmyard manure, vermicompost and spent mushroom substrate were collected. Trichoderma viride, was mixed with well decomposed farm yard manure and incubates for 7 days [5].

In each treatment, seed tubers were dipped for 30 minutes and followed by shade drying before planting.

To make soil free from large soil clods and weeds, about 3-4 deep ploughing followed by harrowing was done. The respective bio control agents were fortified with respective organic amendments. The soil application was done by incorporating bio fortified organic amendments after land preparation. The seed tubers were dipped for 30 minutes and followed by shade drying before planting. After sowing the tubers, ridges and furrow were made in the field and complete plantation procedures were done. The recommended dose for potato as enlisted in was used: FYM: 30 ton ha^-1, Urea: 140 kg ha^-1, DAP: 220 kg ha^-1, Potash: 100 kg ha^-1. All the fertilizer doses were incorporated into the field before sowing except nitrogen which was used half dose as basal dose and half dose after 25 days of plantation [6]. Potato plants were irrigated in furrow. Irrigation was done after 30 days of planting. Flooded irrigation was avoided and water level was maintained below 2/4^th of ridges while irrigating the field. The variety used was Desiree and its day to maturity is around 90 days. Therefore, potato from the experimental field was harvested after 90 days of plantation. The climatic data for the entire duration of the research is given in Figure 1.

Figure 1: Agro meteorological pattern during the cropping period of potato (Source: NASA POWER).

Data collection

The data observation was done from 4 sample plant, centre of each plot, immediately after harvesting [6].

Pathological observations

Disease severity: The disease severity was determined using disease index given. All the tubers from the sample plant were washed in water and visually assessed for scoring the disease severity (Figure 2). The disease scores from disease severity assessment data sets were converted to proportions of surface area covered by diseased using the conversion. Percentage surface area less than 20% has different conversion compared to percentage surface area greater than 20% [7-10]. These conversions should be carried out using mean values after statistical analysis of disease scores. An example is that of potato tubers from each of two plants. The powdery scab severity scores for the seven tubers from one of the plants were 6,4, 5, 5, 6,7, and 6 (mean=5.57), whereas those for the nine tubers from the other plant were 2,2,1,2,1,2,1,2,and 1 (mean=1.56). Mean score converted to proportions of tuber surfaces diseased of 41% and 8% respectively.

Figure 2: Percent disease control by respective treatments against powdery scab of potato at Dailekh, Nepal, 2021.

These conversions will be made arithmetically using the equations:

Y=5X (for disease scores<4); and Y=13.3X-33 (for disease scores>4); where Y=% of surface area diseased, and X=mean disease score.

Percentage Tuber Infection (PTI): Percentage tuber infection is a proportion of infected tuber in a plot [11,12]. The tuber with scores 0 and 1 were categorized as healthy tuber and remaining score were categorized as infected tuber. The PTI was calculated by given formula;

Percent Disease Control (PDC): PDC was calculated by given formula;

Biometric observations

Fresh root weight: The fresh root weight was recorded by removing soil particles from root zone.

Fresh shoot weight: Yield per plot: Yield per plot was recorded as the sum of healthy and infected tuber yield harvested from a plot.

Benefit cost return over control untreated:

Statistical analysis

The collected data were systematically arranged and entered in MS Excel. Then the arranged data were analyzed using the software, R studio. The means were compared by using Duncan’s Multiple Range Test (DMRT) at 5% level of significance (Gomez and Gomez). Effectiveness of treatments was studied based on above mentioned parameter.

Results

Disease severity and percentage tuber infection

The disease severity of powdery scab disease on potato was found significantly influenced by the application of the treatments [13]. Comparing all the treatment, the significantly lower disease severity was found on T2 (5.10) which were statistically at par with T10 and T3 while the significantly higher disease severity was found on T12 (10.48) which was statistically at par with T5, T6 and T11. The influence of different treatments on percentage tuber infection of powdery scab of potato is shown in (Table 2). There was a significant difference in percentage tuber infection by the treatments (Table 3). The percentage tuber infection was significantly lower in T4 (19.22) which were statistically at par with T8 while the percentage tuber infection was significantly higher in T12 (76.25) which were statistically at par with T7 and T6 (Table 4).

Table 3: Influence of different treatments on disease severity and percentage tuber infection of potato powdery scab at 90 DAS in Dailekh, Nepal, 2021.

Table 4: Influence of different treatments on biometric parameters against powdery scab of potato at 90 DAS in Dailekh, Nepal, 2021.

Percent disease control

The bar diagram shows percent disease control by respective treatments against powdery scab of potato. The treatment seed tubers dipped with Trichoderma viride formulation+soil application of Tricoderma viride bio fortified with vermicompost (T2) showed higher (51.30) percent disease control followed by treatment seed tubers dipped with boric acid (T10) while the treatment seed tubers dipped with Pseudomonas fluorescens formulation+soil application of Pseudomonas fluorescens bio fortified spent mushroom substrate (T6) shows lower (3.42) percent disease control followed by treatment seed tuber dipped with Pseudomonas fluorescens formulation+soil application of Pseudomonas fluorescens bio fortified vermicompost (T5) (Table 5) [14].

Table 5: Benefit cost ratio of treatments over untreated control against potato powder scab in Dailekh, Nepal, 2021.

Benefit cost ratio of treatments over untreated control

The highest B:C ratio was observed in treatment seed tubers dip with boric acid T10 (12.70) followed by the treatment seed tubers dip with Trichoderma viride formulation+soil application of Trichoderma viride bio fortified spent mushroom substrate (T3) while the lowest B:C ratio (1.5) was observed in treatment seed tubers dip with Trichoderma viride formulation+soil application of Trichoderma viride bio fortified with vermicomposting (T2) [15-17].

Discussion

The biocontrol agent Trichoderma viride bio fortified with vermicompost @100 kg/ha reduces higher disease severity and highest percent disease control against soil borne disease. Similar result was also found by Subashini, 2021. The antagonistic microbes Trichoderma spp has the ability to parasitized spore balls of Spongospora subterranea under control experimental condition. The report aligns with the experimental findings. The seed treatment with boric acid @3% also reduces disease severity along with higher percent disease control. Similar result was reported in Jan, 2002 on the experiment on effect of seed or soil treatment with fungicides on the control of powder scab of potato. The bio control agent Bacillus subtilis in green house and field condition reduces disease severity against seed and soil borne infection. The report aligns with findings. The reduction of disease severity ultimately had decreased percentage tuber infection and had increased percent disease control in the plot treated with bio control agent and biocontrol agent fortified with organic amendments. The treatment seed tubers dipped with (Metalaxyl+Mancozeb)+soil application of Flusulfamide was found to be incapable in reducing disease severity, lower percent disease control and higher percentage tuber infection. Moreover, chemical treatments have been reported to limited control over powdery scab of potato. Falloon trial had confirmed various chemicals, including, Mancozeb reduced the proportion of diseased tubers in the potato. There is no significant reduction in the yield as no gall formations were seen in root zone in the experimental plot. Study indicates that there is no reduction in yield as powdery scab effect the substandard appearance of tuber. The study is aligns with the findings. For controlling powdery scab no sole method is adequate as suggested by Harrison JG. So, the consortia of seed tuber dip with biological agent and biological agent fortified organic amendments reported effective management in findings.

Conclusion

Among different management treatments, potato seed tuber dip with Trichoderma viride @10 gm/kg coupled with soil application of Trichoderma viride fortified vermicompost @100 kg/ha was found most promising in terms of disease control followed by potato seed dip with boric acid @3 percent. The highest B:C ratio was found in case of potato seed dipped with boric acid @3 percent followed by seed tuber dipped with Trichoderma viride @10 gm/kg coupled with soil application of Trichoderma viride fortified spent mushroom substrate @100 kg/ha as compared to other management treatments. The study revealed the effective control of powdery scab disease using consortia of seed tuber dip with Bio-Control Agents (BCA) and BCA fortified organic amendments.

Acknowledgments

The authors are obliged to help from Agriculture and Forestry University (AFU) and Prime Minister Agriculture Modernization Project (Potato zone) for providing the opportunity to conduct the research.

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