Assessing the relative efficacy of antagonists, organic amendments and chemical means in managing black scurf disease in potato crop

Introduction

Potato (Solanum tuberosum) is herbaceous, starchy, tuberous plant under Solanaceae family. Potato crop is attacked by many fungal, bacterial and viral diseases which are widely spread while few are localized, which significantly affect the growth and production of potato. In recent years, with an increase in potato planting area and continuous cropping, among fungal diseases of potato, soil-borne diseases, including potato black scurf have become increasingly serious. Rhizoctonia solani (teleomorph: Thanatephorus cucumeris) is a fungal pathogen associated with severe diseases in many crop species. It is one of the fungi responsible for black scurf of potato. Rhizoctonia solani Kuhn AG-3 is the main causal organism of black scurf disease of potato and it is a major problem all over the world. Black scurf usually does not affect yield of potato crop if it is low in intensity but the quality of tuber is affected resulting in the poor market value. Erampalli and Johston (2001) [17] revealed that Rhizoctonia solani Kuhn decrease the progeny, tuber quality as well as quantity. In potato, it is associated with stem cankers and tuber blemishes. These diseases can cause both quantitative and qualitative damage to the potato crop. Quantitative losses occur due to infection of stems, stolons and roots that affect tuber size and number, whereas, qualitative losses mainly occur through the production of misshapen tubers and the development of sclerotia on the tuber surface (known as black scurf). On tuber surface, brown to black irregular hard-masses of sclerotia are formed (as shown in Fig. 1). Though these structures adhere tightly to the tuber skin, they are superficial and do not cause damage, even in storage and help to perpetuate the disease from one season to the next. The loss of quality caused by black scurf, particularly for fresh market potatoes, financial loss is the most economically damaging aspect of this disease (Atkinson et al., 2010; Keiser et al., 2012; Kumar et al., 2017) [3,8,10] . According to Keiser (2008) [7] , yield losses caused by black scurf reached upto 50 percent, severely affecting potato production thus resulting in marked economic losses. It is spread in India in different regions with different levels of severity and is a major problem in fields where potato is cultivated year after year in the same field (Arora, 2012) [2] . In Haryana, severe yield losses due to this disease have been reported (Lakra, 1992) [12] . Different options available to control diseases include use of organic amendments, bio-agents and fungicides. Therefore, disease can be managed with help of antagonists and by chemical means. Chemical control of black scurf has been extensively studied in many potato-producing countries (Jeger et al., 1996) [6] . Bioefficacy of different fungicides, i.e., Penflufen 240 FS, Monceren 250 EC, Carbendazim 50 WP and Emisan 6 FS, was evaluated against black scurf of potato by dip treatment on Kufri Bahar cultivar (Kumar and Raj, 2016) [9] . A variety of Trichoderma spp. isolates have been found to effectively control soil borne plant pathogenic fungi such as R. solani, Sclerotium rolfsii, Pythium spp. and Fusarium spp. (Singh J.K et.al., 2017) [14] . Therefore keeping in view, the economic importance of the diseases and inadequate information on the efficacy of fungicides, organic amendments and bio-agents, the present study wasconducted with the objectives "Assessing the relative efficacy of antagonists, organic amendments and chemical means in managing black scurf disease in potato crop".

Materials and Methods

Field experiment was conducted at Research farm of Vegetable Science, CCSHAU Hisar, during two rabi season to test the efficacy of promising fungicides, antagonists and organic amendments which were found best under in vivo/vitro conditions. Infected potato tubers of susceptible cultivar 'Kufri Bahar' were planted during first fortnight of November, first and second year under field conditions (plot size 3.0 x 2.0 m, spacing 60 x 45 cm) using RBD with three replications. The infected tubers were planted in the field after dipping in the solutions of MEMC-6 FS w/v (0.1%), Monceren 250 EC (0.1%) and T. harzianum & T. viride (10 6 conidia/ml suspension) for 10-15 minutes. Carboxy-methyl cellulose (CMC @ 1%) was used as sticker during tuber treatment for antagonists. Organic amendments i.e., vermicompost and Neem cake (20 g/kg soil) were applied as soil application at 20 days before of planting. The disease incidence and disease index/severity were recorded after harvesting of the potato.

Observations recorded

i. Disease incidence was calculated by using the formula described by Ahmed et al. (1995) [1] as described below:

No. of tubers infected Disease incidence (%) = × 100 Total number of tubers observed ii. Disease index (severity) was calculated by using the formula of Kumar and Raj (2016) [9] Sum of all numerical rating Percent disease index (severity) = × 100 Total number of tubers observed × Max. grade

Statistical analysis

The data of in vivo experiments was analyzed by using statistical package of programs OPSTAT (Sheoran, 2006) [13] . Angular (arcsine) transformation was applied for analysis of the percent data in RBD design. Analysis of variance (ANOVA) in one-way or two ways for the analysis of the data wasused to calculate the critical difference (CD) and coefficient of variations (CV) for the significance of the treatments.

Results and Discussion

The results of field experiments on the management of Rhizoctonia solani causing black scurf of potato is presented in table 3. Results indicated that tuber treatment with fungicides, bioagents and organic amendments resulted in significant reduction in disease incidence. In chemical treatments, monceren followed by MEMC, whereas, in antagonists T. harzianum followed by T. viride were found effective, while in case of organic amendments, vermicompost was more effective followed by Neem cake against Rhizoctonia solani. Among all the above treatments, least percent disease severity was observed in monceren treatment that supported minimum disease incidence, whereas, maximum percent disease severity was found in Neem cake treated tubers. Among fungicides, monceren showed highest reduction in disease (98.17 and 99.02%, respective years) over the control with the lowest disease incidence (01.33 and 00.67%, respective years), followed by MEMC which reduced black scurf disease up to 82.57 and 84.46 percent over control with the disease incidence 12.67 and 10.67 percent in respective years. Tuber treated with bioagent T. harzianum showed reduction in disease (63.30 and 66.99%, respective years) over the control with the disease incidence (26.67 and 22.67%, respective year), followed by T. viride treatment. Among the organic amendments, vermicompost which controlled disease up to 47.71 and 48.55 percent during the respective years, were found more effective than Neem cake which was least effective among the treatments that showed lowest reduction (41.28 and 38.84%) in the disease over control with the highest (58.82 and 56.78%) disease incidence in the respective years. Among all the above treatments as shown in table 3, least disease severity was found with monceren treatment than rest of the treatments, whereas, maximum percent disease severity was found in Neem cake treated tubers. A similar type of results on bioefficacy of different fungicides monceren 250 EC (0.25%) and emisan-6 FS (0.25%) was evaluated against black scurf of potato by dip treatment on Kufri Bahar cultivar by Kumar and Raj (2016) [9] which showed disease incidence 01.7 and 19.9 percent with disease control 97.6 and 69.3 percent, as well as reduced disease index were 0.3 and 0.9 percent, respectively in both the conditions. Similar types of findings under in vitro were also found by Buswal et al. (2025) [4] while working with Rhizoctonia solani. Experimental results demonstrated at a concentration of 100 ppm, the monceren fungicide completely inhibited mycelial growth up to 100 percent, followed by MEMC (81.0% inhibition whereas, Trichoderma harzianum, inhibiting mycelial growth by 71.11 percent. Kumar et. al. (2018) [11] reported that the soil amendment of vermicompost could control disease up to 40.00 and 50.01 percent at the dose of 10 and 20 g/kg soil/pot respectively. Similar observations were also made by Tsror et al. (2001) [16] while working with R. solani in field condition. They have reported that T. harzianum, organic cattle manure composts had reduced disease incidence and severity of the pathogen. The present findings are also in conformity with the reports of Singh and Chaudhari (2012) [15] as the black scurf disease of potato was managed effectively by treatment of tuber with T. harzianum @ 8 g/kg and Neem ban @ 5 ml/lt, which showed the disease incidence 20.96 and 25.41 percent and disease control 63.21 and 47.00 percent over control, as well as it reduced the disease index 0.62 and 0.76%, respectively. Trichoderma harzianum @ 10 6 conidia/ml T4 Trichoderma viride @10 6 conidia/ml T5 Vermicompost @ 20g /kg soil T6

Neem Cake @ 20g /kg soil T7 Control (Infected tubers)

Acknowledgement

AcknowledgmentsThe author acknowledges with appreciation the contributions of Dr. Anil Kumar, Ex-Professor and Head, Department of Plant Pathology, CCSHAU, Hisar, whose guidance, technical expertise and financial support were instrumental in the successful execution of this research.

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