Assessing the resistance of different varieties against black leg and soft rot of potato caused by Pectobacterium carotovora subsp. carotovora

Introduction

Potato (Solanum tuberosum L.) is an annual herbaceous, self-pollinated and one of the most important cultivated tuber crop belong to the family Solanaceae. Solanum stenotonum is considered as a probable ancestor of all cultivated potatoes (Reddy et al., 2018). The importance of this food crop is understood by most of the developing countries specially in urban areas. In India, it is considered as a cash crop that provides excellent income to farmers. It is rich in carbohydrate and contains little fat. It is also rich in vitamin C, vitamin B and potassium, while Its skin provides substantial fiber. Lot of compounds in it also contributes to antioxidant activities. Freshly harvested potatoes contains water (75-80%), carbohydrates (16-20%), crude protein (2.5-3.2%), minerals (0.8-1.2%), fats (0.1-0.2%), fiber (0.6%) and some vitamins (Camire et al., 2009). Bacterial diseases pose a serious threat to potato cultivation. Soft rot and blackleg, primarily caused by Pectobacterium carotovora (formerly Erwinia carotovora), are responsible for significant losses both in the field and during storage. These pathogens cause seed tuber decay, poor plant emergence and post-harvest deterioration. Bacterial wilt, caused by Ralstonia solanacearum, is particularly destructive in tropical and subtropical regions due to its soil and tuber-borne nature (Hayward, 1991;Perombelon, 2002). Common scab, caused by Streptomyces scabies, affects tuber quality by producing corky lesions on the surface, thereby reducing market value (Loria et al., 2006). Soft rot is characterized by the breakdown of tuber tissues, which initially appear as small, water-soaked lesions around lenticels or stolon attachment points. Under low humidity, lesions become dark and sunken, whereas high humidity favors rapid enlargement and spread (Czajkowski et al., 2015). Blackleg and soft rot are caused by Gram-negative, facultatively anaerobic, rod-shaped bacteria with peritrichous flagella, belonging to genera Pectobacterium and Dickeya. Pectobacterium carotovora is a soil borne pathogen mainly survives in clay and heavy soil association with low calcium concentration. Bacteria get enter the seed potatoes through wounds and injuries (Olivieri et al., 2004). Therefore, the identification and screening of resistance potato varieties is a crucial step in any integrated disease management program. Varietal screening involves the evaluation of different varieties under artificial inoculation condition to determine their relative resistance for susceptibility to black leg and soft rot disease. This process helps plant breeders and pathologists to identify promising lines that can be used directly in cultivation or as donors in breeding program. Moreover the knowledge gained from screening can assist in understanding the genetic basis of resistance, facilitating the development of improved cultivars through conventional and molecular breeding approaches. This ensures that newly released varieties retain effective resistance in the field. It also contributes to a sustainable crop protection strategy that minimizes dependence on fungicide and supports ecofriendly agriculture. Therefore, some potato cultivars commonly cultivated by farmers in Rajasthan were screened for resistance to tuber soft rot (Rashid et al., 2013).

Materials and Methods

The field experiment was conducted at Horticulture Research Farm, of Rajasthan College of Agriculture, MPUAT, Udaipur, Rajasthan. To know the resistance reaction of soft rot development in potato 10 varieties viz., Kufri Pukhraj, Kufri Khayati, Kufri Sindhuri, Kufri Pushkar, Kufri Surya, Kufri Ganga, Kufri Lima, Kufri Neelima, Kufri Nilkanth and Kufri Bahar were screened under artificial inoculation through pin prick methods. Pcc was isolated from potato tubers expressing soft rot symptoms using the semi-selective medium technique as described by Bdliya and Langerfeld (2005) which was used throughout the experiments. The evaluation was based on the incidence of tuber soft rot. Disease incidence (DI) was determined by counting the number of infected potato tuber expressed as a percentage of the total number of tubers observed. The severity of tuber soft rot was assessed on a scale of 0-5 as described by Bdliya and Langerfeld (2005) where: 0-no symptom of rot 1-1-15% of tuber rotten 2-16-30% of tuber rotten 3-31-45% of tuber rotten 4-46-60% of tuber rotten 5 ≥ 61% of tuber rotten.

Evaluation of potato varieties against the black leg and soft rot of potato

Host resistance is a most effective, easy, eco and environmental friendly approach of disease management. To find out the source of resistance against Pcc, a total of 10 potato varieties were screened under artificially inoculation conditions for consecutive two crop seasons, Rabi 2022-23 and 2023-24. The disease incidence of each test line was recorded as per the standard rating scale of 0-5 as described by Bdliya and Langerfeld (2005).

The two years pooled data presented in Table-2 reveals that among a total of 10 potato varieties screened against Pcc, seven varieties viz., Kufri Pukhraj, Kufri Khayati, Kufri Pushkar, Kufri Surya, Kufri Ganga, Kufri Lima, and Kufri Neelima were found highly resistant lines against the pathogen, while three varieties were categorized as moderate resistant (Kufri Sindhuri, Kufri Nilkanth and Kufri Bahar). Our findings are parallel to the results of various workers Tripathi and Verma (1975) reported that Kufri Deva a potato var. resistant to Erwinia carotovora pv. carotovora contains a higher phenol contents and poly phenol oxidaze activity in the pool and the tuber than the susceptible. C-1769 chlorogenic acid and caffaic acid are present in higher quantities in Kufri Dewa and the oxidation products of these may be important in resistance to the bacterium. Somani et al. (1988) found that there was progressive increase in soft rot incidence in tuber of cultivar (K. Chandramukhi) harvested from January to March and kept for storage. Wounded cork formation in the tuber cannot be taken at the criterion of resistance.

Conclusion

It was concluded from this study that the ten potato varieties screened showed varying responses to tuber soft rot. Among a total of 10 potato varieties screened against Pcc, seven varieties viz., Kufri Pukhraj, Kufri Khayati, Kufri Pushkar, Kufri Surya, Kufri Ganga, Kufri Lima and Kufri Neelima were found highly resistant lines against the pathogen, while three varieties were categorized as moderate resistant (Kufri Sindhuri, Kufri Nilkanth and Kufri Bahar).

Acknowledgement

AcknowledgementThe authors are highly grateful to the Dean, Rajasthan College of Agriculture, Udaipur, Head, Department of Plant Pathology for providing necessary facilities.

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