Potato (S. tuberosum L.) is an important vegetable crop that belongs to the Solanaceae family and is considered a promising food source that can fulfill the food demand of the fast-growing population, which is projected to reach 10 billion by 2050 (Călinoiu et al., 2018; Levaj et al., 2023). The primary goal of potato growers is to achieve higher productivity, enhance the nutritional quality of tubers, minimize losses that may occur in the field as well as during the post-harvest period due to multiple biotic and abiotic stresses, and further implement better management practices (Tiwari et al., 2022). Various biotic and abiotic stressors include heavy rains, frost, pests, diseases, and poor post-harvest management. These stressors contribute to yield loss and deterioration of the nutritional profile in potatoes (Devaux et al., 2020). Moreover, it is reported that more than 40 pathogens and insect pests can damage both the foliage and tubers of potato plants (Tiwari et al., 2020). Several fungal diseases affect potatoes and are responsible for low tuber yield. These include late blight, black scurf, Fusarium wilt, powdery scab, and Fusarium dry rot (Liu et al., 2021). On the other hand, potatoes become more vulnerable to galls, blemishes, and rots owing to their higher moisture content (70%) in post-harvest storage conditions (Ranjan et al., 2021). Earlier, rot in potatoes was considered minor and inevitable. However, it has now become a major concern for potato growers. In cold storage conditions, it adversely affects seed tubers and table-purpose potatoes (Tiwari et al., 2020). Among various fungal complexes that may be responsible for rots in potatoes, Fusarium dry rot, caused by the Fusarium spp. complex, is a destructive soil-borne disease in potatoes (Falert and Akarapisan, 2019). It not only causes a yield loss of approximately 6–25% per year but also reduces the market value of potatoes worldwide (Khedher et al., 2021). The genus Fusarium deteriorates tuber tissues under storage conditions; however, soil- and tuber-borne inoculum can affect plants in the field (Xue et al., 2023).

Fusarium is one of the most destructive genera in the world as it infects almost all crop species (Christian, 2023). This genus is notable for its diversity and the range of diseases it can cause. It comprises over 300 phylogenetically distinct species, including important plant pathogens and opportunistic human pathogens. The species are categorized into several complexes, such as the Fusarium solani complex and the Fusarium oxysporum complex, which include numerous phylogenetically distinct species associated with different diseases affecting both plants and humans (Ekwomadu and Mwanza, 2023). Symptoms of dry rot include sunken and wrinkled brown–to-black tissue patches on tubers with less dry matter and shriveled flesh. During prolonged storage, the wrinkled patches produce cottony white, purple, pink, or brick orange spores and mycelial mass, which can survive in soil or decaying tuber debris (Xue and Yang, 2021). However, there is limited information available about the epidemiology of dry rot disease. The fungus can survive well at 4°C–10°C, posing an equal threat to potatoes used for processing and seed tubers (Tiwari et al., 2020). The virulence of various species of Fusarium depends on the cultivar types of potato and their storage conditions.

Initially, FDR was attributed to a fungus called Fusisporium, which was later identified as F. oxysporum (Tiwari et al., 2020). Currently, 17 different Fusarium spp. and 5 variants cause potato dry rot worldwide (Xue et al., 2023). A European project on F. sambucinum began in 1989, involving diverse methods and global collaboration. Among the Fusarium species causing potato dry rot, F. sambucinum is considered the most aggressive in Europe, China, and North America (Secor and Salas, 2001; Du et al., 2012). In Britain, F. coeruleum is the most prevalent fungus in cold storage facilities (Peters et al., 2008; Sharma et al., 2024), while F. sulphureum is recognized as the most frequent species across Europe and North America (Gachango et al., 2012; Zhao et al., 2024). In North Dakota, F. graminearum and F. sambucinum are the primary species associated with potato dry rot (Tiwari et al., 2020). In Michigan, F. oxysporum is the most common species, although F. sambucinum remains the most aggressive species. Interestingly, F. graminearum, a cereal pathogen, also plays a significant role in potato dry rot in North Dakota and Canada, likely due to wheat-potato crop rotations (Peters et al., 2008; Estrada et al., 2010; Xue et al., 2023; Daami-Remadi, 2012).

In China, F. sambucinum is the most aggressive species in major potato-growing regions, accompanied by F. oxysporum, F. avenaceum, F. acuminatum, and F. equiseti (Du et al., 2012; Ranjan et al., 2021). In Iran, F. sulphureum and F. solani exhibit high incidence and aggressiveness in the predominant potato cultivars. In Egypt, F. sambucinum is the predominant species, followed by F. oxysporum, F. verticillioides, and F. incarnatum (Gherbawy et al., 2019). In India, F. sambucinum was first reported from cold storage facilities in Madhya Pradesh, emphasizing the need for nationwide surveys to evaluate the prevalence of Fusarium species (Tiwari et al., 2020).

The interaction between Fusarium species and potato tubers is characterized by a dynamic relationship that influences disease severity and development rates (Mejdoub-Trabelsi et al., 2015; Khedher et al., 2021). The pathogen’s hemibiotrophic lifestyle, coupled with its ability to produce mycotoxins, allows it to effectively colonize and damage potato tissues (Gutiérrez-Sánchez et al., 2023). Understanding these interactions is crucial for developing effective management strategies to mitigate the impact of dry rot on potato production. In light of the growing concern regarding this disease in processing potato cultivars, the present study was conducted to survey and collect infected potato samples across various cold storage facilities and potato fields in seven major potato-growing areas in Haryana and isolate the Fusarium spp. responsible for potato dry rot, perform pathogenicity tests, and identify the fungal isolates through cultural, morphological, and molecular characterization.

Currently, there is insufficient information on the species diversity of potato dry-rot pathogens in India. Therefore, surveys, sample collection, and pathogen identification experiments were conducted to assess the presence, distribution, and identification of causal organisms for effective plant disease management. In our study, conducted from 2023 to 2024, 55 fungal isolates were collected from various locations in Haryana and were characterized based on their cultural and morphological characteristics. Of these, 53 isolates were maintained throughout the research, while 2 were discarded due to excessive contamination in culture. Of these, 40 isolates were selected and identified at the molecular level (ITS sequencing). We confirmed the fungus up to species level because Fusarium species are widely distributed as saprophytes, soil inhabitants, and pathogens of many plants worldwide. The identification of some species is difficult and is still not clear. The fact that different species are reported under the same name and a single species under different names is also confusing (Theron, 1999). The majority of research on FDR focuses on strains of F. solani and F. sambucinum. However, strains of these species are often referred to by one or more of the synonyms by which they are known by, which complicates conclusions drawn from previous findings for non-specialists. Often, strains of these species have been incorrectly named or identified, resulting in confusion among researchers (Theron, 1999). New initiatives in the traditional area of morphological research, such as computer-aided identification, and modern techniques used by molecular biologists, such as analysis of ITS, translation elongation factor 1-α, ribosomal RNA sequences, and fingerprinting with polymerase chain reaction, have provided new insights into species relations (Theron, 1999). The results revealed that F. sambucinum, F. oxysporum, and F. solani were the most common pathogens causing dry rot in potato tubers in Haryana. This research provides valuable insights into the prevalent species of Fusarium in Haryana, which is the first evidence of its kind in the region. Similarly, Tiwari et al. (2021) identified F. sambucinum and F. oxysporum as major storage fungi causing Fusarium dry rot in potato tubers in the Jalandhar district, Punjab, India. Additionally, they isolated and identified Fusarium proliferatum as the causal pathogen of dry rot disease in the Moga district, Punjab, India, using morpho-molecular analysis. Kumar et al. (2016) conducted surveys in Punjab, India, and identified F. culmorum, F. avenaceum and F. sambucinum through morphological characters and species-specific primers. Erper et al. (2022) conducted a survey in Kyrgyzstan and identified F. sambucinum as the causal pathogen of dry rot in potatoes based on morphological and phylogenetic analysis, which was the first report of its kind in the country. Hussein et al. (2020) found 10 strains of F. solani causing dry rot of potatoes in the Upper Egypt region and identified them using morphological criteria and species-specific primers. Osawa et al. (2021) conducted studies in Nagasaki Prefecture, Japan, and identified F. acuminatum, F. commune and F. oxysporum as causal pathogens of dry rot of potatoes through morphological and DNA sequencing analyses. Similarly, Gherbawy et al. (2021) identified 187 isolates of F. solani, F. keratoplasticum and F. falciforme as the causal agents of dry rot in Upper Egypt, using morphological characteristics and molecular analyses. Azil et al. (2021) collected samples from 152 locations in Algeria and identified 13 species of Fusarium (F. oxysporum, F. venenatum, F. redolens, F. tricinctum, F. sambucinum, F. cf. incarnatum-equiseti, F. nygamai, F. brachygibbosum) and Neocosmospora (N. solani, N. falciformis) and found that F. sambucinum isolates were the most aggressive. The combination of rapid disease development, mycotoxin production, aggressive colonization ability, adaptability to storage conditions, and broad cultivar susceptibility makes Fusarium sambucinum the most aggressive dry rot pathogen of potato tubers. Understanding these factors is crucial for developing effective management strategies against this disease. A joint conclusion was drawn regarding the taxonomic position of F. sambucinum (Nirenberg, 1995a). These results led to the conclusion that strains of F. sambucinum and its synonyms should be divided into three species. These included F. sambucinum, F. torulosum, and F. venenatum. All three species included strains isolated from potatoes (Nirenberg, 1995b). The multi-species involvement of the pathogen exhibited its complexity in various regions. The findings of the study gave insight that the collection of Fusarium strains isolated from potato tubers in different regions might be useful to determine whether the proportions of fungal species in distant regions vary according to environmental conditions. In the future, it would also be interesting to investigate the specialization of the identified Fusarium species not only in different potato varieties but also in other crops.

All strains that were analysed exhibited severe infection and caused significant damage to the tubers. However, the severity of infection varied from isolate to isolate [maximum lesion diameter was observed in isolate PDR 5.1 (33 mm) followed by PDR 12.6 (32 mm), PDR 7.5.1 (26 mm), PDR 12.1 (23 mm), PDR 1.4 (17 mm), PDR 3.2 and PDR 3.3 (16 mm)]. Characterization of the aggressiveness of the Fusarium isolates on potatoes revealed the pathogenicity variations. Some isolates caused sunken dry lesions and vascular discolouration on the tubers, whereas others caused marginal lesions on any of the inoculated tubers and showed minimal growth on the potato tuber. Our study corroborated with the earlier findings of Azil et al. (2021), who also confirmed the pathogenicity tests for a number of chosen Fusarium isolates on potato and found F. sambucinum as the most aggressive one. The variations in lesions might have been due to host-pathogen compatibility factors; however, the limitation of the experiment was that it did not reveal the pathological infection relationship. Fusarium infections in potato tubers, particularly those causing dry rot, are primarily attributed to various species within the Fusarium genus, notably F. sambucinum, F. solani, and F. oxysporum (Gavrilova et al., 2024). Understanding the genetic interactions and susceptibility mechanisms involved in these infections is crucial for developing resistant potato cultivars. The interaction between Fusarium species and potato tubers involves complex genetic factors, with specific susceptibility genes playing a critical role in the plant’s defense mechanisms (Soheili-Moghaddam et al., 2023). Understanding these interactions not only aids in the identification of pathogenic species but also paves the way for developing genetically resistant potato cultivars to combat dry rot and other fungal infections. Further research is necessary to explore the full potential of gene silencing and other biotechnological approaches for enhancing potato resistance to Fusarium infections (Ali et al., 2024). In several studies, silencing of susceptibility genes led to various defensive responses, including enhanced cell death and increased reactive oxygen species (ROS) levels at infection sites, which hindered pathogen colonization. Manipulating these susceptibility genes could be a viable strategy for breeding potato varieties with improved resistance to Fusarium infection (Gogoi et al., 2024). Additionally, we isolated more than one Fusarium species from one infected tuber, and this is due to the compatibility of the microbe-microbe interaction.

The decay of tubers was estimated by measuring the average penetration of pathogens. The extent of penetration varied depending on the cultivar-specific Fusarium isolates used for inoculation and the duration of storage after fungal infection. Interestingly, isolate PDR 12.6 (F. sambucinum) caused the most severe rot in terms of penetration and lesion volume when tested on the cultivar and stored at 18°C for up to 30 days. Bojanowski et al. (2013) reported that the depth of dry rot lesions varies depending on the type of cultivar and prevalence of Fusarium spp. Heltoft et al. (2015) also reported significant variation in lesion depth, diameter, and volume among potato cultivars, depending on infection by different Fusarium spp. Du et al. (2012) and Stefańczyk et al. (2016) reported the aggressiveness of F. sambucinum in terms of lesion depth or penetration on inoculated tubers. Similarly, Mejdoub-Trabelsi et al. (2015) found that combined inoculation of F. sambucinum with F. oxysporum resulted in greater penetration in tubers compared to individual inoculation. The greater aggressiveness of F. sambucinum compared to other Fusarium spp. in terms of dry rot disease incidence and severity has been well documented (Du et al., 2012; Gachango et al., 2012; Liu et al., 2021). Kuzdraliński et al. (2014) reported that foot and crown rot disease of wheat is aggravated in the presence of F. graminearum, F. culmorum, F. poae and F. sporotrichioides.

In this study, dry rot-infected potato samples were collected from Haryana to isolate and identify Fusarium spp. Pathogenicity was confirmed using Koch’s postulates. Overall, this study highlights the dominance of highly aggressive Fusarium sambucinum in the Haryana state. Further studies on the specialization of the identified Fusarium species, not only to different potato varieties but also to other crops, would explain the mechanisms involved. Additionally, determining the profiles of metabolites and their roles in the interactions with host plants would provide further insights. Because of the differences in potato cultivars and climatic conditions, diverse Fusarium species were isolated and identified from the FDR of potatoes in various regions of Haryana. Among them, F. sambucinum was considered the most predominant pathogenic fungus leading to the FDR of potatoes. Moreover, the varieties collected for the isolation of potatoes, and none of the varieties were reported resistant to dry rot. In addition, the cultural, morphological, and molecular analyses decipher the variability in Fusarium species; therefore, this study serves as the guidelines for future research. It would be interesting to determine the agroecological diversity among fungal isolates and their relationship with prevailing agrometeorological parameters. Additionally, this study could be insightful for researchers, scientists, potato growers and industrialists. Moreover, to the best of our knowledge, this is the first study in Haryana conditions and would prove to be a milestone work to build upon. Screening of resistant cultivars, genome editing, early detection markers, and other management options could be research areas for future research.