Abstract

Introduction

Potato (Solanum tuberosum L.) ranks first as a non-cereal food crop for human consumption and has a great potential in ensuring food security in developing nations (FAOSTAT 2019). The diverse distribution pattern and major cultivation as a cash crop in areas having a high level of hunger and malnutrition make it a global crop in sustainable food availability (Haverkort et al. 2013; Devaux et al. 2020; Lal et al. 2020a). The food and agriculture organization (FAO) declared the year 2008 as the international year of the potato. Presently, potato is grown over 19 million hectares area with an annual production of 388 million tons worldwide (FAOSTAT 2019). Around 1.3 billion people consume fresh potatoes as a staple food (50 kg per person annually) in India and China. The consistent increase in potato production in the developing world exceeding developed nations indicates its importance as a source of food, income and employment especially in Asia, Africa and Latin America (Devaux et al. 2020). The greater productivity and nutrition quality improvement is the prime goal for potato breeders, at the same time minimization of losses in the field due to pest, diseases and adverse environmental conditions and better post-harvest management is also critical. Poor crop and post-harvest management, field and storage diseases, frost and heavy rains are some of the most important factors for yield loss and nutritional profile deterioration in potato (Delgado et al. 2017; Lal et al. 2020b; Tiwari et al. 2020a). There are more than 40 pathogens, such as viruses, fungus, nematode, insects and bacteria which cause damage to foliar parts and tubers in potato (Fiers et al. 2012; Kumar et al. 2019, 2020). These biotic agents cause up to 22% direct or indirect losses in the potato production system and threaten the tuber quality and yield (International Potato Center, Lima, Peru https://www.cipotato.org/; Food and Agriculture Organization, United Nations https://www.fao.org/). Potato tubers comprise more than 70% water content which makes them vulnerable to galls, blemishes and rots after harvest during handling, transportation and storage. Earlier, the rots in potato were considered as minor and inevitable, but with changing consumer preferences, these are now a major concern for potato growers which deteriorate seed tuber and table purpose potatoes in cold stores (Bojanowsky et al. 2013). Rots affect the tuber flesh deeply and are mainly classified either as soft rot or dry rot. The soft rot is a bacterial disease showing wet slimy lesions on tubers that engross the whole tuber within a few days of infection. However, dry rot is a fungal disease where a pattern of shrinking, shriveling and non-slimy lesion development is observed on the surface of tubers (Fiers et al. 2012). Potato dry rot is a devastating fungal disease caused by Fusarium worldwide. Soil and seed-borne inoculum can affect the plants in the field but the main damage occurs during storage. Dry rot affects the crop stand by inhibiting the development of potato sprouts and cause losses up to 25% with infection as high as 60% during storage (Wharton et al. 2007). The damage becomes more serious when other diseases, such as soft rot and late blight accompany dry rot during storage. An estimated loss due to this disease in the United States is US$100–250 million annually (https://www.ars.usda.gov). In the Gansu Province of China loss due to dry rot is 88% of total post-harvest losses (Suqin et al. 2004; Du et al. 2012). More than 50% of seed lots in Michigan are reported to have dry rot infections (Gachango et al. 2012). The yield loss of 25–60% is highly dependent on the inoculum level in soil (Stevenson 2001; Heltoft et al. 2016). Worldwide, more than 13 Fusarium species are causing dry rot disease in potato (Cullen et al. 2005). Fusarium sambucinum is considered the most aggressive pathogen for this disease in major parts of Europe, China and North America (Secor and Salas 2001; Du et al. 2012). In Britain, Fusarium coeruleum (Libert) Sacc. is the most prevalent fungus in cold stores (Peters et al. 2008a). Fusarium graminearum (Schwabe) along with F. sambucinum was reported to be the most frequent species causing dry rot in potato in North Dakota (Estrada et al. 2010). Similarly, in Michigan, the Fusarium oxysporum is the most common fungus causing dry rot while F. sambucinum is the most aggressive. Apart from being pathogenic, Fusarium species are also known for producing mycotoxins in food products and dry rot causing species also to produce mycotoxins; sambutoxin, trichothecene, fusarin C, fusaric acid, zearalenone and deoxynivalenol (Desjardins 2006; Daami-remadi 2012; Bojanowski et al. 2013). Some of these toxins also act as pathogenicity factors in developing rots in tubers. Symptoms of the dry rot include sunken and wrinkled brown to black tissue patches on tubers having less dry matter and shriveled flesh. The wrinkled patches during prolong storage produces cottony white, purple, pink or brick orange spore and mycelial mass which survive in soil or rotten tuber debris (Stevenson 2001; Vatankhah et al. 2019). The information on the disease epidemiology is very elusive. The fungus can survive well at 4 °C and 10 °C, therefore, poses an equal threat to seed tubers and potatoes used for processing. The aggressiveness of different species depends upon the storage conditions and cultivars types. The management strategy mainly includes the use of resistant cultivars, disease-free seed potato, cultural practices, bioagents, chemical treatment and storage microenvironment management (Bang 2007; Peters et al. 2008a; Al-Mughrabi et al. 2013; Bojanowski et al. 2013; Jiang et al. 2019). The current scenario demands an exhaustive screening of available cultivars and potato germplasms to identify the source of resistance and to frame a suitable breeding program. Also with the availability of the genome sequence of F. sambucinum (Patil et al. 2017), it is important to identify the potential pathogenicity factors and small secreted proteins that can be targeted in developing dsRNA based therapeutic biomolecules for seed tuber treatment. The role of multifunctional phytoprotectant, such as melatonin and strigolactones is also need to be explored which is highly effective in managing post-harvest losses in horticultural crops (Tiwari et al. 2020b). This review aims to draw attention to the symptomatology, infection process, pathogenomics, role of toxins and management approaches for this pathogen which is very much critical in designing better management strategies.

Symptomatology and etiology of potato dry rot disease

The tubers and roots are the main plant parts that are directly affected by dry rot disease. The pattern of shrinking and shriveling along with lesion development on the outer surface of tubers and roots are common. Simultaneously, the black or brown rot occurs in the internal tissues. The wounds act as the main entry point for the pathogen from where they cause the rotting of the internal tissue giving black, brick orange, whitish or brownish tissue. The tubers showing typical symptoms of dry rot collected from different states of India have been shown (Fig. 1a–c). The indirect effect of infection can be observed as necrotic lesions on the damaged primary and secondary roots of the potato plant (Fig. 2). The first-ever study on potato dry rot by Martius in 1842 revealed that the disease is caused by a fungus named Fusisporium at that time which was later on identified as Fusarium oxysporum (Saccardo and Traverso 1882). Presently, 13 different Fusarium species cause potato dry rot worldwide (Cullen et al. 2005). These are namely F. sulphureum Schlechtend. (syn. F. sambucinum Fuckel), F. coeruleum (Libert) Sacc. (syn. F. solani var. coeruleum), F. avenaceum (Fr.:Fr.) Sacc., F. culmorum (Wm. G. Sm.) Sacc., F. oxysporum Schlechtend. Fr., F. acuminatum Ellis & Everh., F. crookwellense L. W. Burgess, P. E. Nelson & T. A. Toussoun, F. equiseti (Corda) Sacc., F. graminearum Schwabe, F. scirpi Lambotte & Fautrey, F. semitectum Berk. & Ravenel, F. sporotrichioides Sherb. and F. tricinctum (Corda) Sacc. However, this list is still not complete and needs much more exhaustive survey and sampling to identify more Fusarium species involved, such as F. ciliatum, F. torulosum F. reticulatum and F. verticillioides (Gachango et al. 2012). The spore and colony morphology of three most common dry rot causing fungus have been shown in Fig. 1 (d-i) from the part of our ongoing research work.

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Fig. 1

a–c Typical symptoms of dry rot showing shriveled and mummified tubers, d–f Pure culture of Fusarium sambucinum, Fusarium solani, Fusarium oxysporum, g–i Respective fungal spores and mycelia as observed under a compound microscope (40 × magnification)

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Fig. 2

a, b Typical dry rot symptoms showing necrotic lesions on the damaged primary and secondary roots of the potato plant

Distribution pattern based on frequency and aggressiveness of Fusarium species

Fusarium species are the world’s most devastating fungus infecting almost all grown crops and potato is no exception (Estrada et al. 2010). In potatoes, pathogens are responsible for wilt and vascular discoloration and causing rots and seed decay in tubers during storage. The most devastating and frequent species are F. sambucinum, F. solani and F. oxysporum based on geographic location and prevailing atmospheric conditions (Stefańczyk et al. 2016). In the USA (Secor and Salas 2001) and Great Britain (Peters et al. 2008c) F. sambucinum and F. coerulum are the two most frequent fungus causing potato dry rot respectively along with F. avenaceum and F. culmorum as minor rot causing fungi. However, several reports consider F. sulphureum as the most frequent fungus in North America and Europe (Recep et al. 2009; Gachango et al. 2012). F. solani and F. oxysporum are the main fungi associated with dry rots in south Africa (Theron and Holz 1990). The higher incidence and aggressiveness of F. sulphureum and F. solani has been observed in predominant potato cultivars in Iran. Interestingly, F. graminearum the cereal fungus has been reported as the dominant dry rot agent in North Dakota (Estrada et al. 2010), Tunisia (Daami-remadi 2012) and Canada (Peters et al. 2008b). This indicates the host adaptation in Fusarium fungus as wheat and potato crop rotation is common in the cropping system. The worldwide spatial distribution F. sambucinum has been depicted in Fig. 3. In India, a study reported nine species of Fusarium have been associated with dry rots but there is no further study of diversity and distribution of this fungus in storage and fields (Singh et al. 1987). However, the first report of F. sambucinum came from cold stores of Madhya Pradesh (Sagar et al. 2011) and it gave an alarming signal to carry out countrywide surveys and assess the prevalence of this threatening species in cold stores. In China also, the F. sambucinum is the most notorious fungus in major potato growing regions along with four minor species as F. oxysporum, F. avenaceum, F. acuminatum and F. equiseti (Du et al. 2012). More recently in Egypt, the F. sambucinum was identified as the predominant fungus followed by F. oxysporum, F. verticillioides and F. incarnatum (Gherbawy et al. 2019).

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Fig. 3

The map indicates the spatial distribution of dry rot caused by Fusarium sp across the world. On the map, dots with red, green and blue colour denotes Fusarium sambucinum, Fusarium oxysporum and Fusarium graminearum, respectively

Pathogenomics of Fusarium dry rot

Pathogenomics is a high-resolution strategy to develop and analyze the whole genome sequences of pathogenic agents (Fungi, bacteria and viruses) for the identification of pathogenesis and virulence determinants and the regulators of various metabolic activities. It is a modern tool for a better understanding of host−pathogen interactions and to identify the potential targets for efficient chemical control (Rampersad 2020). The genome of more than 12 Fusarium species has already been sequenced during the last two decades (Table ​(Table1).1). An analysis from the genomic studies revealed that the majority of the Fusarium species possess a hemibiotrophic association with the host and they shift from biotrophic to necrotrophic phase within the host depending upon the prevalent microenvironment and host adaptations (Perfect and Green 2001; Ma et al. 2013). A cascade of enzymes, toxins and small secreted proteins are involved in the pathogenesis of these hemibiotrophs. A study reported that virulent F. sambucinum strains can detoxify the sesquiterpene phytoalexins produced by potato (Desjardins and Gardner 1989). These phytoalexins are mainly rhisitin and lumbimin. High virulence was associated with loci designated as Riml through meiotic recombinational analysis. Fleisner et al. 2002 investigated the mechanism which allows the F. sambucinum to tolerate phytoalexins. Their findings strongly suggested the role of ATP-binding cassette multidrug-resistant transporter in secreting toxic substances out of the cells. The gene Gpabc1 codes for this transporter and provides tolerance to phytoalexins. The pathogenicity of this fungus was also correlated with host nonspecific phytotoxin trichothecenes and the disruption of trichidiene synthase gene lead to reduced virulence in F. sambucinum. Another gene enniatin synthase 1 (ESYN1) responsible for mycotoxin production was correlated with the regulation of virulence in F. sambucinum (Eranthodi et al. 2020). The disruption of ESYN1 leads to reduced virulence and reduced lesion size on inoculated tubers. Similar findings are reported in F. avenaceum mediated dry rot disease. Recently autophagy which is a natural mechanism occurring in plants, animals and fungi has been correlated with the regulation of fungal growth, development and virulence. A study by Khalid et al. (2019a) revealed that the autophagy-related gene (ATG 3) is a potential regulator of conidial growth and development and pathogenicity of F. oxysporum in potato. While previously they have reported that ATG22 gene is involved in the pathogenicity of the fungus (Khalid et al. 2019b). The deletion mutant of F. oxysporum showed reduced conidiation and mycelial growth along with reduced lesion size in inoculated tubers. The novel finding demands more researches in this regard to elucidating the vital role of autophagy in dry rot fungus pathogenicity. Cutinase enzymes are actively involved in the pathogenicity of F. solani in potato. These enzymes can be used as markers to identify the pathogenic F. solani isolates. The role of Fusarium specific specialized effectors and pathogenicity genes, such as “Secreted In Xylem” (SIX) genes and Fusarium transcription factor (FTF)-encoded genes (FTF1 and FTF2) has already been established in F. oxysporum f. sp. lycopersici (FOL) mediated tomato infection and it will be interesting to explore similar aspects in potato. Likewise, the function of Fgl1 gene, a secreted lipase has been established as a virulence factor of F. graminearum of barley, maize and wheat, and its function in potato is still not explored. Recently the F. graminearum is emerging as major species involved in dry rot in potato. An insight into the genome of this fungus reveals that there is high genetic diversification in infection-related genes and that’s the main factor for its environmental adaptability (Paper et al. 2007; Kamran et al. 2020). This could also be the main reason for shifting of this fungus from wheat to potato host. Further, researches are needed in this direction to analyze the host shift and adaptation strategies of this fungus which will aid in restricting the survival of pathogen and provide management options. The genome sequence of most devastating species, F. sambucinum is available and further studies are now focused on improved understanding of (i) pathogenicity and virulence determinants (structures and functions), (ii) shift of biotrophic to necrotrophic life style, (iii) molecular basis of infection process, (iv) genetic diversity and species complex due to specific genomic regions (v) prediction of disease outbreak due to new strains (vi) emergence of fungicide-resistant strains.

The transcriptome analysis is a significant tool for understanding host−pathogen interactions and identifying the genes responsible for the virulence of pathogen and resistance or susceptibility of the host. A transcriptomic analysis involving F. solani f. sp. eumartii a tolerant potato cultivar “Spunta” has revealed the activation of inducible defense responses (Ippolito et al. 2010). The involvement of several PR proteins, chitinases and peroxides has been largely demonstrated in this study. However, the upregulation of a wide range of MAPK (mitogen-activated protein kinase), such as CIPK (calcineurin B-like protein-interacting protein kinase), SAPK8 (osmotic stress/ABAe activated protein kinase 8), CTR1-like kinase and shaggy related kinase denotes the complex level of physiological remodeling in response to fungus attack in potato. Interestingly, some of the RNA processing proteins, such as zinc finger motif RNA binding proteins, Glycine-rich RNA-binding proteins, DEAD-box RNA helicase, mRNA splicing factor (STA1), have also been found up-regulated in active defense response which needs exhaustive studies as the role of these transcription factors are poorly understood. A series of studies involving F. solani f. sp. eumarti and potato cultivar Spunta have already reported the role of cyclophilin coding StCyp, transcriptional coactivator StMBF1, St-ACO3 coding for an ACC oxidase and MAP kinase StMPK1in induced defense response in potato tubers (Blanco et al. 2006; Zanetti et al. 2002; Godoy et al. 2001). Some of these identified genes are involved in tolerance of many abiotic and pathogen stresses in different crops and further study in this regard may lead to a successful management strategy against combined biotic and abiotic stresses in crop plants.

The comparative genomics studies between dry rot causing Fusarium spp. revealed that F. sambucinum possesses perfect microsatellites while F. verticelloides microsatellites are in the compounded form (Patil et al. 2017). There are very limited genes characterized in F. sambucinum, such as major facilitator superfamily (MSF) genes which were confirmed within the genome sequence. An one-way average nucleotide identity (ANI) among Fusarium spp. by comparing 100 housekeeping gene sequences revealed the closest association between F. sambucinum (Strain FS-4) and F. graminearum (Strain PH-1) (99.12%) (Patil et al. 2017). However, the least relationship was observed with F. verticillioides (Strain 7600) (97.81%). The phylogeny based on the Translation Elongation Factor 1α (TEF1α) gene depicted a close evolutionary relationship between F. sambucinum and F. culmorum, causal agent of foot, stalk and root rot, seedling and ear blight in cereals and grasses. An exhaustive comparative analysis of recently sequenced genome with other Fusarium spp. genomes will provide greater understandings of evolutionary relationships, fungus origins and pathogenicity.

Infection-related to dry rot and the life cycle of the Fusarium species

The dry rot causing Fusarium species are both seed and soil borne. Although the dry rot is considered a major threat for tubers in storage, but its ill effects can also be observed in the field in the form of wilting and root degradation of potato plants (Mahdavi et al. 2009). There are also some indications that fungal isolates differ in their ability to cause wilt symptoms and dry rots in potato (Secor and Salas 2001). This is an important matter of investigation as very few studies highlight the Fusarium wilt in potato plants and the majority of researches focus on Fusarium-induced dry rot of tubers. The wounds developed on the tubers during harvesting, handling and transportation become the entry point for fungal spores and these infested tubers initiate the dry rot in storage. The fungus can initiate infection only when the tuber skin is ruptured. The infection hypha grows in intercellular spaces in live cells and becomes intracellular only when the cell is dead. But this also varies with species as F. coeruleum shows both intercellular and intracellular growth pattern while F. avenaceum kills the penetrated cells and grows intracellular right from the beginning of infection (Stevenson 2001; Bojanowski et al. 2013).

The survival of Fusarium spores in soil and on plant debris acts as the main reservoir of inoculum and major source of tubers infections in the field (Peters et al. 2008c; Cullen et al. 2005). The surviving spores in soil cause rotting in progeny tubers only after wounds developed due to intercultural operations (Bojanowski et al. 2013). The transmissions of fungal spores from mother tubers to progeny tubers also depends upon the Fusarium sp. involved in causing these rots. It has been observed that different Fusarium sp. have a different rate of sporulation belowground and hence the extent of infection also varies accordingly (Cullen et al. 2005; Bojanowski et al. 2013). It was observed that F. sulphureum transmission is greater from contaminated seed tuber while F. coeruleum transmits more readily from rotten mother tuber. F. sulphureum preferably sporulates on stem bases whereas F. coeruleum rapidly sporulates outside rotten tubers (Choiseul et al. 2001; Cullen et al. 2005; Bojanowski et al. 2013). The optimum temperature for mycelial growth of F. sambucinum, F. graminearum, F. oxysporum, F. solani and F. culmorum is 20–25 °C whereas for sporulation 25–30 °C temperature is required. F. solani var. coeruleum needs 25–30 °C and 20–25 °C, respectively for growth and sporulation. Usually, in cold stores, a temperature above 10 °C increases the Fusarium growth while<5 °C is known to reduce infection (Secor and Salas 2001). However, F. sambucinum and F. graminearum have shown mycelial growth below 5 °C, which is the main reason for dry rot development even at extremely low temperatures (Daami-remadi 2012). Temperature above 40 °C completely restricts the growth of all the fungal species involved in dry rot disease. A pictorial representation of the occurrence and spread of dry rot in field and storage has been illustrated in Fig. 4.

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Fig. 4

An illustration of the dry rot disease cycle consisting of storage and field phase. The disease is initiated from the soil and/or seed borne inoculum under field conditions. The tubers harvested from infected plants may possess the inoculum and under ambient storage conditions cause severe rots in tubers kept in cold stores

Toxins in disease development

Mycotoxins play a critical role in host−pathogen interactions (Aiko and Mehta 2016; Nagaraja et al. 2016). These toxins are considered as a secondary determinant of pathogenicity and the main weapon of Fusarium species in developing dry rots in potato. These Fusarium toxins have been classified as trichothecene and non-trichothecene mycotoxins and reported in many hosts affected by this genus (Mills 1990; Bojanowski et al. 2013; Nagaraja et al. 2016). Trichothecens are the sesquiterpenes causing toxicity in plants as well as mycotoxicosis in animals and humans (Desjardins 1995; Bojanowski et al. 2013). Fusarium species infecting potato and cereal grains mainly produce non-macrocyclic trichothecenes categorized as type A (includes diacetoxyscirpenol [DAS] and T-2 toxin) and type B (includes nivalenol [NIV] and deoxynivalenol [DON]) (Desjardins 2006; Delgado et al. 2010). Much dry rot causing Fusarium species (F. sambucinum, F. coeruleum, F. oxysporum, F. equiseti, F. graminearum) produce trichothecenes DON, DAS, NIV and T-2 toxin in tissues of rotten tubers as previously documented (Bojanowski et al. 2013). Fumonisins, zearalenones (ZEA), sambutoxin, fusaric acids, fusarin C and enniatins are the major non-trichothecene mycotoxins associated with dry rots (Bojanowski et al. 2013; Eranthodi et al. 2020). The occurrence of this group of toxins in rotted tubers is concerning as these toxins are associated with deadly animal diseases, such as ZEA cause estrogenic syndromes in swine, Fumonisins have carcinogenic and hepatotoxic effects, sambutoxins are associated with hemorrhage in the stomach and intestines of rats (Kim and Lee 1994; Desjardins 2006; Bojanowski et al. 2013).

Earlier it was observed that these toxins are produced not only in rotted tissues of the infected tubers but also on distant healthy-looking tissues which were a matter of great concern for consumers as normally the rotted tissue is removed and the rest part is used for cooking. However, Delgado et al. (2010) reported that the tissue surrounding the rotted lesions by F. graminearum accumulates a non-lethal amount of toxins within 7 months of storage. This aspect also warrants exhaustive researches as the type of cultivar and prevalent Fusarium species in a particular area might be the factor for toxin distribution in the rotted and healthy tissues. The effect of cooking on the inactivation of trichothecenes in potato infected with F. sambucinum indicates that thermal treatment is unable to completely inactivate these toxins and it needed more than 4 h of cooking to eliminate these toxins. This is another future line of work to safeguard the health of the consumers. The data regarding the effect of these toxins on the health of consumers is also lacking. The toxins associated with dry rot causing Fusarium species are described in Table ​Table22.

Genetic resistance and molecular breeding

Worldwide, most of the commonly growing potato cultivars are susceptible to Fusarium dry rot (Daami-remadi 2012; Bojanowski et al. 2013; Heltoft et al. 2015; Chen et al. 2020). In China, Du et al. 2012 screened 21 cultivars and 46 breeding lines against F. sambucinum (NM5-1-S). All these 67 potato clones were found susceptible to dry rot disease. However, the most tolerant cultivar against F. sambucinum was Desiree (Du et al. 2012). Cultivar susceptibility varied based on the dominance of Fusarium species in a location-specific manner. In Tunisia, cultivar Mondial and Spunta showed less susceptibility to F. sambucinum and F. oxysporum f. sp. tuberose whereas cultivar Liseta was less susceptible to F. oxysporum and F. graminearum (Trabelsi et al. 2016). In Iran, 43 potato cultivars were screened against F. sulphureum, F. solani and F. oxysporum and cultivar Saturna was found resistant among all the tested cultivars (Esfahani 2005). Cultivar Owyhee Russet had shown significant resistance to dry rots as compared with Russet Burbank. Owyhee Russet was moderately resistant to F. solani var. coeruleum but susceptible to F. sambucinum (Yilma et al. 2012). While screening the potato cultivars against dry rots it is important to consider storage temperatures, as some reports have highlighted the role of storage temperature in the susceptibility of cultivars against several Fusarium species. Also, the aggressiveness of the Fusarium species varies according to storage temperatures (Daami-remadi 2012). Cultivars placed in less susceptible groups against F. sambucinum at temperature 30 °C moved to highly susceptible groups at 15 °C (Mejdoub-Trabelsi et al. 2012). Breeding for dry rot resistant potato cultivars is presently not very efficient due to laborious phenotyping (Chen et al. 2020). The inoculation technique has also been constantly evolved to facilitate the screening of tubers of resistant cultivars and germplasm. Different inoculum methods include delivery of spore suspension of mycelia plug in the wounded tuber using the micrometer-type syringe, a cork borer, steel pin tools, a drill or a metal cylinder (Ayers and Robinson 1954; Peters et al. 2008b; Estrada et al. 2010; Sagar et al. 2011; Chen et al. 2020). Recently Chen et al. (2020) developed a simple and efficient cross-contamination-free technique denoted as plastic screw wounding which will aid in screening potato lines against Fusarium dry rot. Due to variability in disease response of host tubers depending on storage and prevalent species, ongoing studies should focus on ranking the resistance of cultivars based on these factors. The effect of mixed infections of Fusarium species should also be considered in such studies as tubers in field and storage face several of these species at a time. The occurrence of soft rot also influences the resistance of given potato tubers against dry rot therefore correlations also need much more elaborative studies to understand the underlying mechanism of dry rot and wet rot occurrence in potato.

Management of Fusarium dry rot disease

Host-induced gene silencing

Host-induced gene silencing (HIGS) conferred through an RNAi-based mechanism restricting the expression of selected genes of the pathogen has the potential to control Fusarium diseases of economically important crop plants (Rampersad 2020). There are good examples of RNAi-mediated silencing of targeted genes as in wheat against F. culmorum (Chen et al. 2016) and F. graminearum (Koch et al. 2016; Kamran et al. 2020), banana against F. oxysporum f. sp. cubense (Ghag and Ganapathi 2019), tomato against F. oxysporum f. sp. lycopersici (Singh et al. 2020; Tetorya and Rajam 2018), barley against F. graminearum (Koch et al. 2016) and tobacco against F. verticillioides (Tinoco et al. 2010). Unfortunately, there is not a single report of RNAi-mediated disease suppression in dry rots in potato. This warrants the need for exploration of these aspects which will give a valuable management option for this disease. The phytoprotectant melatonin is emerging as an environmentally friendly chemical to manage post-harvest biotic stresses in horticultural crops (Tiwari et al. 2020b; Moustafa-farag et al. 2020). There is a need to explore the role of novel phytohormones in dry rot suppression. The major strategies to manage potato dry rot disease are highlighted in Fig. 5.

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Fig. 5

The flow chart highlights the major strategies to manage dry rot disease of potato in field and storage conditions. The disease management in cold stores relies on proper curing and handling of the harvest coupled with storage unit sanitization. Management in felid conditions is possible through adopting adequate phytosanitary measures, applying suitable chemical and bioagents and planting tolerant cultivars

Conclusion and future thrust

Globally, Fusarium dry rot is a disease having economic importance. There are more than 13 species of dry rot causing Fusarium reported worldwide and the genetic diversity varies depending upon the geographical location. The frequency of occurrence and aggressiveness of dry rot causing Fusarium strains also differ depending upon the prevalent cultivars and environmental conditions in a location-specific manner. It is very important to screen the available cultivars and newly developed germplasm against the pathogen to develop a ranking for susceptibility and resistance. The susceptibility/resistance of a particular cultivar varies depending upon Fusarium species and storage temperature; hence, it should be considered for designing a breeding program. Marker-assisted selection is the need of the hour to identify certain resistant QTLs for this disease. There is a dire need to formulate unique forward genetic approaches for identifying and overexpressing genes that inactivate or detoxify mycotoxins. It will help to develop tolerant cultivars against toxin-producing Fusarium species. The development of an integrated disease management approach that includes the use of certified disease-free seeds, preventing the injury of tubers during harvesting, curing and transportation, optimum storage conditions and applying the recommended dose of registered chemicals can efficiently manage the disease. The emergence of fungicide-resistant strains demands the use of GRAS compounds, microbial antagonists and silver nanoparticles in managing the disease with less environmental hazard and minimum pest resurgence. Novel phytohormones like melatonin and strigolactones should also be tried in potato plants and/or tubers as these biochemicals have given promising results in managing post-harvest diseases of commercial crops. The availability of genomic data demands further functional analysis and proteomics of pathogenicity genes only then these genes can be targeted for designing non-transgenic and transgenic management approaches. The Fusarium species are having versatile and novel combinations of virulence determinants and pathogenicity factors. Host-induced gene silencing has demonstrated a good potential in mitigating Fusarium diseases in some important commercial crops and it will be interesting to explore its role in dry rot suppression in potatoes. The successful management of dry rot will depend upon the additional research on the identified gaps and collaborative efforts of stakeholders (scientists, industrialists and farmers) in formulating an integrated management approach from farm to storage.

Acknowledgements

Author contributions

RKT, RK and MKL designed the outline of the article, composed the manuscript and figures. KCN, KNC and DK searched the literature and related information, SS, VS, RA and MK provided scientific feedback and critical comments to revise the content.

Compliance with ethical standards

References