**2. Symptoms of dry rot, infection process of** *Fusarium* **and potato tuber tissue reaction**

The symptom of potato dry rot includes sunken and wrinkled brown to black tissue patch on tuber with less dry matter and shriveled flesh. The initial symptoms of dry rot of potato appear on tubers at wound sites as shallow small brown lesions after

*Potato Dry Rot Caused by* Fusarium *spp. and Mycotoxins Accumulation and Management DOI: http://dx.doi.org/10.5772/intechopen.100651*

approximately one month of postharvest storage. The infected lesions enlarge in all directions, then the periderm sinks and collapses, eventually, the growing lesion may appear as concentric rings as the underlying dead tissue desiccates [1, 4]. Cavities underneath the rotted tissue are usually associated with cottony white, purple, pink or brick orange spore and mycelia of pathogenic fungus [30]. The whole rotted tubers always become shriveled and mummified (**Figure 1**). Dry rot lesions may be infected by some bacterial pathogens and cause soft rot decay, especially when the tubers are wet or stored at high relative humidity storage conditions [3]. *Fusarium* species that causes dry rot can also indicate themselves as seed tuber decay and in-field wilt.

*Fusarium* spp. cannot infect the healthy potato tuber through the stomata or lenticels when the tuber is in the absence of wounds. The pathogenic fungus successfully infect tuber only if the tuber's skin is ruptured [3], the fungus only invades the tuber through wound or natural orifice during pre-harvest or storage and transportation (**Figure 2**). The pathogenic hyphae are initial at intercellular, then become intracellular in dead cells. Histological studies showed that *F. coeruleum* infected through the intercellular spaces, the adjacent host cells remaining alive for some time; however, *F. avenaceum* infected through killing and penetrating the cells where it came into contact [3]. Lesions at the infected site can be prevented by the accumulation of suberin polyphenolic (SPP) and suberin polyaliphatic (SPA) [3, 31]. SPP and SPA can effectively prevent the spread of hyphae of the pathogen, and as wound periderm can be sealed with SPP and SPA [3]. In fact, the formation of SPP and SPA is the process of wound healing. Wound healing can suppress the development of dry rot by walling off infection sites and preventing lesions from expanding [3]. *F. sulphureum* infected tuber tissues were indicated to accumulate SPP and SPA [31].

#### **Figure 1.**

*(a) and (b) Respective spores and mycelia, (c) and (d) Respective typical symptoms of dry rot showing shriveled and mummified tubers.*

**Figure 2.** *Fusarium spp. infects potato tuber by wound or natural orifice.*

The wound healing process includes two stages of wound-induced suberization: the closing layer formation and wound periderm development, accompanied by deposition of SPP and SPA on the wounded site [32]. It was reported that both SPP and SPA can resist bacteria and fungi invade by the formation of an effective physical barrier [33]. Jiang et al. [31] suggested some synthesis substances, such as benzo-(1, 2, 3)-thiadiazole-7-carbothioic acid s-methyl ester (BTH) can accelerate the wound healing of potato tuber by elevation of phenylpropanoid metabolism.

### **3. Mycotoxins production associated with dry rot of potato**

The dry rot, caused by some species of *Fusarium* spp., is associated with mycotoxins accumulation. Mycotoxins is a kind of secondary metabolites produced by pathogenic fungus under the favorable temperature and humidity condition, which can pose a potential risk to human health and food safety [34]. The mycotoxin produced by *Fusarium* spp. can be divided into two kinds of non-trichothecene and trichothecenes. The typical non-trichothecene produced by *Fusarium* spp. are listed in **Table 2**.

Beauvericin (BEA), enniatins (ENNs), zearalenones (ZEA), fumonisins (FUM), sambutoxin (SAM), fusaric acids (FA) and fusarin C (FUS) are usually detected in dry rot of potato tuber. BEA and ENN are cyclic hexadepsipeptides, which has antimicrobial, insecticidal, phytotoxic and cytotoxic characteristic properties [45]. ZEA belong to non-steroidal estrogenic mycotoxins, accompanied with estrogenic syndromes in some experimental animals [46]. FUM have been linked to leukoencephalomalacia, in horses and rabbits and have hepatotoxic and carcinogenic influences, as well as esophageal carcinoma in human, phytotoxic symptoms in plants [47]. SAM was detected in dry rot of potato caused by *F. sambucinum* and *F. oxysporum* [42, 44], which can lead to hemorrhage in the stomach and intestines, loss of body weight, feed refusal and death in rats. Consumption of FUS produced by *Fusarium* species has been associated epidemiologically with some diseases in human [46]. El-Hassan et al. [27] indicated that a significant positive correlation between FA accumulation and dry rot incidence.

The trichothecenes are the main kind of mycotoxins detected in dry rot of potato, which is a kind of chemically related sesquiterpenes compound. Presently, more than 190 known trichothecenes are detected. According to their chemical structure, they can be classified into four groups: types A, B, C, and D, the chemical structure are shown in **Figure 3**.

*Potato Dry Rot Caused by* Fusarium *spp. and Mycotoxins Accumulation and Management DOI: http://dx.doi.org/10.5772/intechopen.100651*


*Note: BEA: beauvericin, ENNs: enniatins, FA: fusaric acid, FUM: fumonisin, FUS: fusarin C, SAM: sambutoxin, ZEA: zearalenones.*

#### **Table 2.**

*Non-trichothecenes produced by* Fusarium *species in dry rot of potato.*

**Figure 3.** *Basic chemical structure of trichothecenes.*

Types A and B are usually found in cereal grains, animal feed, and human food made from contaminated grains. In addition, they were also found in potato tubers infected by *Fusarium* spp. Trichothecenes have phytotoxicity and mycotoxicoses which can pose a severe threat for human and animal health [22]. The typical symptoms are vomiting, feed refusal, and diarrhea when animal intake the food

contaminated trichothecene, in severe case, trichothecenes have the potentiality leading to cancer, deformity and mutation [48]. Members of the genus *Fusarium* produce simple or non-macrocyclic trichothecenes while more complex macrocyclic trichothecenes are produced by fungi of the genera *Stachybotrys* and *Trichothecium* as well as other fungi [46]. Some *Fusarium* species associated with dry rot of potato were shown to produce trichothecenes in dry rot of potato tuber (**Table 3**). Type A and B are usually detected in rotted potato tuber tissue. Xue et al. [22] suggested that 3-ADON, T-2, FX and DAS were found in dry rot of potato caused by *F. sulphureum*, *F. solani* and *F. sambucinum*, Meanwhile, these mycotoxins were found not only in the lesion but also in the adjacent asymptomatic tissue, whose concentration showed a strong trend of decline with increase in distance from the infection point. Ellner et al. [55] indicated that 4,15-DAS and DAS were found in not only rotten tissue but also in distant healthy looking tissue in potato tuber infected with *F. sambucinum*, which had a strong decline in trichothecenes concentration with


*Note: 3-ADON: 3-acetyldeoxynivalenol, 15-ADON: 15-acetyldeoxynivalenol, DAS: diacetoxyscirpenol, 4,15-DAS: 4,15-diacetoxyscirpenol, DON: deoxynivalenol, FX: fusarenone X, HT-2: HT-2 toxin, MAS: monoacetoxyscirpenol, 4-MAS: 4-acetyl-monoacetoxyscirpenol, 15-MAS: 15-acetyl-monoacetoxyscirpenol, NIV: nivalenol, NEO: neosolaniol, SCR: scirpentriol, 15-SCRP: 15-acetylscripenol, and T-2: T-2 toxin.*

#### **Table 3.**

*Trichothecenes produced by* Fusarium *species in dry rot of potato.*

*Potato Dry Rot Caused by* Fusarium *spp. and Mycotoxins Accumulation and Management DOI: http://dx.doi.org/10.5772/intechopen.100651*

an increasing distance from the visible rotted tissues. Similarly, Delgado et al. [51] reported that DON, NIV, FX, 3-ADON, 15-ADON were detected in dry rot of potato caused by *F. graminearum*, which also had the similar decline trend in trichothecenes concentration with an increasing distance from the rotted tissues.

In order to investigate the stability for heat, the effect of cooking on the trichothecenes was carried with potato tubers infected with *F. sambucinum,* the results indicated that the content of 4,15-DAS reduced 26% and 81% after 1 h and 4 h of cooking at 100°C, respectively [57]. The long cooking times required to degrade the structure of the trichothecens, which make it difficult that thermal treatment can be used as the degradation method for food or feed contaminated with trichothecenes. Although mycotoxins, considered thermally stable [57], are found in tuber invaded by different *Fusarium* spp., no sufficient data are currently available to evaluate the health risk for human health.
