Internal Fruit Rot Research Articles

First report of Stagonosporopsis cucumeris causing internal fruit rot on Oriental melon (Cucumis melo L.) in Korea.

Oriental melon (Cucumis melo L.) is a popular Korean, Japanese, and Chinese fruit (Shin et al. 2017). In April 2022, abnormal fruit (n=20) that were collected in Sangju in Gyeongbuk Province (36°27'54.6"N, 128°10'49.7"E), Korea showed approximately 5% disease incidence with severity of 10-15%. Initial symptoms included shriveling, soaking, softening, dark discoloration, and sunken lesions. Internally, a rot extended to flesh, darkening from brown to black, and producing black mycelial masses. Two fungal strains (OM-rot-01 and OM-rot-02) were isolated and exhibited similar culture characteristics: aerial mycelium that was flat and pale grey to olivaceous on potato dextrose (PDA), malt extract (MEA), and oatmeal agar (OA) after seven days at 25°C and produced abundant buff-colored pycnidial ascomata on OA. Asci were bitunicate, clavate to cylindrical, 48.4 to 69.0 × 6.1 to 6.9 μm (n=10), and ascospores were biseriate, sparse, ellipsoidal, straight to slightly curved, hyaline, smooth, apex obtuse, 1-septate, 11.1 to 14.9 × 3.8 to 5.4 μm (n=20). Conidiomata were pycnidial, mostly solitary, irregular, pale brown to black, semi-immersed, 150 to 220 × 120 to 200 μm. Conidia were oblong or ovoid, smooth, thin-walled, hyaline, aseptate, 4.4 to 6.7 × 2.0 to 2.8 μm (n=35), with 1-3 guttules per conidium. The morphological characteristics corresponded to those of Stagonosporopsis cucumeris (Hou et al. 2020). For molecular identification, genomic DNA was extracted from strains (OM-rot-01 and OM-rot-02), and the ITS regions, partial 28S rDNA (LSU), beta-tubulin (TUB2), and RNA polymerase II second largest subunit (RPB2) genes were amplified and sequenced (White et al. 1990; Woudenberg et al. 2009; Vilgalys & Hester 1990; Liu et al. 1999). The obtained sequences revealed 99-100% homology with S. cucumeris accessions (MH858625, MH870265, MT005554, and MT018021). The sequences were deposited in GenBank with accession nos. for ITS regions (OP788058, OP788059), 28S rDNA (OP788094, OP788095), TUB2 (OP810568, OP810569), and RPB2 (OP810570, OP810571). Phylogenetic analysis combined with ITS, LSU, TUB2, and RPB2 concatenated sequences using neighbor-joining method revealed that the strains were S. cucumeris. To confirm pathogenicity, OM-rot-01 was inoculated onto ripe, asymptomatic Oriental melon fruit (n=6). After they were surface sterilized with 70% alcohol, fruit were wounded using a sterilized needle and corkborer, and 5-mm-diameter mycelial plugs were attached to the wound sites, followed by covering of the fruit with aluminum foil and maintenance in a plastic box (>90% relative humidity) at 25°C. Non-wounded fruit were inoculated and incubated in a similar manner, and fruit that were inoculated with PDA plugs served as controls (n=3). The aluminum foil was removed after three days of inoculation, and other conditions were kept constant. After six days, typical internal fruit rot symptoms were observed in both wounded and non-wounded fruit; brown to black rot extended into flesh, whereas control fruit remained asymptomatic. Fungi reisolated from lesions were morphologically identical to OM-rot-01; identity was confirmed by molecular analysis, fulfilling Koch's postulates, and the pathogenicity test was conducted three times. S. cucumeris was found as a canker on Cucumis sativus in the Netherlands (Hou et al. 2020), but has not been reported elsewhere as a pathogen on Cucumis spp. To our knowledge, this is the first report of S. cucumeris causing internal fruit rot on Oriental melon in Korea. This disease poses a threat to melon production, so accurate identification of the pathogen is a key starting point for development of sustainable management practices.

Automated detection of internal fruit rot in Hass avocado via deep learning-based semantic segmentation of X-ray images

Internal rot of avocado fruit (Persea americana), attributable to fungal infection, occurs at the end of the ripening process and causes only minor changes in the appearance and texture of the fruit surface. Manual inspection of rot by sight and touch commonly conducted in countries importing avocado fruit is time-consuming, labor-intensive, and subjective. In this context, X-ray line scanning has been proven as an advantageous method of fruit rot detection because of its speed of data acquisition and the indication of internal rot by bright regions in associated images. However, some fruit internal disorders exhibit only poor changes in contrast, resulting in low detectability by traditional image processing. This study aimed to test the effectiveness of a detection model using deep learning-based semantic segmentation in identifying two types of fruit rot, stem-end and body rot, in Hass avocados. Therefore, U-net+ + was trained and validated via 5-fold cross-validation to classify every pixel in an X-ray image as either infected or not. Then, each X-ray image was binarily classified based on either the presence or absence of internal fruit rots, achieving an accuracy of 0.98. Furthermore, the percentage of infected area was quantified with a root mean squared error (RMSE) of 3.15 %. Lastly, the proposed model detected both stem-end and body rot as well as rot along low-contrast fruit edges. The results of this study indicate that the proposed automatic inspection system using deep learning-based X-ray image analysis can effectively detect internal rot in Hass avocado fruit. This non-destructive, objective detection model can therefore increase efficiency and reduce misclassification in post-harvest avocado inspection. Furthermore, deep learning-based X-ray imaging has potential for applications in fruit inspection for internal cavities attributable to diseases or wounds.

Characterization of Pseudomonas syringae Isolated from Systemic Infection of Zucchini in Australia.

Zucchini plants with symptoms including twisted petioles, necrotic leaves, crown rot, and internal fruit rot were found in Bundaberg, Australia, at a commercial field for the first time during late autumn 2016, resulting in direct yield losses of 70 to 80%. Three Pseudomonas syringae strains isolated from symptomatic leaf (KL004-k1), crown (77-4C), and fruit (KFR003-1) were characterized and their pathogenicity evaluated on pumpkin, rockmelon, squash, and zucchini. Biochemical assays showed typical results for P. syringae. The three isolates differed, however, in that two produced fluorescent pigment (KFR003-1 and 77-4C) whereas the third, KL004-k1, was nonfluorescent. Multilocus sequence analysis classified the isolates to phylogroup 2b. The single-nucleotide polymorphism analysis of core genome from the Australian and closely related international isolates of P. syringae showed two separate clusters. The Australian isolates were clustered based on fluorescent phenotype. Pathogenicity tests demonstrated that all three isolates moved systemically within the inoculated plants and induced necrotic leaf symptoms in zucchini plants. Their identities were confirmed with specific PCR assays for P. syringae and phylogroup 2. Pathogenicity experiments also showed that the Eva variety of zucchini was more susceptible than the Rosa variety for all three isolates. Isolate KL004-k1 was more virulent than 77-4C on pumpkin, rockmelon, squash, and zucchini. This study expands the knowledge of P. syringae isolates that infect cucurbits and provides useful information for growers about the relative susceptibility of a range of cucurbit species.

Internal fruit rot of sweet pepper caused by Fusarium lactis in Japan and fungal pathogenicity on tomato and eggplant fruits

Internal fruit rot of sweet pepper caused by Fusarium lactis in Japan and fungal pathogenicity on tomato and eggplant fruits

Possibilities of modified atmosphere packaging to prevent the occurrence of internal fruit rot in bell pepper fruit (Capsicum annuum) caused by Fusarium spp

Bell pepper (Capsicum annuum L.), with its wide array of colors and flavors, plays an important role in many different cuisines around the world. Yet once harvested, it is a highly perishable fruit and needs appropriate post-harvest handling. Recently, post-harvest internal rotting (IFR) by Fusarium lactis species complex isolates (FLASC), became an additional challenge to maintain shelf-life and quality of bell pepper fruit. Therefore, modified atmosphere packaging (MAP) was explored as a possible technique to postpone symptom development of infected bell peppers. Four artificially infected bell pepper cultivars with different susceptibility towards IFR were stored under MAP conditions for a maximum of 14 d at challenging conditions of 20 °C resembling unrefrigerated shelf life conditions. Each week, 5 fruit of each object were analyzed for IFR symptom development and additional physicochemical and quality parameters. For all cultivars, MAP packaged fruit showed less severe fungal proliferation compared to controls after 14 d. As total titratable acid (TA), total soluble solids (TSS) and vitamin C concentrations in fruit remained rather stable throughout the experiment, fungal development was likely to be postponed directly due to reduced oxygen levels in the pouches rather than a decreased host susceptibility by influencing fruit metabolism. Since no significant differences of disease development were observed between sensitive and less sensitive cultivars for both colors, sensitivity for IFR seems not likely to be caused by different post-harvest disease development patterns but rather by differences in the initial susceptibility for flower infection under normal growth conditions. Based on our results, MAP can indeed be considered a useful tool to ameliorate IFR development during post-harvest storage of bell pepper under conventional temperatures of 7−16 °C.

Effects of environmental conditions on growth of Stagonosporopsis cucurbitacearum causing internal fruit rot in cucurbits

Effects of environmental conditions on growth of <i>Stagonosporopsis cucurbitacearum</i> causing internal fruit rot in cucurbits

First Report of Postharvest Stemphylium Rot of Mango (Mangifera indica) Caused byStemphylium vesicariumin Pakistan

First Report of Postharvest Stemphylium Rot of Mango (<i>Mangifera indica</i>) Caused by<i>Stemphylium vesicarium</i>in Pakistan

Symptom development and decreased sugar content from internal fruit rot of netted melon caused by &lt;i&gt;Pantoea ananatis&lt;/i&gt; group II and its host range

Symptom development and decreased sugar content from internal fruit rot of netted melon caused by &lt;i&gt;Pantoea ananatis&lt;/i&gt; group II and its host range

Hot water treatments to control internal rot of ‘MD-2’ pineapple fruit caused by Fusarium verticillioides

Postharvest fungal infections in LSQUOMD-2RSQUO pineapple (Ananas comosus) fruit cause the majority of losses during export. The leading strategy for decay control is the use of synthetic fungicides, but constraints associated with the use of these products have led to the search for alternative methods to reduce fungal infections. Hot water treatments have the potential to improve the postharvest life on various fruits by controlling the germination of several pathogens. In this research, the efficacy of hot water dips at several temperatures and times for the control of Fusarium verticillioides rot of pineapple during cold storage was assessed. Results showed that, relative to untreated fruit, pineapples treated with the fungicide prochloraz (3 cm3 L(‑1)) resulted in a 59.2% disease reduction after 21 days storage at 8°C and 90% RH; on the other hand, fruits immersed at 40°C for one minute resulted in a 35.3% reduction in F. verticillioides, whereas the reduction in internal fruit rot in pineapples dipped at 50°C for one minute was 22.4%. Moreover, during storage for 21 days at 8°C, treatment at 40°C for one minute significantly (p<0.05) reduced weight loss, maintained firmness of pineapple and slowed changes in soluble solid content (SSC), titratable acidity (TA) and pH. In conclusion, the results suggest that a dip at 40°C for one minute may reduce internal fruit rot produced by F. verticillioides during postharvest storage without any negative effect on physicochemical quality. It is a residue-free method, respectful of human health and the environment.

First Report of Fruit Rot of Bell Pepper Caused by Fusarium incarnatum in Pakistan

Evidence of fruit rot disease was observed in 12 bell pepper (Capsicum annuum L.) fields located in the Chakwal district (32°56′00″N, 72°51′30″E) of Pakistan during the period June 2016 to 2017. Disease incidence was estimated to be between 15 and 24%. Yield loss in affected fields was estimated as 11%. Symptoms of disease were seen as water-soaked, discolored necrotic lesions predominantly around the calyx. There were also symptoms of internal rot as seeds and the inner fruit surface were covered with white to light gray fungal growth. In the case of severe disease symptoms, fungal growth was also observed externally at the calyx end. The disease progressed as a soft decay with leakage. Diseased fruits were cut into 5-mm² pieces, surface disinfested with 1% NaOCl for 2 min, rinsed thrice with sterile distilled water, and incubated on potato dextrose agar (PDA) at 25 ± 2°C for 3 to 4 days under continuous fluorescent light. Eighteen isolates of similar morphology were purified using the hyphal tip technique. Colonies were fast growing, fluffy, white with pale cream to beige coloration on the reverse side of the Petri dish. Microconidia were hyaline, single celled to one septate, and 3.5 to 5.0 × 2.7 to 4.0 μm (mean = 4.0 × 3.8 μm). Mesoconidia were fusoid, usually three septate, and 9.8 to 17.5 × 3.0 to 4.5 μm (mean = 13.4 × 4.0 μm). Macroconidia were three to five septate, cylindrical, slightly curved, tapered at the apex, and 26.2 to 37.4 × 3.5 to 4.8 μm (mean = 32.5 × 4.2 μm). Based on morphological characteristics, the fungus was tentatively identified as Fusarium incarnatum (Leslie and Summerell 2006). DNA from two representative isolates, FICW7 and FICW16, was amplified with translation elongation factor (EF1-α) and β-tubulin genes using primers EF1/EF2 (O’Donnell et al. 1998) and Bt1a/Bt1b (Glass and Donaldson 1995), respectively. The obtained sequences for EF1-α (accession nos. MF977815 and MG770586) and β-tubulin (MF977818 and MG770587) were deposited in GenBank. The MegaBLAST and Fusarium ID database analysis revealed 99 to 100% homology to the Fusarium incarnatum-equiseti species complex, GenBank accession no. JF270273 (EF1-α), and AB587036 (β-tubulin) respectively. Pathogenicity tests of six isolates were conducted on three healthy bell pepper fruits per isolate, wound inoculated with a 20-μl drop of 10⁶ spores/ml. Three control fruits per isolate were inoculated with 20-μl droplets of sterile distilled water. Inoculated and control fruits were incubated in moist chambers at 25°C. After 3 to 5 days, white fluffy mycelial growth surrounded by water-soaked necrotic lesions appeared identical to the symptomatic fruits observed in the field/tunnel. No symptoms were observed on control fruits. The fungi isolated from the diseased fruits were morphologically similar to the original isolates on PDA. The pathogen was previously reported to cause the internal fruit rot disease of bell pepper in Trinidad (Ramdial et al. 2016). This is the first report of F. incarnatum (Desm.) Sacc. causing fruit rot on bell pepper in Pakistan. New strategies need to be developed for effective management of disease.

Modelling greenhouse climate factors to constrain internal fruit rot (Fusarium spp.) in bell pepper

Internal fruit rot in bell pepper is an important fungal disease which results in mycelium growth and/or necrosis on the ovarium and fruit flesh. It is mainly caused by members of the Fusarium lactis species complex and emerged as a major threat for bell pepper production worldwide. Infection already starts during anthesis, but the symptoms are only visible later on in the production chain. An accurate prediction of the disease incidence in the greenhouse based on environmental parameters is an important step towards a sustainable disease control. Based on a large dataset (2011–2016), a binomial, logistic regression model was developed. This model enables an accurate prediction of internal fruit rot occurrence based on simple and robust input parameters such as temperature and relative humidity during anthesis. Spore density was included as a simplified, practical parameter describing the presence or absence of internal fruit rot 1 week earlier. The obtained model was validated with an independent dataset of five different commercial bell pepper greenhouses. The chance of internal fruit rot infection increased with temperature and relative humidity. Once a greenhouse is infected, only lower temperatures can reduce future risks. However, the chance of the disease to occur remains very high. This prediction model offers a strong instrument for growers to optimize greenhouse climate conditions to restrain internal fruit rot incidence. In addition, the model can be used to apply accurate biological or chemical treatments to achieve a more sustainable greenhouse control. A guideline table for climate adjustment is presented.

Environmental effects on growth and sporulation of Fusarium spp. causing internal fruit rot in bell pepper

Internal fruit rot in bell pepper (Capsicum annuum L.) is mainly caused by members of the Fusarium lactis species complex (FLASC) and to a lesser extent by Fusarium oxysporum and Fusarium proliferatum. Despite the importance of the disease, there is hardly no information about growth, sporulation and germination dynamics of FLASC. In order to understand the dominance of FLASC as main pathogen of internal fruit rot, the effects of temperature (5 °C – 35 °C), water activity (aw 0.76–0.96), pH (pH 3 - pH 9) and oxygen concentration (2.5% - 20%) on growth and sporulation of all three Fusarium species were compared. In addition, germination kinetics were also investigated. FLASC showed optimal mycelium growth and sporulation in the narrow range of 25 °C, while both other strains were also tolerant for higher temperatures to 30 °C. FLASC was also characterized by a broad pH optimum from pH 3–7 while F. oxysporum (pH 4–7) and F. proliferatum (pH 5–8) were more demanding concerning pH. In addition, optimal sporulation occurred in the acid region for FLASC (pH 3) whilst neutral and alkaline pH were more favourable for the other species. Germination kinetics revealed that FLASC did not benefit from an earlier and/or faster germination process. A thorough understanding of the growth characteristics and dominance of FLASC as main pathogen for internal fruit rot is inevitable to develop sustainable control measures for the disease.

Influence of floral morphology and fruit development on internal fruit rot in bell pepper

Influence of floral morphology and fruit development on internal fruit rot in bell pepper

Evaluation of Postharvest Stem-End Rot on Coconut Fruits

Evaluation of Postharvest Stem-End Rot on Coconut Fruits Vicente Mussi-Dias, Maria das Graças Machado Freire Abstract The stem-end rot on coconut fruits is the main postharvest crop disease, causing heavy losses especially when the product is sold fresh. The efficient and practical control of this plant disease has been difficult to date, such as the damage evaluation, which has been done exclusively by the incidence of the disease. However, the incidence parameter alone does not provide a satisfactory understanding of the lesion area and the intensity it can achieve during the storage period, and about the environmental conditions in which the fruits are subjected to the aggressiveness of Lasiodiplodiatheobromae, when it is confirmed as the causal agent of the disease, and the control measures applied. Thus, in this study we propose to evaluate the basal rot development in coconut fruits during postharvest and to prepare and validate a diagrammatic scale to enable the estimation of disease severity. Fruits were inoculated and the external and internal symptoms of disease developments were photographed to measure the damaged area, which were grouped into eight disease levels. Sixty images were assessed by 30 evaluators for three consecutive times at intervals of 7 days and data were subjected to linear regression analysis. Hence, it was possible to create and validate a diagrammatic scale to evaluate the disease severity on coconut fruits with an accurate, precise and reproducible manner. Furthermore, the proposed scale allowed us to distinguish the aggressiveness of different isolates of the fungus through the symptoms of internal fruit rot. Full Text: PDF DOI: 10.15640/jaes.v4n2a4

First Report of Internal Fruit Rot of Sweet Pepper in Korea Caused by Fusarium lactis

In June 2010, an internal fruit rot of sweet pepper (Capsicum annuum L.) fruit was found in a commercial greenhouse in Ilsan City, Korea. Disease incidence reached approximately 5% of 30 tons of harvested peppers. Affected fruits commonly did not show external symptoms. However, when the fruit was cut open, an internal rot and pinkish gray mycelium were observed on the seeds and the inner surface of fruit. Discolored soft patches, browning, and necrosis were observed on the outer surface of some fruits. Fragments (5 × 5 mm2) of the affected tissues were surface sterilized with 1% NaOCl for 30 s and then rinsed twice in sterile distilled water. The pieces were placed on water agar and incubated at 25°C for 4 to 6 days. Twenty-nine Fusarium isolates were obtained from 12 diseased fruits and maintained on synthetic low nutrient agar (SNA) at 10°C. The isolates were cultured on carnation leaf agar (CLA) and SNA at 23°C with 12 h of near-ultraviolet light per day for 14 days. Microconidia were abundant, borne in short, zig-zag chains or false heads, obovoid or clavate with a flattened base, and measured 4.3 to 7.1 × 2.2 to 3.3 μm. Macroconidia were sparse, thin walled, slender, straight to slightly curved, and measured 32 to 48 × 2.8 to 3.9 μm. Sporodochia were rare on CLA and chlamydospores were absent. The translation elongation factor 1-alpha (EF-1α) gene was amplified from four isolates (SPF01, SPF09, SPF16, and SPF22) by PCR assay using ef1 and ef2 primers (2), and the 700-bp amplification products were sequenced. The nucleotide sequences were deposited in GenBank (Accession Nos. JF411956 to JF411959). BLAST analysis showed 98% homology with the EF-1α sequence of Fusarium lactis NRRL25200 (GenBank Accession No. AF160272). All isolates were identified as F. lactis based on morphological and molecular characteristics (1). Pathogenicity tests of the four isolates were conducted by inoculating flowers on plants of the orange pepper cv. Orange Glory (3). A spore suspension was prepared by flooding 5-day-old cultures on potato dextrose agar with sterile distilled water. When the plants started to flower, each flower was inoculated by placing 20 μl of spore suspension (1 × 106 conidia/ml) on each flower. Four isolates of F. lactis were each inoculated onto three flowers on each of seven plants. Flowers from the same number of plants inoculated with sterile distilled water were used as the control treatment. Inoculated plants were kept in a greenhouse at 25°C by day and 20°C by night. Sixty days after inoculation, mature fruits were harvested and cut open to check for internal rot. Approximately 70% of inoculated fruits showed internal rot and pinkish gray mycelial growth on the inner surface of the fruits. No symptoms were observed on the control fruits. Fungal cultures resembling F. lactis were reisolated from inoculated fruits for all four isolates, fulfilling Koch's postulates. F. lactis has been reported on sweet pepper in the Netherlands and Canada (3). To our knowledge, this is the first report of internal fruit rot of sweet pepper caused by F. lactis in Korea. Although disease severity was low in this greenhouse, the economic impact on sweet pepper could be significant because the disease can reduce the quality, quantity, and market value of pepper fruits.

Genetic diversity and mycotoxin production of Fusarium lactis species complex isolates from sweet pepper

An internal fruit rot disease of sweet peppers was first detected in Belgium in 2003. Research conducted mostly in Canada indicates that this disease is primarily caused by Fusarium lactis Pirotta. Ninety-eight Fusarium isolates obtained from diseased sweet peppers from Belgium, as well as from other countries (Canada, the Netherlands and the United Kingdom) were identified by sequencing the translation elongation factor 1α (EF). Of these 98 isolates, 13 were identified as F. oxysporum Schltdl., nine as F. proliferatum (Matsush.) Nirenberg and two belonged to clade 3 of the F. solani species complex. Of the 74 remaining isolates, the EF sequence showed 97% to 98% similarity to F. lactis. Of these isolates, the β-tubulin (TUB), calmodulin (CAM) and the second largest subunit of RNA polymerase II (RPB2) genes were also sequenced. Analysis of the combined sequences revealed that the 74 isolates share nine combined sequences that correspond to nine multilocus sequence types (STs), while the F. lactis neotype strain and one other strain, both isolated from figs, form a separate ST. Together, these 10 STs represent a monophyletic F. lactis species complex (FLASC). An unusually high level of genetic diversity was observed between (groups of) these STs. Two of them (ST5 and ST6) fulfilled the criteria for species recognition based on genealogical exclusivity and together represent a new monophyletic species lineage (FLASC-1). The seven other STs, together with the F. lactis neotype ST, form a paraphyletic species lineage in the African clade of the Gibberella fujikuroi species complex (GFSC). From each of the 10 STs, the mycotoxin production was assessed using a multi-mycotoxin liquid chromatography mass spectrometry method. Out of the 27 analyzed mycotoxins, beauvericin and fumonisins were detected in sweet pepper tissue and in maize kernels. The 10 STs clearly differed in the amount of mycotoxin produced, but there was only limited congruence between the production profile and the phylogenetic analysis. Furthermore, the morphological characterization (based on mycelial growth rate and the length of macroconidia) showed distinct differences between the 10 STs, but again there was limited congruence with the phylogenetic results. In conclusion, the data presented in this study demonstrate that 75% of the isolates obtained from sweet pepper with internal fruit rot belong to a F. lactis species complex (FLASC), including a new FLASC-1 monophyletic species, and that the members of this complex display great genetic and phenotypic diversity.

Mycotoxin production by isolates of Fusarium lactis from greenhouse sweet pepper (Capsicum annuum)

Internal fruit rot, caused by Fusarium lactis, is an important disease of sweet pepper (Capsicum annuum) in Canadian greenhouses. Production of the mycotoxins fumonisin B₁ (FB₁), moniliformin (MON) and beauvericin (BEA) by F. lactis (17 isolates) and the related species F. proliferatum (three isolates) and F. verticillioides (one isolate), which are also associated with internal fruit rot, was evaluated on rice medium. All 21 isolates examined were found to produce BEA, at concentrations ranging from 13.28 to 1674.60 ppm, while 13 of 17 F. lactis isolates and two of three F. proliferatum isolates produced MON (0.23 to 181.85 ppm). Only one isolate of F. lactis produced detectable levels of FB₁ in culture, whereas all three F. proliferatum isolates and the F. verticilloides isolate produced this mycotoxin (0.28 to 314 ppm). Production of FB₁, MON and BEA was also evaluated in inoculated pepper fruits showing mild or severe symptoms of infection. FB₁ could be detected in both lightly and heavily diseased fruit tissue after inoculation with F. lactis, F. proliferatum or F. verticilloides, at concentrations ranging from 0.61 to 8.04 ppm. BEA was also detected in lightly and heavily diseased fruit tissue inoculated with F. lactis, as well as in heavily diseased tissue inoculated with F. proliferatum (3.00 to 19.43 ppm), but not in tissue inoculated with F. verticilloides. MON was detected in all tissues inoculated with F. proliferatum or F. verticilloides, and in heavily diseased tissue inoculated with F. lactis (0.03 to 0.27 ppm). The three mycotoxins were also found in naturally infected sweet pepper fruits exhibiting symptoms of internal fruit rot and collected from a commercial greenhouse. The production of MON, BEA and FB₁ alone or in combination by isolates of F. lactis suggests that development of internal fruit rot of sweet pepper is an important food safety concern, and that every effort should be made to cull infected fruit before it makes it to market.

Production and Migration of Mycotoxins in Sweet Pepper Analyzed by Multimycotoxin LC-MS/MS

In this work the presence and migration behavior of mycotoxins formed in sweet pepper, inoculated by Fusarium species involved in internal fruit rot, were investigated. Two different commercial sweet pepper cultivars were inoculated with two different Fusarium proliferatum isolates that were sampled from diseased peppers. After 10 days of incubation at 20 °C in a closed container, the lesion caused by the fungal infection was dissected. Around the lesion, up to three concentric rings of pepper fruit tissue with a width of 5 mm were cut out and analyzed using a multimycotoxin LC-MS/MS method. The analyses resulted in the detection of beauvericin and fumonisins B(1), B(2), and B(3). Beauvericin was detected only in the lesions (95%), and the levels varied between 67 and 73800 μg/kg. Fumonisins B(1), B(2), and B(3) were detected in the lesions and in the surrounding tissue, indicating migration of these toxins into healthy parts of the sweet pepper. In the lesion the fumonisin B(1) level varied between 690 and 104000 μg/kg. Even in the outer ring fumonisin B(1) was still present. Mostly it was present at a lower level than in the lesion, with a maximum level of 556 μg/kg. A similar migration behavior was obtained for fumonisins B(2) and B(3), but lower levels were detected in the lesions, up to 10900 and 1287 μg/kg, respectively. The analysis of 20 pepper samples resulted in the detection of beauvericin or alternariol. Seven samples were contaminated, and the level of beauvericin was 124 μg/kg (N = 1), whereas the level of alternariol varied from below the LOQ (6.6 μg/kg) to 101 μg/kg (N = 6).

Pantoea ananatis strains are differentiated into three groups based on reactions of tobacco and welsh onion and on genetic characteristics

Ninety-six strains of Pantoea ananatis were isolated from 14 plant species including melon, rice, tea and other crops of economic importance. They were classified into three groups (group I, II, III) based on a welsh onion stabbing assay, tobacco infiltration test, and polymerase chain reaction to detect indole acetic acid (IAA) biosynthesis genes (iaaM and iaaH) and a cytokinin biosynthesis gene (etz). Group Ι strains were characterized as causing significant blight symptom on welsh onion and inducing a hypersensitive response (HR)-like reaction on tobacco leaves after 36–48 h and encompassed 20 isolates from foxtail millet, hydrangea, pineapple, river water and rice. These 20 isolates did not possess iaaM, iaaH, or etz genes. Group II, consisting of 34 melon isolates, harbored iaaM,iaaH and etz genes, but did not cause either blight on welsh onion or HR-like reaction on tobacco. Group III strains did not have the iaaM, iaaH, and etz genes, nor did they cause any reaction on welsh onion or tobacco. The 42 strains in group III were isolated from bamboo grass, Chinese silver grass, citrus, dogwood, melon, mugwort, silk tree, sweet corn, tea and welsh onion. Representative strains of the three groups were tested for pathogenicity on melon and rice. Group Ι strains caused palea browning on rice but not internal fruit rot on melon. On the contrary, group II strains did not cause disease on rice but caused internal fruit rot on melon. Group III strains were not pathogenic on rice or melon. These results suggested that the host range of P. ananatis may be predicted by the reactions of welsh onion and tobacco and detection of iaaM, iaaH and etz genes. These tools may serve as rapid tests to identify the pathogenicity groups of P. ananatis.

Histopathology of internal fruit rot of sweet pepper caused by Fusarium lactis

The etiology of internal fruit rot of greenhouse-grown sweet pepper, caused by the fungus Fusarium lactis, was investigated during anthesis and fruit development using stereo, fluorescence and scanning electron microscopy. Proliferation of fungal mycelium was observed on the surface of the stigma one day after inoculation (DAI). Mycelial growth was also visible in the transmitting tissues of the style and inside the ovary at 5 and 6 DAI. When externally symptomless sweet pepper fruits were sectioned 45 DAI, typical internal fruit rot symptoms were observed. Culturing of hyphal-like strands and ovules from inoculated flowers on potato dextrose agar (PDA) confirmed the presence of F. lactis. Similarly, symptomless seeds from infected fruit also yielded colonies of the fungus on PDA. These findings support the hypothesis that internal fruit rot of greenhouse sweet pepper caused by F. lactis is initiated through the infection of the stigma and style during anthesis. Moreover, symptomless seed infection may contribute to disease spread between greenhouses, although further work is needed to understand how F. lactis becomes established and spreads from infected seeds to flowers.