Academic literature on the topic 'Diseases and pests; Rhizopus stolonifer'

Rhizopus soft rot, caused primarily by Rhizopus stolonifer, is one of the most common postharvest diseases of sweetpotato and is often considered the most devastating. Traditionally, Rhizopus soft rot has been effectively controlled using postharvest dips in dicloran fungicides; however, due to changes in market preferences, use of these fungicides is now limited. This, along with the lack of labeled and effective fungicides for control of Rhizopus soft rot in sweetpotato, creates the need for integrated strategies to control the disease. The effects of storage temperature (13, 23, and 29°C), relative humidity (80, 90, and 100%), and initial inoculum levels (3-, 5-, and 7-mm-diameter mycelial plugs) on progression of Rhizopus soft rot in ‘Covington’ sweetpotato were examined. Percent decay due to Rhizopus soft rot infection was significantly reduced (P < 0.0001) at a low temperature (13°C) but was not significantly affected by changes in relative humidity or initial inoculum level (P >0.05). Sporulation of R. stolonifer was also significantly reduced at the lowest temperature of 13°C. High relative humidity (>95%) significantly increased sporulation of R. stolonifer and sporulation also increased as initial inoculum level increased. Efficacy of chlorine dioxide (ClO2) fumigation, UV-C irradiation, and postharvest dips in alternative control products were also investigated for control of Rhizopus soft rot. Static ClO2 treatments were effective in reducing sporulation on treated roots but had no significant impact on incidence of Rhizopus soft rot. UV irradiation at 3.24 KJ/m2 1 h after inoculation as well as dips in aqueous ClO2 and StorOx 2.0 significantly (P < 0.05) reduced disease incidence. Understanding the epidemiological factors favoring Rhizopus soft rot and identifying alternative control strategies allow for improved recommendations to limit postharvest losses in sweetpotato.

Fifteen fungal pathogens, viz. Penicillium chrysogenum, Penicillium expansum, Monilinia fructigena, Trichothecium roseum, Cladosporium herbarum, Aspergillus niger, Coprinus psychromorbidus, Alternaria alternaria, Phytophthora palmivora, Pythium sp., Fusarium solani, Alternaria sp., Monilinia sp., Guignardia bidwellii and Rhizopus stolonifer isolated from rotted fruits were evaluted for the production of different enzyme on solid culture media. All the isolates produced enzymes on the media used, 87.67% of the isolated fungi were found to produce amylases, 80.00% of the fungi produced lipases, 73.33% produced proteases, cellulases by 66.67% and pectinases by 60.00%. The array of enzymes produced differs between different fungi. Penicillium sp., Alternaria alternata, Rhizopus stolonifer and Alternaria sp. were found to produce all the tested enzymes on culture media. These pathogens are known to attack almost all the plants, fruits, vegetables and cause many diseases. The differences in the enzymatic production of different fungal pathogens represent their virulence and specificity in causing different fruit rot diseases.

Severe outbreaks of bunch rots (BR) have occurred recently during harvest of table grapes (Vitis vinifera L.) in Chile. Previously, BR was almost exclusively associated with Botrytis cinerea Pers.:Fr. (2,3); however, in 2000 to 2002, BR symptoms were associated with black molds and possibly nonfilamentous yeasts and bacteria. Cvs. Thompson Seedless, Flame Seedless, Ruby Seedless, and Red Globe were severely affected. Symptoms start at the pedicels as soft, watery rots that partially or completely decay infected berries. Longitudinal cracks are produced, a black mold usually develops along the crack fissures, and the skin of the berry turns light gray. Isolations on potato dextrose agar acidified with 1 N lactic acid (APDA) at 0.5 ml/liter, consistently yielded Rhizopus stolonifer (Ehrenb. ex Fr.) Vuillemin and Aspergillus niger Tiegh. R. stolonifer on APDA produced a white-to-gray aerial and nonseptate mycelium, black and globose sporangia with an elliptical collumela, one-celled, globose to oval, striated, almost hyaline sporangiospores, rhizoids, and stolons. A. niger produced septate mycelium. Single-celled, black, rough walled, globose conidia developed on short chains on the second phialides at the tip of globose, upright conidiophores. Mature (soluble solids >16%) detached berries of cv. Thompson Seedless were inoculated with sporangiospores (≈107 spores per ml) of R. stolonifer isolates RS6, RS52, RS73, and RS79 and conidia (≈108 conidia per ml) of A. niger isolates AN12, AN69, and AN75. When berries were aseptically punctured with a sterile hypodermic syringe prior to inoculation, 60 to 86.7% and 42.5 to 100% of berries were infected with R. stolonifer and A. niger, respectively, and both developed BR symptoms (significantly different from control berries) after 48 h in humid chambers at 23°C. Injuries were needed for infection since no infection or only 23.3% of noninjured berries were infected with R. stolonifer and A. niger, respectively. For both pathogens, there was a significant (P < 0.043) interaction between isolates and the presence or absence of injuries. Both pathogens were successfully reisolated on APDA. Fungicide sensitivity tests were performed on detached cv. Thompson Seedless berries challenged by placing an ≈6 μl-drop of inoculum suspension (106 or 107 spores per ml of R. stolonifer isolate RS52 and A. niger isolate AN12, respectively) on injured berries. Pyraclostrobin (0.067 mg/ml) mixed with nicobifen at 0.134 mg/ml (BAS 516 01 F at 0.201 mg a.i./ml, BASF) and copper oxide at 1.2 mg/ml (Cuprodul 60 WP, Quimetal Chile) significantly (P < 0.01) inhibited infection (100% control) by R. stolonifer and A. niger. R. stolonifer was completely controlled by dicloran at 1.88 mg/ml (Botran 75 WP) and partially controlled by captan at 1.6 mg/ml (Captan 80 WP), but A. niger was not controlled by either fungicide. To our knowledge this is the first report of R. stolonifer causing BR of table grape in Chile (4). The severe outbreaks may be associated with warm weather conditions during harvest and injuries caused by birds, insects, or cultural practices. Infection caused by R. stolonifer or A. niger may be followed by sour rot organisms (yeasts or bacteria), as has been suggested elsewhere (1,2). References: (1) E. Gravot et al. Phytoma 543:36, 2001. (2) W. B. Hewitt Page 26 in: Compendium of Grape Diseases, American Phytopathological Society, St. Paul, MN, 1994. (3) B. A. Latorre and G. Vásquez. Aconex (Chile) 52:16, 1996. (4) F. Mujica and C. Vergara. Flora Fungosa Chilena. Universidad de Chile, Facultad de Agronomiacute;a, Santiago, Chile, 1980.

In recent years, growers in Michigan and other sugar beet (Beta vulgaris) production areas of the United States have reported increasing incidence of root rot with little or no crown or foliar symptoms in sugar beet with Rhizoctonia crown and root rot. In addition, Rhizoctonia-resistant beets have been reported with higher levels of disease than expected. In examining beets with Rhizoctonia root rot in Michigan, over 50% of sampled roots had a second potential root rot pathogen, Rhizopus stolonifer. Growing conditions generally were not conducive to disease production by this pathogen alone, so we investigated the potential for interaction between these two pathogens. In greenhouse tests, four of five sugar beet varieties had more severe root rot symptoms when inoculated with both pathogens than when inoculated with either pathogen alone. This synergism occurred under conditions that were not conducive to disease production by R. stolonifer. Host resistance to Rhizoctonia crown and root rot reduced diseases severity, but was insufficient to control the disease when both pathogens were present. This raises concerns about correct disease diagnosis and management practices and indicates that a root rot complex may be important on sugar beet in Michigan.

The application of ultraviolet light (UV-C, 254 nm) hormesis on fruits and vegetables to stimulate beneficial responses is a new method for controlling storage rots and extending the shelf-life of fruits and vegetables. The present study was aimed at treating tomatoes (Lycopersicon esculentum) with different UV-C dosages (1.3 to 40 KJ/m2) to induce resistance to black mold (Alternaria alternata), gray mold (Botrytis cinerea), and Rhizopus soft rot (Rhizopus stolonifer). These diseases were effectively reduced when tomatoes were inoculated following UV-C irradiation. UV-C treated tomatoes were firmer in texture and less red in color than the control tomatoes, indicating a delay in ripening. Slower ripening and resistance to storage rots of tomatoes are probably related. The positive effect of UV-C on tomatoes decreased as treatments were performed at stages of increased ripeness.

Postharvest soft rots of sweetpotato caused by Rhizopus stolonifer (Rhizopus soft rot) and Dickeya dadantii (bacterial root rot) occur sporadically and can result in significant losses. A 3-year field study related preharvest conditions, including soil texture, chemistry, and fertility; air temperature; soil temperature and moisture; and various cultural practices (153 total variables), to postharvest susceptibility to both diseases in 75 sweetpotato fields in North Carolina and 63 sweetpotato fields in Louisiana. Storage roots were sampled from each field, cured, stored, and inoculated with each pathogen after 100 to 120 days in storage. Disease susceptibility was measured as incidence of diseased storage roots 10 days following inoculation. There was wide variation from field to field in incidence of both diseases (0 to 100% for Rhizopus soft rot and 5 to 95% for bacterial root rot) in both states in each year. Correlations between disease incidence and each of the preharvest variables revealed numerous significant correlations but the variables that correlated with disease incidence were different between North Carolina and Louisiana. Models for both diseases were built by first using forward stepwise regression to identify variables of interest, followed by a mixed-model analysis to produce a final reduced model. For North Carolina fields, postharvest Rhizopus soft rot susceptibility was described by the percentage of the soil cation exchange capacity occupied by calcium, amount of plant-available soil phosphorus, percent soil humic matter, mean air temperature, mean volumetric soil moisture at 40 cm in depth, and mean soil temperature at 2 cm in depth. Postharvest bacterial soft rot susceptibility was described by soil pH and the number of days of high soil temperature late in the season. For Louisiana fields, Rhizopus soft rot susceptibility was described by a complex of variables, including late-season air and soil temperature and late-season days of extreme soil moisture. For bacterial root rot, days of low air temperature and days of high soil temperature late in the season as well as days of low soil moisture best described variation. Although the influence of preharvest variables on postharvest susceptibility was profound for each disease, the complexity of factors involved and differences between the data for the two states makes development of a predictive system extremely difficult.

The in vitro antifungal activities and mechanism of action of tea polyphenols (TP), tea saponin (TS) and their combination were evaluated against <i>Rhizopus stolonifer</i>. The results showed that both TP and TS inhibited the mycelial growth in a dose-dependent manner, and their combination at the ratio of 7:3 exhibited synergistic antifungal interaction. We also observed that the treatment of TP or TS significantly induced the production of H₂O₂ and resulted in membrane lipid peroxidation, thus leading to an increase in cell membrane permeability and the leakage of K⁺, soluble protein and soluble sugar. Moreover, combining them for treatment increased the induction of H₂O₂ production and oxidative damage. Scanning electron microscopic observations also showed the damage to the hyphal cell structure. It was concluded that TP, TS and their combination inhibit the growth of <i>R. stolonifer</i> through the induction of H₂O₂ production, leading to cell membrane oxidative damage and intracellular constituent leakage. These findings suggest that TP and TS can potentially be used as an alternative to control postharvest fruit diseases caused by <i>R. stolonifer.</i>

Tomatoes are one of the most widely produced and consumed vegetable in Nepal. Fungal pathogens deteriorate the quality and quantity of tomato and cause health hazards to the consumers as well as economic loss to the traders. This study was carried out to identify some fungal diseases associated with post-harvest deterioration of stored tomato fruits in Balkhu Agriculture and vegetable Market of Kathmandu, Nepal. Collected samples were cultured in Potato Dextrose Agar (PDA) media in complete randomized design. Fifteen species of fungi namely Alternaria alternata, A. solani, Aspergillus niger, Botrytis cinerea, Fulvum fulva, Colletotrichum truncatum, Curvularia spicifera, Fusarium oxysporum, Dipodascus geotrichum, Mucor mucedo, Penicillium chrysogenum, Phytophthora infestans, Boeremia exigua, Pythium aphanidermatum and Rhizopus stolonifer were identified. These were responsible for 14 different diseases of Alternaria fruit rot, Anthracnose, Black mold rot, Botrytis Bunch Rot, Damping off/ fruit rot, Drechslera mold, Fusarium rot, Mucor rot, Penicillum rot, Boeremia blight, Phytophthora rot, Rhizopus rot, Russet, and, Sour rot. The presence of these fungi and corresponding rot diseases on stored tomato indicates the need for management of fungi, farm sanitation and improved market in order to prevent field-to-storage transmission of pathogen.

Five types of symptom were recorded on two varieties of rose plant. The symptoms were Black spot, Leaf spot1, Leaf spot2, Blight and Anthracnose. The study revealed the presence of 20 species of fungi belonging to 17 genera. The isolated fungi were Alternaria alternata (Fr.) Keissler, Arthrinium saccharicola Stevenson, Aspergillus flavus, Link., A. niger van Tiegh., Botrytis allii Munn, Cercospora sp., Cladosporium cladosporioides (Fresen.) de Vries, C. oxysporum Berk. & Curt., two species of Colletotrichum, Curvularia brakyospora Boedijn, Curvularia pallescens Boedijn, Fusarium sp., Epicoccum purpurascens Ehreneb ex Schlecht; Link, Gibberella sp., Marssonina rosea (Lib.) Died, Nigrospora sphaerica (Sacc.) Masson, Pestalotiopsis guepinii (Desm.) Stay. with its two culture types, Penicillium sp., Rhizopus stolonifer (Ehrenb. Ex. Fr) Vuill. and Trichoderma viride Pers. ex Fries. The frequency (%) of association of P. guepinii was higher than any other fungi. Pestalotiopsis guepinii and its two culture types were found to be pathogenic to rose plant. DOI: http://dx.doi.org/10.3329/jbas.v38i2.21347 Journal of Bangladesh Academy of Sciences, Vol. 38, No. 2, 225-233, 2014

A Podridão Mole, causada por espécies do gênero Rhizopus, sendo a espécie R. stolonifer a mais comum, é uma das principais doenças pós-colheita de pêssegos. O desenvolvimento do patógeno prejudica a comercialização de pêssegos em mercados atacadistas e varejistas, consistindo em uma das principais causas de rejeição de frutos e da redução do preço de venda da caixa de pêssego. O fungo pode causar podridões em outros frutos e vegetais com níveis similares de perdas. Essa doença está intimamente relacionada à presença de danos físicos ou mecânicos, exemplificados pela presença de injúrias na superfície do fruto, já que Rhizopus é conhecido por penetrar seus hospedeiros via ferimentos. Poucos trabalhos investigaram os mecanismos de penetração do patógeno em pêssegos. Alguns concluíram que o fungo não produz enzimas que auxiliem na penetração direta de frutos. No entanto, observações da ocorrência da doença em pêssegos aparentemente não injuriados sugerem que a penetração direta pode ocorrer. A principal medida de controle da doença consiste no manejo cuidadoso dos frutos justamente para evitar ferimentos. O objetivo desse trabalho consistiu em avaliar os mecanismos de penetração de R. stolonifer em pêssegos, injuriados ou intactos, e caracterizar o progresso espaço-temporal da Podridão Mole nesses frutos. A atividade de enzimas esterases produzidas pelo fungo foi avaliada qualitativamente, a partir da reação de discos de micélio e suspensões de esporos do patógeno em água ou solução nutritiva em diferentes períodos de incubação (0, 4 e 8 horas) com substrato indoxil acetato, para observação da produção de cristais de coloração azul índigo. Os tratamentos que continham discos de micélio e suspensão de esporos em solução nutritiva, após 8 horas de incubação, adquiriram tonalidades mais escuras de azul, devido à formação de cristais oriundos da reação entre enzimas esterases e substrato. Avaliações ao espectrofotômetro foram conduzidas para determinar a quantidade de enzimas produzidas por R. stolonifer quando cultivado em meios com glicose ou cutina, como únicas fontes de carbono. O patógeno foi capaz de crescer em ambos os meios e observou-se maior atividade de enzimas esterases quando o patógeno foi cultivado em meio com cutina. Solução de diisopropil fluorofosfato, inibidor de enzimas cutinases, foi depositada sobre frutos e impediu a manifestação da Podridão Mole em pêssegos inoculados com suspensão de esporos do fungo em solução nutritiva. Pêssegos feridos ou não foram inoculados com suspensão de esporos de R. stolonifer em água e solução nutritiva para estudo do progresso espaço-temporal da Podridão Mole. Frutos sadios colocados próximos a frutos inoculados artificialmente apresentaram sintomas da doença, a qual se disseminou com mesma taxa de progresso em todos os tratamentos. O processo infeccioso de R. stolonifer em pêssegos e nectarinas também foi observado em microscopia óptica e eletrônica de varredura e verificou-se a penetração direta de tecidos intactos pelo fungo. Os resultados obtidos nesse trabalho demonstraram que R. stolonifer é capaz de penetrar diretamente frutos intactos através de esporos germinados em aporte nutritivo externo ao fruto e estolões miceliais. Essas estruturas produzem enzimas esterases, principalmente cutinases, que auxiliam no processo infeccioso.
Soft Rot, caused by Rhizopus stolonifer, is one of the main postharvest diseases on peaches. The pathogen development is prejudicial to the stone fruit commercialization in wholesale and retail markets and the disease can cause reduction in the price of peaches, being one of the main causes of fruit rejection. The pathogen has been responsible for causing rots in other types of fruit and vegetables, with similar level of losses. The disease is related to the occurrence of mechanical and physical damages and the presence of injuries on the fruit surface contributes to the infection by Rhizopus, which is known as a strictly wound parasite. Few studies have investigated the mechanisms of the pathogen penetration in peaches. Some have concluded that the fungus does not produce enzymes that assist in the direct penetration of fruit. However, observations of disease occurrence on apparently uninjured peaches suggest that direct penetration can occur. Careful management to avoid injuries on the fruit is the most important disease control measure. The objective of this research was to evaluate the penetration mechanisms of R. stolonifer on injured or uninjured peaches and characterize the spatio-temporal progress of Soft Rot on these fruit. To determine the esterase enzymes activity, produced by the pathogen, micelial discs and spore suspensions of R. stolonifer on water or nutrient solution in different incubation periods (0, 4 and 8 hours) were added to indoxyl acetate solution, to observe the presence of crystals of indigo blue color. The treatments with micelial discs or spore suspensions on nutrient solution, after 8 hours of incubation, showed darker shade of blue, because of the production of crystals from the reaction between the esterase enzymes and the indoxyl acetate. Spectrophotometer evaluations were carried out to determine the amount of enzymes produced by R. stolonifer when it was grown on culture media with glucose or cutin, as sole carbon sources. The pathogen was able to grow on both media and higher esterase activity was observed when the fungus was grown on cutin media. Diisopropyl fluorophosphate solution, a cutinase inhibitor, was placed over the fruit and prevented Soft Rot development on peaches inoculated with the fungus spore suspension on nutrient solution. Injured or uninjured peaches were inoculated with R. stolonifer spore suspensions on water or nutrient solution to study the spatiotemporal progress of Soft Rot. Healthy fruit placed next to artificially inoculated peaches showed symptoms of the disease, which has spread with the same rate of progress in all treatments. The infectious process of R. stolonifer on peaches and nectarines was also studied on optic and scanning electron microscopy and direct penetration of intact tissues by the fungus was observed. The results of this work showed that R. stolonifer is capable of direct penetration on uninjured peaches by spores germinated on external nutrient support and by micelial stolons. These structures produce esterase enzymes, especially cutinase, that help in the infectious process.

Peanuts contribute significantly to food security in western Kenya due to their high nutritional value and cash crop potential. However, the crop is highly susceptible to aflatoxin contamination. Yet little information is available on the extent of contamination in the region. This study explores the level and extent of contamination of peanuts by aflatoxins, Aspergillus section Flavi, Rhizopus and Penicillium spp. in western Kenya. A survey of 769 households was carried out in the Busia and Homa bay districts of Kenya. Information on peanut pre- and post-harvest practices was collected through person-to-person interviews. Aflatoxin levels of samples collected from each household were determined by indirect competitive ELISA method. Isolation of Aspergillus section Flavi, Penicillium and Rhizopus spp. was done on Modified Dichloran Rose Bengal (MDRB) agar, while identification of specific fungal species was done on Czapek yeast extract agar (CYA). Screening isolates of A. flavus and A. parasiticus for aflatoxin production was done in high sucrose yeast extract (YES) liquid medium, and the aflatoxin types identified on TLC plates, using analytical grades of aflatoxin B1, B2, G1 and G2 as reference standards. Common household preparation techniques (roasting, making peanut paste and boiling peanuts) were evaluated for effectiveness in reducing aflatoxin levels in peanuts. The boiling procedure was modified to test the effect of magadi (locally available salt used mainly to soften legumes, vegetables or maize while cooking), ammonium persulphate and sodium hypochlorite during soaking. Magadi, sodium bicarbonate and locally prepared ash was subsequently used to boil the nuts after soaking. Aflatoxin levels ranged from zero to 7525 ìg/kg. Most samples were safe to consume, based on the European Union and Kenya Bureau of Standards tolerance levels, with 63.7 per cent of all samples having undetectable levels, and only 7.54 per cent being contaminated based on KEBS standards. Peanuts from the Busia district, which has more of Lower Midland 1 (mean annual rainfall of 1600-1800 mm) and Lower Midland 2 (mean annual rainfall of 1300-1700 mm) agro-ecological zones had significantly (÷2=14.172; P=0.0002) higher levels of aflatoxin compared to the Homa bay district, that has more of the drier Lower Midland 3 agroecological zone (mean annual rainfall of 900-1500mm). Improved cultivars had significantly (÷2=9.748; P=0.0018) lower levels of aflatoxin compared to local cultivars. Over 60 per cent of all samples had A. flavus S-strain, A. flavus L-strain and A. niger. A. flavus S-strain was positively correlated with aflatoxin levels. As expected, grading of peanuts post-harvest significantly reduced the incidence of A. flavus S- and L-strains, while peanuts collected from farmers who belonged to producer marketing groups had a significantly lower incidence of A. flavus S- and L-strains, A. niger and Rhizopus spp. The incidence of A. flavus L-strain, A. niger and Rhizopus spp. was significantly higher in local landraces compared to the improved cultivars. Over 60 per cent of isolates produced Aflatoxin B1. Intermediate processes such as sorting and dehusking led to a significant decline in levels of aflatoxin. Soaking peanuts in water, magadi, NaOCl and ammonium persulphate significantly reduced aflatoxin levels by 27.7, 18.4, 18.3 and 1.6 per cent respectively; while boiling the peanuts in magadi, local ash, baking powder and water reduced aflatoxin levels by 43.8, 41.8, 28.9 and 11.7 per cent respectively. Using magadi during boiling increased the acceptability of the boiled peanuts while reducing the aflatoxin levels. The impact of aflatoxin levels in peanuts studied in this research is within safe limits except a few samples, and therefore aflatoxin contamination of peanuts at household level is not a serious threat. Contamination by aflatoxin and post-harvest fungi can be reduced by focusing on improved control strategies for wetter and more humid zones such as planting improved peanut cultivars and controlling pre-harvest pest damage. Conventional household peanut preparation techniques should be explored as possible aflatoxin management strategies in Kenya. The aflatoxin binding properties of locally available salts such as magadi and locally prepared ash should be further investigated.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.