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Potato Dextrose Agar (potato + dextrose_agar)
Selected AbstractsRapid Screening Method of Cassava Cultivars for Resistance to Colletotrichum gloeosporioides f.sp. manihotisJOURNAL OF PHYTOPATHOLOGY, Issue 1 2002C. N. FOKUNANG An in vitro method for assessing cassava anthracnose disease (CAD) resistance was developed as a preliminary screen to a CAD-resistant breeding programme. Potato dextrose agar (PDA) media was amended by extracts from the stem cortex of 10 cassava cultivars (30001; 30572, 30211, 88/02549, 88/00695, 88/01336, 91/00344, 91/00313, 91/00684 and 91/00475), and assayed for efficacy of inhibition of the growth of Colletotrichum gloeosporioides f. sp. manihotis isolates (05FCN, 10FCN, 12FCN, and 18FCN). Morphological and physiological data indicated that there was a significant difference (P , 0.05), in mycelial growth, spore germination and sporulation among the four isolates on PDA amended with cassava stem extracts. Extracts from cassava cultivars 30211, 91/00684 and 91/00313 showed higher inhibition of germ tube development, mycelial growth and sporulation of the fungal isolates, whereas cultivars 88/02549 and 88/01336 showed the least inhibition. The 10 cultivars were further tested in both greenhouse and field conditions, under disease pressure for two planting seasons, to corroborate resistance to the fungus as observed in vitro. Greenhouse and field trials with the 10 cassava cultivars showed a significant difference (P , 0.05) in CAD resistance. Cultivars 88/02549 and 88/01336 were highly CAD-susceptible, as shown in the in vitro assays and confirmed in the greenhouse and field tests. The other eight cultivars were either resistant (30211, 91/00684), or moderately resistant (30572, 88/00695, 91/00475, 91/00344, 30001 and 91/00313) to CAD. The study shows that an in vitro screening assay of cassava for resistance to CAD could serve as a convenient preliminary screening technique to discriminate CAD-resistant from CAD-susceptible cassava cultivars. The in vitro screening method considerably reduces time and labour in comparison with the current screening techniques of cassava, which involve field planting, inoculation and evaluation. [source] DESIGN, CONSTRUCTION AND VALIDATION OF A SANITARY GLOVE BOX PACKAGING SYSTEM FOR PRODUCT SHELF-LIFE STUDIESJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 3 2001ZEHRA AYHAN A glove box has been constructed as pan of an integrated pilot plant scale pulsed electric field processing and packaging system to facilitate studies of product shelf-life with selected packaging materials. The glove box was sanitized using combination of hydrogen peroxide and germicidal UV light. A HEPA air filter provided positive pressure of bacteria-free air. Nonselective nutrient broth was sterilized and filled into presanitized bottles inside the glove box. Negative and positive controls were included in the experiment. All bottles were incubated at 22C and 37C for two weeks and checked for rnicrobial growth by measuring optical density at 600 nm using a spectrophotometer and by plating on plate count agar and potato dextrose agar for total aerobic and, yeast and mold counts, respectively. No turbidity or microbial growth was observed in the media filled in the sanitized bottles using the sanitized glove box at 22 and 37C. PEF processed orange juice using this system had a shelf-life of more than 16 weeks at 4C. [source] Fungistatic Activity of Heat-Treated Flaxseed Determined by Response Surface MethodologyJOURNAL OF FOOD SCIENCE, Issue 6 2008Y. Xu ABSTRACT:, The objective of this study was to evaluate the effect of heat treatment on the fungistatic activity of flaxseed (Linum usitatissimum) in potato dextrose agar (PDA) medium and a fresh noodle system. The radial growth of Penicillium chrysogenum, Aspergillus flavus, and a Penicillium sp. isolated from moldy noodles, as well as the mold count of fresh noodle enriched with heat treated flaxseed, were used to assess antifungal activity. A central composite design in the response surface methodology was used to predict the effect of heating temperature and time on antifungal activity of flaxseed flour (FF). Statistical analysis determined that the linear terms of both variables (that is, heating temperature and time) and the quadratic terms of the heating temperature had significant (P < 0.05) effects on the radial growth of all 3 test fungi and the mold count log-cycle reduction of fresh noodle. The interactions between the temperature and time were significant for all dependent variables (P < 0.05). Significant reductions in antifungal activities were found when FF was subjected to high temperatures, regardless of heating time. In contrast, prolonging the heating time did not substantially affect the antifungal activities of FF at low temperature. However, 60% of the antifungal activity was retained after FF was heated at 100 °C for 15 min, which suggests a potential use of FF as an antifungal additive in food products subjected to low to mild heat treatments. [source] Growth of Botrytis cinerea and Strawberry Quality in Ozone-enriched AtmospheresJOURNAL OF FOOD SCIENCE, Issue 5 2003A. Nadas ABSTRACT Botrytis cinerea cultures were stored on potato dextrose agar in air with or without 1.5 ,L/L ozone at 2 °C. Cultures stored in the presence of ozone grew slower. Strawberry fruits (Fragaria×ananassa cv. Camarosa) were stored for 3 d at 2 °C in air with or without 1.5 ,L/L ozone and then transferred to room temperature. Each group was inoculated with B. cinerea grown in air with or without ozone. Visible mycelial growth developed more rapidly on fruit previously stored in air. Ozone-enriched cold storage of naturally infected ,Camarosa' fruit reduced decay incidence, weight loss, and fruit softening, but resulted in a reversible loss of fruit aroma. [source] First Report of Rhizoctonia solani AG-7 on Cotton in EgyptJOURNAL OF PHYTOPATHOLOGY, Issue 4 2010Kamel A. Abd-Elsalam Abstract Eighty-two isolates of Rhizoctonia solani were recorded from roots of naturally-infected seedlings of the Egyptian cotton (Gossypium barbadense L.). Anastomosis groups (AGs) of the isolates were determined by using 13 different AGs testers. Three (3.7%) of the isolates were identified as R. solani AG7, while the remaining isolates were belonging to the AG 2-1, AG4 and AG5. The identification of the three isolates was based on the frequency of the C2 reaction with the AG7 tester isolate. No fusion was observed between AG7 and isolates representing the other 13 AGs. Colonies of AG7 isolates grown on potato dextrose agar (PDA), malt yeast agar (MYA) and melt peptone agar (MPA) were brown to dark brown with aerial mycelium and sclerotia. The isolates had pitted sclerotial clusters and brownish exudates after 21 days of culturing on PDA, but without clear zonation. Pathogenicity test under greenhouse conditions revealed that AG7 caused the common symptoms of damping,off, which included seed rot, lesions on the hypocotyls and root rot. [source] Gerbera jamesonii, a New Host of Fusarium oxysporum f.sp. tracheiphilumJOURNAL OF PHYTOPATHOLOGY, Issue 1 2010Marco Troisi Abstract The random amplified polymorphic DNA (RAPD) technique was used to analyze the total genomic DNA of pathogenic isolates of Fusarium oxysporum on Gerbera jamesonii by comparing them to representatives of the formae speciales chrysanthemi and tracheiphilum. A close genetic relationship was observed among most of the new isolates from G. jamesonii. They shared RAPD markers with the tested representatives of the forma specialis chrysanthemi. Some isolates of those tested from diseased G. jamesonii were placed in a different cluster, which included representative isolates of forma specialis tracheiphilum. This is the first report of F. oxysporum f.sp. tracheiphilum on G. jamesonii. A rapid protocol for DNA extraction directly from fungal colonies grown on potato dextrose agar allowed complete analysis in less than 4 h. [source] Acetic Acid, Ethanol and Steam Effects on the Growth of Botrytis cinerea in vitro and Combination of Steam and Modified Atmosphere Packaging to Control Decay in KiwifruitJOURNAL OF PHYTOPATHOLOGY, Issue 2 2009Anastasia L. Lagopodi Abstract The effects of acetic acid fumigation, ethanol fumigation, and steam heat treatment on growth of Botrytis cinerea in vitro were investigated. The effect of steam heat treatments in combination with modified atmosphere packaging (MAP) on Botrytis decay development on ,Hayward' kiwifruit was also studied. The fungus was grown in Petri dishes on potato dextrose agar. Ethanol fumigation with 100 ,l/l for 3 or 6 min, or 200 ,l/l for 6 min enhanced the growth of B. cinerea. The effect of acetic acid on growth of B. cinerea was time and dosage-dependent. Fumigation with 1 ,l/l for 6 min, 2 ,l/l for 3 min, and 4 ,l/l for 3 min promoted radial growth of the fungus when compared to the growth of the untreated control. Fumigation with 2 ,l/l for 6 min delayed the growth of the fungus for the first 6 days, while fumigation with 6 ,l/l for 3 min delayed the growth of the fungus after the sixth day. Fumigation with 4 or 6 ,l/l acetic acid for 6 min, and 8 ,l/l acetic acid for 3 or 6 min resulted in complete inhibition of fungal growth. Steam heat treatment at 45°C for 6 min, and at 48, 51, and 54°C for 3 or 6 min completely inhibited fungal growth in vitro. Furthermore, steam treatments at 47, 50, and 53°C for 3 or 6 min completely inhibited decay at the stem end of kiwifruit kept at 10°C in MAP for 12 days. However, none of the steam treatments inhibited decay in wounds on the surface of the fruit kept in MAP. [source] Isolates of Microdochium nivale and M. majus Differentiated by Pathogenicity on Perennial Ryegrass (Lolium perenne L.) and in vitro Growth at Low TemperatureJOURNAL OF PHYTOPATHOLOGY, Issue 5 2006I. S. Hofgaard Abstract Pink snow mould is a serious disease on grasses and winter cereals in cold and temperate zones during winter. To better understand the basis for the variation in pathogenicity between different isolates of Microdochium nivale and M. majus and to simplify selection of highly pathogenic isolates to use when screening for resistance to pink snow mould in perennial ryegrass, we sought traits correlated with pathogenicity. Isolates of M. nivale were more pathogenic on perennial ryegrass than isolates of M. majus, as measured by survival and regrowth of perennial ryegrass after infection and incubation under simulated snow cover. Pathogenicity as measured by relative regrowth was highly correlated with fungal growth rate on potato dextrose agar (PDA) at 2°C. Measuring fungal growth on PDA therefore seems to be a relatively simple method of screening for potentially highly pathogenic isolates. In a study of a limited number of isolates, highly pathogenic isolates showed an earlier increase and a higher total specific activity of , -glucosidase, a cell wall-degrading enzyme, compared with less pathogenic isolates. None of the M. majus isolates was highly pathogenic on perennial ryegrass. Our results indicate biological differences between M. nivale and M. majus and thus strengthen the recently published sequence-based evidence for the elevation of these former varieties to species status. [source] Effect of benzyl isothiocyanate on tomato fruit infection development by Alternaria alternataJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 9 2005R Troncoso-Rojas Abstract Benzyl isothiocyanate (BITC) is known to be a strong antifungal compound in vitro against different fungi. The effectiveness of benzyl isothiocyanate to control Alternaria alternata growth in vitro and in vivo was tested. BITC in vitro activity was evaluated in A alternata growing on potato dextrose agar and exposed to 0.025, 0.05, 0.1, 0.2 or 0.4 mg ml,1. In vivo activity was evaluated by exposing A alternata -inoculated tomato fruits for either 18 or 36 h to 0.28 or 0.56 mg ml,1 BITC packed on low-density polyethylene film (LDPF) bags. Additionally, the effect of BITC on post-harvest physiology and tomato quality throughout storage at 20 °C was evaluated daily by monitoring respiration rate and ethylene production, whereas total soluble solids, pH, titratable acidity and fresh weight loss were measured every 3 days. Results showed that the minimal inhibitory concentration of BITC in vitro was 0.1 mg ml,1. A combined use of 0.56 mg ml,1 BITC with LDPF for 18 h was the optimum treatment to control Alternaria rot in packed tomato fruit. No effect of BITC on respiration rate, ethylene production, total soluble solids, pH, weight loss and titratable acidity was observed. Results suggest that BITC can be used as a post-harvest treatment to control Alternaria rot in tomato fruit without detrimental effects on the tomato post-harvest quality. Copyright © 2005 Society of Chemical Industry [source] Protein kinase A subunits of the ascomycete pathogen Mycosphaerella graminicola regulate asexual fructification, filamentation, melanization and osmosensingMOLECULAR PLANT PATHOLOGY, Issue 6 2006RAHIM MEHRABI SUMMARY As in many fungi, asexual reproduction of Mycosphaerella graminicola in planta is a complex process that requires proper differentiation of the infectious hyphae in the substomatal cavities of foliar tissue before pycnidia with conidia can be formed. In this study, we have investigated the role of the cAMP signalling pathway in development and pathogenicity of this pathogen by disruption of the genes encoding the catalytic (designated MgTpk2) and regulatory subunit (designated MgBcy1) of protein kinase A. The MgTpk2 and MgBcy1 mutants showed altered phenotypes in vitro when grown under different growth conditions. On potato dextrose agar (PDA), MgBcy1 mutants showed altered osmosensitivity and reduced melanization, whereas the MgTpk2 mutants showed accelerated melanization when compared with the M. graminicola IPO323 wild-type strain and ectopic transformants. MgTpk2 mutants also secreted a dark-brown pigment into yeast glucose broth medium. In germination and microconidiation assays, both mutants showed a germination pattern similar to that of the controls on water agar, whereas on PDA filamentous growth of MgTpk2 mutants was impaired. Pathogenicity assays showed that the MgTpk2 and MgBcy1 mutants were less virulent as they caused only limited chlorotic and necrotic symptoms at the tips of the inoculated leaves. Further analyses of the infection process showed that MgTpk2 and MgBcy1 mutants were able to germinate, penetrate and colonize mesophyll tissue, but were unable to produce the asexual fructifications, which was particularly due to inappropriate differentiation during the late stage of this morphogenesis-related process. [source] Effects of temperature on germination and hyphal growth from conidia of Ramularia rhei and Ascochyta rhei, causing spot diseases of rhubarb (Rheum rhaponticum)PLANT PATHOLOGY, Issue 5 2006Y. Zhao Rhubarb leaf and petiole spot disease, caused by Ramularia rhei and Ascochyta rhei, has gradually become more noticeable in the UK field crop. Conidial germination and subsequent colony growth of R. rhei and A. rhei were investigated under in vitro conditions on potato dextrose agar and in vivo on leaf discs. Results indicated that the two fungi responded differently to temperature. Ramularia rhei was better adapted to temperatures , 25°C, with an optimum around 20°C, whereas A. rhei was more adapted to temperatures , 15°C, with an optimum > 25°C. Overall, conidia of R. rhei germinated and subsequent colonies grew at greater rates than those of A. rhei on leaf discs at temperatures , 25°C. These results indicated that it is important to identify the causal agent of leaf and petiole spot diseases in rhubarb field crops in order to estimate disease risks accurately. [source] | |||||||||||||