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Annette L. Wszelaki and Elizabeth J. Mitcham

Controlled atmospheres have been proven an effective postharvest disease deterrent for strawberries both in transport and storage. However, these treatments do not provide residual protection once the commodity is removed from the atmosphere, and the atmospheres can cause off-flavors in the fruit. Elevated oxygen atmospheres are a novel addition to this technology and could potentially provide better decay control without the harmful effects on fruit flavor aspects. Elevated oxygen will potentially discourage microbial growth, as anaerobes grow best under very low oxygen levels and aerobes grow best under atmospheric oxygen. Threshold elevated oxygen levels to prevent Botrytis cinerea growth in vitro and in vivo on strawberry were assessed. Botrytis cultures (mycelial plugs and spores) and fresh strawberry fruit were exposed to 21%, 40%, 60%, and 80% oxygen atmospheres at 5 °C for 5, 7, and 14 d. Growth of cultures from mycelial plugs was evaluated after treatment and during post-treatment incubation by measuring the diameter of the fungus. Spore germination and germ tube elongation were evaluated every 24 h for 3 days after treatment by counting the number of germinated spores and measuring elongation, respectively. Strawberry quality including firmness, color, soluble solids, titratable acidity, ethylene production and respiration rates, and presence of defects were evaluated upon removal from the elevated oxygen atmospheres as well as after 1, 3, and 5 d storage in air at 20 °C simulating market conditions.

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Marilyn H.Y. Hovius and Irwin L. Goldman

Breeders have found field screening for onion white rot resistance to be unreliable since consistently moderate to high disease levels that significantly differentiate cultivars, do not occur over field sites and years. The objective was to see if a greenhouse or laboratory technique could predict field reaction of onion accessions. Onion (Allium cepa) accessions were grown in fields naturally infested with the white rot causing fungus (Sclerotium cepivorum) in 1999 and 2000 (New Zealand) and in 2000 and 2001 (Canada). The field disease levels were low at three sites, moderate at two and high at one. Field screening was not a reliable predictor of white rot reaction when disease incidence was low. Onion accessions were screened for resistance in the greenhouse using nonsterile muck soil (NSMS) and sterile muck soil (SMS) with S. cepivorum sclerotia as the inoculum source. Total disease incidence was significantly higher in the NSMS compared to the SMS and accessions showed significant variability for white rot reaction in both soils. Two laboratory-based techniques were used to test the effect of onion volatiles on mycelium growth in culture. The volatiles from susceptible accessions resulted in faster radial growth of S. cepivorum mycelium (on water agar) and height of aerial mycelium (on potato dextrose agar) than volatiles from resistant accessions. Disease incidence in the greenhouse, S. cepivorum culture growth rates on water agar media and aerial mycelial height were all good predictors of field disease incidence in a covariance analysis. The best predictor was aerial mycelial height, which was predictive of field disease incidence in four out of six field sites. Onion breeders can use the methods described in this study in breeding for white rot resistance.

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M.V. Bhaskara Reddy, Essaid Ait Barka, F. Castaigne and Joseph Arul

The antifungal activity of chitosan, a bioplymer of β-1-4 gluscosamine, against Alternaria alternata, causal agent of black mold of tomato, was investigated. Chitosan was incorporated into potato dextrose broth (PDB) at concentrations of 100, 200, 400, 800, 1600, 3200, and 6400 μg·ml–1, growth and toxin production by the fungus were assessed after a 15-day incubation period. Chitosan significantly affected both growth and toxin production at higher concentrations. However, at lower concentrations, toxin production was affected more than the growth, as evidenced by minimum inhibitory concentrations (MIC) of chitosan derived for toxin production and mycelial growth. Excess sporulation of the fungus was observed in the presence of chitosan, but the spore viability was affected. Chitosan induced aggregation of fungal cells, abnormal shape, excess branching, and hyphal contortion. It also induced leakage of proteins from the fungal cells. The virulence of the toxin in culture filtrate of the fungus from different concentrations of chitosan was assayed by administering on tomato discs. Phospholipid content, electrolyte leakage, xylanase, and pectin methylesterase activity were measured in the culture filtrate administered tomato tissue. Decreased trend in causing electrolyte leakage, phospholipid degradation, and activation of xylanase and pectin methylesterase were observed with increasing concentrations of chitosan. The results showed that chitosan inhibits fungal growth at higher concentrations than toxin production. Further toxin produced at lower concentrations of chitosan was less virulent. Thus chitosan has potential as an antifungal agent.

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Mary C. Koelsch, Janet C. Cole and Sharon L. von Broembsen

Common periwinkle and `Bowles' periwinkle production has declined in the southern United States due to foliar diseases caused by Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz. and Phoma exigua Desmaz. var. inoxydabilis Boerema & Vegh in Vegh et al. Our study determined whether several labeled and experimental fungicides could control pathogens causing foliar diseases in common periwinkle in vitro and outdoors during two consecutive summers. Five concentrations of each of eight fungicides were used to test inhibition of mycelial growth of P. exigua var. inoxydabilis and two isolates of C. gloeosporioides on fungicide-amended agar. All concentrations of propiconazole inhibited growth of P. exigua var. inoxydabilis (100%) and both isolates of C. gloeosporioides (>96%). Cyproconazole completely inhibited mycelial growth of P. exigua var. inoxydabilis. Thiophanate methyl/mancozeb partially inhibited growth of C. gloeosporioides (50%). In outdoor trials, plants were sprayed weekly with the following fungicides and rates (in g a.i./liter): thiophanate methyl/mancozeb, 1.35; propiconazole, 0.14; thiophanate methyl, 0.84; triforine, 0.27; cyproconazole, 0.08; triforine–CC 17461, 0.27; or CGA 173506, 0.90. Thiophanate methyl/mancozeb was most effective at reducing foliar necrosis during both seasons. Shoot dry weights of plants treated with thiophanate methyl/mancozeb were significantly higher at the end of each growing season than those of plants treated with the other fungicides or the nontreated control plants. Chemical names used: dimethyl [(1,2-phenylene)-bis (iminocarbonothioyl)] bis [carbamate] and a combination of zinc ion and manganese ethylenebisdithiocarbamate (thiophanate methyl/mancozeb); 1-[2-(2′,4′-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl-methyl]-1H-1,2,4-triazole (propiconazole); dimethyl [(1,2-phenylene)-bis (iminocarbonothioyl)] bis [carbamate] (thiophanate methyl); N,N′-[1,4-piperazinediylbis (2,2,2-trichloroethylidene)] bis [formamide] (triforine); 2-(4-chlorophenyl)-1-(1H-1,2,4-triazol-l-yl)-butan-2-ol (cyproconazole); N,N′-[1,4-piperazinediylbis (2,2,2-trichloroethylidene)] bis [formamide] with micro emulsion (triforine–CC 17461); 4-(2-2-difluoro-1,3-benzodioxol-4-yl) pyrrole-3-carbonitrile (CGA 173506).

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Nancy E. Maness, James E. Motes and Kenneth E. Conway

Aerial blight of rosemary (Rosemarinus officinalis) caused by Rhizoctonia solani (AG-4) is a problem in production of rooted cuttings. Two separate studies were conducted on rosemary cuttings during propagation. Four levels of R. solani were mixed into potting medium at the rates of 0, 0.01, 0.1 and 1.0 percent (w/w). Seven treatments were evaluated: Trichoderma harzianum alone, Laetisaria arvalis alone, iprodione (single application, full rate), CGA 173506 (single application, full rate), T. harzianum + iprodione (single application, 1/2x rate), L. arvalis + CGA 173506 (single application, 1/2x rate), and a control. Biocontrol agents were mixed into medium at a rate of 5g/kg medium. Mycelial growth began by day four on the medium surface in the 0.1 and 1.0 R. solani levels. By day six, cuttings showed signs of infection. Disease incidence increased with higher levels of R. solani inoculum. At levels 0.01, 0.1 and 1.0, the L. arvalis plus 1/2x rate one time application CGA 173506 and iprodione alone (full rate one time application) gave the best control of aerial blight in both experiments. In the first experiment, iprodione alone and T. harzianum plus 1/2x rate iprodione gave the most root growth at the 0.01, 0.1 and 1.0 R. solani levels. In the second experiment, L. arvalis plus 1/2x rate CGA 173506 gave best root growth. At level 0, treatments were not significantly different in either experiment.

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Néstor Curvetto, Débora Figlas and Silvia Delmastro

Nutritive agar formulations with additions of poplar (Populus alba) sawdust, wheat (Triticum durum) bran, or milled sunflower (Helianthus annuus) seed hulls (SSH) were evaluated for mycelium cultivation of shiitake (Lentinula edodes), in petri dishes. Sawdust, 2, 3 and 4 g·L-1 (0.27, 0.40 and 0.53 oz/gal) added to MYA (malt, yeast extract and agar) medium did not improve the mycelium growth rate, while media that included 1, 2, and 3 g·L-1 (0.13, 0.27, and 0.40 oz/gal) wheat bran or 2, 3, and 4 g·L-1 (0.27, 0.40, and 0.53 oz/gal) milled SSH exhibited a significant increase in the mycelium growth rate, at 25 °C (77 °F). The use of SSH obtained directly from the oil industry was evaluated as a substrate for the cultivation of shiitake mushroom via synthetic logs in plastic bags. A linear growth test was used to previously assay the mycelium growth rate in substrate compositions with different contents of SSH, wheat bran, and poplar sawdust, at 25 °C. The largest mycelial growth rates were 2.75, 2.88, and 2.93 mm·d-1 (0.108, 0.113, and 0.115 inch/day) for the substrates formulated with 8 SSH: 2 wheat bran, 9 SSH: 1 poplar sawdust, and 8 SSH: 1 wheat bran: 1 poplar sawdust by weight, respectively. The synthetic logs showed a daily production rate of 2 kg shiitake/100 kg dry substrate for a 55 days cycle production with a simple formula containing 37.5% SSH, 0.5% calcium carbonate (CaCO3), 2% calcium sulfate (CaSO4), and 60% water. Addition of wheat bran to the SSH-based synthetic log produced no significant differences on biological efficiency, mushroom production, or productivity.

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Andres A. Reyes

The virulence of Mucor mucedo (L.) Fr. (the cause of mucor rot) and Botrytis cinerea Pers. (gray mold) on vegetables stored at 13C for 7 days or 1C for 70 days varied with the host and controlled atmosphere (CA). M. mucedo was severely pathogenic at 13C to cucumber (Cucumis sativus L.), eggplant (Solarium melongena L. var. esculentum Nees), pepper (Capsicum annum L.), and tomato (Lycopersicon esculentum Mill.), but not to bean (Phaseolus vulgaris L.). The fungus did not infect carrot (Daucus carota L. var. sativa DC.), celery (Apium graveolens L. var. dulce DC.), onion (Allium cepa L.), or parsnip (Pastinaca sativa L.) at 1C. B. cinerea was virulent on all of these crops at 13 or 1C. The severity of mucor rot and gray mold on eggplant stored at 13C for 14 days was suppressed most in a CA of 7.5% CO + 1.5% O2 and least in 1.5% 02, in comparison with the air control. Similarly, the growth and sporulation of each pathogen on eggplant-extract agar maintained at 13C for 4 or 14 days were suppressed most in 7.5% CO + 1.5% O2; suppression was least in 1.5% O2. The suppression of diseases on eggplant was highly correlated with the suppression of mycelial growth and sporulation of pathogens on agar.

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M.E. Valverde, P. Fallah Moghaddam, M.S. Zavala-Gallardo, J.K. Pataky, O. Paredes-Lopez and W.L. Pedersen

Ear gall development was evaluated after inoculating sweet corn (Zea mays L.) hybrids with Ustilago maydis (DC) Corda by injecting sporidial suspensions into silk channels when silks had emerged ≈3 to 6 cm from ear shoots. Gall incidence was ≈35% in two inoculation trials. About 0.5% of the noninoculated control plants was infected. Gall weight increased ≈250% to 500% between 14 and 21 days after inoculation, reaching a maximum of ≈280 to 600 g. Gall tissue was nearly 100% black and had lost its spongy integrity 19 to 21 days after inoculation, when mycelial cells formed powdery teliospores. A 1- or 2-day harvest window during which huitlacoche yield and quality were optimized corresponded to the time at which 60% to 80% of the gall tissue was black. The optimal huitlacoche harvest time varied among hybrids from 17 to 19 days after inoculation, but we suspect that optimal harvest time varies from ≈15 to 24 days after inoculation, depending on the growth stage at which the host is inoculated and the environmental conditions following inoculation. Differences among sweet corn hybrids in gall incidence, gall size, and coverage of mature galls by husk leaves were observed and could be used to select sweet corn hybrids that are well suited for producing huitlacoche.

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Kimberly H. Krahl

A screening technique was developed for studying resistance to powdery mildew disease in 25 diverse Pulmonaria L. species and cultivars. Healthy Pulmonaria plants were inoculated by drawing naturally infected leaves of P. angustifolia `Blaues Meer' across the abaxial surface of three healthy, mature leaves per test plant. Inoculated leaves were rated for powdery mildew infection using a scale of 0-5, where 0 = no visible sign of infection, 1 = 1% to 20%; 2 = 20% to 40%; 3 = 40% to 60%; 4 = 60% to 80%; 5 = 80% to 100% of leaf surface covered with white mycelial growth. Each genotype was inoculated and evaluated four times. The data revealed a wide and continuous range of variability for powdery mildew disease incidence in the 25 lungwort genotypes that may be indicative of quantitative resistance. The majority of lungwort genotypes exhibited low levels of resistance to powdery mildew. Four cultivars (P. hybrid `Spilled Milk', P. hybrid `Excaliber', P. rubra `Redstart', and P. rubra `David Ward') and one selection (P. longifolia ssp. cevennensis) exhibited high levels of resistance to powdery mildew. Since Pulmonaria species intercross readily, these genotypes may be useful in the future development of new powdery mildew resistant Pulmonaria cultivars.

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W.T. Liu, C.L. Chu and T. Zhou

Fumigation with 1 mg·L-1 of thymol vapor retarded mycelial growth of Monilinia fructicola (G. Wint.) Honey. Mean colony diameter was reduced from 49 mm in the control to 13 mm when the conidia were cultured on potato dextrose agar. Fumigation of apricots (Prunus armeniaca L.) with 2 mg·L-1 of thymol vapor reduced the germination of M. fructicola conidia to 2% compared with 98% on untreated fruit. Microscopic observations showed that the spores fumigated with thymol were shrunken and had collapsed protoplasts. In in vivo experiments, surface-sterilized apricots and plums (Prunus salicina L.) were inoculated with conidia of M. fructicola by applying 20 μL of a spore suspension to wounds on the fruit, and then were fumigated with thymol or acetic acid. The incidence of brown rot was reduced to 3% and 32% when `Manch' apricots were fumigated with thymol or acetic acid at 5 mg·L-1, respectively, compared with 64% incidence in untreated fruit. Fumigation of `Violette' plums with thymol or acetic acid at 8 mg·L-1 reduced brown rot from 88% in the control to 24% and 25%, respectively. Fumigation of `Veeblue' plums with thymol at 4 mg·L-1 reduced brown rot from 56% in the control to 14%. Fumigation of apricots with thymol resulted in firmer fruit and higher surface browning, but total soluble solids and titratable acidity were not affected. Fumigation of plum with thymol resulted in higher total soluble solids, but firmness and titratable acidity were not affected. Thymol fumigation caused phytotoxicity on apricots but not on plums.