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Xiaoling He, Susan C. Miyasaka, Yi Zou, Maureen M.M. Fitch, and Yun J. Zhu

oomycete Phytophthora colocasiae , and yield losses of 25% to 95% are estimated in taro-growing countries ( Brooks, 2000 ; Plucknett et al., 1970 ; Sharma et al., 2009 ). Southern blight is caused by the fungus Sclerotium rolfsii and is a problem in a

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Stephanie G. Harvey, Heather N. Hannahan, and Carl E. Sams

Allyl isothiocyanate (AITC) is the predominant isothiocyanate produced by damaged tissues of Indian mustard (Brassica juncea (L) Czerniak). This study investigated Indian mustard and AITC mediated suppression of mycelial growth and sclerotial germination of Sclerotium rolfsii Saccardo, a common soilborne pathogen. Indian mustard (IM) treatments of 0, 0.1, 0.2, 0.6, 1.0, 2.0, 4.1, 5.1, 10.2, 20.4, 40.8, 81.6, and 163.3 g·L-1 (weight of reconstituted mustard per liter of air) were evaluated for suppression of mycelial growth. Treatment effect was evaluated by measuring the radial growth of mycelia. Sclerotia were placed in culture tubes containing 18 g autoclaved soil and covered with an additional 5 g soil. AITC at concentrations of 0, 4.0, 16.0, 64.0, 256.0, 1024.0, or 4096.0 μmol·L-1 was injected into the tubes. Treated sclerotia were removed from tubes and plated on potato dextrose agar to determine viability. Mycelial growth was inhibited with IM treatments (P < 0.01). Inhibiting concentrations (IC) of IM for mycelial growth inhibition of 50% and 90% were 0.7 and 1.0 g·L-1, respectively, with death resulting with >2 g·L-1. Inhibition attributable to AITC alone was lower than that achieved by IM producing equivalent amounts of AITC. Germination of sclerotia was negatively correlated with AITC concentration (r = 0.96; P < 0.01). The IC50 and IC90, of AITC were 249.0 and 528.8 μmol·L-1, respectively, at 42 hours. The lethal concentration for sclerotia was not reached; only suppression occurred at the highest treatment concentrations. Sclerotium rolfsii mycelia were sensitive to the IM volatiles and were suppressed at low concentrations. Sclerotia were more resistant than the mycelia and required higher concentrations of AITC to suppress germination.

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Brooke A. Edmunds, Mark L. Gleason, and Stephen N. Wegulo

Eighteen cultivars of hosta (Hosta spp.), selected to represent a wide range of size, leaf shape and color, and genetics, were evaluated for reaction to Sclerotium rolfsii var. delphinii in a greenhouse in Ames, Iowa in 2000 and 2001. Bare-root, single-eye plants were planted in 15.2-cm (6-inch) pots in a soil-containing (2000) and soilless (2001) mix and grown in a greenhouse for 3 months. Plants were then inoculated by placing a carrot disk infested with mycelium of S. rolfsii at the base of the plant. Disease severity was assessed weekly for 6 weeks as percent symptomatic petioles. Disease development varied significantly (P < 0.05) among cultivars. Overall, `Lemon Lime', `Munchkin', `Nakaiana', `Platinum Tiara', and `Tardiflora' had the most severe symptoms and `Halcyon' showed the least disease.

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Stephanie G. Harvey and Carl E. Sams

Isothiocyanates are volatile chemicals produced by damaged tissues of Brassica species. Allyl isothiocyanate (AITC), the predominant isothiocyanate in Indian mustard (B. juncea), has been shown to control pest in laboratory and field experiments. We investigated the effectiveness of AITC against the germination of sclerotia of Sclerotium rolfsii Saccardo, a common soilborne pathogen of tomato. Sclerotium rolfsii was cultured on PDA from a field isolate. Mature sclerotia were collected and placed in polyester mesh bags. Culture tubes (16 × 150 mm) were packed with 18 g clay loam soil. A sclerotia-bag was placed in each tube and covered with an additional 5 g soil. Soil was maintained at 60% field capacity for the duration of the experiment. AITC was injected into each tube through a septum. Treatments consisted of 0, 5.6, 11.2, 22.4, and 44.8 μmol AITC/L of atmosphere and an ethanol control. AITC in each tube was sampled using SPME and analyzed on GC-MS. Tubes remained sealed for 42 h at 30 °C. Sclerotia were then removed from tubes and bags and plated on PDA to determine viability. Radial growth was measured to determine the effects of AITC. Mycelial growth was negatively correlated to AITC concentration (P < 0.01). The highest concentration of AITC resulted in a 40.3% reduction in mycelial growth. Although the AITC concentrations used in this study did not kill sclerotia of S. rolfsii, they did suppress mycelial growth from germinating sclerotia. At higher concentrations, or mixed with other chemicals, AITC may prove to be an affective control for this pathogen.

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P.W. Leeper, E.L. Cox, B.T. Scully, G.F. Oerther, E.E. Burns, and R.D. Lineberger

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Don R. La Bonte, Paul W. Wilson, Arthur Q. Villordon, and Christopher A. Clark

caused by Rhizopus stolonifer (Ehr. ex. Fr.) Lind. Incidence of circular spot, caused by Sclerotium rolfsii Sacc., has been low and similar to ‘Beauregard’ (0% to 5%). Insect Resistance ‘Evangeline’ has not been formally tested for relative

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Don R. La Bonte, Arthur Q. Villordon, Christopher A. Clark, Paul W. Wilson, and C. Scott Stoddard

. ex. Fr.) Lind. Incidence of circular spot, caused by Sclerotium rolfsii Sacc., has been low (0% to 3%), similar to ‘Beauregard’ (0% to 5%) in this reaction. Insect Resistance ‘Murasaki-29’ has not been formally tested for relative insect

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Xiaoling He, Susan C. Miyasaka, Maureen M.M. Fitch, Sawsan Khuri, and Yun J. Zhu

with an inserted chitinase gene from rice showed moderately increased tolerance of the fungal pathogen Sclerotium rolfsii ( He et al., 2008 , 2010 ). Insertion of the OxO gene into taro also resulted in a modest increase in resistance to S. rolfsii

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Clive Kaiser, Philip B. Hamm, Stacy Gieck, Nicholas David, Lynn Long, Mekjell Meland, and J. Mark Christensen

at pH conditions higher than pH 5.6, the normal pH of agar, potassium silicate enhanced this suppression in a linear manner. Suppression of Phytophthora cinnamomi , Phytophthora capsici , Sclerotinia sclerotiorum , Sclerotium rolfsii , Pythium F

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Timothy G. Porch, James R. Smith, James S. Beaver, Phillip D. Griffiths, and Craig H. Canaday

poor yields of the 2004 Juana Diaz trial, compared with those of 2008, were likely caused by an increased prevalence of southern blight caused by Sclerotium rolfsii Sacc. and higher temperature conditions. Seed yields of both TARS-HT2 and ‘Montcalm