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J.O. Kuti, G.V. Latigo, and J.O. Bradford

Soil-borne pathogens such as Macrophomina phaseolina (the causative agent of charcoal rot) and Phymatotrichum omnivorum (the causative agent of cotton root rot) contribute to mortality of transplanted guayule (Parthenium argentatum, Gray) seedlings in southern Texas. In order to select guayule genotypes for resistance to these pathogens, it would be useful to develop reliable greenhouse inoculation procedures for screening guayule seedlings. Twelve-week-old guayule seedlings (`11591', a USDA standard breeding line) were inoculated using two inoculation methods (soil-drenching and root-dipping) in two soil media (field soil and commercial soil mix). Plants were rated for disease severity 2 to 5 months after inoculation and pathogens were re-isolated from diseased plants to establish Koch postulates. The soil drenching technique, using field soil, caused rapid development of disease symptoms that were consistent with re-isolation frequencies of pathogens from the diseased plant tissues.

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David Noshad, Andrew Riseman, and Zamir Punja

Many daphne cultivars are susceptible to fungal root pathogens and require frequent fungicide applications during production. To identify taxon differences to disease susceptibility, we evaluated 32 Daphne species and cultivars for resistance to the soil-borne pathogen, Thielaviopsis basicola (Berk. and Broome) Ferr., by both in vitro- and in vivo-based methods. Disease-free plant roots were inoculated with the pathogen through topical application of a spore suspension and observed weekly for disease development/progression. Significant variation for disease severity among the taxa evaluated was determined using a plant disease index. Plant reactions ranged from highly resistant, e.g., D. tangutica and D. retusa, to highly susceptible, e.g., D. cneorum. In addition, a high correlation was found between the in vitro and in vivo techniques for the seven selected species, indicating that they are comparable. However, the in vitro assay provided results in significantly less time than the in vivo assay.

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Nathan Shoaf, Lori Hoagland, and Daniel S. Egel

suppress development of diseases caused by several soil-borne pathogens, including Fusarium oxysporum ( Elmer and Pignatello, 2011 ; Matsubara et al., 2002 ), Rhizoctonia solani ( Jaiswal et al., 2014 ), Ralstonia solanacearum ( Nerome et al., 2005

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Richard L. Fery, Philip D. Dukes Sr., and Judy A. Thies

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Anas Eranthodi, Mohammad Babadoost, and Bernhard Trierweiler

This study was conducted to develop a reliable method for control of set-borne inoculum of Verticillium and Fusarium species that cause the internal discoloration of horseradish roots. Horseradish propagative root stocks (sets), 0.5 to 3.0 cm in diameter and 20 to 25 cm long, were treated by immersing them into water at 44, 45, 46, 47, 48, 49, and 50 °C for 10, 20, and 30 min. Treated and untreated sets were cultured on acidified potato dextrose agar to determine the presence of the pathogens in the sets. Treatments at temperatures lower than 46 °C did not control the set-borne inoculum of the pathogens. Treated and untreated sets were also planted in the greenhouse and fields to assess the effects of the thermotherapy on germination of the sets and vigor of the plants. Treatments at 48 °C or greater either delayed or reduced set germination and reduced plant vigor. The most effective treatment for control of the set-borne pathogens without adverse effects on set germination or plant vigor was determined to be 47 °C for 20 min.

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Mary C. Stevens, Rui Yang, and Joshua H. Freeman

fumigant to control insect pests in stored grain ( Hooper et al., 2003 ). EDN has since been examined as a soil fumigant in the United States as well as other countries with acceptable efficacy against weed pests, plant-parasitic nematodes, and soil-borne

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M.B. Fiely and T.E. Morelock

Spinach (Spinacia oleracea L.) varies in tolerance to saturated soil conditions. Plant vigor was assessed for plants flooded in autoclaved and nonautoclaved field soil. Decline of vigor was more rapid for plants flooded in nonautoclaved field soil, indicating that flooding tolerance may be influenced by soil borne pathogens.

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M.B. Fiely and T.E. Morelock

Spinach (Spinacia oleracea L.) varies in tolerance to saturated soil conditions. Plant vigor was assessed for plants flooded in autoclaved and nonautoclaved field soil. Decline of vigor was more rapid for plants flooded in nonautoclaved field soil, indicating that flooding tolerance may be influenced by soil borne pathogens.