@article{elliott_lewis_shew_gutierrez_nicholson_2008, title={Evaluation of tobacco germplasm for seedling resistance to stem rot and target spot caused by Thanatephorus cucumeris}, volume={92}, ISSN={["0191-2917"]}, DOI={10.1094/PDIS-92-3-0425}, abstractNote={ Stem rot and target spot of tobacco, caused by Rhizoctonia solani and its teleomorph Thanatephorus cucumeris, respectively, can cause serious problems in production of tobacco (Nicotiana tabacum) seedlings. Previous screens for genetic resistance in tobacco have been limited. The objective of this study was to evaluate 97 genotypes composing several classes of tobacco and related Nicotiana spp. for seedling resistance to stem rot and target spot. Significant differences in disease incidence initially were observed among the genotypes for both stem rot and target spot; however, resistance to target spot was not observed when disease pressure was high. Partial resistance to stem rot was observed in several genotypes in repeated tests. These accessions may be useful as a source of resistance to R. solani in future breeding efforts. }, number={3}, journal={PLANT DISEASE}, author={Elliott, P. E. and Lewis, R. S. and Shew, H. D. and Gutierrez, W. A. and Nicholson, J. S.}, year={2008}, month={Mar}, pages={425–430} }
 @article{gutierrez_mila_2007, title={A rapid technique for determination of races of Phytophthora nicotianae on tobacco}, volume={91}, ISSN={["1943-7692"]}, DOI={10.1094/PDIS-91-8-0985}, abstractNote={ A laboratory technique for determining races of Phytophthora nicotianae on tobacco (Nicotiana tabacum) was developed and compared with a commonly used greenhouse method. The laboratory technique was based on production and inoculation of tobacco seedlings in tissue culture plates. Three P. nicotianae isolates from North Carolina previously determined as race 0 and 1 were used. Four tobacco cultivars and two breeding lines with different types of resistance were used as differential cultivars: K-326, K-346, NC-71, NC-1071, L8, and Ky14xL8. Plants were evaluated 7 and 14 days after inoculation. Five differential cultivars (K-326, K-346, NC-1071, NC-71, and L8) were determined to be sufficient to differentiate races 0 and 1. Cv. Ky14xL8 was ineffective for differentiation of races and produced inconsistent results. The laboratory technique was as effective as the greenhouse technique for distinguishing different races of P. nicotianae for every isolate in all experiments. Additionally, the most reliable results for both methods were obtained when evaluations were made 14 days after inoculation. The laboratory technique was validated with 21 isolates collected from four counties in North Carolina. The laboratory technique produced results 2 weeks faster than the greenhouse technique and required significantly less space and labor than the greenhouse technique for the same number of isolates. Additionally, the larger number of seedlings used in the laboratory technique increased the robustness of the results, especially for isolates for which race identification was unclear with the greenhouse technique. We propose that the laboratory technique has the potential for evaluation of tobacco resistance in other pathosystems as well. }, number={8}, journal={PLANT DISEASE}, author={Gutierrez, Walter A. and Mila, Asimina L.}, year={2007}, month={Aug}, pages={985–989} }
 @article{gutierrez_shew_2000, title={Factors that affect development of collar rot on tobacco seedlings grown in greenhouses}, volume={84}, ISSN={["1943-7692"]}, DOI={10.1094/PDIS.2000.84.10.1076}, abstractNote={ Collar rot, caused by Sclerotinia sclerotiorum, is an important disease of tobacco transplants produced under greenhouse conditions. Factors that affect the development of the disease were studied, including age of seedlings, presence of an external source of nutrients (leaf extract), clipping (leaf removal) practices, exposure to low temperature, and leaf injury caused by heat and a chemical. Flue-cured tobacco seedlings, cultivar K-326, were grown in polystyrene cell trays floating on a nutrient solution. Trays were maintained in a phytotron growth chamber with a 28/18°C day/night temperature regime. Seedlings were inoculated with ascospores of S. sclerotiorum at the desired stage of growth by placing mature apothecia in the growth chamber and inducing ascospore release and deposition. Disease incidence was determined by examining seedlings for the presence of stem lesions over the next 15 to 21days. Seedlings between 35 and 53 days old were more susceptible to collar rot than younger or older seedlings. Inoculum efficiency was highest and disease was most severe when an external source of nutrients was present on leaf surfaces. Clipping of leaf tips did not increase disease, but if the leaf pieces created by clipping were left on seedlings, collar rot development was enhanced compared with treatments where debris was removed. Heat and chemical injuries that resulted in necrotic tissue provided highly susceptible infection courts for ascospores of S. sclerotiorum, but exposure to low temperature, which caused no visible injury, did not enhance infection. Adoption of cultural practices that minimize accumulation of leaf debris and eliminate factors that cause necrotic injury on leaves should greatly reduce the severity of collar rot of tobacco seedlings. }, number={10}, journal={PLANT DISEASE}, author={Gutierrez, WA and Shew, HD}, year={2000}, month={Oct}, pages={1076–1080} }
 @article{gutierrez_shew_1998, title={Identification and quantification of ascospores as the primary inoculum for collar rot of greenhouse-produced tobacco seedlings}, volume={82}, ISSN={["0191-2917"]}, DOI={10.1094/PDIS.1998.82.5.485}, abstractNote={ Collar rot, caused by Sclerotinia sclerotiorum, is a severe disease of tobacco seedlings grown in greenhouses. A semiselective medium was adapted and used to detect the presence and quantity of ascospores in commercial greenhouses. Petri dishes of the semiselective medium were placed inside and outside of greenhouses in four counties during the transplant production period in 1995 and 1996. Ascospores were present throughout the production period each year (February to April) and were confirmed to be the primary inoculum for the disease. Significant differences were observed in the number of ascospores trapped within and between counties. Peak numbers of ascospores were trapped between 10 and 12 a.m., and higher numbers of ascospores were trapped outside than inside houses. In general, distribution of ascospores inside houses was uniform unless a high concentration of apothecia was present very close to one section of the greenhouse. The semiselective medium and trapping technique used in this study may allow development of a forecasting system for collar rot of tobacco based on the presence and level of pathogen inoculum. }, number={5}, journal={PLANT DISEASE}, author={Gutierrez, WA and Shew, HD}, year={1998}, month={May}, pages={485–490} }
 @article{gutierrez_shew_melton_1997, title={Sources of inoculum and management for Rhizoctonia solani damping-off on tobacco transplants under greenhouse conditions}, volume={81}, ISSN={["0191-2917"]}, DOI={10.1094/PDIS.1997.81.6.604}, abstractNote={ Damping-off and target spot are important diseases of tobacco transplants produced under greenhouse conditions. Identification of sources of inoculum for these diseases caused by Rhizoctonia solani is an important first step in disease management. Control strategies based on sanitation and the eradication of primary inoculum were studied. Potting mix and Styrofoam trays used in transplant production were assayed to determine if they were sources of primary inoculum. Eleven sources of potting mix were sampled over a 2-year period. None of the mixes contained viable inoculum of R. solani. R. solani was isolated from previously used trays after 1 year of storage by removing and plating pieces of Styrofoam from individual tray cells on alkaline water agar (AWA). Sclerotia and melanized hyphae of R. solani were observed in the cracks present in the cells of the trays. Dry heat (70 to 80°C for 2 h) and chemical (sodium hypochlorite and sodium chloride) treatments reduced the levels of inoculum on trays up to 45% compared to controls, but only methyl bromide and steam treatments (80°C for 0.5 to 2.0 h) eradicated inoculum of R. solani from trays. Elimination of primary inoculum from previously used trays effectively controlled target spot and stem rot diseases caused by R. solani. }, number={6}, journal={PLANT DISEASE}, author={Gutierrez, WA and Shew, HD and Melton, TA}, year={1997}, month={Jun}, pages={604–606} }