Previous and Current Graduate Student Projects
Small Fruit | Vegetable Pathology | Weed Science
Small Fruit
Title of research project:
Name of student: Jessica Gigot
Degree: PhD
Department / Program: Department of Horticulture and Landscape Architecture / NWREC Small Fruit Horticulture
Advisors: Tom Walters
Start year: 2008
Year of completion:
Abstract:
Publications:
Vegetable Pathology
Title of research project: Effect of soil temperature and moisture on the transmission of Phytophthora infestans from potato seed tubers to sprouts
Name of student: Raina Spence
Degree: MS
Department / Program: Department of Plant Pathology / NWREC Vegetable Pathology
Advisors: Debra Ann Inglis
Start year: 2000
Year of completion: 2002
Abstract: Potato late blight is a widespread disease that causes great economic loss to the potato industry. The casual organism, Phytophthora infestans, is able to move from infected seed tubers to growing sprouts, and thus initiate an epidemic. The process by which transmission of the pathogen from the tuber to sprout occurs is not entirely understood. A series of growth chamber and greenhouse experiments were performed to determine the impact of soil temperature and moisture on the transmission of the pathogen from the inoculated seed. In all experiments, the ‘White Rose’ cultivar was utilized. The seed tubers were atomized with sporangia shortly after cutting and then planted in Sunshine #1 potting mix. Testing of numerous inoculum densities demonstrated that when a seed piece was infected with 25 to 50 sporangia, transmission was most likely to occur. Higher doses of inoculum resulted in seed piece decay. Lower soil temperatures (13°C and 16°C) inhibited soft rotting bacteria and seed pieces were slower to decay, allowing the pathogen to survive for longer periods of time in the infected but intact tuber tissue. Transmissions were observed across all temperature treatments (13, 16, 19, and 22°C), but seemed to be linked with tuber age. Inoculated seed pieces across experiments in which transmissions were detected ranged from 1-14% for 9-14 month old potato seed, whereas transmissions ranged from only 0-1% for 3-5 month old potato seed. Temperature shifts appeared to promote transmission of the pathogen from seed piece to sprout. In one experiment, the incidence of transmission from inoculated seed pieces was 6.7 and 0% when temperatures were kept constant at 13 and 19°C, or from 19 to 13°C, respectively, 20 days after planting. Experiments carried out in the greenhouse often resulted in many transmissions, which may have been an effect of fluctuating temperature. Soil moisture did not appear to have a significant impact on transmission, but the impact also may have been overshadowed by the effect of seed age.
Publications:
Spence, R.M. 2002. Effect of soil temperature and moisture on the transmission of Phytophthora infestans from potato seed tubers to sprouts. M.S. thesis.
Title of research project: Management of seedborne Stemphylium botryosum and Cladosporium variabile causing leaf spot of spinach seed crops in western Washington
Name of student: Pablo Hernandez-Perez
Degree: MS
Department / Program: Department of Plant Pathology / NWREC Vegetable Seed Pathology
Advisors: Lindsey du Toit
Start year: 2002
Year of completion: 2005
Abstract: Up to 50% of the spinach seed planted in the USA and up to 20% of the world supply of spinach seed is produced in the Pacific Northwest. Washington is the primary spinach seed producing state in the USA, where Cladosporium and Stemphylium leaf spots can cause significant losses in spinach seed crops. Stemphylium botryosum was determined to be present in each of 66 spinach seed lots produced in 2003 in the USA, Denmark, the Netherlands, and New Zealand (mean incidence of 29.38% per lot). Cladosporium variabile-like fungi were present in 26 of the 66 lots (mean incidence of 0.37% per lot). Of 24 isolates of S. botryosum and 15 isolates of C. variabile-like fungi, 11 and 5, respectively, were pathogenic on spinach; 10 isolates of Cladosporium were C. macrocarpum. Pathogenic S. botryosum was detected in 11-year-old seed lots. Stemphylium botryosum and C. variabile were detected in the pericarp and embryo of spinach seed. Cladosporium variabile and Verticillium spp.were largely eliminated from spinach seed soaked in 1.2% NaOCl for ≥10 min, and the incidence of S. botryosum was reduced significantly, but this pathogen was not eradicated by chlorine treatment. Seed germination was not affected by 40 min soak in 1.2% NaOCl. Cladosporium variabile was eradicated from spinach seed soaked in hot water at 40oC for 10 min. Stemphylium botryosum was eradicated from a lightly infected seed lot by hot water treatment at ≥55oC for ≥10 min but could not be eradicated from heavily infected lots even when treated at 60oC for 40 min. Seed germination was adversely affected by hot water treatment at 50oC for ≥30 min or ≥55oC for ≥10 min.Cladosporium variabile and S. botryosum were transmitted from infected spinach seed planted in the greenhouse and maintained under misters at 14.4 to 21.4oC and 74.5 to 95.4% relative humidity. Lesions first appeared on cotyledon tips (direct seed transmission), followed by cotyledon blades and first true leaves (secondary spread). Seed transmission rates ranged from 0.4 to 18.1% and 3.7 to 10.3% of the incidence of infected seed planted for C. variabile and S. botryosum, respectively.
Publications:
Hernandez-Perez, P., and du Toit, L.J. 2006. Seedborne Cladosporium variabile and Stemphylium botryosum in spinach. Plant Disease 90:137-145
du Toit, L.J., Derie, M.L., and Hernandez-Perez, P. 2005. Verticillium wilt in spinach seed production. Plant Disease 89:4-11.
du Toit, L.J., and Hernandez-Perez, P. 2005. Efficacy of hot water and chlorine for eradication of Cladosporium variabile, Stemphylium botryosum, and Verticillium dahliae from spinach seed. Plant Disease 89:1305-1312.
du Toit, L.J., Derie, M.L., and Hernandez-Perez, P. 2005. Evaluation of fungicides for control of leaf spot in spinach seed crops, 2004. Fungicide & Nematicide Tests 60:V044.
du Toit, L.J., Derie, M.L., and Hernandez-Perez, P. 2005. Evaluation of yield loss caused by leaf spot fungi in spinach seed crops, 2004. Fungicide & Nematicide Tests 60:V047.
du Toit, L.J., Derie, M.L., and Hernandez-Perez, P. 2004. Evaluation of fungicides for control of leaf spot in spinach seed crops, 2003. Fungicide & Nematicide Tests 59:V115.
Title of research project: The survival and transmission of Phytophthora infestans on volunteer potato tubers
Name of student: Jessica Gigot
Degree: MS
Department / Program: Department of Plant Pathology / NWREC Vegetable Pathology
Advisors: Debra Ann Inglis
Start year: 2004
Year of completion: 2006
Abstract: Laboratory and greenhouse experiments were performed to address the role of i) pathogen genotype, ii) inoculation technique and inoculation location, and iii) temperature on Phytophthora infestans (Pi) survival and transmission. Tubers inoculated with a US-8 isolate (MV04-28) using a wounding technique had a higher percentage of infected tuber surface area (65.90 %) produced a larger percent lesion size (59.34 %), and had a higher amount of soft rot per tuber (82.67 %) than those inoculated with US-11 isolate (MV110-b) (23.17, 33.33, and 49.33 %, respectively). Inoculations performed at the mid-section did not result in any Pi transmission. However, inoculation at the apical or stem end resulted in transmission rates ranging from 15 to 34 %. More transmission occurred at the stem or apical end of the tuber when tubers were inoculated at the stem end as opposed to the apical end. Overall, more transmission events were observed from tubers infected with the US-8 isolate. Temperatures (4.4, 7.2, 10.0 oC) representative of winter soil conditions in northwestern Washington influenced the colonization of Pi on tuber tissue and the amount of sporulation on tuber lenticels and eyes. Tubers incubated at 4.4 oC had a significantly (P<0.05) lower percentage of infected tuber surface area and a lower number of lenticels and eyes with Pi sporulation after 3- and 8-day, rather than 15-incubation periods compared to those incubated at 10 oC. Following a 3 wk incubation period, sporulation on the cut tuber surface was observed at 4.4, 7.2 and 10 oC. Temperatures (13, 16, 19 oC) representative of spring soil conditions in northwestern Washington influenced the amount of sporulation on tuber lenticels and eyes, with the most sporulation occurring at 19 oC (18 %) on tubers inoculated with the US-8 isolate. Sporulation of Pi on infected tubers after a 6-day incubation period in potting soil was observed for all three spring temperatures after inoculation with both genotypes and ranged from 8.3 to 83 %. Blighted tubers that survive and sporulate in the spring could likely support the transmission of Pi from infected tuber tissue to sprouts. However, results suggest that survival of Pi on potato tubers in soil may only be possible at cool temperatures or when infections, by a less aggressive genotype, originate at either the apical or stem end.
Publications:
Gigot, J.A., Gundersen, B. and Inglis, D.A. 2007. Colonization and sporulation of Phytophthora infestans on volunteer potatoes under western Washington conditions. Amer J Potato Research (submitted).
Gigot, J., Gundersen, B. and Inglis, D. 2005. Sporulation of Phytophthora infestans on whole potato tubers. Phytopathology 89:S34. (Abstr.)
Gigot, J. The survival and transmission of Phytophthora infestans on volunteer potato tubers. Master's thesis. Washington State University.
Title of research project: Evaluation of Seed and Drench Treatments for Management of Damping-Off and Seedling Blight Pathogens of Spinach for Organic Production
Name of student: Jaime Cummings
Degree: MS
Department / Program: Department of Plant Pathology / NWREC Vegetable Seed Pathology
Advisors: Lindsey du Toit
Start year: 2005
Year of completion: 2007
Abstract: There are many concerns regarding losses due to soilborne pathogens in organic production systems. The purpose of this research was to evaluate seed and drench treatments for management of soilborne diseases for organic vegetable production. Inoculation rate trials were conducted for three soilborne pathogens, Pythium ultimum, Fusarium oxysporum f. sp. spinaciae, and Rhizoctonia solani, to determine appropriate rates for treatment assessment. Efficacy of treatments was evaluated in the greenhouse against each pathogen using spinach. Treatments included products that were EPA-registered and approved for use in organic agriculture, and products that were being developed for compliance with organic standards. Seed health and germination assays were conducted for each seed treatment to determine potential effects on seedborne fungi, or germination. Selected treatments were evaluated further under field conditions at three locations in western Washington.
Publications:
Cummings, J.A., and du Toit, L.J. Greenhouse evaluation of seed and drench treatments for organic management of damping-off and seedling blight pathogens of spinach. Plant Disease:manuscript in Progress.
Cummings, J.A., du Toit, L.J., and Miles, C.A. 2008. Evaluation of seed and drench treatments for organic management of soilborne diseases of spinach in western WA. Plant Disease Management Reports 2:V134.
Cummings, J.A., du Toit, L.J., and Miles, C.A. 2008. Evaluation of seed and drench treatments for organic management of soilborne diseases of spinach in Sequim, WA. Plant Disease Management Reports 2:V133.
Cummings, J.A. 2007. Evaluation of seed and drench treatments for management of damping-off and seedling blight pathogens of spinach for organic production. M.S. thesis, Washington State University, Department of plant pathology.
du Toit, L.J., Derie, M.L., Brissey, L.M., Cummings, J.A. 2007. Evaluation of limestone amendments for control of Fusarium wilt in a spinach seed crop, 2006. Plant Disease Management Reports 1:V091.
Weed Science
Title of research project: Weed Control in Vegetables and Management of Potato Scab in an Organic Production System in Northwestern Washington
Name of student: Tyler Breum
Degree: MS
Department / Program: Department of Crop and Soil Sciences / NWREC Weed Science
Advisors: Tim Miller, Debra Ann Inglis, Cathy Perillo
Start year: 2003
Year of completion: 2008
Abstract: Weed and disease management are major concerns for organic farmers, especially during transition; however, research in the development and evaluation of weed and disease control techniques in organic cropping systems is limited. In fall of 2003, a field trial was initiated at the Washington State University Mount Vernon Northwest Washington Research and Extension Center to evaluate the effects of several rotational crops, cover crops, and fertilization programs on disease incidence resulting from soil-borne pathogens as well as determining the effectiveness of several weed control techniques in organic rotational crops. Weed control programs were tested on two rotations of spinach seed, broccoli, cucumber, and potato and consisted of pre-emergence flaming followed by post-emergence flaming using a high-efficiency infrared flamer and/or post-emergence herbicides (clove oil at 10% and 20% acetic acid at full strength) applied in a narrow band immediately beside the crop row using a shielded sprayer. The infrared flamer provided effective post-emergence weed control in all crops, although some crop injury was usually apparent. Application of vinegar (20% acetic acid) and clove oil were less effective than flaming. Vinegar caused slight injury to weed foliage, including yellowing but not killing even soft-leaved plants such as pale smartweed (Polygonum lapathifolium)and common chickweed (Stellaria media). Clove oil activity was substantially improved when applied at 15% in 2005 and 2006 than when used at 10% in 2004. Anticipated outcomes include finding both cultural and chemical strategies to help farmers reduce vegetable crop yield loss due to competition with weeds and diseases.
Publications:
Breum, T.J., C. Steen, and T.W. Miller. Evaluation of organic weed control methods in northwestern Washington. Abstract and poster presentation, Western Society of Weed Science, Portland, OR.
Breum, T.J., C. Steen, and T.W. Miller. Weed control in organic vegetable production using organic herbicides and flame. Abstract and oral presentation, Weed Science Society of America, Chicago, IL.
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