Lindsey J. du Toit

Washington State University | WSU · Department of Plant Pathology

Fusarium wilt of spinach, caused by Fusarium oxysporum f. sp. spinaciae, is a significant limitation for producers of vegetative spinach and spinach seed crops during warm temperatures and/or on acid soils. Identification of isolates of F. oxysporum f. sp. spinaciae, and distinction of isolates of the two known races entails time-intensive pathogen...

Onion (Allium cepa L.) bacterial diseases can cause catastrophic crop losses. Chemical and biological control products are not curative and have mixed or limited efficacy at preventing onion bacterial diseases. Cultural management strategies, such as appropriate irrigation and nitrogen (N) management practices, can reduce the risk for bacterial inf...

Two pathogenicity groups of Fusarium oxysporum f. sp. spinaciae, the causal agent of Fusarium wilt of spinach (Spinacia oleracea L.), were described recently based on virulence of isolates on proprietary spinach inbreds. In this study, a wide range in severity of wilt was observed for 68 spinach cultivars inoculated with an isolate of each pathogen...

White rust, caused by Albugo occidentalis, is one of the major yield-limiting diseases of spinach (Spinacia oleracea) in some major commercial production areas, particularly in southern Texas in the United States. The use of host resistance is the most economical and environment-friendly approach to managing white rust in spinach production. The ob...

In January 2021, leaf spots were observed on 1 of 22 proprietary spinach cultivars in a trial under high tunnels in Albion, ME. Approximately 1% of plants were symptomatic with <30% leaf area affected. Some spinach growers reported ≤100% incidence in high tunnels in the northeastern USA. Leaf spots on the cultivar in Albion were <5 mm in diameter a...

Genotype-by-sequencing (GBS) was used to explore the genetic diversity and structure of Spinacia turkestanica, and the selective sweeps involved in domestication of cultivated spinach, S. oleracea, from S. turkestanica. A total 7,065 single nucleotide polymorphisms (SNPs) generated for 16 Spinacia oleracea and 76 S. turkestanica accessions placed t...

Main conclusion A maize receptor kinase controls defense response to fungal pathogens by regulating jasmonic acid and antimicrobial phytoalexin production. Abstract Plants use a range of pattern recognition receptors to detect and respond to biotic threats. Some of these receptors contain leucine-rich repeat (LRR) domains that recognize microbial...

Spinach (Spinacia oleracea L.) is a member of the Caryophyllales family, a basal eudicot asterid that consists of sugar beet (Beta vulgaris L. subsp. vulgaris), quinoa (Chenopodium quinoa Willd.), and amaranth (Amaranthus hypochondriacus L.). With the introduction of baby leaf types, spinach has become a staple food in many homes. Production issues...

Two fields of coriander (Coriandrum sativum L.) seed crops of proprietary cultivars were observed in the Columbia Basin of Washington in July 2020 with 40 and 90% incidence of plants showing stunting and leaf and stem discoloration, sometimes with mild leaf curl. Foliar discoloration ranged from yellow to red and purple. Sweep-netting along the fie...

Arizona is an important region of the USA for winter production of baby leaf crops such as spinach (Spinacia oleracea), table beet (Beta vulgaris subsp. vulgaris Condivita Group), and Swiss chard (B. vulgaris subsp. vulgaris Cicla Group). In the winter of 2019, severe leaf spots were observed at 80% incidence and 40% severity per plant in a 1-ha ba...

Although the maritime Pacific Northwest (PNW) is the only region of the United States suitable climatically for spinach seed production, the acidic soils are highly conducive to spinach Fusarium wilt caused by Fusarium oxysporum f. sp. spinaciae. A soil bioassay developed to quantify the risk of spinach Fusarium wilt in fields has been offered to s...

Fusarium wilt of spinach, caused by Fusarium oxysporum f. sp. spinaciae (Fos), is an important disease during warm conditions in production regions with acid soils, yet little is known about what confers pathogenicity to spinach in Fos genetically. To identify candidate fungal genes that contribute to spinach Fusarium wilt, each of 69 geographicall...

Leaf spot diseases of spinach caused by Colletotrichum spinaciae, has become a major production constraint in several production areas, including Texas, in recent years. Leaf spot symptoms were observed in several fields in Texas in 2016 and 2017 with typical anthracnose-like symptoms, and leaves with small, circular, and sunken lesions which appea...

Leaf spot diseases have become a major concern in spinach production in the United States Determining the causal agents of leaf spots on spinach, their prevalence and pathogenicity, and fungicide efficacy against these pathogens is vital for effective disease management. Spinach leaves with leaf spots were collected from Texas, California, Arizona,...

Light leaf spot, caused by the ascomycete Pyrenopeziza brassicae Sutton & Rawlinson, is an established disease of Brassicaceae in the United Kingdom (UK), continental Europe, and Oceania (OC, including New Zealand and Australia). The disease was reported in North America (NA) for the first time in 2014 on Brassica spp. in the Willamette Valley of w...

Carrot (Daucus carota ssp. sativus) production can be affected by a wide range of pests and pathogens. At least five diseases of carrot are caused by bacterial pathogens, 36 by fungal and oomycete pathogens, two by phytoplasmas, and 13 by viruses; and seven genera of nematodes and two genera of parasitic plants affect carrot. In addition, numerous...

Blackleg (Phoma stem canker) of crucifers is a globally important disease caused by the ascomycete species complex comprising of Leptosphaeria maculans and Leptosphaeria biglobosa. Six blackleg isolates recovered from Brassica rapa cv. Mizspoona in the Willamette Valley of Oregon were characterized as L. biglobosa based on standard pathogenicity te...

Phoma betae is an important seedborne pathogen of table beet worldwide that is capable of causing foliar, root, and damping-off diseases. Ten microsatellite and mating type markers were developed to investigate the genetics of P. betae populations in table beet root crops in New York and in table beet seed crops in Washington, from where table beet...

Onions are highly responsive to arbuscular mycorrhizal fungi (AMF), but little is known about AMF communities in onion crops (approximately 10,000 ha) in the semiarid, irrigated region of the Columbia Basin of Washington and Oregon. AMF communities and root colonization were compared in organic and conventional onion fields, and between paired conv...

U.S. organic farmers surveyed listed improved seedling germination and Alternaria leaf blight resistance as top breeding priorities for production of organic carrots. Nematode resistance is also very important for growers. Flavour was deemed the most important consumer trait to improve in carrots, and nutrition the most important product quality fo...

Blackleg, caused by Leptosphaeria maculans (Desm.) Ces. & De Not., is a seed-borne pathogen endemic in the Canadian prairies, Midwestern and southern United States, Australia, and Europe (Rimmer et al. 2007). The canola production region of the Pacific Northwest United States was considered free of blackleg until 2011, when L. maculans was found in...

Buckwheat (Fagopyrum esculentum, Polygonaceae) seed is milled into a flour to make soba noodles and is used whole or milled in breads, pastries, soups, and porridges. Buckwheat was grown on ∼5,000 ha in Washington State in 2016, and central Washington is an important region for buckwheat seed production. Symptoms of downy mildew were observed in bu...

Bacterial pathogens of onion (Allium cepa) plants and their undetected presence in seed can cause substantial losses to onion producers. In this study, 23 Pseudomonas syringae strains were isolated from five onion plants and 18 onion seeds. The symptoms on leaves and seed stalks were irregular lesions with necrotic centres and water soaked margins....

Fusarium wilt of spinach is caused by the soilborne fungus Fusarium oxysporum f. sp. spinaciae and occurs in most regions of spinach production. The disease is favored by acid soils and warm temperatures, and the fungus can survive extended periods as chlamydospores or by asymptomatic colonization of the roots of nonhost plant species. The 10- to 1...

Stunting caused by Rhizoctonia spp. is economically important in irrigated onion bulb crops in the semiarid Columbia Basin of Oregon and Washington, where cereal winter cover crops commonly are planted the previous fall to prevent wind erosion of soil. The cover crop is killed with herbicide application just before or shortly after onion seeding, s...

Organic vegetable production accounted for 19% of the total organic acreage in Washington State in 2013, with 1,700 ha of certified organic vegetable pea. However, production is challenged constantly with the threat of poor emergence after planting due to damping-off caused by Pythium spp. A survey of Pythium spp. in organic vegetable production ar...

Onion stunting caused by Rhizoctonia spp. is an important soilborne disease on very sandy soils in the Columbia Basin of Oregon and Washington. From 2010 to 2013, 251 isolates of Rhizoctonia or Rhizoctonia-like spp. were obtained from soil and onion plant samples collected from inside and outside patches of stunted plants in 29 onion fields in the...

Isolates of Rhizoctonia and Rhizoctonia-like spp. (n = 179) were baited selectively from soil and plant samples collected from irrigated pea crops in the semiarid Columbia Basin of Oregon and Washington from 2011 to 2013, and characterized to species, subspecies, and anastomosis groups (AG) based on sequences of the internal transcribed spacer regi...

Gatch, E. W., and du Toit, L. J. 2015. A soil bioassay for predicting the risk of spinach Fusarium wilt risk. Plant Dis. 99:512-526. The maritime Pacific Northwest is the only region of the United States suitable for production of spinach seed, a cool-season, daylength-sensitive crop. However, the acidic soils of this region are highly conducive to...

In 2011, bacterial blight of arugula (Eruca vesicaria subsp. sativa; cv. Roquette) was observed in organically grown plants under overhead irrigation in a field near Delano, MN. Approximately 80 to 100% of each planting was affected, with greater rates of infection occurring after periods of high humidity. Small, water-soaked, angular spots apparen...

Thirty-five onion genotypes were evaluated for resistance to stunting caused by Rhizoctonia solani anastomosis group 8 (AG 8) in a growth chamber set at 15 ± 1 8C. The trial was repeated. Resistance to R. solani AG 8 was defined as a lack of significant difference in plant height, root length, and/or total dry biomass between inoculated and noninoc...

Xanthomonas hortorum pv. carotae (Xhc) causes bacterial blight of carrot (Daucus carota L.), is endemic in the primary regions of carrot seed production, and is readily seed-transmitted. Genetic resistance to Xhc is not well documented in commercially available carrot cultivars, and there has been little public research on screening for resistance....

Onion (Allium cepa) is an economically important vegetable crop in the United States, generating nearly $900 million annually in farm receipts. Pests such as onion thrips (Thrips tabaci) and a thrips-transmitted virus disease, Iris yellow spot (IYS), caused by Iris yellow spot virus (IYSV), have emerged in recent years as high priority, invasive, o...

In 2012 and 2013, foliar symptoms were observed in certified organic, 2- to 4-ha crops of Echinacea angustifolia and E. purpurea in Grant and Klickitat counties, WA. White pustules were predominant on the abaxial leaf surface, increased in number, and coalesced on E. angustifolia, with 100% infection by the end of the season; in contrast, symptoms...

AimTo develop multiplex TaqMan real-time PCR assays for detection of spinach seedborne pathogens that cause economically important diseases on spinach.Materials and Methods Primers and probes were designed from conserved sequences of the internal transcribed spacer (for Peronospora farinosa f. sp. spinaciae and Stemphylium botryosum), the intergeni...

In summer 2012, bacterial blight symptoms (2) were observed on leaves of carrot plants in 7 out of 70 plots of carrot breeding lines at the Purdue University Meig Horticulture Research Farm, Lafayette, IN. Symptoms included small to large, variably shaped, water-soaked to dry, necrotic lesions, with or without chlorosis, at <5% incidence. Microscop...

In October 2012, symptoms of cavity spot (1) were observed on roots of two 50 ha, Red Core Chantenay processing carrot (Daucus carota L. subsp. sativus (Hoffm.)) crops in the Columbia Basin of central Washington. Symptoms consisted of sunken, elliptical lesions (3 to 15 mm long) on the root surface. Approximately 6% of the roots in each crop were a...

During 2009 and 2010, 45 isolates of Rhizoctonia spp. were recovered from onion bulb crops in the semiarid Columbia Basin of Oregon and Washington, in which patches of severely stunted onion plants developed following rotation with winter cereal cover crops. Characterization of isolates recovered from naturally infested soil and roots was performed...

Molecular assays to detect and quantify DNA from viable cells of the seedbome pathogen Xanthomonas hortorum pv. carotae in carrot seed were developed and evaluated for use on nontreated and hot-water-treated seed lots. Both a TaqMan real-time polymerase chain reaction (PCR) assay and a loop-mediated isothermal amplification (LAMP) dilution endpoint...

In 2005, Verticillium dahliae was first reported to be pathogenic to spinach seed crops in the Pacific Northwest, with symptoms only developing after initiation of the reproductive stage of plant growth, and to be prevalent on commercial spinach seed lots produced in Denmark, The Netherlands, and the United States. In this study, the genetic divers...

U.S. organic farmers surveyed listed improved seedling germination and Alternaria leaf blight resistance as top breeding priorities for field production of organic carrots. Nematode resistance is also very important for growers. Flavor was deemed the most important consumer trait to improve in carrots, and nutrition the most important product quali...

Spinach is an economically important vegetable crop in the United States that has undergone dramatic industry changes in recent years and is valued at over $250 million annually. Spinach downy mildew disease, caused by the oomycete pathogen Peronospora farinosa f. sp. spinaciae (Pfs), continues to be a major production constraint for commercial spi...

Okubara, P. A., Harrison, L. A., Gatch, E. W., Vandemark, G., Schroeder, K. L., and du Toit, L. J. 2013. Development and evaluation of a TaqMan real-time PCR assay for Fusarium oxysporum f. sp. spinaciae. Plant Dis. 97:927-937. Fusarium oxysporum f. sp. spinaciae, causal agent of spinach Fusarium wilt, is an important soilborne pathogen in many are...

In 2005, Verticillium dahliae was first reported to be pathogenic to spinach seed crops in the Pacific Northwest, with symptoms only developing after initiation of the reproductive stage of plant growth, and to be prevalent on commercial spinach seed lots produced in Denmark, The Netherlands, and the United States. In this study, the genetic divers...

Washington State University (WSU) personnel conduct an annual onion (Allium cepa) cultivar trial and storage evaluation in the Columbia Basin of central Washington, USA, to provide stakeholders with information on the suitability of onion cultivars for production in this region. The trial is a collaborative effort of university personnel, local oni...

The influence of postharvest curing temperature and duration on development of slippery skin (caused by Burkholderia gladioli pv. alliicola) and sour skin (caused by B. cepacia) in onion (Allium cepa) bulbs during storage was evaluated by inoculating bulbs of the storage cultivars ‘Redwing’ and ‘Vaquero’ with each of the pathogens after harvest, cu...

Verticillium dahliae is a pathogen of spinach (Spinacia oleracea) during spinach seed crop production but not in vegetative leafy spinach crops, because plants remain asymptomatic until bolting has been initiated (conversion from vegetative to reproductive growth). The objectives of this research were to evaluate a set of USDA spinach germplasm acc...

In December 2011, symptoms typical of Cladosporium leaf spot caused by Cladosporium variabile (4) were observed in organic “baby leaf” spinach (Spinacia oleracea) crops of the cultivars Amazon, Missouri, Tasman, and Tonga in the Imperial Valley (Imperial County, CA and Yuma County, AZ). Leaves had small, circular lesions (1 to 3 mm in diameter), so...

In July of 2010, dry, oval lesions, each with a salmon-colored center and bleached overall appearance, were observed on the leaves and neck of onions plants growing in production fields of Newaygo, Ottawa, Kent, and Ionia counties, Michigan. Acervuli and setae that are characteristic of Colletotrichum spp. were observed with a dissecting microscope...

A commercial skullcap (Scutellaria lateriflora, family Lamiaceae) crop with wilted and necrotic plants was examined in Washington State in 2008. Three fungal isolates were obtained and identified as Verticillium dahliae based on morphology and sequencing of the internal transcribed spacer DNA region. All three skullcap isolates caused typical Verti...

Spinach (Spinacia oleracea) has become an increasingly important vegetable crop in many parts of the world. Significant changes in production practices, particularly in the U.S. and E.U., have occurred in the past 10–15years as a result of increased product demand. These changes likely increased the incidence and severity of downy mildew, caused by...

Enterobacter bulb decay is a recently described storage disease of onion (Allium cepa) bulbs caused by Enterobacter cloacae. The disease is generally considered minor but, on occasion, can cause significant losses for onion producers. The impact of postharvest curing temperature and duration on Enterobacter bulb decay of onion was evaluated by inoc...

Sixty-nine storage onion (Allium cepa) cultivars; (seven white, five red, and 57 yellow cultivars) were evaluated in the Washington State University Onion Cultivar Trials in the semiarid Columbia Basin of central Washington in 2007-08 and/or 2008-09. Each cultivar was inoculated with Enterobacter cloacae, cured, stored under commercial storage cond...

The fungal pathogen Verticillium dahliae has resulted in significant losses in numerous crops in coastal California, but lettuce remained unaffected until the mid-1990s. Since then outbreaks have decimated entire fields, but the causes of this sudden susceptibility of lettuce remain elusive. The population structure of V. dahliae isolated from coas...

The efficacy of 14 seed and drench treatments for control of soilborne damping-off pathogens in organic production of spinach was evaluated in a greenhouse study The efficacy of each treatment was compared With nontreated seed and seed treated with,I conventional fungicide for control of Fusarium oxysporum f. sp spinaciae. Pythium ultimum, and Rhiz...

From 1998 through 2002, commercial chives (Allium schoenoprasum) in coastal California (Monterey County) were damaged by an undescribed disease. Initial symptoms were chlorosis and tan-colored necrosis at the leaf tips; as the disease progressed, extensive tan-to-light brown discoloration extended down affected leaves, resulting in their death. The...