Sowthistle Plants Research Articles

Optimising fertigation of hydroponically grown sowthistle (Sonchus oleraceus L.): The impact of the nitrogen source and supply concentration

The efficient use of water and nutrients in leafy vegetable crops can be improved by effective water management, whereas the form of the supplied nitrogen may affect their quality and productivity. Sowthistle (Sonchus oleraceus L.), a widespread weed collected and consumed as a wild vegetable in the past, currently attracts a high interest for commercial cultivation due to its high nutritional value. The present study evaluated the effects of different nitrogen concentrations: N50: 50 mg L−1; (N 3.6 mmol L−1), N100: 100 mg L−1; (N 7.1 mmol L−1), N200: 200 mg L−1; (N 14.3 mmol L−1), and N300: 300 mg L−1; (N 21.4 mmol L−1) and different ammonium/total-N ratios (Nr: 0.01, 0.05, 0.10, 0.15) on growth, physiological parameters, antioxidant capacity and nutrient accumulation in the different plant parts of sowthistle, grown in Nutrient Film Technique hydroponic system. Total N was ammonium N plus nitrate N. Plant growth, total phenols, and antioxidant capacity were higher at the two intermediate N concentrations, whereas flavonoid and nitrogen content, as well as irrigation water productivity increased only with 200 mg N L−1 (N 14.3 mmol L−1), compared to the other three N concentrations. The accumulation of nitrogen in leaves and roots was lower, while leaf stomatal conductance was enhanced by increased N concentrations in the nutrient solution. Higher Nr ratios than ≥ 0.05 decreased plant dry matter, total phenols, flavonoids, and antioxidant capacity in leaf extracts, and negatively affected nitrogen translocation from roots to leaves. Sowthistle plants treated with a Nr of 0.05 exhibited a less intense oxidative stress, with decreased lipid peroxidation and hydrogen peroxide production, and increased superoxide dismutase and catalase activities, compared to those treated with higher Nr ratios. Increased Nr resulted in the accumulation of phosphorus and magnesium in leaves while the highest irrigation water productivity was obtained in plants grown with a Nr of 0.05. In conclusion, to increase yield, nutritional value and efficiency of water and nitrogen use in sowthistle grown in closed hydroponic systems, a N concentration of 200 mg L−1 of N (N 14.3 mmol L−1) and a Nr of 0.05 are suggested.

Olive-mill and grape-mill waste as a substitute growing media component for unexploded vegetables production

Olive tree and grapevine cultivations are the main crops in the Mediterranean area, resulting to high yields but also a great amount of wastes after processing, with environmental and human health concerns, after their disposal. The present study was conducted in order to evaluate the potential use of olive-mill wastes (OMW) and grape-mill wastes (GMW) in different ratios (0-5-10-20-40% v/v) with peat, as a peat substitute material, for the production of Portulaca oleracea (purslane) and Sonchus oleraceus (sowthistle) plants. Both GMW and OMW addition in the substrate mixture affected purslane's and sowthistle growth and disturb plant's physiological metabolism at ≥20% and ≥10% of the waste, respectively. Sowthistle plants that grew with GMW up to 10% on the substrate, had increased growth indicators (or remained unaffected) compared to the control. Leaf stomatal conductance was decreased proportionally with the increase of the ratios the tested materials into the growing mixtures. The antioxidant status of both plants was significantly affected by the addition of the waste materials into the growing media. Plants in cases appeared to be under stress conditions, as this was revealed by the increment in stress indicators as the lipid peroxidation and the internal concentration of hydrogen peroxide, and as a consequence, antioxidative (catalase, superoxide dismutase, peroxidase) enzyme metabolism was found increased. It can be concluded, that both GMW and OMW have the potential to be used in the growing media at low ratios of 10% and 5%, respectively, providing healthy plants, with increased antioxidant and mineral value.

The effect of weediness with common wild oat and sow-thistle on spring wheat productivity in the forest-steppe of the Middle Volga region

The current paper has presented the study results of the effect of weediness with common wild oat and sow-thistle on spring wheat productivity through 2012–2015. The purpose of the work was to find out the effect of weediness with common wild oat and sow-thistle in the forest-steppe of the middle Volga region. Using common wild oats, the trials were carried out according to the following scheme: 1) without weeds (control); 2) 10–15 common wild oat stalks per 1 m2 ; 3) 20–30 stalks per 1 m2 ; 4) 50–70 stalks per 1 m2 ; 5) 100–120 stalks per 1 m2 ; 6) 150–200 stalks per 1 m2 . Using sow-thistle the scheme was as follows: 1) without weeds (control); 2) 1 sow-thistle plant per 1 m2 ; 3) 2 plants per 1 m2 ; 4) 4 plants per 1 m2 ; 5) 6 plants per 1 m2 ; 6) 8 plants per 1 m2 . There was found that weediness with 26 common wild oat stalks per 1 m2 reduced productivity of 1 ha on 18% through four years, weediness with 62 stalks reduced it on 24%, with 115 on 38% and with 185 on 44%. Weediness with 26 common wild oat stalks per 1 m2 decreased spring wheat productivity on 0.33 t/ha in 2012, on 0.56 t/ha in 2013, on 0.94 and 0.68 t/ha in 2014 and 2015. Weediness with 185 stalks per 1 m2 decreased spring wheat productivity on 1.18 and 0.95 t/ha in 2012 and 2013, on 2.10 and 1.91 t/ha in 2014 and 2015. In arid years of 2014 and 2015, productivity shortfall caused by weeds increased. In the trials on the effect of sow-thistle on spring wheat productivity, on average, through four years of study, one weed reduced it on 8%, two weeds on 11%, four weeds on 19%, six weeds on 21% and eight weeds on 24%. On average, through four years, 13 common wild oat stalks per 1 m2 reduced the density of spring wheat on 9%, 26 stalks reduced it on 10%, 62 stalks reduced it on by 17%, and 185 stalks reduced it on 31%. At the same time, the number of productive stalks decreased on 2, 15, 22, and 40%, respectively, and kernel percentage of a head decreased on 4, 13, 16, and 23%. Weediness with two sow-thistle plants per 1 m2 reduced the number of spring wheat plants on 9%, four plants per 1 m2 reduced it on 15, six plants per 1 m2 reduced it on 18%, eight plants per 1 m2 reduced it on 21%. The number of productive stems decreased on 16, 20, 21 and 25%, respectively. Grain loss per stem caused by common wild oats was 16.2, grain loss caused by sow-thistle was 175 kg/ha.

First Report of Golovinomyces sonchicola Causing Powdery Mildew on Sonchus oleraceus in Mexico.

Sonchus oleraceus, common sow thistle, is native to Europe, Northern Africa, and Western Asia. This plant has become a common weed throughout the world. In Mexico, this weed has become widely naturalized by replacing indigenous plants and invading many agricultural areas. During the spring of 2018 and 2019, common sow thistle plants showing typical symptoms and signs of powdery mildew, were collected from agricultural fields in Ahome, Sinaloa, Mexico. As much as 30% of plants were diseased and 60 to 95% of the foliage was affected. Mycelium was conspicuous and white-gray, and on stems and both surfaces of leaves. Appressoria were nipple-shaped to crenulate. Conidiophores (n= 30) were hyaline, cylindrical, erect, and up to 150 μm long. Foot-cells (n= 30) were distinctly curved, 47 to 75 × 10 to 13 μm, slightly constricted, followed by 1-3 shorter cells and formed conidia in chains. Conidia (n= 100) were ellipsoid to doliiform to subcylindrical, 28 to 37 × 14 to 19 μm, lacked fibrosin bodies, and germinated from the apex. Chasmothecia were not observed. The morphological characters were consistent with those of the anamorphic state of Golovinomyces sonchicola (Braun and Cook 2012, Jakše et al. 2019). A voucher specimen (accession no. FAVF215) was deposited in the Herbarium of the Faculty of Agriculture of El Fuerte Valley at the Autonomous University of Sinaloa (Juan Jose Rios, Sinaloa, Mexico). To confirm the morphological identification, genomic DNA was extracted from mycelium and conidia, and the internal transcribed spacer (ITS) region and part of the 28S gene were amplified by PCR and sequenced. The ITS region of rDNA was amplified using the primers ITS5/ITS4 (White et al. 1990). For amplification of the 28S rRNA partial gene, a nested PCR was performed using the primer sets PM3 (Takamatsu and Kano 2001)/TW14 (Mori et al. 2000) and NL1/TW14 (Mori et al. 2000) for the first and second reactions, respectively. Phylogenetic analyses using the maximum parsimony and maximum likelihood methods (Braun et al. 2019), including ITS and 28S sequences of isolates of Golovinomyces spp. were performed and confirmed the results obtained from the morphological analysis. Isolate FAVF215 grouped in a clade with the other isolates of G. sonchicola. The ITS and 28S sequences were deposited in GenBank under accession numbers MW425872 and MW442972, respectively. Pathogenicity was demonstrated by gently dusting conidia from infected leaves onto leaves of 20 healthy plants and covered with plastic bags for 24 h. Ten non-inoculated plants served as controls. All plants were maintained in a greenhouse at 25 to 35ºC. All inoculated plants developed similar symptoms to those observed in the field from natural infections after 12 days, whereas powdery mildew symptoms and signs were not observed on control plants. The morphology asexual structures of fungus on inoculated plants were identical to those on naturally infected plants, fulfilling Koch's postulates. Inoculation tests were repeated twice with identical results. Based on the morphological data and phylogenetic analysis, the fungus was identified as G. sonchicola. This fungus has been reported causing powdery mildew on S. oleraceus in Germany, The Netherlands, Slovenia, and The United Kingdom (Farr and Rossman 2021). To the best of our knowledge, this is the first report of G. sonchicola causing powdery mildew on S. oleraceus in Mexico. This powdery mildew pathogen may represent an option for the biological control of common sow thistle.

A new stem nematode, Ditylenchus oncogenus n. sp. (Nematoda: Tylenchida), parasitizing sowthistle from Adriatic coast dunes in southern Italy

Morphological and molecular analyses of a stem nematode causing a severe disease on infected sowthistle (Sonchus bulbosus) plants, involving the formation of gall-like structures on infected leaves and stems, have led to the description of a new species named Ditylenchus oncogenus n. sp. Morphologically, the new species is characterized by a medium to large body size (all adults more than 1 mm in length); a delicate stylet (9.0-11.0 μm long) with minute, rounded knobs; a long post-vulval uterine sac (c. 65% of the vulva-anus distance); six incisures at the lateral fields and characteristic D. destructor-pattern of spicules (with pronounced ventral tumulus and anteriorly pointed, less sclerotized, cuticle parts present within the lamina). The results of molecular analysis of rRNA gene sequences, including the D2-D3 expansion regions of 28S rRNA, internal transcribed spacer (ITS) rRNA, partial 18S rRNA gene, the protein-coding mitochondrial gene, cytochrome oxidase c subunit I (COI), and the heat-shock protein 90 (hsp90) gene, support the new species status. The results of a host-suitability test indicated that the new species does not parasitize potato (Solanum tuberosum) tubers and broad bean (Vicia faba) seedlings. Histopathological observations on naturally infected sowthistle tissues revealed that D. oncogenus n. sp. causes floral stem neoplasia and midrib leaf gall formation on the type, and to date only known, host. The galls were characterized by extensive hyperplasia, where several necrotic cells in the neoplasic area were directly damaged by feeding of the nematode, whereas a number of adjacent cells showed typical cytological changes, such as granulated cytoplasm with hypertrophied nuclei and nucleoli.

Growth and Reproduction of Annual Sowthistle (Sonchus asper L.) in Response to Environmental Light

Sowthistle (Sonchus asper L.) is believed to be a highly resource demanding species that spreads mainly by seeds. In this study, the effect of light availability on plant size and seed production was investigated. Sowthistle plants showed high phenotypic plasticity in their height, number of leaves, leaf length and number of branches per plant in relation to light availability. Seed mass production per plant ranged from >3.5 g in the control to less than 0.2 g in the 50% light availability treatment. It was concluded that changing the canopy architecture of crops can suppress growth and seed production in this plant. The results of this research can be used to develop models in crop-weed competition.

First Report of Tomato mosaic virus on Common Sow Thistle in Iran.

The natural incidence of Tomato mosaic virus (ToMV) in common sow thistle (Sonchus oleraceus) from vegetable fields was assessed to determine the role of this weed species as a virus inoculum source. Twenty sow thistle plants with virus-like foliar symptoms including mosaic and malformations were collected from five vegetable fields in Tehran province, Iran, and analyzed by double antibody sandwich (DAS)-ELISA for the presence of ToMV, Tobacco mosaic virus (TMV), and Cucumber mosaic virus (CMV) using specific polyclonal antibodies (Agdia, Elkhart, IN). Six out of the 20 sow thistle plants tested by ELISA were infected with ToMV. This virus was detected in three of five vegetable fields surveyed, while CMV and TMV were not detected. Mosaic symptoms were associated with the ToMV infection, similar to those caused by TMV in common sow thistle in Iran (2). Viral infection was confirmed by RT-PCR using previously described specific primers to amplify a region in the coat protein gene of ToMV (3). The RT-PCR resulted in the amplification of an expected fragment of ~480 bp from ToMV-infected but not from healthy plants. The nucleotide sequence of the amplified DNA fragment was purified (GeneJET Gel Extraction Kit, Fermentas, Germany), directly sequenced, and deposited in GenBank as Accession No. KF527464. BLAST analysis showed 95 to 97% and 98 to 100% identity at the nucleotide and amino acid levels, respectively, with comparable sequences of other ToMV isolates (GenBank AF062519, FN985165, GQ280794, and JX857634). Mechanical inoculation of sow thistle plants with sap of symptomatic sow thistles reproduced symptoms of field-infected sow thistles. The presence of ToMV in the inoculated plants was confirmed by ELISA and RT-PCR. This suggested that ToMV could be the causal agent of the disease on sow thistle. In our earlier studies, the distribution and genetic diversity of ToMV isolates infecting vegetable crops and weed plants were studied (1); however, to our knowledge, this is the first report of ToMV infecting common sow thistle in Iran.

Growth and phenolic content of sowthistle grown in a closed-type plant production system with a UV-A or UV-B lamp

This study was conducted to determine the effects of UV-A and UV-B wavelengths on the growth and content of antioxidant phenolic compounds in sowthistle (Ixeris dentata Nakai), a medicinal plant, grown in a closed plant-production system. In study I, sowthistle plants were continuously exposed to UV-A light. In study II, two UV treatments [repeated UV-B (R): 4 h·d−1 for 6 days, gradual UV-B (G): from 1 to 7 h·d−1 for 6 days] were applied to the sowthistle plants. As a result, contents of total phenolics and antioxidants in UV-A-treated plants were significantly (50 and 30%, respectively) higher than those in the control plants after 3 d of UV treatment without growth inhibition. Moreover, plants continuously exposed to UV-A for 5 d had 50% higher total flavonoid content than the control. The phenylalanine ammonia-lyase (PAL) activity supported the accumulation of phytochemicals in plants exposed to UV-A. The UV-B (R) treatment led to a more rapid decrease in the chlorophyll fluorescence ratio than UV-B (G) treatment. The UV-B (R) or UV-B (G) treatment produced more total phenolics, flavonoids, and antioxidants, although both UV-B treatments significantly inhibited plant growth measured at 2 days after treatment. The UV irradiation also enhanced PAL activity at 2 and 3 days after treatment, suggesting biosynthetic activation of secondary metabolites. Therefore, application of UV-A or UV-B light can be used as a strategy to improve antioxidant phenolic compounds of sowthistle plants grown in closed plant production systems.

Geographical Distribution and Survival of Iris yellow spot virus in Spiny Sowthistle, Sonchus asper, in Georgia.

Iris yellow spot virus (IYSV) has occurred in Georgia since 2003. IYSV is transmitted by onion thrips, Thrips tabaci. During a weed survey in the Vidalia onion-growing zone (VOZ), spiny sowthistle (Sonchus asper) was identified as a host for IYSV. Spiny sowthistle is widespread in Georgia, and this presented an opportunity to study the natural spread of IYSV and assess its potential role in IYSV epidemiology. From 2007 to 2009, during the spring season, 2,011 sowthistle samples were collected from various counties within and outside the VOZ. The samples were tested for IYSV infection by enzyme-linked immunosorbent assay and confirmed by reverse-transcription polymerase chain reaction and sequencing. IYSV sequences from sowthistle were 98 to 99% identical to onion IYSV sequences from onion originated from Georgia. By the third year, IYSV-infected sowthistle plants were found in 79% of the counties in the VOZ and in 61% of the sampled counties in all directions, except to the east of the VOZ. Furthermore, thrips-mediated transmission assays confirmed that T. tabaci can efficiently transmit IYSV from onion to sowthistle. Sowthistle also supported T. tabaci survival and reproduction. These findings demonstrate that sowthistle plants can serve as an IYSV inoculum source and as a thrips reservoir.

Modelling the morphogenesis of annual sowthistle, a common weed in crops

This paper presents an architectural model of sowthistle which is an important weed in most crops. The sowthistle model was developed using the Lindenmayer systems formalism and parameterised according to measurements of structure of several sowthistle plants. The growth relationships of the sowthistle architecture were captured by the model and simulated graphically. The model reproduced the architectural development of individual plant organs faithfully when verified for leaf number, plant height and leaf area at different temperatures. Future improvement of the model and its practical aspects are described.

A Canopy Architectural Model to Study the Competitive Ability of Chickpea with Sowthistle

Improving the competitive ability of crops is a sustainable method of weed management. This paper shows how a virtual plant model of competition between chickpea (Cicer arietinum) and sowthistle (Sonchus oleraceus) can be used as a framework for discovering and/or developing more competitive chickpea cultivars. The virtual plant models were developed using the L-systems formalism, parameterized according to measurements taken on plants at intervals during their development. A quasi-Monte Carlo light-environment model was used to model the effect of chickpea canopy on the development of sowthistle. The chickpea-light environment-sowthistle model (CLES model) captured the hypothesis that the architecture of chickpea plants modifies the light environment inside the canopy and determines sowthistle growth and development pattern. The resulting CLES model was parameterized for different chickpea cultivars (viz. 'Macarena', 'Bumper', 'Jimbour' and '99071-1001') to compare their competitive ability with sowthistle. To validate the CLES model, an experiment was conducted using the same four chickpea cultivars as different treatments with a sowthistle growing under their canopy. The growth of sowthistle, both in silico and in glasshouse experiments, was reduced most by '99071-1001', a cultivar with a short phyllochron. The second rank of competitive ability belonged to 'Macarena' and 'Bumper', while 'Jimbour' was the least competitive cultivar. The architecture of virtual chickpea plants modified the light inside the canopy, which influenced the growth and development of the sowthistle plants in response to different cultivars. This is the first time that a virtual plant model of a crop-weed interaction has been developed. This virtual plant model can serve as a platform for a broad range of applications in the study of chickpea-weed interactions and their environment.

Molecular Characterization of Aster Yellows Phytoplasma Associated with Valerian and Sowthistle Plants by PCR–RFLP Analyses

AbstractIn Alberta, Canada, valerian grown for medicinal purposes and sowthistle, a common weed, showed typical aster yellows symptoms. Molecular diagnosis was made using a universal primer pair (P1 / P7) designed to amplify the entire 16S rRNA gene and the 16 / 23S intergenic spacer region in a direct polymerase chain reaction (PCR) assay. This primer pair amplified the DNA samples from valerian and sowthistle and reference controls (AY‐27, CP, PWB, AY of canola, LWB). They produced the expected PCR products of 1.8 kb, which were diluted and used as templates in a nested PCR. Two primer pairs R16F2n / R2 and P3 / P7 amplified the DNA templates giving PCR products of 1.2 and 0.32 kb, respectively. No PCR product was obtained with either set of primers and DNA isolated from healthy plants. Restriction fragment length polymorphism (RFLP) was used to analyse the partial 16S rDNA sequences (1.2 kb) of all phytoplasma DNA samples after restriction with four endonucleases (AluI, HhaI, MseI and RsaI). The restriction patterns of these strains were found to be identical with the RFLP pattern of the AY phytoplasma reference control (AY‐27 strain). Based on the RFLP data, the two strains are members of subgroup A of the AY 16Sr1 group. We report here the first molecular study on the association of AY phytoplasmas with valerian and sowthistle plants.

Spray deposition on plant surfaces: a modelling approach

For pesticides to effectively manage pests, they must first be deposited on the target (typically a plant surface) in a manner in which the active ingredient(s) can be readily taken up by the target organism. A plant architectural model that enables the location of various plant components in 3-D space combined with a particle trajectory model has been used to study the interception of spray droplets by various vegetative elements. Results from the simulation are compared with wind tunnel studies of glyphosate deposition on cotton (Gossypium hirsutum L. var. Sicala), sow thistle (Sonchus oleraceus L.) and wild oats (Avena ludoviciana Durieu). An air induction flat fan nozzle (AI110015 at 500 kPa pressure) and an extended range flat fan nozzle (XR11002 at 280 kPa pressure) were predicted to have similar glyphosate deposition on cotton and sow thistle plants, whereas the extended range nozzle resulted in higher deposit on wild oats. Spray deposition (µg cm-2) on wild oat plants at the 5-leaf stage was more than double the amount of deposition on sow thistle or wild oat plants at the 2-leaf stage. The model was in good agreement with the experimental data except that it tended to over predict deposition on sow thistle plants.

First Report of the Rust Miyagia pseudosphaeria on Sonchus oleraceus in the Americas.

In January 2002, a rust was observed on leaves and stems of the weed Sonchus oleraceus L. (annual sowthistle) in Santa Barbara, CA. Infected plants were collected in Santa Barbara and Monterey counties, CA. Specimens were examined microscopically and compared with a published description (1) and herbarium specimens at the USDA National Fungus Collection, Beltsville, Maryland. The fungus was identified as Miyagia pseudosphaeria (Mont.) Jorst. based on characteristics of the uredinia and urediniospores. The uredinial sori were subepidermal, erumpent, and single or in groups. Sori were surrounded by peripheral, laterally connected, chestnut brown paraphyses that initially enclosed the developing urediniospores and eventually opened partially at the apex, breaking the host epidermis and remaining as a wall surrounding the spores. The urediniospores were ellipsoid, ovoid, or pyriform with yellowish, often granular, contents and measured 21.5 to 43 × 17 to 26.5 μm. The urediniospore walls were hyaline and finely echinulate and 2.5 to 3.5 μm thick with germ pores sometimes evident in median view. The paraphyses were 70 to 140 × 6 to 8 μm, thick-walled, hyaline below, chestnut brown above, and often somewhat wider or dichotomously branched at the apex. To test pathogenicity, a spore suspension (4.7 × 104 spores/ml) was sprayed onto 7-week-old annual sowthistle plants. Plants were incubated in a dew chamber for 48 h and maintained in a greenhouse at 22 to 24°C. Signs of rust were observed after 2 weeks, and microscopic examination confirmed that the same fungus was present. Uninoculated control plants did not develop rust. Using the same method, plants of prickly sowthistle (S. asper (L.) Hill) were inoculated and also developed the disease. All inoculation experiments were conducted two times and the results were the same. The rust was found on almost all annual sowthistle plants examined in Santa Barbara County, especially well-nourished specimens growing as weeds in irrigated landscapes, vegetable fields, or in container nurseries. Diseased plants were found in and around vegetable fields in Monterey County. M. pseudosphaeria is macrocyclic, autoecious, and known only on Sonchus spp. It has been reported from northern Africa, China, Europe, Japan, New Zealand, and the former Soviet Union. To our knowledge, this is the first report of M. pseudosphaeria in the Americas. Voucher specimens have been deposited in the U.S. National Fungus Collection (BPI 842025, 842055 to 842060, and 842230). Images can be viewed at nt.ars-grin.gov .

Evaluation of the "fall rosette" procedure for perennial sowthistle control in fallow

Field experiments conducted near Grande Prairie, Alberta, compared the effectiveness of the fall rosette procedure to other procedures used in a year of fallow for the control of perennial sowthistle (Sonchus arvensis L.). The fall rosette procedure, which consisted of discontinuing normal cultivation in late July, allowing the perennial sowthistle plants to grow for 6 wk and then applying glyphosate plus dicamba at 0.6 + 0.6 kg ha−1 plus Agral 90 at 0.5% vol/vol of spray volume, reduced shoot density by 84, 90 and 96% approximately 1 yr after imposition in 1992, 1993 and 1994, respectively. By comparison, the bud stage procedure, which consisted of allowing plants to grow to the bud stage in the spring/early summer, applying the same herbicide treatment and conducting tillage for the rest of the year, reduced shoot densities by 58, 86 and 85% when imposed in the same years, respectively. The fall rosette procedure was also more effective than frequent tillage throughout the growing season without herbicide, or than chemfallow (glyphosate plus dicamba applied in early July and again in early September, with or without late fall tillage) in reducing perennial sowthistle shoot density. Mowing, whenever the perennial sowthistle reached 8–10 cm in height, did not reduce shoot density. Key words: Fall rosette, bud stage, Sonchus arvensis L., tillage, mowing, chemfallow

First Report of Powdery Mildew of Pepper in North-Central Mexico.

Pepper plants showing general yellowing and white spots on the lower surface as well as brown spots on the upper surface of the lowest leaves were observed during the 1998 crop season in the states of Chihuahua, Zacatecas, and Aguascalientes (north central area of México). Light defoliation was observed. Samples were collected in Chihuahua and Zacatecas to identify the pathogen, which showed navicular conidia. A conidial suspension was sprayed on pepper varieties, but only Hungarian Yellow Wax showed powdery mildew lesions. The average size of the conidia from Zacatecas was 61.2 × 18.2 μm while those from Chihuahua measured 58.2 × 17.6 μm, which is coincident with the description given for an Oidiopsis sp. The perfect stage is Leveillula taurica (1). Cleistothecia were not observed. In Zacatecas the disease was not detected in tomato fields or in sowthistle (Sonchus oleraceae) plants contiguous to, or within, infected pepper fields. Powdery mildew incidence ranged from 35 to 80% in Ancho type and from 0 to 55% in Mirasol type pepper fields in Zacatecas. The number of powdery mildew lesions per leaf in most cases varied from 1 to 3. Incidence was higher in fields where the canopy was closed and warmer and wetter conditions may have allowed the disease to progress. Reference: (1) J. B. Jones et al. 1991. Compendium of Tomato Diseases. American Phytopathological Society, St. Paul, MN.

Characterization of the Beet Yellow Stunt Virus Coat Protein Gene

ABSTRACT The beet yellow stunt virus (BYSV) genome contains at least nine open reading frames (ORFs) that code for proteins ranging from 6 to 66 kDa. Based on amino acid sequence comparisons, the coat protein (CP) was previously identified as the product of ORF7. We expressed the product of ORF7 in bacteria and confirmed that ORF7 codes for the BYSV CP by immunoblotting. BYSV is a phloem-limited virus, and virus CP antigen of a quality sufficient for diagnostic antisera production has not been available. To produce BYSV antigen free of plant host contaminants, ORF7 was cloned into a pMAL bacterial expression vector. The resulting fusion protein was affinity-purified and used as an antigen to raise anti-BYSV CP antisera in rabbits and guinea pigs. Using these antisera, an indirect double-antibody sandwich (DAS) enzyme-linked immunosorbent assay (ELISA)-based diagnostic system was developed. This indirect DAS-ELISA format enabled reliable detection of BYSV in tissue extracts from virus-infected lettuce diluted up to 5,000 times. The diagnostic system developed may enable large-scale epidemiological studies of BYSV using simple serological techniques. The antisera raised had a titer exceeding 1 x 10(5) in immunoblots and easily detected the 23.7-kDa BYSV CP in virus-infected lettuce and sowthistle plants. In these two plant species, BYSV CP was detected as two closely migrating bands during electrophoresis, which may suggest posttranslational CP modifications. To further characterize the BYSV CP gene, the 5'-untranslated region (UTR) of the BYSV CP subgenomic RNA (sgRNA) was cloned and sequenced. The CP-encoding, approximately 1.9-kb sgRNA has an AT-rich, 66-nucleotide-long 5'-UTR colinear to the genomic sequence upstream of ORF7.

Transmission of Cucurbit Potyviruses by Uroleucon pseudambrosiae (Homoptera: Aphididae), an Aphid Trapped During Epidemics of Watermelon Mosaic Virus 2 in Florida

As part of epidemiological studies of watermelon mosaic virus 2 (WMV-2) in Florida, aphids were collected in green tile water traps in 1989 and 1990. A Uroleucon sp. accounted for >25% of the aphids trapped. The same aphid was found infesting most of the wild lettuce ( Lactuca graminifolia Michaux.) and spiny-leaved sowthistle ( Sonchus asper [L.] Hill) plants growing near plots of watermelon and was identified as Uroleucon pseudambrosiae (Olive) (formerly Dactynotus pseudambrosiae ). The vector propensity of this aphid was estimated and compared with that of three other known vectors of WMV-2, both in arena tests and in tests using single aphids given limited acquisition and inoculation access. U. pseudambrosiae transmitted virus relatively inefficiently in controlled-access tests but was not significantly different from Aphis spiraecola Patch and Aphis illinoisensis Shimer in virus transmission in arena tests. Myzus persicae (Sulzer) was the most efficient vector in all tests. This is the first report of U. pseudambrosiae transmitting WMV-2. Based on its abundance and the estimate of its vector propensity, we think that this species could play an important role in the epidemiology of WMV-2 in areas in which both aphid and virus are commonly found.

Electron microscopy of sowthistle yellow vein virus in cells of sowthistle plants

Electron microscopy of sections of leaves ( Sonchus oleraceus L.) infected with sowthistle yellow vein virus (SYVV) showed that the virus could infect parenchyma, developing xylem, and phloem cells. Virus was found in cells of leaves showing chlorosis and vein-clearing; none was seen in the adjacent green areas. Virus was localized predominantly in the nucleus and rarely in the cytoplasm. In either location, cell organelles were not interspersed with viral aggregates, although both polysomes and endoplasmic reticulum were normally at the periphery of cytoplasmic viral aggregates. In most cells areas of the perinuclear space were enlarged to accommodate aggregates of virus particles which were often invaginated into the nucleus.

WEEDS AS RESERVOIR HOSTS OF THE LETTUCE BIG-VEIN VIRUS

The lettuce big-vein virus (BVV) was recovered from 2 of 23 lettuce plants (Lactuca sativa L.) and 2 of 24 sow thistle (Sonchus oleraceus L.) plants sampled in 1962 and 1963 in areas of the lower Sacramento Valley where lettuce had not previously been grown. BVV is considered to be an indigenous virus of plant species in the Compositae family; these apparently are symptomless hosts and the presence of BVV is noted only when lettuce is planted under favorable environmental conditions. A BVV-Olpidium isolate from sow thistle was shown to be a physiological strain differing from the lettuce isolate in transmitting BVV to sow thistle and multiplying well in sow thistle roots. In addition, the susceptibility of Lactuca spp., Cichorium spp., and Taraxacum officinale to BVV-lettuce Olpidium was tested; only Laciuca serriola, Lactuca saligna, Cichorium sp., and a sow thistle from Japan showed good symptoms, Lactuca gracoglossum and Lactuca virosa showed symptoms poorly. Of the symptomless species, Olpidium and BVV were recovered from Lactuca muralis, T. officinale, and chicory (cv. asparagus) but not from endive (cv. No. 5) or chicory (cv. Large rooted). Sow thistle yellow-vein virus produces symptoms suggestive of big vein in sow thistle but its identity as a distinct virus transmitted by Nasonovia lactucae (L.) was confirmed.