Cruciferous Weeds Research Articles

Characterization of Emerging Xanthomonas campestris Isolates on the Nonnative Weed Garlic Mustard (Alliaria petiolata).

Nonnative plant infestations provide unique opportunities to investigate pathogen emergence with evolutionarily recent plant introduction events. The widespread distribution of invasive plants and their proximity to genetically related crops highlights the risks of nonnative plants acting as ancillary hosts and fostering microbial recombination and pathogen selection. Garlic mustard (Alliaria petiolata) is a widespread, nonnative cruciferous weed that grows throughout North America and along the forested edges of diverse agricultural fields. The recent identification of a novel Xanthomonas campestris pv. incanae strain isolated from a diseased A. petiolata population led to the current investigation of the distribution and diversity of X. campestris isolates from naturally infected A. petiolata. A total of 14 diseased A. petiolata sites were sampled across three states, leading to the identification of diverse X. campestris pathotypes and genotypes. Pathogenicity assays and multilocus sequence analyses identified pathogenic X. c. pv. incanae and X. c. pv. barbareae strains collected from disparate A. petiolata populations. Moreover, independently collected X. c. pv. incanae strains demonstrated a broad cruciferous host range by infecting cabbage (Brassica oleracea var. capitata), garden stock (Matthiola incana), and the cover crop yellow mustard (Guillenia flavescens). This study highlights the genetic variability and host potential of natural X. campestris populations and the potential risks to Brassica crops via widespread, dense garlic mustard reservoirs.

The manifestation of diseases and phytophages of weeds associated with the cultivation of flax, the possibility of their use as biological plant protection agents

Materials on the study of diseases and phytophages of weeds associated with flax cultivation and on the results of their use in biological plant protection are presented. It has been established that the developed biopreparation (a mixture of inoculum of smut / urocystosis / couch-grass (the disease causative agent Urocystis agropyri / P./ S.) and rust /puccinia / yellow thistle (pathogen Puccinia suaveollens /Pers./) reduces the sowings contamination with these weeds. When sowing flax in regions new to this crop (for example, in the Tula region), phytophages unusual for this crop (for example, rapeseed flea) can significantly damage not flax, but cruciferous weeds. Studies have established that Cirsium setosum in flax sowings is often affected by a specific rust /puccinia / (pathogen Puccinia suaveollens /Pers./ R. [= P. obtegens /Lk./ Tul.]), causing on average about 20% of cases of its destruction without the formation of seeds.

Intraspecific Variability and Distribution Difference within the Ribosomal Introns of the Discrete Plasmodiophora brassicae Group in Japan: A Case Study for Complex Dynamics of Intron Evolution

Analysis of the ribosomal introns of Plasmodiophora brassicae populations infecting the cruciferous weed Cardamine occulta revealed the complex dynamics of size, intraspecific variability, and distribution. The results showed that P. brassicae populations from the weed have lost multiple introns in the small and large subunits of the ribosomal RNA genes. Moreover, the retained introns, despite a largely mutual share of conserved parts with the cosmopolitan strains, contained numerous novel structures. These structural differences comprise a high level of polymorphisms, such as transversion point mutations occurring at sites involving the intronic splicing sites or insertions/deletions at the binding sites. Two geographical P. brassicae populations from C. occulta carried a lengthy intron-encoded ORF and putative mobile elements established in the large subunit. A few P. brassicae populations from the Brassica crops also harbored polymorphic introns that shared common mutated motifs with the weed-affecting group. The diversity of ribosomal introns observed from those investigated populations demonstrated the genetic distinction of the P. brassicae populations from C. occulta. The genetic variations might play a key role in the adaptability of the weed-infecting populations and are more likely related to the process of pathogenesis for the cosmopolitan P. brassicae infecting the Brassica crops.

CRUCIFEROUS WEEDS (BRASSICACEAE) IN ORGANIC GRAIN PRODUCED IN WESTERN SIBERIA AND THE PHYTOSANITARY RISKS ASSOCIATED WITH THEM

The results of herbological analyzes of seed lots of agricultural crops grown in Western Siberia under the conditions of organic farming in 2019–2020 are presented. It was found that five species of identified cruciferous weeds are regulated by grain importing countries and can often be found in organic crop products.

Cruciferous Weeds Do Not Act as Major Reservoirs of Inoculum for Black Rot Outbreaks in New York State.

Cruciferous weeds have been shown to harbor diverse Xanthomonas campestris pathovars, including the agronomically damaging black rot of cabbage pathogen, X. campestris pv. campestris. However, the importance of weeds as inoculum sources for X. campestris pv. campestris outbreaks in New York remains unknown. To determine if cruciferous weeds act as primary reservoirs for X. campestris pv. campestris, fields that were rotating between cabbage or had severe black rot outbreaks were chosen for evaluation. Over a consecutive 3-year period, 148 cruciferous and noncruciferous weed samples were collected at 34 unique sites located across five New York counties. Of the 148 weed samples analyzed, 48 X. campestris isolates were identified, with a subset characterized using multilocus sequence analysis. All X. campestris isolates originated from weeds belonging to the Brassicaceae family, with predominant weed hosts being shepherd's purse (Capsella bursa-pastoris), wild mustard (Sinapis arvensis), yellow rocket (Barbarea vulgaris), and pennycress (Thlaspi arvense). Identifying pathogenic X. campestris weed isolates was rare, with only eight isolates causing brown necrotic leaf spots or typical V-shaped lesions on cabbage. There was no evidence of cabbage-infecting weed isolates persisting in an infected field by overwintering in weed hosts; however, similar cabbage and weed X. campestris haplotypes were identified in the same field during an active black rot outbreak. X. campestris weed isolates are genetically diverse both within and between fields, but our findings indicate that X. campestris weed isolates do not appear to act as primary sources of inoculum for B. oleracea fields in New York.

Oilseed Rape Yield Performance in the Clearfield® System under Varying Management Intensities

Oilseed rape production is under pressure due to a limited availability of herbicides. Therefore, the performance in terms of management intensity (MI) and herbicide strategy (HS) and the involved yield formation was evaluated in a two-year Clearfield® oilseed rape field experiment. Furthermore, weed density and weed composition were also investigated. The variants of MI were standard sowing density (StS; seed rate: 50 seeds m−2, primary tillage: plow, row width: 12 cm), reduced sowing density (RD; seed rate: 25 seeds m−2, primary tillage: plow, row width: 50 cm), and strip-till (ST; seed rate: 25 seeds m−2, primary tillage: strip tillage, row width: 50 cm). The variants of HS were preemergence strategy (PES; application of dimethachlor, napropamide, clomazone in preemergence and application of prapaquizafop in postemergence) and Clearfield® strategy (CLS; application of imazamox, quinmerac in preemergence, no postemergence herbicide application). In the first year of the trial, there were no interactions between the factors in terms of grain yield. Grain yield in StS was 3.85 t and 5.2% significantly lower than in ST, and the value of RD was not significantly different from StS and ST. Grain yield in CLS was 3.7 t and 2.7% lower than in PES. In the second year of the trial, the grain yield in ST CLS was significantly lower, and there were no significant differences between the other variants. Higher weed emergence was observed in CLS RD (2.7 to 4 times higher weed density compared to PES RD) and CLS ST (2.8 to 4.5 times higher weed density compared to PES ST). No significant differences existed between StS PES and StS CLS in both trial years. The Clearfield® system offers significant advantages in the control of cruciferous weeds. Although these did not occur on the trial fields, the Clearfield® system in this study showed to be an alternative to the more common pre-emergence system, especially with regard to the parameter grain yield.

Cruciferous weeds (Brassicaceae) in agrocenoses of the Siberian Federal District as regulated objects in importing countries

One of the necessary requirements for the export of agricultural products is the absence of harmfulorganisms regulated by the importing country. Plants from 19 genera of the Brassicaceae family are listed as regulatedpests in 28 importing countries. In the agrocenoses of the Siberian Federal District, 22 species of weed cruciferous plantshave been identified. Of these, 9 species (41 %) are included in the lists of organisms regulated by importing countries.

Influence of intra‐row cruciferous surrogate weed growth on crop yield in organic spring cereals

AbstractIn Northern Europe, inter‐row hoeing has become a popular tactic for controlling weeds in organic cereals. Hoeing is highly effective and can be implemented from crop emergence until stem elongation to maintain a nearly weed‐free inter‐row zone. However, hoeing has a lesser effect on weeds growing in the intra‐row zone, where crop–weed proximity results in heightened competition. In the hoed cereal system, it is investigated whether tall‐growing, competitive, cruciferous weeds in the intra‐row zone affect crop biomass, yield and thousand kernel weight (TKW). An additive experimental design is employed to enable the fitting of rectangular hyperbolas, describing and quantifying the effects of increasing intra‐row surrogate weed density on crop growth parameters. Regressions were studied under the influence of crop (spring barley and spring wheat), row spacing (narrow [12.5 or 15.0 cm] and wide [25.0 cm]) and nitrogen rate (50 and 100 kg NH4‐N/ha). Cruciferous surrogate weeds were found to impact crop yield and quality severely. For example, ten intra‐row plants/m2 of surrogate weed Sinapis alba reduced grains yields by 7%–14% in spring barley and by 7%–32% in spring wheat with yield losses becoming markedly greater in wheat compared to barley as weed density increases. Compared to wheat, barley limited yield and quality losses and suppressed intra‐row weed growth more. Row spacing did not have a consistent effect on crop or weed parameters; in one of six experiments, the 25 cm row spacing reduced yields and increased intra‐row weed biomass in wheat. Nitrogen rate did not affect crop or weed parameters. Results warrant the implementation of additional tactics to control intra‐row weeds and limit crop losses.

Selectivity and efficacy of herbicide GF-3488, containing synthetic auxins halauxifen-methyl and clopyralid, in winter oilseed rape crops in Ukraine

Halauxifen-methyl is a new synthetic auxin, which in combination with another auxin-like herbicide clopyralid is the active ingredient of complex herbicide GF-3488, that is used for dicotyledonous weeds control in winter oilseed rape crops. The reason of this study was a necessity to test crop selectivity and efficacy of GF-3488 to control dicotyledonous weeds in winter oilseed rape crops in Ukraine and also the possibility of GF-3488 application in the tank mixture with graminicide or/and insecticide to control monocotyledonous weeds and insects. A randomized block experiment was conducted in 2015—2017 in 4 locations. It was found that under spring applying, the GF-3488 is not inferior to another widely used herbicide Galera Super on selectivity to the crop. Herbicide GF-3488 at the rate 1.0 l/ha was significantly better than Galera Super at the rate 0.3 l/ha in controlling of annual dicotyledonous weeds Papaver rhoeas L., Galium aparine L., Consolida regalis S.F. Gray and was effective to control of certain types of cruciferous weeds, which are resistant to Galera Super. Adding graminicide Fusilade Forte and insecticide Nurelle D did not affect the GF-3488 selectivity to the crop and had no negative impact on dicotyledonous weeds control. Efficacy of monocotyledonous weeds control by graminicide did not change in the mixture with GF-3488. It was concluded that herbicide GF-3488 is effective on winter oilseed rape against dicotyledonous weed species. Therefore for the simultaneous control of dicotyledonous and monocotyledonous weeds in winter oilseed rape in the spring after the renewal of the crop vegetation herbicide GF-3488 is advisable to be used in a tank mixture with graminicides, and for simultaneous protection against weeds and pests it can be mixed with insecticides.

Identification of Delia spp. (Robineau-Desvoidy) (Diptera, Anthomyiidae) and its cruciferous hosts in Mexico.

Soil pests of cruciferous crops in Mexico have been gaining importance in recent years; such is the case of Delia spp. (Robineau-Desvoidy) (Diptera, Anthomyiidae), of which, to date, there are no studies on the correct identification of associated species, as well as the range of hosts. In an integrated pest management program, it is essential to know this information to design and implement adequate phytosanitary measures. Plants infested by Delia spp. were collected in the states of Guanajuato, Puebla, and Mexico from June to November 2017 and March to December 2018 in commercial plantations of cruciferous crops (Brassicaoleracea L. var. italica, botrytis and capitata), B.napus L., and Raphanussativus L.) as well as some cruciferous weeds (R.raphanistrum L., Sisymbriumirio L., B.campestris L., Capsellabursa-pastoris L., and Lepidiumvirginicum L.) in the edges of these crops. The two species found in this study, Deliaplanipalpis (Stein) and Deliaplatura (Meigen), identified using male genitalia was corroborated by molecular techniques. Both species emerged from all the sampled hosts, except for C.bursa-pastoris and L.virginicum. The association of the two species in cruciferous crops and weeds, provides valuable information for the management of these insects not only in cruciferous crops but other ones that are strongly attacked by D.platura.

Competence of Xanthomonas campestris from Cruciferous Weeds and Wallflower (Erysimum cheiri) to Induce Black Rot in Cabbage

In order to verify the role of cruciferous weeds and ornamentals to serve as a source of primary inoculum of Xanthomonas campestris pv. campestris (Xcc), the causal agent of black rot of Brassicas, Xanthomonas isolates from shepherd’s purse (Capsella bursa-pastoris), fanweed (Thlaspi arvense) and wallflower (Erysimum cheiri) were characterized by molecular data and by their pathogenicity on kohlrabi and shepherd’s purse. These characteristics were compared to those of xanthomonads isolated from infested Brassica crops and contaminated transplants. Only one of 30 Xanthomonas isolates from shepherd’s purse in boundary ridges and field paths adjacent to Brassica fields, and from plants outside the Brassica growing area, was able to induce black rot (BR) on kohlrabi; nearly all of them (except one) were able to cause black rot like symptoms with black vascular veins (BRL) on shepherd’s purse. Six of ten tested isolates from different asymptomatic weeds growing in BR infested cauliflower fields were able to induce BR on kohlrabi, but all isolates caused BRL on shepherd’s purse. All Xanthomonas isolates from symptomatic wallflower induced BR on kohlrabi and BRL on shepherd’s purse. Inoculations with isolates from BR infested cauliflower, representing the pathovar campestris (Xcc), always led to BR on kohlrabi and BRL on shepherd’s purse. The isolates from rucola and radish field crops and from Brassica transplants showed typical symptoms of the pathovars campestris (Xcc) and raphani (Xcr), respectively. In a PCR with the newly designed primer set SP-1, only the isolates which were able to induce BR on kohlrabi could be detected. The sequence analysis of the gyrB-gene showed that all Xanthomonas isolates which induced BR on kohlrabi clustered in one major clade, while the remaining isolates clustered into several different clades. Based on these results, the authors conclude that Xanthomonas isolates from shepherd’s purse may not constitute a serious risk to serve as primary inoculum for BR epidemics in Brassicas. By contrast, Xanthomonas isolates from wallflower have this potential. Most of the isolates from cruciferous weeds and the wallflower isolates do not fit into the actual classification of Xanthomonas campestris pathovars.

Back-trajectory modelling and DNA-based species-specific detection methods allow tracking of fungal spore transport in air masses

Recent advances in molecular detection of living organisms facilitate the introduction of novel methods to studies of the transport of fungal spores over large distances. Monitoring the migration of airborne fungi using microscope based spore identification is limited when different species produce very similar spores. In our study, DNA-based monitoring with the use of species-specific probes allowed us to track the aerial movements of two important fungal pathogens of oilseed rape (Brassica napus L.), i.e., Leptosphaeria maculans and Leptosphaeria biglobosa, which have identical spore shape and size. The fungi were identified using dual-labelled fluorescent probes that were targeted to a β-tubulin gene fragment of either Leptosphaeria species. Spore identification by Real-Time PCR techniques capable of detecting minute amounts of DNA of selected fungal species was combined with back-trajectory analysis, allowing the tracking of past movements of air masses using the Hybrid Single Particle Lagrangian Integrated Trajectory model. Over a study period spanning the previous decade (2006–2015) we investigated two specific events relating to the long distance transport of Leptosphaeria spp. spores to Szczecin in North-West Poland. Based on the above mentioned methods and the results obtained with the additional spore sampler located in nearby Szczecin, and operating at the ground level in an oilseed rape field, we have demonstrated that on both occasions the L. biglobosa spores originated from the Jutland Peninsula. This is the first successful attempt to combine analysis of back-trajectories of air masses with DNA-based identification of economically important pathogens of oilseed rape in Europe. In our studies, the timing of L. biglobosa ascospore dispersal in the air was unlikely to result in the infection of winter oilseed rape grown as a crop plant. However, the fungus could infect other host plants, such as vegetable brassicas, cruciferous weeds, spring rapeseed and winter rapeseed growing as a volunteer plant.

Cruciferous weeds in oil seed rape – appearance and control

Different cruciferous weeds were drilled in autumn 2011 and 2012 in a field near Munster. Beside common species like hedge mustard (Sisymbrium officinale Scop.), shepherd`s purse (Capsella bursa-pastoris), pennycress (Thlaspiarvense), tall hedge mustard (Sisymbrium loeselii) and flixweed (Descurainia sophia), we tried to establish weeds that are not common on arable land in Germany until now. These were: Yellow rocket (Barbarea vulgaris), hoary cress (Lepidium draba) and Turkish rocket (Bunias orientalis). In autumn 2011 emergence of the sown weeds was poor. In the second year of experiment we got good emergence of the named weeds excluding hoary cress (Lepidium draba). In autumn 2011 and 2012 different herbicidecombinations were applied across the stripes. The best results were achieved with Colzor Trio (clomazone + dimethachlor + napropamid) which was applied in pre-emergence state, a spray sequence Butisan Gold (metazachlor + quinmerac + dimethenamid-P) applied in pre-emergence followed by Salsa (ethametsulfuronmethyl) + Trend (adjuvant) in post-emergence and Clearfield-Vantiga (metazachlor + quinmerac + imazamox) + Dash (adjuvant), also applied in post-emergence state of the weeds.Keywords: Acetolactatsynthase-inhibitors, brassicaceae, chemical control, germination, oil seed rape, outdoorKreuzblutler als Unkrauter im Raps – Aussehen und KontrolleZusammenfassungIm Herbst der Jahre 2011 und 2012 wurden verschiedene Kreuzblutler auf einem Feld in der Nahe von Munster ausgesat. Neben weit verbreiteten Arten wie Wegrauke (Sisymbrium officinale), Hirtentaschelkraut (Capsella bursa-pastoris), Ackerhellerkraut (Thlaspi arvense), Loselsrauke (Sisymbrium loeselii) und Besenrauke (Descurainia sophia), versuchten wir auch Arten zu etablieren, die auf Ackerflachen in Deutschland noch nicht allgemein vertreten sind. Dazu gehorten Barbarakraut (Barbarea vulgaris), Pfeilkresse (Lepidium draba) und Orientalische Zackenschote (Bunias orientalis). Im Herbst des Jahres 2011 liefen nur wenige Unkrauter auf. Im zweiten Versuchsjahr war mit Ausnahme der Pfeilkresse (Lepidium draba) ein guter Aufgang der ausgesaten Unkrauter festzustellen. Quer zu den Unkrautstreifen wurden im Herbst 2011 wie im Herbst 2012 verschiedene Herbizid-Kombinationen ausgebracht. Die besten Ergebnisse konnten mit Colzor Trio, welches im Vorauflauf eingesetzt wurde, einer Spritzfolge aus Butisan Kombi im Vorauflauf, gefolgt von Salsa + Trend im Nachauflauf und Clearfield-Vantiga + Dash, welches auch im Nachauflauf eingesetzt wurde, erzielt werden.Stichworter: Acetolactatsynthase-Hemmer, Brassicaceae-Arten, chemische Kontrolle, Freiland, Keimung, Raps

The relative attractiveness of Brassica napus, B. rapa, B. juncea and Sinapis alba to pollen beetles

It is often suggested that weeds from the same family as the crop plant may increase insect pest damages by providing shelter and additional oviposition opportunities. We compared the relative attractiveness of Brassica rapa L., B. juncea L., Sinapis alba L. and B. napus L. (Capparales: Brassicaceae) to the pollen beetle and its hymenopteran parasitoids in field conditions. Our results revealed that none of the investigated plants increased the pest abundance on B. napus plants. On the contrary, B. juncea and S. alba lured beetles away from B. napus during its damage-susceptible stage. The parasitism rate of pollen beetle larvae was the highest on B. juncea plants, indicating that cruciferous weeds could improve the natural control of the pollen beetle by providing additional hosts for parasitoids. Therefore, close relatives of oilseed rape might be used to trap pollen beetle adults, but also to support populations of natural enemies that could decrease the number of beetles.

Pathogenic and genetic diversity in Plasmodiophora brassicae (clubroot) from Japan

Clubroot disease, caused by Plasmodiophora brassicae Woronin, affects various cruciferous crops. Variations in pathogenicity and virulence are present among field populations of P. brassicae. Many races (pathotypes) have been reported in Japan as well as in other countries using various differential systems. Populations can be classified into four pathotypes using two clubroot-resistant (CR) cultivars of Chinese cabbage as differential hosts in Japan. However, it was recently indicated that each population is often heterogenic and composed of multiple genotypes (races or pathotypes). Breakdown in CR cultivars of Chinese cabbage is a problem in some areas of Japan and may contribute to the selective propagation of minor pathogenic genotypes on the CR cultivars. Clubroot has also been recorded on five species of cruciferous weeds in Japan. In particular, clubroot of Cardamine flexuosa is widely distributed in Japan. Some populations of C. flexuosa are often moderately pathogenic on Chinese cabbage and turnip. Therefore, the epidemiological relationship between clubroot of cruciferous crops and that of the weed has been noted but not thoroughly clarified. The relationship between pathogenic and genetic variations has also been examined among populations from cruciferous crops and weeds in Japan. The result implies an interesting genetic relationship among Williams’ races, among pathotypes determined using CR cultivars of Chinese cabbage and among populations from crops and C. flexuosa. This review includes an introduction of the status of studies on pathogenic and genetic diversity in P. brassicae from Japan.

Broad-scale cruciferous weed patch classification in winter wheat using QuickBird imagery for in-season site-specific control

This article explores the potential use of multi-spectral high-spatial resolution QuickBird imagery to detect cruciferous weed patches in winter wheat fields. In the present study, research was conducted on six individual naturally infested fields (field-scale study: field area ranging between 3 and 52 ha) and on a QuickBird-segmented winter wheat image (broad-scale study: area covering approximately 263 winter wheat fields, approximately 2 656 ha) located in the province of Cordoba (southern Spain). To evaluate the feasibility of mapping cruciferous weed patches in both the field-scale and broad-scale studies, two supervised classification methods were used: the Maximum likelihood classifier (MLC) and vegetation indices. Then, the best classification methods were selected to develop in-season site-specific cruciferous weed patch treatment maps. The analysis showed that cruciferous weed patches were accurately discriminated in both field-scale and broad-scale scenarios. Thus, considering the broad-scale study, classification accuracies of 91.3 and 89.45 % were obtained using the MLC and blue/green (B/G) vegetation indices, respectively. The site-specific treatment maps obtained from the best classifiers indicated that there is a great potential for reducing herbicide use through in-season, cruciferous weed patch site-specific control on both a field-scale and broad-scale. For example, it can be determined that by applying site-specific treatment maps on a broad-scale, herbicide savings of 61.31 % for the no-treatment areas and 13.02 % for the low-dose herbicide areas were obtained.

Black rot-A devastating disease of crucifers: A review

Crucifers are popular temperate vegetables and occupy important place among vegetables in India as well as in the world. India is the second largest producer of crucifers in the world. These crops are affected by many diseases during the growing period which reduce the yield as well as the quality of the produce. Amongst all the diseases, black rot caused by Xanthomonas campestris pv. campestris (Pam.) Dowson is the most destructive one causing heavy losses. The disease affects primarily above ground parts of the plant at any stage of growth and causes high losses, in yield and quality especially in tropical and subtropical regions during the rainy season. All vegetables in the cruciferous family, including broccoli, brussels sprouts, cabbage, cauliflower, chinese cabbage, kale, mustard, radish, rutabaga, and turnip are susceptible to black rot. Many cruciferous weeds such as Shepherd's Purse, wild mustard, and yellow rocket are also known to be hosts of this pathogen. The pathogen is seed borne and also survives in the infected plant debris as well as cruciferous weed hosts. The disease can be managed through cultural practices, resistant hosts, seed treatment with hot water and antibiotics, fungicides, biological control as well as chemical control methods.

Xanthomonas campestris pv. campestris (cause of black rot of crucifers) in the genomic era is still a worldwide threat to brassica crops

Xanthomonas campestris pv. campestris (Xcc) (Pammel) Dowson is a Gram-negative bacterium that causes black rot, the most important disease of vegetable brassica crops worldwide. Intensive molecular investigation of Xcc is gaining momentum and several whole genome sequences are available. Bacteria; Phylum Proteobacteria; Class Gammaproteobacteria; Order Xanthomonadales; Family Xanthomonadacea; Genus Xanthomonas; Species X. campestris. Xcc can cause disease in a large number of species of Brassicaceae (ex-Cruciferae), including economically important vegetable Brassica crops and a number of other cruciferous crops, ornamentals and weeds, including the model plant Arabidopsis thaliana. Black rot is a systemic vascular disease. Typical disease symptoms include V-shaped yellow lesions starting from the leaf margins and blackening of the veins. Collections of Xcc isolates have been differentiated into physiological races based on the response of several brassica species lines. Black rot is a seed-borne disease. The disease is favoured by warm, humid conditions and can spread rapidly from rain dispersal and irrigation water. The control of black rot is difficult and relies on the use of pathogen-free planting material and the elimination of other potential inoculum sources (infected crop debris and cruciferous weeds). Major gene resistance is very rare in B. oleracea (brassica C genome). Resistance is more readily available in other species, including potentially useful sources of broad-spectrum resistance in B. rapa and B. carinata (A and BC genomes, respectively) and in the wild relative A. thaliana. The reference genomes of three isolates have been released. The genome consists of a single chromosome of approximately 5 100 000 bp, with a GC content of approximately 65% and an average predicted number of coding DNA sequences (CDS) of 4308. Three different secretion systems have been identified and studied in Xcc. The gene clusters xps and xcs encode a type II secretion system and xps genes have been linked to pathogenicity. The role of the type IV secretion system in pathogenicity is still uncertain. The hrp gene cluster encodes a type III secretion system that is associated with pathogenicity. An inventory of candidate effector genes has been assembled based on homology with known effectors. A range of other genes have been associated with virulence and pathogenicity, including the rpf, gum and wxc genes involved in the regulation of the synthesis of extracellular degrading enzymes, xanthan gum and lipopolysaccharides. http://www.xanthomonas.org/

Applying Neural Networks to Hyperspectral and Multispectral Field Data for Discrimination of Cruciferous Weeds in Winter Crops

In the context of detection of weeds in crops for site-specific weed control, on-ground spectral reflectance measurements are the first step to determine the potential of remote spectral data to classify weeds and crops. Field studies were conducted for four years at different locations in Spain. We aimed to distinguish cruciferous weeds in wheat and broad bean crops, using hyperspectral and multispectral readings in the visible and near-infrared spectrum. To identify differences in reflectance between cruciferous weeds, we applied three classification methods: stepwise discriminant (STEPDISC) analysis and two neural networks, specifically, multilayer perceptron (MLP) and radial basis function (RBF). Hyperspectral and multispectral signatures of cruciferous weeds, and wheat and broad bean crops can be classified using STEPDISC analysis, and MLP and RBF neural networks with different success, being the MLP model the most accurate with 100%, or higher than 98.1%, of classification performance for all the years. Classification accuracy from hyperspectral signatures was similar to that from multispectral and spectral indices, suggesting that little advantage would be obtained by using more expensive airborne hyperspectral imagery. Therefore, for next investigations, we recommend using multispectral remote imagery to explore whether they can potentially discriminate these weeds and crops.

Airborne multi-spectral imagery for mapping cruciferous weeds in cereal and legume crops

Cruciferous weeds are competitive broad-leaved species that cause losses in winter crops. In the present study, research on remote sensing was conducted on seven naturally infested fields located in Cordoba and Seville, southern Spain. Multi-spectral aerial images (four bands, including blue (B), green (G), red (R) and near-infrared bands) taken in April 2007 were used to evaluate the feasibility of mapping cruciferous patches (Diplotaxis spp. and Sinapis spp.) in winter crops (wheat, broad bean and pea) and compare the accuracy of different supervised classification methods (vegetation indices, maximum likelihood and spectral angle mapper). The best classification method was selected to develop site-specific cruciferous treatment maps. Cruciferous patches were efficiently discriminated with red/blue (R/B) and blue/green (B/G) vegetation indices and the maximum likelihood classifier. At all of the locations, the accuracy of the results obtained from the spectral angler mapper was relatively low. The cruciferous weed-classified imagery of each location were created according to the method that provided the best discrimination results and were used to obtain site-specific treatment maps for in-season post-emergence control measures or herbicide applications for subsequent years. By applying the site-specific treatment maps, herbicide savings from 71.7 to 95.4% for the no-treatment areas and from 4.3 to 12% for the low-dose herbicide were obtained.