Figure 1 - uploaded by Pascal Poupard
Content may be subject to copyright.
Development of Alternaria dauci conidia (isolate P2) on the leaf surface of susceptible carrot cv. Presto (a), or partially resistant cvs Bolero (b) and Texto (c) at 1 day post-inoculation. Leaf samples were stained with methyl blue and observed by light microscopy. A, appressoria-like structure; C, conidium; GT, germ tube.
Source publication
Alternaria leaf blight (ALB), caused by Alternaria dauci, is one of the most damaging foliar diseases of carrot worldwide. The aim of this study was to compare different methods for evaluating levels of carrot resistance to ALB. Three techniques were investigated by comparison with a visual disease assessment control: in vivo conidial germination,...
Context in source publication
Context 1
... dauci conidial germination was observed on leaf surfaces of the three carrot cultivars 1 d.p.i. The per- centage of conidial germination was not significantly dif- ferent from 100% in any of the tested cultivars (data not shown). When considering the mean number of germ tubes per conidium (Fig. 1), the difference between the three cultivars was significant (P<0AE05): the number was lower on cv. Presto (1AE26±0AE18) than cv. Bolero (2AE80±0AE24), and highest on cv. Texto ...
Citations
... The symptoms of this pathogen can be easily confused with the attack of Cercospora carotae. The leaves that are in a very advanced stage of the attack have spots with necrotic appearance of black-brown colour, surrounded by a chlorothic halo (Scott and Wenham, 1972;Boedo et al., 2010). ...
This work is a bibliographic approach to the historical and most recent taxonomy on Alternaria genus. The genus Alternaria consists largely of species of saprophytic, endophytic and parasitic fungi. The United States Fungal host index ranks the genus Alternaria on the 10th place based on the number of host plants, with over 4,000 species. Govind et al. (2016) tells us that most species of this genus are missing the sexual form, with the exception of a few species, which have, in addition to the anamorphic form, the telemorphic form. With the discovery of several species and due to the superficiality of past research, the inclusion of this genus in the taxonomy has become problematic. At the beginning, the taxonomic classification was performed according to the morphology of the species. This bibliographic approach wants to clarify some of the aspects concerning the old and actual taxonomy ambiguities of Alternaria genus. The method used is consulting the scientific literature. The present reclassification of the species was performed by analysing the DNA of each species in 2013 by Woudenberg et al. and fit the Alternaria species in 25 sections. In 2016 Lawrence et al. added 2 other sections and in 2019 Ghafri et al. forms a new section based on the new species Alternaria omanensis. In conclusion Alternaria genus is now divided in 28 sections, each section contains species that are genetically related. Even though most of the ambiguities have been clarified at present, there are still ambiguities regarding the species within and between sections.
... Furthermore, 30 plants were randomly selected and surveyed on each of the producers fields and disease severity was rated on percentage leaf area loss. The disease severity was based on a scale described in Boedoab et al. (2010): where 0 = no disease, 1 = 1 to 25 % leaf infection, 2 = 26 to 50 % leaf infection, 3 = 51 to 75 % leaf infection, 4 = 76 to 100 % leaf infection. Separation of means was done using the least significant difference (LSD) and Fisher's protected test (p ≤ 0.05). ...
Alternaria leaf blight (ALB) has been shown in recent years to be one of the major potential disease threats of sunflower capable of causing yield losses in all major production areas. The aim of this study was to determine the causal agent, prevalence and geographical distribution of ALB in the major sunflower production areas of South Africa. Surveys were conducted during 2012/13, 2013/14 and 2014/15 growing seasons at commercial sunflower production fields and at commercial cultivar trials. In the three growing seasons, twenty-nine sunflower commercial production sites were surveyed for ALB disease severity. Furthermore, four cultivars (AGSUN8251, PHB65A25, SY4200 and PAN7049) were surveyed for ALB during cultivar trials in a total of 25 localities during the three growing seasons. The plants were surveyed between 90 to 120 days after planting and leaves showing ALB symptoms were collected. Alternaria alternata was identified as the primary disease-causing organism of ALB in all the fields. The site Bothaville-Wesselsbron consistently had the lowest ALB disease severity during the 2013/14 and 2014/15 growing seasons, whereas Potchefstroom had the highest disease severity in all three growing seasons. Pearson's correlation coefficient was greatest for temperature (r = 0.6 in 2012/13, r = 0.71 in 2013/14 and r = 0.84 in 2014/15) and disease severity in all the growing seasons. Information about the distribution of sunflower diseases is important and this survey demonstrated that A. alternata is widespread across sunflower production areas in South Africa and may result in potential yield losses.
... (dry rot), Sclerotinia sclerotiorum (sclerotinia rot) and bacteria (bacterial soft rot). Modern strategies of black rot and bacterial soft rot control involve multiple methods, including planting of pathogen free seed, seed testing, seed treatments, crop rotation, scouting, computer forecasting models, applications of fungicides, and appropriate postharvest handling of carrots (Farrar et al., 2004;Survilienė, Valiuškaitė, 2006;Boedo et al., 2010;Collier et al., 2017). Results in the Table 3 show that hybrid 'Jitka' root-crops were the most susceptible (6.0-9.4%) to black rot of carrots and bacterial soft rot (2.5-4.0%) ...
The new carrot (Daucus sativus Röhl.) hybrids ‘Ieva’ and ‘Rokita’ and the garlic (Allium sativum L.) cultivar ‘Dangiai’ were developed at the Institute of Horticulture, Lithuanian Research Centre for Agriculture and Forestry during 2012–2015. The breeding direction was to increase vegetable production and to improve its quality. Carrot roots of the new hybrids have good properties for storage and maintenance of biochemical components. The hybrids ‘Ieva’ and ‘Rokita’ were compared with three foreign hybrids ‘Jitka’, ‘Maestro’ and ‘Champion’. Lithuanian hybrids were distinguished by the highest marketable yield ranging from 64.6 to 66.7 t ha⁻¹. The hybrid ‘Ieva’ accumulated the highest content of carotene 21.8 mg 100 g⁻¹, total sugar 8.6% and dry soluble solids 11.5%. Roots of the hybrid ‘Rokita’ were the most resistant to black rot of carrots and bacterial soft rots. Good adaptability, productivity and a stable number of cloves per bulb is characteristic of the new garlic cultivar ‘Dangiai’. The overwinter survival rate of plants was 98%, the productivity – 14.6 t ha⁻¹ and the average weight per bulb – 75 g. The carrot hybrids ‘Ieva’ and ‘Rokita’ and the garlic cultivar ‘Dangiai’ have been included in the National Plant Variety List and in the EC Common Catalogue of Varieties of Vegetable Species. © 2018, Lithuanian Institute of Agriculture. All rights reserved.
... Known resistant carrot genotypes show classical horizontal resistance, i.e., the resistance is quantitative, with multigenic determinism involving major QTLs (Le Clerc et al., 2015) conferring resistance to a large number of A. dauci isolates. Partially resistant carrot cultivar showed qualitative resistance diversity (Boedo et al., 2010). In other resistance characterization studies (Boedo et al., 2008;Lecomte et al., 2011), we explored several hypotheses including the involvement of chemical warfare in both fungal aggressiveness and plant partial resistance. ...
Qualitative plant resistance mechanisms and pathogen virulence have been extensively studied since the formulation of the gene-for-gene hypothesis. The mechanisms involved in the quantitative traits of aggressiveness and plant partial resistance are less well-known. Nevertheless, they are prevalent in most plant-necrotrophic pathogen interactions, including the Daucus carota–Alternaria dauci interaction. Phytotoxic metabolite production by the pathogen plays a key role in aggressiveness in these interactions. The aim of the present study was to explore the link between A. dauci aggressiveness and toxin production. We challenged carrot embryogenic cell cultures from a susceptible genotype (H1) and two partially resistant genotypes (I2 and K3) with exudates from A. dauci strains with various aggressiveness levels. Interestingly, A. dauci-resistant carrot genotypes were only affected by exudates from the most aggressive strain in our study (ITA002). Our results highlight a positive link between A. dauci aggressiveness and the fungal exudate cell toxicity. We hypothesize that the fungal exudate toxicity was linked with the amount of toxic compounds produced by the fungus. Interestingly, organic exudate production by the fungus was correlated with aggressiveness. Hence, we further analyzed the fungal organic extract using HPLC, and correlations between the observed peak intensities and fungal aggressiveness were measured. One observed peak was closely correlated with fungal aggressiveness. We succeeded in purifying this peak and NMR analysis revealed that the purified compound was a novel 10-membered benzenediol lactone, a polyketid that we named ‘aldaulactone’. We used a new automated image analysis method and found that aldaulactone was toxic to in vitro cultured plant cells at those concentrations. The effects of both aldaulactone and fungal organic extracts were weaker on I2-resistant carrot cells compared to H1 carrot cells. Taken together, our results suggest that: (i) aldaulactone is a new phytotoxin, (ii) there is a relationship between the amount of aldaulactone produced and fungal aggressiveness, and (iii) carrot resistance to A. dauci involves mechanisms of resistance to aldaulactone.
... The most common methods of control include use of clean seed, crop rotation, cultivar selection, and fungicide applications. Partial resistance in some carrot cultivars offers limited protection but still requires frequent fungicide applications (Boedo et al., 2010). There has long been interest in genetic resistance and other nonfungicidal approaches to control of ALB (Farrar et al., 2004). ...
Plant scientists make inferences and predictions from phylogenetic trees to solve scientific
problems. Crop losses due to disease damage is an important problem that many plant breeders would like to solve, so the ability to predict traits like disease resistance from phylogenetic
trees derived from diverse germplasm would be a significant approach to facilitate cultivar improvement. Alternaria leaf blight (ALB) is among the most devastating diseases of carrots (Daucus
spp., Apiaceae) worldwide. Thus, new approaches to identify resistant germplasm to this disease are needed. In a study of 106 accessions of wild and cultivated Daucus and related genera, we determined plant height is the best explanatory variable to predict ALB resistance using a phylogenetic linear regression model. Using the estimated area under the disease progress curve, the most resistant species to ALB were the non-carrot relative Ammi visnaga (L.) Lam. and the wild carrot relative D. crinitus Desf. A permutation tail probability test was conducted considering phylogenetic signal to evaluate the strength of association between the Daucus phylogeny and ALB resistance. We found that species belonging to clade A, which
includes carrots and other Daucus possessing 2n = 18, 20, or 22 chromosomes, are slightly more resistant to ALB than members of other clades of the Daucus phylogeny.
... In the case of the carrot-A. dauci pathosystem, several resistance mechanisms seem to be involved (Boedo et al., 2010), including the jasmonic acid pathway (Lecomte et al., 2011), and defense molecules (Lecomte et al., 2012). Here, we explore the role of toxin resistance in the carrot-A. ...
Alternaria leaf blight, caused by the necrotrophic fungus Alternaria dauci, is the most damaging foliar disease in carrot production. Fungicide use has variable efficiency, and presents economic and ecological costs. Popular partially resistant cultivars exist, but their resistance level is still unsatisfactory. A better knowledge on carrot A. dauci resistance mechanisms may help to produce more resistant cultivars faster. More generally, partial resistance mechanisms in plants are still poorly understood. In order to better understand partial resistance to leaf blight in carrot, we implemented an a priori approach, investigating the role of different resistance mechanisms in the carrot-A. dauci interaction. It has been suggested that Alternaria dauci produces toxins, such as zinniol. The work presented here is centered on the role played by these toxins in the plant-fungus interaction, and more especially plant resistance. Plant cell suspensions from several genotypes were treated with raw fungal extracts. A good correlation was found between whole plant resistance to the fungus and metabolic activity of the cell suspensions after 48 h of exposure. Similar results were obtained using different techniques and different exposure times. Additionally, it was found that the toxicity of fungal extracts was due to secreted apolar compounds, which did not include zinniol. Zinniol is only produced when the fungus is grown in anoxic conditions. Nevertheless, fungal growth condition and zinniol content do not impact extract toxicity. Moreover, zinniol was not toxic to plant cells at physiological concentration.
... Differences in aggressiveness among A. dauci isolates collected worldwide has, however, never been investigated. In previous papers focusing on different aspects of A. dauci -carrot interactions, such as infection processes, ALB resistance evaluation or genetic determinism (Dugdale et al., 2000;Pawelec et al., 2006;Boedo et al., 2008Boedo et al., , 2010Le Clerc et al., 2009), only one or two isolates were generally used. It would be very important to assess the aggressiveness of A. dauci isolates before using them in future studies. ...
... The first objective of the present study was to compare the aggressiveness of a set of A. dauci isolates after inoculation of a susceptible carrot cultivar which had previously been used as a positive disease control in several studies (Ben-Noon et al., 2001;Pawelec et al., 2006;Boedo et al., 2008Boedo et al., , 2010Le Clerc et al., 2009). For that purpose, A. dauci isolates were chosen from a worldwide collection of this fungal species to represent high diversity according to geographic origin and polymorphism in the intergenic spacer (IGS) regions of nuclear rDNA. ...
... Caporal) were used (Table 1). FRA001 and FRA017 were chosen as reference isolates because of their use in previous studies (Pawelec et al., 2006;Boedo et al., 2008Boedo et al., , 2010Le Clerc et al., 2009). For production of conidia, fungal isolates were grown in Petri dishes on V8 juice agar medium (200 mL V8 vegetable juice, 3 g CaCO 3 , 15 g agar L )1 , pH 6AE8), incubated in darkness at 22 ± 2°C for 7 days, and then exposed to 12 h nearultraviolet light (Philips, TL-D 36 W) alternating with 12 h darkness at 22 ± 2°C for 10-15 days. ...
The host range of Alternaria dauci was investigated in a greenhouse. Two strains were inoculated onto nine cultivated Apiaceae species, two wild Daucus species and six cultivated non-Apiaceae species representing six botanic families. Lesions of various intensities were observed on all dicot species, but no symptoms developed on the two monocots studied. Typical A. dauci conidia were observed after in vitro incubation of necrotic leaves. Fungal strains were isolated from lesions and A. dauci was diagnosed on the basis of conidium morphology and specific conventional PCR findings. Genotyping of individual isolates performed with microsatellite markers confirmed the presence of the inoculated strain. Our results strongly suggest that species other than carrot can be alternative hosts. Those results are important to consider for a better management of Alternaria leaf blight in carrot fields.
... L'évaluation du taux d'envahissement des tissus par qPCR permet également de cibler la phase pré-symptomatique et plus particulièrement, le degré d'envahissement des tissus de la plante par le champignon. Boedo et al. (2010) ont montré que 15 jours après inoculation, la masse fongique est significativement plus importante chez le génotype sensible Presto que chez deux génotypes résistants, Boléro et Texto. L'optimisation du protocole qPCR permet d'utiliser des plaques PCR 384 puits, un volume réactionnel réduit, et une extraction d'ADN avec le kit PL2-PL3 de la société Macherey Nagel. ...
... Tableau 1 : Comparaison de l'évolution de la maladie et du dosage in planta d'A. dauci par QPCR pour un génotype sensible (H1), trois partiellement résistants (H4, I2, et K3) et deux témoins commerciaux (B : variété Boléro résistante et P : variété sensible Presto) inoculés selon la méthode par goutte(Boedo et al., 2010) Un test d'inoculation en gouttes sur feuille non détachée a également été développé parBoedo et al. (2010) permettant de caractériser la résistance des génotypes à Alternaria dauci. Ce test miniaturisé est réalisé en serre en analysant 5 plantes par génotype. ...
... Tableau 1 : Comparaison de l'évolution de la maladie et du dosage in planta d'A. dauci par QPCR pour un génotype sensible (H1), trois partiellement résistants (H4, I2, et K3) et deux témoins commerciaux (B : variété Boléro résistante et P : variété sensible Presto) inoculés selon la méthode par goutte(Boedo et al., 2010) Un test d'inoculation en gouttes sur feuille non détachée a également été développé parBoedo et al. (2010) permettant de caractériser la résistance des génotypes à Alternaria dauci. Ce test miniaturisé est réalisé en serre en analysant 5 plantes par génotype. ...
... This requires the precise identification of the QTLs responsible for different resistance factors likely to be efficient in different genetic backgrounds. The evaluation of genetic variation of carrot resistance to Alternaria dauci has been performed in different environments, mainly in field studies in Brazil (Vieira et al. 1991;Boiteux et al. 1993), the USA (Simon and Strandberg 1998), and France (Le Clerc et al. 2009Clerc et al. , 2015 or in greenhouses and laboratories (Pawelec et al. 2006;Boedo et al. 2010). However, genetic loci associated with variation in resistance were only evaluated with a biparental population by Le Clerc et al. (2009). ...
... However until now, the mechanism underlying this lower progression has still not been elucidated. There is probably more than one mechanism involved, as suggested by previous results on these accessions or others (Le Clerc et al. 2009;Boedo et al. 2010;Lecomte et al. 2014) such as the limitation of fungal spore germination on different genotypes, the speed of colonization and the differential resistance to fungal toxins. More investigations are under current progress. ...
Key message
Combining biparental and multiparental connected population analyses was useful for the identification of 11 QTLs in two new genetic backgrounds of carrot resistance to
Alternaria dauci
and for breeding recommendations.
Abstract
Leaf blight due to the fungus Alternaria dauci is the major carrot foliar disease worldwide. Some resistance QTLs have been previously identified in one population, but the evaluation of additional genetic backgrounds with higher level of resistance would give opportunities for breeders to combine them by pyramiding. For this purpose, two segregating populations were evaluated twice across 4 years in the same environment (1) to compare the efficiency of the single vs. the connected populations approach for characterizing the new sources of carrot resistance to Alternaria dauci; (2) to evaluate the stability of QTLs over the years; and (3) to give recommendations to breeders for marker-assisted selection. Single and connected analyses were complementary; their combination allowed the detection of 11 QTLs. Connected analyses allowed the identification of common and specific QTLs among the two populations and the most favorable allele at each QTL. Important contrasts between allelic effects were observed with four and five most favorable alleles coming from the two resistant parental lines, whereas two other favorable alleles came from the susceptible parental line. While four QTLs were consistent across years, seven were detected within a single year. The heritabilities for both populations PC2 and PC3 were high (75 and 78 %, respectively), suggesting that the resistance of carrot to A. dauci was little affected by these environmental conditions, but the instability of QTL over years may be due to changing environmental conditions. The complementarity between these parental lines in terms of interesting allelic combinations is also discussed.
... The Daucus carota genotypes used in this study were Bolero, Presto, K3, I2, H4 and H1. Bolero and Presto are Nantaise type hybrid cultivars used as standards for resistance and susceptibility, respectively, as in [17,38], while K3, I2, H4 and H1 are breeding material. H1 plants were obtained by self-pollinating a single plant of a susceptible S3 line obtained from French genetic background at Vilmorin (France). ...
... H4 was obtained from a partially resistant South American cultivar. All fungal material used in this study was from the A. dauci reference strain FRA017, which was also used in previous studies [33,38,39]. This strain was isolated in 2000 from naturally infected carrot leaves collected in Gironde, France. ...
... All plant cultivation and inoculation procedures have already been described in detail in [39] (plant cultivation) and [38] (fungus cultivation, inoculum production, drop inoculation). Briefly, plants were grown in greenhouse conditions in boxes containing peat moss/sand mixture for 6 weeks. ...
Although different mechanisms have been proposed in the recent years, plant pathogen partial resistance is still poorly understood. Components of the chemical warfare, including the production of plant defense compounds and plant resistance to pathogen-produced toxins, are likely to play a role. Toxins are indeed recognized as important determinants of pathogenicity in necrotrophic fungi. Partial resistance based on quantitative resistance loci and linked to a pathogen-produced toxin has never been fully described. We tested this hypothesis using the Alternaria dauci - carrot pathosystem. Alternaria dauci, causing carrot leaf blight, is a necrotrophic fungus known to produce zinniol, a compound described as a non-host selective toxin. Embryogenic cellular cultures from carrot genotypes varying in resistance against A. dauci were confronted with zinniol at different concentrations or to fungal exudates (raw, organic or aqueous extracts). The plant response was analyzed through the measurement of cytoplasmic esterase activity, as a marker of cell viability, and the differentiation of somatic embryos in cellular cultures. A differential response to toxicity was demonstrated between susceptible and partially resistant genotypes, with a good correlation noted between the resistance to the fungus at the whole plant level and resistance at the cellular level to fungal exudates from raw and organic extracts. No toxic reaction of embryogenic cultures was observed after treatment with the aqueous extract or zinniol used at physiological concentration. Moreover, we did not detect zinniol in toxic fungal extracts by UHPLC analysis. These results suggest that strong phytotoxic compounds are present in the organic extract and remain to be characterized. Our results clearly show that carrot tolerance to A. dauci toxins is one component of its partial resistance.
