Fusarium oxysporum f. sp. lactucae race 4 causes vascular necrosis and wilting of lettuce. First observed in Belgium in 2015, the lack of disease resistance in commercial cultivars allowed this pathogen to spread to nearly the entire Belgian production area within 4 years. Different levels of disease development were observed in different commercial greenhouses. To help explain this variation, we collected 78 Fusarium isolates and characterized them both physiologically and genetically. Molecular race identification indicated that 91% of the isolates belonged to race 4, while 6% of the isolates belonged to race 1, which was not previously reported in Belgium. Pathogenicity assays using differential cultivars confirmed the molecular race assignment of selected isolates. Cultivar Patriot was identified as a suitable new differential cultivar to race 4. Race 4 isolates were more aggressive than race 1 isolates at 24 degrees C, but only when using chlamydospore inoculum instead of a root dip assay containing microconidia. Variation in pathogenicity and aggressiveness of the races may explain differences in disease development in commercial greenhouses. Based on genotyping-by-sequencing (GBS), race 1 and race 4 isolates were highly similar to reference isolates. Fusarium curvatum, F. oxysporum f. sp. tulipae and F. oxysporum f. sp. rhois were phylogenetically separated from F. oxysporum f. sp. lactucae races 1 and 4 based on the GBS data, but not when using multilocus sequence data. Within F. oxysporum f. sp. lactucae race 4, the GBS data differentiated two rather homogeneous groups, suggesting at least two introductions. However, the two groups did not differ in aggressiveness.

Summary Lignin is one of the main factors causing lignocellulosic biomass recalcitrance to enzymatic hydrolysis. Glasshouse‐grown poplars severely downregulated for CINNAMYL ALCOHOL DEHYDROGENASE 1 (CAD1), the enzyme catalysing the last step in the monolignol‐specific branch of lignin biosynthesis, have increased saccharification yields and normal growth. Here, we assess the performance of these hpCAD poplars in the field under short rotation coppice culture for two consecutive rotations of 1 yr and 3 yr. While 1‐yr‐old hpCAD wood had 10% less lignin, 3‐yr‐old hpCAD wood had wild‐type lignin levels. Because of their altered cell wall composition, including elevated levels of cinnamaldehydes, both 1‐yr‐old and 3‐yr‐old hpCAD wood showed enhanced saccharification yields upon harsh alkaline pretreatments (up to +85% and +77%, respectively). In contrast with previous field trials with poplars less severely downregulated for CINNAMYL ALCOHOL DEHYDROGENASE (CAD), the hpCAD poplars displayed leaning phenotypes, early bud set, early flowering and yield penalties. Moreover, hpCAD wood had enlarged vessels, decreased wood density and reduced relative and free water contents. Our data show that the phenotypes of CAD‐deficient poplars are strongly dependent on the environment and underpin the importance of field trials in translating basic research towards applications.

In glasshouses practising monoculture of butterhead lettuce in Belgium, high densities of pin nematodes (Paratylenchusspp.) are frequently associated with reduced plant growth. Growers currently apply chemical soil disinfestation measures to manage this problem, although stricter phytosanitary regulations are forcing a shift towards integrated management. Efficient implementation of such management requires knowledge about the factors influencing nematode population dynamics, and the damage threshold for lettuce. The nematode populations in five Belgian glasshouses were monitored for at least 1 year by frequently soil sampling at 0-30 cm and 30-60 cm depth. An undescribed species ofParatylenchuswas identified in all glasshouses based on morphological and molecular features. High nematode densities (>20,000 (100 ml soil)(-1)) occurred in winter and spring. Chemical soil disinfestation lowered these populations greatly, although up to 14% survived in the deeper soil layer. After soil steaming under negative pressure, no pin nematodes were found. After 2 months of black fallow pin nematode densities were reduced by 50%-76%. Lamb's lettuce, parsley and wild rocket were found to be poor hosts in a pot experiment, while reproduction factors (P-f/P-i) on lettuce cultivars varied between 1 and 3. In three experiments with butterhead lettuce 'Cosmopolia' in pots with a series of 9 or 10 densities ofParatylenchussp. [up to 35,000 (100 ml soil)(-1)], no damage to lettuce heads was observed. However, root weight and root quality were reduced, and the corresponding damage thresholds were rather low [1,754 and 362Paratylenchussp. (100 ml soil)(-1), respectively]. Management strategies such as crop rotation, soil disinfestation or fallow are recommended to avoid pin nematode population build-up.

Basal rot is a common disease in Belgian lettuce, which is mainly controlled by fungicides and chemical soil disinfestation. A seasonal appearance of the basal rot pathogens: Rhizoctonia solani, Sclerotinia spp., Botrytis cinerea and Pythium spp. has been reported, but lettuce growers use standard spraying schemes, irrespective of the occurrence of the pathogen. Due to stricter regulations and environmental concerns the superfluous use of fungicides should be omitted. We investigated if the use of fungicides could be reduced by only controlling the active pathogens. Therefore, lettuce was continuously grown in three glasshouses without any fungal disease control and the active pathogens causing basal rot were identified. The occurrence of basal rot pathogens appeared to be glasshouse specific and the different basal rot pathogens were active throughout the year. However, a seasonal appearance of R. solani anastomosis groups and Pythium spp. was observed with AG4-HGI and Pythium ultimum active at higher temperatures and AG2–1, AG-BI, AG1-IB and Pythium sylvaticum at lower temperatures. We report for the first time the isolation of AG-BI from infected plants. Each R. solani anastomosis group had its own optimal growth rate in vitro. Differences in pathogenicity between R. solani anastomosis groups were observed on detached leaves. AG1-IB and AG4-HGI were most pathogenic, followed by AG2–1 and AG-BI. These results show that the fungicide spraying scheme should be adapted to the occurring pathogens in the glasshouse. This information is of high importance in developing a sustainable control strategy for basal rot pathogens.

Summary The root-lesion nematode, Pratylenchus penetrans, causes growth reduction in glasshouse-grown lettuce and is mainly controlled by chemical soil disinfestation. Integrated management strategies require more knowledge about the population dynamics and damage threshold densities. We monitored the population during 2.5 years in a commercial glasshouse by sampling soil in the same four 1 m2 spots at 0-30 cm and 30-60 cm depth. The grower grew lettuce in rotation with leek, applied 1,3-dichloropropene in summer and left the field fallow during winter. Growing leek reduced the nematode population slightly but chemical soil disinfestation lowered the numbers drastically, although 41% of the nematodes in the deeper layer survived. Black fallow resulted in a slight increase of the population, probably due to hatching. Two pot experiments with ten densities of P. penetrans were conducted to estimate the damage threshold for a summer and autumn cultivar (‘Cosmopolia’ and ‘Brighton’, respectively). The thresholds for lettuce weight were 669 and 3834 P. penetrans (100 ml soil)−1 in summer and autumn, respectively, but with considerable variability in estimated parameters. The thresholds for root damage were much lower: 204 and 48 P. penetrans (100 ml soil)−1. Nematode numbers did not increase on lettuce in the pot tests (maximum multiplication rate was 0.40) but increased slightly in the commercial setting. These results show that populations of P. penetrans build up slowly when butterhead lettuce is rotated with leek and fallow, but chemical soil disinfestation is required to avoid numbers resulting in root damage.

HomePlant DiseaseVol. 102, No. 5First Report of Fusarium oxysporum f. sp. lactucae Race 4 on Lettuce in Belgium PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Fusarium oxysporum f. sp. lactucae Race 4 on Lettuce in BelgiumJ. Claerbout, S. Venneman, I. Vandevelde, A. Decombel, P. Bleyaert, A. Volckaert, J. Neukermans, and M. HöfteJ. ClaerboutSearch for more papers by this author, S. VennemanSearch for more papers by this author, I. VandeveldeSearch for more papers by this author, A. DecombelSearch for more papers by this author, P. BleyaertSearch for more papers by this author, A. VolckaertSearch for more papers by this author, J. NeukermansSearch for more papers by this author, and M. Höfte†Corresponding author: M. Höfte; E-mail: E-mail Address: monica.hofte@ugent.beSearch for more papers by this authorAffiliationsAuthors and Affiliations J. Claerbout , Department of Plants and Crops, Laboratory of Phytopathology, Ghent University, 9000 Gent, Belgium S. Venneman I. Vandevelde , PSKW (Proefstation voor de groenteteelt), 2860 Sint-Katelijne-Waver, Belgium A. Decombel P. Bleyaert , Inagro vzw, 8800 Rumbeke-Beitem, Belgium A. Volckaert J. Neukermans , PCG (Provinciaal Proefcentrum voor de Groenteteelt Oost-Vlaanderen vzw), 9770 Kruishoutem, Belgium M. Höfte † , Department of Plants and Crops, Laboratory of Phytopathology, Ghent University, 9000 Gent, Belgium. Published Online:16 Mar 2018https://doi.org/10.1094/PDIS-10-17-1627-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat In Belgium, lettuce (Lactuca sativa L.) is an important crop that is mainly grown in soil in glasshouses. During autumn 2015, wilting symptoms on butterhead lettuce ‘Halewyn’ (Rijk Zwaan, the Netherlands) and an unknown cultivar were observed in two different commercial glasshouses in the Province of Antwerp, Belgium. The disease incidence was around 10 and 20%, respectively, with a disease severity of 9 and 18%. Since 2015 the disease has spread very fast; already 15% of the glasshouse lettuce production area in Flanders (northern part of Belgium) is infested. Dwarf growth and yellowing of the outer leaves were noticed on affected plants, followed by complete wilting and death. The vascular tissue showed a brown to red discoloration. Affected root and leaf tissues were surface-sterilized with 1% NaOCl for 30 s and washed three times with sterile water. The plant tissues were cut into 1 cm2 pieces and plated on potato dextrose agar amended with streptomycin sulfate (100 mg/liter) and incubated at room temperature (19 to 22°C). Consistently dense fungal colonies with pale cream to purplish mycelia grew out of the plant tissues. Microconidia, macroconidia, and chlamydospores typical for Fusarium oxysporum were observed. Microconidia from isolates Fus1.01 and Fus1.02, coming from the two different glasshouses, measured respectively 5.99 to 8.64 (mean 6.98) × 2.75 to 4.39 (mean 3.32) µm and 6.75 to 11.50 (mean 8.42) × 2.75 to 4.59 (mean 3.61) µm. Chlamydospores were terminal and intercalary, rough walled, and measured 6.86 to 10.72 (mean 8.25) µm for Fus1.01 and 6.13 to 10.80 (mean 8.55) µm for Fus1.02. Macroconidia were straight to slightly curved with three septa and measured 24.49 to 31.27 (mean 27.27) × 2.93 to 4.42 (mean 3.84) µm for Fus1.01 and 20.91 to 26.09 (mean 22.58) × 3.42 to 4.70 (mean 3.98) µm for Fus1.02. Subsequently, DNA from single-spore cultures (Fus1.01 and Fus1.02) was extracted using the Invisorb Spin Plant Mini Kit (Stratec Molecular). The translation elongation factor 1-α (EF1-α) gene was amplified using primers EF1/EF2 (O’Donnell et al. 1998) and sequenced in both directions by LGC Genomics (Berlin) using Sanger sequencing technology. The EF1-α sequences of both isolates showed 100% similarity with the EF1-α sequence of F. oxysporum f. sp. lactucae strain S1 (accession no. DQ837657) (Mbofung et al. 2007) and were deposited (MG599512 and MG599513). By using specific primers FPUF and FPUR (Gilardi et al. 2016), we could show that both isolates belong to race 4. Moreover, pathogenicity tests with three different lettuce cultivars (‘Costa Rica No. 4’, ‘Banchu Red Fire’, and ‘Romana Romabella 30 CN’) provided by Rijk Zwaan (the Netherlands) were conducted to confirm the positive result with the primers FPUF and FPUR and to complete Koch’s postulates. Roots of 2-week-old lettuce plants were dipped in a 5 × 105 spores/ml suspension, and five plants per cultivar were used. The experiment was carried out twice. Inoculated lettuce seedlings were planted in 100 g of steamed potting substrate and were maintained in a climate room at 24°C. In both experiments, wilting was observed after 4 weeks for the cultivars Costa Rica No. 4 and Romana Romabella 30 CN, but no symptoms could be seen on the cultivar Banchu Red Fire. F. oxysporum was consistently reisolated from all inoculated cultivars. These results are consistent with pathogenicity tests carried out before with two isolates of F. oxysporum f. sp. lactucae race 4 from the Netherlands (Gilardi et al. 2016) and indicate that this new race is also the causal agent of Fusarium wilt on lettuce in Belgium. This report shows that race 4 is spreading fast and imposes a serious risk to other lettuce production areas in Europe.References:Gilardi, G., et al. 2016. Plant Pathol. 66:677. https://doi.org/10.1111/ppa.12616 Crossref, ISI, Google ScholarMbofung, G. Y., et al. 2007. Phytopathology 97:87. https://doi.org/10.1094/PHYTO-97-0087 Link, ISI, Google ScholarO’Donnell, K., et al. 1998. Proc. Natl. Acad. Sci. U.S.A. 95:2044. https://doi.org/10.1073/pnas.95.5.2044 Crossref, ISI, Google ScholarDetailsFiguresLiterature CitedRelated Vol. 102, No. 5 May 2018SubscribeISSN:0191-2917e-ISSN:1943-7692 Metrics Article History Issue Date: 20 Apr 2018Published: 16 Mar 2018First Look: 22 Dec 2017Accepted: 19 Dec 2017 Page: 1037 Information© 2018 The American Phytopathological SocietyFundingVLAIOGrant/Award Number: 140984Cited byFusarium isolates from Belgium causing wilt in lettuce show genetic and pathogenic diversity16 November 2022 | Plant Pathology, Vol. 97Discovery and fine mapping of a novel resistance locus to Fusarium wilt race 2 in lettuce (Lactuca sativa L.)29 July 2022 | Euphytica, Vol. 218, No. 8Marulda solgunluğa neden olan Fusarium oxysporum f. sp. lactucae etmenine karşı Metarhizium anisoplae’nın biyokontrol potansiyelinin belirlenmesi31 March 2022 | European Journal of Science and TechnologyFusarium oxysporum f.sp. lactucaeCABI Compendium, Vol. CABI CompendiumGenetic Resistance of Lactuca spp. against Fusarium oxysporum f. sp. lactucae Race 1HortScience, Vol. 56, No. 12Low temperatures favour Fusarium wilt development by race 4 of Fusarium oxysporum f. sp. lactucae12 May 2021 | Journal of Plant Pathology, Vol. 103, No. 3Development of PCR-based marker for resistance to Fusarium wilt race 2 in lettuce (Lactuca sativa L.)31 May 2021 | Euphytica, Vol. 217, No. 6The Population of Fusarium oxysporum f. sp. lactucae in California and ArizonaKelley R. 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Plants have developed a variety of mechanisms to cope with abiotic and biotic stresses. In a previous subcellular localization study of hydrogen peroxide-responsive proteins, two peptides with an unknown function (designated ARACIN1 and ARACIN2) have been identified. These peptides are structurally very similar but are transcriptionally differentially regulated during abiotic stresses during Botrytis cinerea infection or after benzothiadiazole and methyl jasmonate treatments. In Arabidopsis (Arabidopsis thaliana), these paralogous genes are positioned in tandem within a cluster of pathogen defense-related genes. Both ARACINs are small, cationic, and hydrophobic peptides, known characteristics for antimicrobial peptides. Their genes are expressed in peripheral cell layers prone to pathogen entry and are lineage specific to the Brassicaceae family. In vitro bioassays demonstrated that both ARACIN peptides have a direct antifungal effect against the agronomically and economically important necrotrophic fungi B. cinerea, Alternaria brassicicola, Fusarium graminearum, and Sclerotinia sclerotiorum and yeast (Saccharomyces cerevisiae). In addition, transgenic Arabidopsis plants that ectopically express ARACIN1 are protected better against infections with both B. cinerea and A. brassicicola. Therefore, we can conclude that both ARACINs act as antimicrobial peptides.

ABSTRACTGrowth day length, CO2 levels and H2O2 all impact plant function, but interactions between them remain unclear. Using a whole‐genome transcriptomics approach, we identified gene expression patterns responding to these three factors in Arabidopsis Col‐0 and the conditional catalase‐deficient mutant, cat2. Plants grown for 5 weeks at high CO2 in short days (hCO2) were transferred to air in short days (SD air) or long days (LD air), and microarray data produced were subjected to three independent studies. The first two analysed genotype‐independent responses. They identified 1549 genes differentially expressed after transfer from hCO2 to SD air. Almost half of these, including genes modulated by sugars or associated with redox, stress or abscisic acid (ABA) functions, as well as light signalling and clock genes, were no longer significant after transfer to air in LD. In a third study, day length‐dependent H2O2‐responsive genes were identified by comparing the two genotypes. Two clearly independent responses were observed in cat2 transferred to air in SD and LD. Most H2O2‐responsive genes were up‐regulated more strongly in SD air. Overall, the analysis shows that both CO2 and H2O2 interact with day length and photoreceptor pathways, indicating close networking between carbon status, light and redox state in environmental responses.

Poly-ADP-ribose polymerase (PARP) post-translationally modifies proteins through the addition of ADP-ribose polymers, yet its role in modulating plant development and stress responses is only poorly understood. The experiments presented here address some of the gaps in our understanding of its role in stress tolerance and thereby provide new insights into tolerance mechanisms and growth. Using a combination of chemical and genetic approaches, this study characterized phenotypes associated with PARP inhibition at the physiological level. Molecular analyses including gene expression analysis, measurement of primary metabolites and redox metabolites were used to understand the underlying processes. The analysis revealed that PARP inhibition represses anthocyanin and ascorbate accumulation under stress conditions. The reduction in defense is correlated with enhanced biomass production. Even in unstressed conditions protective genes and molecules are repressed by PARP inhibition. The reduced anthocyanin production was shown to be based on the repression of transcription of key regulatory and biosynthesis genes. PARP is a key factor for understanding growth and stress responses of plants. PARP inhibition allows plants to reduce protection such as anthocyanin, ascorbate or Non-Photochemical-Quenching whilst maintaining high energy levels likely enabling the observed enhancement of biomass production under stress, opening interesting perspectives for increasing crop productivity.

Visible light is the basic energetic driver of plant biomass production through photosynthesis. The constantly fluctuating availability of light and other environmental factors means that the photosynthetic apparatus must be able to operate in a dynamic fashion appropriate to the prevailing conditions. Dynamic regulation is achieved through an array of homeostatic control mechanisms that both respond to and influence cellular energy and reductant status. In addition, light availability and quality are continuously monitored by plants through photoreceptors. Outside the laboratory growth room, it is within the context of complex changes in energy and signalling status that plants must regulate pathways to deal with biotic challenges, and this can be influenced by changes in the highly energetic photosynthetic pathways and in the turnover of the photosynthetic machinery. Because of this, defence responses are neither simple nor easily predictable, but rather conditioned by the nutritional and signalling status of the plant cell. This review discusses recent data and emerging concepts of how recognized defence pathways interact with and are influenced by light-dependent processes. Particular emphasis is placed on the potential roles of the chloroplast, photorespiration, and photoreceptor-associated pathways in regulating the outcome of interactions between plants and pathogenic organisms.

The term 'photosynthetic control' describes the short- and long-term mechanisms that regulate reactions in the photosynthetic electron transport (PET) chain so that the rate of production of ATP and NADPH is coordinated with the rate of their utilization in metabolism. At low irradiances these mechanisms serve to optimize light use efficiency, while at high irradiances they operate to dissipate excess excitation energy as heat. Similarly, the production of ATP and NADPH in ratios tailored to meet demand is finely tuned by a sophisticated series of controls that prevents the accumulation of high NAD(P)H/NAD(P) ratios and ATP/ADP ratios that would lead to potentially harmful over-reduction and inactivation of PET chain components. In recent years, photosynthetic control has also been extrapolated to the regulation of gene expression because mechanisms that are identical or similar to those that serve to regulate electron flow through the PET chain also coordinate the regulated expression of genes encoding photosynthetic proteins. This requires coordinated gene expression in the chloroplasts, mitochondria, and nuclei, involving complex networks of forward and retrograde signalling pathways. Photosynthetic control operates to control photosynthetic gene expression in response to environmental and metabolic changes. Mining literature data on transcriptome profiles of C(3) and C(4) leaves from plants grown under high atmospheric carbon dioxide (CO(2)) levels compared with those grown with ambient CO(2) reveals that the transition to higher photorespiratory conditions in C(3) plants enhances the expression of genes associated with cyclic electron flow pathways in Arabidopsis thaliana, consistent with the higher ATP requirement (relative to NADPH) of photorespiration.