Lactuca Species Research Articles

Lactuca super-pangenome reduces bias towards reference genes in lettuce research

BackgroundBreeding of lettuce (Lactuca sativa L.), the most important leafy vegetable worldwide, for enhanced disease resistance and resilience relies on multiple wild relatives to provide the necessary genetic diversity. In this study, we constructed a super-pangenome based on four Lactuca species (representing the primary, secondary and tertiary gene pools) and comprising 474 accessions. We include 68 newly sequenced accessions to improve cultivar coverage and add important foundational breeding lines.ResultsWith the super-pangenome we find substantial presence/absence variation (PAV) and copy-number variation (CNV). Functional enrichment analyses of core and variable genes show that transcriptional regulators are conserved whereas disease resistance genes are variable. PAV-genome-wide association studies (GWAS) and CNV-GWAS are largely congruent with single-nucleotide polymorphism (SNP)-GWAS. Importantly, they also identify several major novel quantitative trait loci (QTL) for resistance against Bremia lactucae in variable regions not present in the reference lettuce genome. The usability of the super-pangenome is demonstrated by identifying the likely origin of non-reference resistance loci from the wild relatives Lactuca serriola, Lactuca saligna and Lactuca virosa.ConclusionsThe super-pangenome offers a broader view on the gene repertoire of lettuce, revealing relevant loci that are not in the reference genome(s). The provided methodology and data provide a strong basis for research into PAVs, CNVs and other variation underlying important biological traits of lettuce and other crops.

Oilseed Cakes: A Promising Source of Antioxidant, and Anti-Inflammatory Agents-Insights from Lactuca sativa.

This study evaluated the antioxidant and antibacterial properties of methanolic extracts derived from oilseed cakes of Lactuca sativa (lettuce), Nigella sativa (black seed), Eruca sativa (rocket), and Linum usitatissimum (linseed). Lettuce methanolic extract showed the highest potential, so it was selected for further investigation. High-performance liquid chromatography (HPLC-DAD) analysis and bioassay-guided fractionation of lettuce seed cake extract led to the isolation of five compounds: 1,3-propanediol-2-amino-1-(3',4'-methylenedioxyphenyl) (1), luteolin (2), luteolin-7-O-β-D-glucoside (3), apigenin-7-O-β-D-glucoside (4), and β-sitosterol 3-O-β-D-glucoside (5). Compound (1) was identified from Lactuca species for the first time, with high yield. The cytotoxic effects of the isolated compounds were tested on liver (HepG2) and breast (MCF-7) cancer cell lines, compared to normal cells (WI-38). Compounds (2), (3), and (4) exhibited strong activity in all assays, while compound (1) showed weak antioxidant, antimicrobial, and cytotoxic effects. The anti-inflammatory activity of lettuce seed cake extract and compound (1) was evaluated in vivo using a carrageenan-induced paw oedema model. Compound (1) and its combination with ibuprofen significantly reduced paw oedema, lowered inflammatory mediators (IL-1β, TNF-α, PGE2), and restored antioxidant enzyme activity. Additionally, compound (1) showed promising COX-1 and COX-2 inhibition in an in vitro enzymatic anti-inflammatory assay, with IC50 values of 17.31 ± 0.65 and 4.814 ± 0.24, respectively. Molecular docking revealed unique interactions of compound (1) with COX-1 and COX-2, suggesting the potential for targeted inhibition. These findings underscore the value of oilseed cakes as a source of bioactive compounds that merit further investigation.

Differential Sources of Resistance from Lactuca serriola Against Three Races of Xanthomonas hortorum pathovar vitians (Brown, 1918) Morinière et al. 2020 Causing Bacterial Leaf Spot of Lettuce.

Bacterial leaf spot (BLS) of lettuce (Lactuca sativa L.) is caused by the bacterium Xanthomonas hortorum pv. vitians which is hypothesized to have at least three races of the pathogen present in North America as defined by their differential resistance phenotypes in lettuce cultivars/accessions. Though resistance to X. hortorum pv. vitians race 1 has been identified in cultivated lettuce, numerous other X. hortorum pv. vitians strains cause disease on cultivars carrying this resistance locus. Thus far, resistance to these 'additional' X. hortorum pv. vitians strains has not been adequately described in L. sativa or in any other wild Lactuca species sexually compatible with cultivated lettuce. We have performed an extensive screening of approximately 500 Lactuca accessions from L. sativa, L. serriola, L. saligna, L. virosa, L. aculeata, L. altaica, and L. perennis species to identify accessions resistant to these additional X. hortorum pv. vitians races. Following the initial screenings, greenhouse tests confirmed that X. hortorum pv. vitians race 2 and race 3 could be defined using Lactuca sativa accessions. Race 2 strain BS3217 had an incompatible response (hypersensitive response) on ten Lactuca serriola accessions including PI491114 and PI491108, while race 1 (BS0347) and race 3 (BS2861) strains of X. hortorum pv. vitians showed a compatible response (disease) on these genotypes. L. serriola accession ARM09-161 (and selections derived from it) was the only genotype resistant to the race 3 strain BS2861. L. serriola accessions identified in this study to be resistant to race 2 and race 3 of X. hortorum pv. vitians, together with race 1 resistant cultivars, can be used for pyramiding resistance loci against the three races of the BLS-causing pathogen.

Comparison of Anticancer, Antioxidant, Enzyme Inhibitory Effects and Phytochemical Contents Between Edible Lettuce (Lactuca sativa) and a New Wild Species (Lactuca anatolica).

In this study, the bioactive components, enzyme inhibitory, antioxidant and anticancer potentials of edible (L. sativa) and a new species (L. anatolica) of Lactuca were evaluated and compared. The quantitative analyzes of the bioactive components of L. sativa (LS) and L. anatolica (LA) were analyzed quantitatively by GC-MS and Orbitrab HPLC-HRMS. Antioxidant, enzyme inhibitory and anticancer properties were analyzed by various assays. In general, LA exhibited more stronger antioxidant properties compared to LS. The extracts showed similar inhibitory effects on these enzymes. It was determined that LS was dominant in terms of linoleic acid (23.71 %), while LA contained a high level of α-linolenic acid (31.70 %). LA and LS inhibited the viability of A549 and MCF-7 cells in a dose-dependent manner. IC50 values for LA, LS and cisplatin were determined as 120.3, 197.5, 4.3 μg/mL in A549 cell line and 286.2, 472.8, 7.2 μg/mL in MCF-7 cell line, respectively. It was revealed that LA and LS treatment at 50 μg/mL concentrations in A549 cells completely suppressed the colony forming capacity, and treatment with IC50 doses inhibited cell migration, and triggered apoptosis by regulating caspase-3, cPARP, p53 and p21. The findings of this study suggested that these species have significant pharmacological potential.

Genetic diversity of Ulva lactuca from the intertidal zone in Ulee Lheue beach Aceh, Indonesia

Ulee Lheue Beach in Banda Aceh was developed for tourism. The macroalgae and seaweed species found in this area have been widespread but never exploited. Among these species is the green seaweed, Ulva lactuca, commonly known as sea lettuce. The physiological variations and genetic features of the seaweed can be attributed to the variations in the coastal environment. This study aims to describe the molecular identity of the genetic diversity of U. lactuca from the intertidal zone at Ulee Lheue Beach. The development of molecular biotechnology has enabled identification the gene expression through genomic DNA to PCR amplification. Genetic distance was determined using UPGMA. The results from 600-bp fragments were analyze the genetic diversity. A total of 15 (31%) expression identified as polymorphic (0.500). Heterozygosity (He) and allelic differential (Na) diversity were found of 1.500–3.000. The highest PIC was observed in the rbcL1, with a correlation between subpopulations of 0.459. PCR amplification using the degenerate primer rbcL1 produced fragments ranging from 300 to 460 bp, whereas the expression of UL2 was detected at 448 and 500 bp using the rbcL2 primer. The phylogenetic identify are shown two (2) clusters. The populations of UL1, UL3, and UL4 were found a close relationship. Furthermore, the UL1 and UL2 populations were further divided into distinct clusters but related to the main branch of UL3. Based on this research, the concern of U. lactuca species for industrial and biotechnology destinations, we can describe a suitable method for obtaining he genetic distances between species.

Extraction of Cellulose from Ulva lactuca Algae and Its Use for Membrane Synthesis.

Green algae are a sustainable source of biopolymers for the global demand due to their high photosynthetic efficiency. This article describes the extraction of cellulose from plant systems represented by Ulva lactuca species. In order to extract various substances, algae were finely ground with the help of solvents (liquid media). This was carried out to achieve the necessary conditions that help reduce the resistance this phase shows in regard to the transport and transfer of the species being extracted. The highest yield of extracted cellulose (20,944%) was obtained for the following factors: S/L = 1/20; conc. ethanol = 90%, conc. salts = 4 g/L. Hydrogel membranes are a unique class of macromolecular networks that contain a large fraction of aqueous solvent within their structure. With the cellulose extracted from algae, we obtained membranes which underwent the process of swelling in liquid media (ethyl alcohol) of different concentrations. The swelling of biocellulose membranes in alcoholic solutions of high concentrations was investigated. It was observed that the process of absorption of the alcoholic solution by the membrane occurred rapidly in the first part. After stabilization, the membranes continued to absorb at a slower rate until stabilization or saturation concentration was reached.

Contribution to the knowledge of Lactuca L. (Asteraceae) in the United Arab Emirates

We present new data on the distribution of Lactuca species and review the currently documented data on the genus in the United Arab Emirates (UAE). L. serriola L. is recorded for the first time from Abu Dhabi Emirate. L. dissecta D. Don, L. serriola, and L. orientalis (Boiss.) Boiss. were already reported from other emirates. Detailed morphological descriptions, types, distribution maps, and a key to Lactuca species in the UAE are included. We also highlight the deficiency of the documentation with herbarium specimens in the UAE.

Genome assembly and analysis of Lactuca virosa: implications for lettuce breeding.

Lettuce (Lactuca sativa L.) is a leafy vegetable crop with ongoing breeding efforts related to quality, resilience, and innovative production systems. To breed resilient and resistant lettuce in the future, valuable genetic variation found in close relatives could be further exploited. Lactuca virosa (2x = 2n = 18), a wild relative assigned to the tertiary lettuce gene pool, has a much larger genome (3.7 Gbp) than Lactuca sativa (2.5 Gbp). It has been used in interspecific crosses and is a donor to modern crisphead lettuce cultivars. Here, we present a de novo reference assembly of L. virosa with high continuity and complete gene space. This assembly facilitated comparisons to the genome of L. sativa and to that of the wild species L. saligna, a representative of the secondary lettuce gene pool. To assess the diversity in gene content, we classified the genes of the 3 Lactuca species as core, accessory, and unique. In addition, we identified 3 interspecific chromosomal inversions compared to L. sativa, which each may cause recombination suppression and thus hamper future introgression breeding. Using 3-way comparisons in both reference-based and reference-free manners, we show that the proliferation of long-terminal repeat elements has driven the genome expansion of L. virosa. Further, we performed a genome-wide comparison of immune genes, nucleotide-binding leucine-rich repeat, and receptor-like kinases among Lactuca spp. and indicated the evolutionary patterns and mechanisms behind their expansions. These genome analyses greatly facilitate the understanding of genetic variation in L. virosa, which is beneficial for the breeding of improved lettuce varieties.

Genome of the epiphytic bacterium Achromobacter denitrificans strain EPI24, isolated from a macroalga located in the Colombian Caribbean

Marine macroalgae are being recognized as reservoirs of biologically active compounds, as their surfaces are susceptible to the colonization of microorganisms which can produce enzymes with a wide range of molecular architectures. Among these bacteria, Achromobacter is responsible for the biosynthesis of laccases. In this research, we performed a bioinformatic pipeline to annotate the sequenced complete genome of the epiphytic bacterium Achromobacter denitrificans strain EPI24, from the macroalgal surface of the Ulva lactuca species; this strain showed laccase activity which has been previously assessed on plate assays. The genome of A. denitrificans strain EPI24 has a size of ∼6.95 Mb, a GC content of 67.33%, and 6,603 protein-coding genes. The functional annotation of the A. denitrificans strain EPI24 genome confirmed the presence of genes encoding for laccases, which could have functional properties of interest in processes such as the biodegradation of phenolic compounds under versatile and efficient conditions.

Comparison of the Allelopathic Potential of Non-Native and Native Species of Mediterranean Ecosystems.

Allelopathy is a frequent interaction between species in Mediterranean ecosystems and it is also one of the proposed strategies to explain the colonisation of invasive species. To confirm the importance of allelopathic potential as a mechanism of invasion of non-native species in Mediterranean ecosystems, it would be advisable to compare the allelopathic effects of non-native plants with native plants on the same target species and thus avoid overestimating the role of phytotoxicity in the invasion process. The main objective of this work was to compare the allelopathic activity of native species typical of Mediterranean ecosystems, classified as allelopathic, with the allelopathic activity of non-native species that may have an invasive character in these ecosystems. To this end, we selected three native species (Cistus ladanifer, Pistacia lentiscus, and Pistacia terebithus) and three non-native species (Acacia dealbata, Acer negundo, and Salix babylonica), and we analysed their effect on the species Lactuca sativa and the native species Lavandula stoechas and Echium plantagineum. The tests on L. sativa showed that all species have allelopathic activity. The tests on L. stoechas and E. plantagineum revealed that P. terebinthus exerted the greatest effect, being the only species that maintained an inhibitory effect at extract concentrations of 50% and 25% in all the analysed parameters, except in germination and cotyledon emergence for E. plantagineum. There were no significant differences in the effect on germination between non-native and native species, although significant differences were found in the effect on root size in the three analysed concentrations, with the native species producing greater inhibition. In conclusion, these species exert a negative effect on the selected native target species, but the negative effect of the native species is greater than that of the non-native species. These results indicate that it is important to compare the allelopathic effects of invasive and native species to correctly estimate the phytotoxic effect of invasive species on their invasiveness.

Chemical composition of different plant part from Lactuca serriola L.- focus on volatile compounds and fatty acid profile.

The family Asteraceae comprises many species that have medicinal importance in terms of their chemical components. Some species of the genus Lactuca have been used in folk medicine for a long time ago. One of them is L.serriola L., a wild plant that is a weed in agriculture. To date, few studies have been published on its chemical profile. In this research, we investigated the volatile compounds andfatty acids of L.serriola roots, leaves, and seeds. To this end, a microsteam distillation-solid phase microextraction technique (MSD-SPME) followed by a gaschromatography-mass spectrometry analysis was performed. Aldehydes and terpenoids were predominantly present in the leaves with phenylacetaldehyde as the major compound (up to 18%) while2-ethyl hexanol (up to 36.9%) was the most abundant substance in the roots. Among the fatty acids, nonadecanoic acid (38.3%) was the main one detected in the leaves, while linoleic acid (57.7%) was predominant in the seeds. Some ofthe detected constituents have already demonstrated importance in medicinal and industrial areas. As a result, this species could be further investigated for its biological features and be considered as a source of ingredients beneficial in different fields, including pharmaceuticals.

Bioengineered intestinal tubules as a tool to test intestinal biological efficacy of lettuce species

Lettuce (Lactuca sativa) is one of the most consumed and cultivated vegetables globally. Its breeding is focused on the improvement of yield and disease resistance. However, potential detrimental or beneficial health effects for the consumer are often not targeted in the breeding programs. Here, a bioengineered intestinal tubule was used to assess the intestinal efficacy of extracts from five plant accessions belonging to four Lactuca species. These four species include the domesticated L. sativa, closely related wild species L. serriola, and phylogenetically more distant wild relatives L. saligna and L. virosa. We assessed the epithelial barrier integrity, cell viability, cell attachment, brush border enzyme activity, and immune markers. Extracts from L. sativa cv. Salinas decreased cell attachment and brush border enzyme activity. However, extracts from the non-edible wild species L. saligna and L. virosa reduced the epithelial barrier functions, cell attachment, cell viability, and brush border enzyme activity. Since wild species represent a valuable germplasm pool, the bioengineered intestinal tubules could open ways to evaluate the safety and nutritional properties of the lettuce breeding material originating from crosses with wild Lactuca species.

Plastome-based phylogeny and biogeography of Lactuca L. (Asteraceae) support revised lettuce gene pool categories.

This study generated and analyzed complete plastome and internal transcribed spacer (ITS) data of 46 Lactuca species, 13 African endemic (AE) Lactuca species, and 15 species from eight related genera in Lactucinae. The new plastome and nuclear ITS sequences were then used to reconstruct the phylogenetic relationships of Lactuca species. The whole-plastome data were used to estimate divergence time and ancestral area reconstruction of the identified major Lactuca lineages. The results showed that Lactuca species are generally similar in plastome size, Guanine and Cytosine (GC) content, gene structure, and categories, although crop lettuce (Lactuca sativa L.) and its gene pool relatives were found to have one unique pseudogene (ψ ndhF), and accD, atpF, cemA, clpP, and rpl22 showed signs of positive selection. Our phylogenomic analysis demonstrated that Lactuca is monophyletic after excluding Lactuca alatipes Collett and Hemsl and AE Lactuca species. AE Lactuca species are morphologically distinct from core Lactuca lineage and need to be excluded from Lactua. The core Lactuca species most likely originated from Asia-Temperate W ~6.82 Mya and then dispersed globally and formed nine clades. Finally, the lettuce gene pool concept was amended according to the phylogenetic and historical biogeographic analyses. This study revised the circumscription of Lactuca, revealed robust phylogenetic relationships within the genus, and provided insights into Lactucinae phylogeny. The lettuce gene pool species could be used as potential genetic resources for lettuce breeding.

Gas chromatography – mass spectrometry analysis of acetone extract of Lactuca tatarica (L.) C. A. Mey. roots

Research work is devoted to the chemical investigation of the roots of the Lactuca tatarica (L.) C. A. Mey. by gas chromatography – mass spectrometry method. From the crude extract that is obtained from the roots, the presence of natural compounds of various groups has been detected. As a result, 25 different substances including acyclic compounds (methyl myristate, palmitic acid methyl ester, ethyl palmitate, methyl elaidate, methyl stearate, ethyl oleate, etc.) have been identified from the solid mass of the research object. The most abundant fatty acid esters are methyl oleate (6.831 %) and palmitic acid methyl ester (2.902 %). In addition, the triterpenoid compounds (lupeol acetate, cycloartenol acetate, 3β,13β,14β-13, 27-cycloursan-3-ol acetate) which are characteristic of the L. tatarica have been identified. Lupeol acetate is the predominant component which makes up 56.35 % of the whole obtained substances. Elaidic acid which belongs to the fatty acids group, bis(2-ethylhexyl)phthalate which belongs to the aromatic dicarboxylic acid esters and other compounds have also been identified. Among the identified substances, some are found previously from the other species of the genus Lactuca L. but with regards to the L. tatarica to the best of our knowledge the majority of them are firstly being reported in this study. The investigated plant is widespread in the lowlands and coastal areas of Azerbaijani flora. The availability of some pharmacological effective compounds (lupeol acetate, 3β,13β,14β-13, 27-cycloursan-3-ol acetate, olean-12-en-3-yl acetate) makes the research significant in terms of chemical aspect. Therefore, the results of this investigation open up new horizons for future studies in various fields including the pharmaceutical one.

Optimisation of Vitamin B12 Extraction from Green Edible Seaweed (Ulva lactuca) by Applying the Central Composite Design.

Vitamin B12, only found naturally in animal-based foods, is essential for brain functions and various chemical reactions in the human body. Insufficient vitamin B12 leads to vitamin B12 deficiency, common among strict vegetarians due to their limited intake of animal-based foods. Nevertheless, extensive studies have demonstrated that macroalgae, specifically the Ulva lactuca species, are rich in vitamin B12 and could be further exploited in future dietary applications. In the current study, the ideal extraction method of vitamin B12 from dried U. lactuca was developed and optimised to achieve the maximum vitamin B12 yield. The effects of several extraction parameters, including the solvent-to-solvent, methanol:water (MeOH:H2O), and solute-to-solvent ratios, and pH on the total vitamin B12 content were analysed through a two-level factorial and central composite design. The highest vitamin B12 content, particularly cyanocobalamin (CN-Cbl), was recovered through the ultrasonic-assisted extraction (UAE) of oven-dried U. lactuca at 3 g:60 mL of solute-to-solvent and 25:75% of MeOH to H2O ratios at pH 4. The extraction of CN-Cbl from oven-dried U. lactuca that employed the UAE method has elevated CN-Cbl content recovery compared to other extraction methods.

Pollen Morphology of Lactuca L. (s. lat.) (Cichorieae - Asteraceae) from Hindukush, Western Himalyan and Karakorum Ranges and its taxonomic significance

ABSTRACT Pollen morphology of 15 species of the genus Lactuca L. (s. lat.) of the tribe Cichorieae from the Hindukush, Western Himalayan and Karakorum Ranges has been studied using Light microscope (LM) and Scanning Electron Microscope (SEM). Pollen morphology of six species viz., L. erostrata Bano & Qaiser, L. glaucifolia Boiss., L. persica Boiss., L. crambifolia (Bunge) Boiss., L. chitralensis (Tuisl.) Ghafoor, Qaiser & Roohi Bano and L. picridiformis Boiss., was never studied before. Pollen were found to be isopolar, spheroidal to oblate-spheroidal, elliptic to rarely circular in equatorial view, hexagonal in polar view, trizonocolporate and echinolophate with 15 lacunae. Morphometric analysis of the pollen characters was conducted using Agglomerative cluster analysis with Euclidean distance and Ward’s method to compute the dissimilarity matrix, and a dendogram was prepared. Two pollen-types primarily based on the diameter of polar and equatorial axis of the pollen grain were recognized. Keys to the pollen types, subtypes and to the species are provided. The present palynological findings to a greater extent are in agreement with the results of current phylogenetic studies based on molecular evidences. Moreover, both the pollen types are well correlated with the general morphology of the investigated species of the genus Lactuca L. (s.lat) and provided additional micromorphological characters for the delimitation of the species.

SEAFEEDTM: INOVASI PAKAN FUNGSIONAL UNTUK TERNAK RUMINANSIA BERBASIS SELADA LAUT LOKAL SUMBAWA Ulva lactuca (Linnaeus) YANG DIFORTIFIKASI DENGAN PROBIOTIK, PREBIOTIK DAN POSTBIOTIK

Sumbawa Island is included in the Thousand Cow Village program because it has a high potential of cattle reaching more than 738,000 heads in 2020. However, the limited number of quality cattle feed producers in Sumbawa causes local farmers to rely heavily on expensive commercial feed. Alternative uses of forage and fresh grass are also commonly used, but they have the potential to pose a serious threat to the health of the digestive tract of cattle and become the largest contributor to methane gas in the atmosphere. The “SeafeedTM” innovation, is a functional feed product for ruminant livestock made from local Sumbawa sea lettuce from the Ulva lactuca species, a species of green algae with high nutrition which is very abundant in the northern waters of Sumbawa Island and its potential has not been utilized optimally. The protein content which reaches 14% and soluble fiber >45% in Ulva lactuca sea lettuce makes this species a very prospective candidate to be used as a high-quality feed source. The ingredients used are sea celery (Ulva lactuca), bran, premix-porbiotic & prebotik, and molasses. A simple method of manufacture with a mixed composition, namely 10% sea cress, premix-probiotics & prebiotics, 30% molasses and 60% bran. Seafeed is an innovative ruminant feed made from local seaweed from Sumbawa which has complete nutritional content to support the growth of livestock. The content of probiotics, prebiotics, and postbiotics makes this product into the category of functional feed that functions to increase immunity in livestock. It is hoped that this product can be developed commercially to support the ability of farmers on Sumbawa Island to utilize local biological natural resources as feed ingredients so that dependence on commercial feed supplies can be reduced.

Distribution and ecology of wild lettuces Lactuca serriola L. and Lactuca virosa L. in central Chile

Abstract Wild lettuces (Lactuca L.) provide valuable genetic resources for crop breeding, but are also significant invasive weeds. We explored the distributions, habitats, and ecological characteristics of populations of wild Lactuca species in central Chile. We documented two species – Lactuca serriola L. (prickly lettuce) and Lactuca virosa L. (opium/bitter lettuce) in 204 localities. These observations indicate that: i) both allochthonous (Euroasian) Lactuca species occur and are able to regenerate in central Chile; ii) L. serriola forms dense populations in urbanized areas; iii) both species can expand along transport corridors to high elevations; iv) the spread of L. virosa and persistence of dense populations in elevations above 2,000 m a.s.l. prove the invasiveness of this species in extreme climates; v) both species may contain novel traits of interest for germplasm conservation.

CYTOLOGICAL VARIATION OF (AAG)7 REPEAT ON LETTUCE CHROMOSOMES BY FLUORESCENCE IN SITU HYBRIDIZATION (FISH)

Cytological studies using fluorescence in situ hybridization (FISH) technique provides phylogenetical information in closely related taxa and have been widely applied for karyotyping and studying chromosomal organization and evolution in plant species. In the present study, FISH using a microsatellite sequence of (AAG)7 as the probe was performed in order to discriminate the chromosomes in four Lactuca species, i.e., L. sativa, L. serriola, L. saligna, and L. virosa. The experiment was carried out in April to September 2018 at Laboratory of Genetic and Plant Breeding of Breeding of Graduate School of Horticulture, Chiba University, Japan. Different distribution patterns of (AAG)n signals were shown on the chromosomes in the four Lactuca species studied, In L. sativa and L. serriola, FISH with (AAG)7 sequences revealed dispersed distribution patterns with one pair of bright signals, respectively. While in L. saligna and L. virosa, distinct signals with different intensities were observed in two pairs of chromosomes of L. saligna and five pairs of chromosomes of L. virosa. In conclusion, the AAG repeat signals could be used as cytogenetic landmarks for chromosome identification in Lactuca species.

Genetics of Partial Resistance Against Verticillium dahliae Race 2 in Wild and Cultivated Lettuce.

Lettuce (Lactuca sativa) is one of the most economically important vegetables in the United States, with approximately 50% of the domestic production concentrated in the Salinas Valley of California. Verticillium wilt, caused by races 1 and 2 of the fungal pathogen Verticillium dahliae, poses a major threat to lettuce production in this area. Although resistance governed by a single dominant gene against race 1 has previously been identified and is currently being incorporated into commercial cultivars, identification of resistance against race 2 has been challenging and no lines with complete resistance have been identified. In this study, we screened germplasm for resistance and investigated the genetics of partial resistance against race 2 using three mapping populations derived from crosses involving L. sativa × L. sativa and L. serriola × L. sativa. The inheritance of resistance in Lactuca species against race 2 is complex but a common quantitative trait locus (QTL) on linkage group 6, designated qVERT6.1 (quantitative Verticillium dahliae resistance on LG 6, first QTL), was detected in multiple populations. Additional race 2 resistance QTLs located in several linkage groups were detected in individual populations and environments. Because resistance in lettuce against race 2 is polygenic with a large genotype by environment interaction, breeding programs to incorporate these resistance genes should be aware of this complexity as they implement strategies to control race 2.