Association of Child Masking With COVID-19-Related Closures in US Childcare Programs.

Importance: It is not known how effective child masking is in childcare settings in preventing the transmission of SARS-CoV-2. This question is critical to inform health policy and safe childcare practices. Objective: To assess the association between masking children 2 years and older and subsequent childcare closure because of COVID-19. Design, Setting, and Participants: A prospective, 1-year, longitudinal electronic survey study of 6654 childcare professionals at home- and center-based childcare programs in all 50 states was conducted at baseline (May 22 to June 8, 2020) and follow-up (May 26 to June 23, 2021). Using a generalized linear model (log-binomial model) with robust SEs, this study evaluated the association between childcare program closure because of a confirmed or suspected COVID-19 case in either children or staff during the study period and child masking in both early adoption (endorsed at baseline) and continued masking (endorsed at baseline and follow-up), while controlling for physical distancing, other risk mitigation strategies, and program and community characteristics. Exposures: Child masking in childcare programs as reported by childcare professionals at baseline and both baseline and follow-up. Main Outcomes and Measures: Childcare program closure because of a suspected or confirmed COVID-19 case in either children or staff as reported in the May 26 to June 23, 2021, end survey. Results: This survey study of 6654 childcare professionals (mean [SD] age, 46.9 [11.3] years; 750 [11.3%] were African American, 57 [0.9%] American Indian/Alaska Native, 158 [2.4%] Asian, 860 [12.9%] Hispanic, 135 [2.0%] multiracial [anyone who selected >1 race on the survey], 18 [0.3%] Native Hawaiian/Pacific Islander, and 5020 [75.4%] White) found that early adoption (baseline) of child masking was associated with a 13% lower risk of childcare program closure because of a COVID-19 case (adjusted relative risk, 0.87; 95% CI, 0.77-0.99), and continued masking for 1 year was associated with a 14% lower risk (adjusted relative risk, 0.86; 95% CI, 0.74-1.00). Conclusions and Relevance: This survey study of childcare professionals suggests that masking young children is associated with fewer childcare program closures, enabling in-person education. This finding has important public health policy implications for families that rely on childcare to sustain employment.

Evaluating implementation of LEAPS, a youth-led early childhood care and education intervention in rural Pakistan: protocol for a stepped wedge cluster-randomized trial.

BACKGROUND: The Sustainable Development Goals (SDGs) highlight the importance of investments in early childhood care and education (ECCE) and youth development. Given Pakistan's large young population, and gender and urban-rural inequalities in access to education, training, and employment, such investments offer opportunities. LEAPS is a youth-led ECCE program that trains female youth, 18-24 years, as Community Youth Leaders (CYLs) to deliver high-quality ECCE for children, 3.5-5.5 years, in rural Sindh, Pakistan. METHODS: We use a stepped wedge cluster-randomized trial to evaluate implementation of LEAPS. Ninety-nine clusters will be randomized to receive the intervention in one of three 7-month steps (33 clusters/step). The primary outcome is children's school readiness (indexed by the total score on the International Development and Early Learning Assessment (IDELA)). Secondary child outcomes are children's IDELA domain scores and executive functions. Data are collected in cross-sectional surveys of 1089 children (11 children/cluster from 99 clusters) aged 4.5-5.5 years at four timepoints (baseline and at the end of each step). Additionally, we will enroll three non-randomized youth participant open cohorts, one per step (33 CYLs: 66 comparison youth per cohort; 99:198 in total). Youth cohorts will be assessed at enrollment and every 7 months thereafter to measure secondary outcomes of youth personal and professional development, depressive symptoms, and executive functions. A non-randomized school cohort of 330 LEAPS students (10 students/cluster from 33 clusters) will also be enrolled and assessed during Step 1 after intervention rollout and at endline. The quality of the learning environment will be assessed in each LEAPS ECCE center and in a comparison center at two timepoints midway following rollout and at endline. A concurrent mixed-methods implementation evaluation will assess program fidelity and quality, and the extent to which a technical support strategy is successful in strengthening systems for program expansion. A cost evaluation will assess cost per beneficiary. Data collection for implementation and cost evaluations will occur in Step 3. DISCUSSION: Youth-led models for ECCE offer a promising approach to support young children and youth. This study will contribute to the evidence as a means to promote sustainable human development across multiple SDG targets. TRIAL REGISTRATION: ClinicalTrials.gov NCT03764436 . Registered on December 5, 2018.

COVID-19 Vaccine Uptake Among US Child Care Providers.

OBJECTIVES: Ensuring high coronavirus disease-2019 (COVID-19) vaccine uptake among US child care providers is crucial to mitigating the public health implications of child-staff and staff-child transmission of severe acute respiratory syndrome coronavirus 2; however, the vaccination rate among this group was previously unknown. METHODS: To characterize vaccine uptake among US child care providers, we conducted a multistate cross-sectional survey of the child care workforce. Providers were identified through various national databases and state registries. A link to the survey was sent via e-mail between May 26 and June 23, 2021. A 37.8% response yielded 21 663 respondents, with 20 013 satisfying inclusion criteria. RESULTS: Overall COVID-19 vaccine uptake among US child care providers (78.2%, 90% confidence interval: 77.5% to 78.9%) was higher than the US general adult population (65%). Vaccination rates varied between states from 53.5% to 89.4%. Vaccine uptake among respondents differed significantly (P < .01) based on respondent age (70.0% for ages 25-34, 91.6% for ages 75-84), race (70.0% for Black or African Americans, 92.5% for Asian Americans), annual household income (70.8% for <$35 000, 85.1% for >$75 000), and child care setting (73.0% for home-based, 79.7% for center-based). CONCLUSIONS: COVID-19 vaccine uptake among US child care providers was higher than the general US adult population. Those who were younger, lower income, Black or African American, resided in states either in the Mountain West or the South, and/or worked in home-based child care programs reported the lowest rates of vaccination. State public health leaders and lawmakers should prioritize these subgroups to realize the largest gains in vaccine uptake among providers.

Addressing challenging behaviors in challenging environments: Findings from Ohio's early childhood mental health consultation system.

Early childhood mental health consultation (ECMHC) has been promoted by the federal government as a promising model for reducing early childhood expulsions and suspensions and is now implemented by numerous states. Despite growing ECMHC proliferation, this study is only the second randomized controlled trial of ECMHC, extending the methodologies of the first to include assessment of effects on random peers. Classrooms were assigned randomly to treatment or waitlist-control condition (n = 51 classrooms, 57 preschool teachers, and 190 preschoolers). Evaluation measures were collected at both pretreatment and posttreatment, following approximately six consultation visits. Classroom and teacher outcomes were evaluated with ordinary least squares regressions, while hierarchical linear modeling was used to evaluate child-level outcomes, accounting for the nested study design. Treatment children (both the target children who prompted the referral for ECMHC and random peers) evidenced significant improvements in social and emotional skills. Promising trend findings were noted for child behavior problem reduction and teacher pedagogical approach and locus of control. No significant effects were found on likelihood of expulsion and classroom mental health climate. This is the first ECMHC to demonstrate effects on nontarget peers in a rigorous randomized controlled trial. Programmatic and methodologic limitations and implications are discussed.

COVID-19 Transmission in US Child Care Programs.

OBJECTIVES: Central to the debate over school and child care reopening is whether children are efficient coronavirus disease 2019 (COVID-19) transmitters and are likely to increase community spread when programs reopen. We compared COVID-19 outcomes in child care providers who continued to provide direct in-person child care during the first 3 months of the US COVID-19 pandemic with outcomes in those who did not. METHODS: Data were obtained from US child care providers (N = 57 335) reporting whether they had ever tested positive or been hospitalized for COVID-19 (n = 427 cases) along with their degree of exposure to child care. Background transmission rates were controlled statistically, and other demographic, programmatic, and community variables were explored as potential confounders. Logistic regression analysis was used in both unmatched and propensity score-matched case-control analyses. RESULTS: No association was found between exposure to child care and COVID-19 in both unmatched (odds ratio [OR], 1.06; 95% confidence interval [CI], 0.82-1.38) and matched (OR, 0.94; 95% CI, 0.73-1.21) analyses. In matched analysis, being a home-based provider (as opposed to a center-based provider) was associated with COVID-19 (OR, 1.59; 95% CI, 1.14-2.23) but revealed no interaction with exposure. CONCLUSIONS: Within the context of considerable infection mitigation efforts in US child care programs, exposure to child care during the early months of the US pandemic was not associated with an elevated risk for COVID-19 transmission to providers. These findings must be interpreted only within the context of background transmission rates and the considerable infection mitigation efforts implemented in child care programs.

Correction to: The LsVe1L allele provides a molecular marker for resistance to Verticillium dahliae race 1 in lettuce.

Following publication of the original article [1], the author reported a processing error in Figure 5. This has been corrected in the original article.

A chromosome-anchored eggplant genome sequence reveals key events in Solanaceae evolution.

With approximately 450 species, spiny Solanum species constitute the largest monophyletic group in the Solanaceae family, but a high-quality genome assembly from this group is presently missing. We obtained a chromosome-anchored genome assembly of eggplant (Solanum melongena), containing 34,916 genes, confirming that the diploid gene number in the Solanaceae is around 35,000. Comparative genomic studies with tomato (S. lycopersicum), potato (S. tuberosum) and pepper (Capsicum annuum) highlighted the rapid evolution of miRNA:mRNA regulatory pairs and R-type defense genes in the Solanaceae, and provided a genomic basis for the lack of steroidal glycoalkaloid compounds in the Capsicum genus. Using parsimony methods, we reconstructed the putative chromosomal complements of the key founders of the main Solanaceae clades and the rearrangements that led to the karyotypes of extant species and their ancestors. From 10% to 15% of the genes present in the four genomes were syntenic paralogs (ohnologs) generated by the pre-γ, γ and T paleopolyploidy events, and were enriched in transcription factors. Our data suggest that the basic gene network controlling fruit ripening is conserved in different Solanaceae clades, and that climacteric fruit ripening involves a differential regulation of relatively few components of this network, including CNR and ethylene biosynthetic genes.

The LsVe1L allele provides a molecular marker for resistance to Verticillium dahliae race 1 in lettuce.

BACKGROUND: Verticillium wilt caused by the fungus Verticillium dahliae race 1 is among the top disease concerns for lettuce in the Salinas and Pajaro Valleys of coastal central California. Resistance of lettuce against V. dahliae race 1 was previously mapped to the single dominant Verticillium resistance 1 (Vr1) locus. Lines of tomato resistant to race 1 are known to contain the closely linked Ve1 and Ve2 genes that encode receptor-like proteins with extracellular leucine-rich repeats; the Ve1 and Ve2 proteins act antagonistically to provide resistance against V. dahliae race 1. The Vr1 locus in lettuce contains a cluster of several genes with sequence similarity to the tomato Ve genes. We used genome sequencing and/or PCR screening along with pathogenicity assays of 152 accessions of lettuce to investigate allelic diversity and its relationship to race 1 resistance in lettuce. RESULTS: This approach identified a total of four Ve genes: LsVe1, LsVe2, LsVe3, and LsVe4. The majority of accessions, however, contained a combination of only three of these LsVe genes clustered on chromosomal linkage group 9 (within ~ 25 kb in the resistant cultivar La Brillante and within ~ 127 kb in the susceptible cultivar Salinas). CONCLUSIONS: A single allele, LsVe1L, was present in all resistant accessions and absent in all susceptible accessions. This allele can be used as a molecular marker for V. dahliae race 1 resistance in lettuce. A PCR assay for rapid detection of race 1 resistance in lettuce was designed based on nucleotide polymorphisms. Application of this assay allows identification of resistant genotypes in early stages of plant development or at seed-level without time- and labor-intensive testing in the field.

Genomic signatures of heterokaryosis in the oomycete pathogen Bremia lactucae.

Lettuce downy mildew caused by Bremia lactucae is the most important disease of lettuce globally. This oomycete is highly variable and rapidly overcomes resistance genes and fungicides. The use of multiple read types results in a high-quality, near-chromosome-scale, consensus assembly. Flow cytometry plus resequencing of 30 field isolates, 37 sexual offspring, and 19 asexual derivatives from single multinucleate sporangia demonstrates a high incidence of heterokaryosis in B. lactucae. Heterokaryosis has phenotypic consequences on fitness that may include an increased sporulation rate and qualitative differences in virulence. Therefore, selection should be considered as acting on a population of nuclei within coenocytic mycelia. This provides evolutionary flexibility to the pathogen enabling rapid adaptation to different repertoires of host resistance genes and other challenges. The advantages of asexual persistence of heterokaryons may have been one of the drivers of selection that resulted in the loss of uninucleate zoospores in multiple downy mildews.

Effectiveness of a youth-led early childhood care and education programme in rural Pakistan: A cluster-randomised controlled trial.

BACKGROUND: The United Nation's Sustainable Development Goals encompass lifelong learning from birth to youth to adulthood (Goal 4) and economic opportunities for young people (Goal 8). The targets include improving access to quality early childhood care and education (ECCE) as well as learning and training opportunities for adolescents and youth. Cross-generational models for young children and youth may offer opportunities to address the interconnections between goals and targets for the next generation. We investigated whether an ECCE programme for young children (3.5-6.5 years) delivered by female youth (18-24 years) in rural Pakistan would be effective on children's school readiness. METHODS: In partnership with the National Commission for Human Development in Pakistan, we implemented the 'Youth Leaders for Early Childhood Assuring Children are Prepared for School' (LEAPS) programme to train female youth to deliver ECCE. The effectiveness of the LEAPS programme on children's school readiness was evaluated in a cluster-randomised controlled trial. We randomly allocated five clusters (villages) to receive the intervention (n = 170 children) and five clusters to control (n = 170 children). Children's school readiness was assessed after nine months of intervention exposure using the International Development and Early Learning Assessment tool. Analyses was by intention-to-treat. The trial is registered with ClinicalTrials.gov, number NCT02645162. FINDINGS: At endline, the intervention group had significantly higher school readiness scores (n = 166, mean percentage score 59.4, 95% CI 52.7 to 66.2) compared with the control group (n = 168, mean percentage score 45.5, 95% CI 38.8 to 52.3). The effect size (Cohen's d) was 0.3. CONCLUSION: Trained female youth delivered an ECCE programme that was effective in benefitting young children's school readiness. The cross-generational model is a promising approach to support early child development; however, further evaluation of the model is needed to assess the specific benefits to youth including their skills and economic development.

Comparative genomics of downy mildews reveals potential adaptations to biotrophy.

BACKGROUND: Spinach downy mildew caused by the oomycete Peronospora effusa is a significant burden on the expanding spinach production industry, especially for organic farms where synthetic fungicides cannot be deployed to control the pathogen. P. effusa is highly variable and 15 new races have been recognized in the past 30 years. RESULTS: We virulence phenotyped, sequenced, and assembled two isolates of P. effusa from the Salinas Valley, California, U.S.A. that were identified as race 13 and 14. These assemblies are high quality in comparison to assemblies of other downy mildews having low total scaffold count (784 & 880), high contig N50s (48 kb & 52 kb), high BUSCO completion and low BUSCO duplication scores and share many syntenic blocks with Phytophthora species. Comparative analysis of four downy mildew and three Phytophthora species revealed parallel absences of genes encoding conserved domains linked to transporters, pathogenesis, and carbohydrate activity in the biotrophic species. Downy mildews surveyed that have lost the ability to produce zoospores have a common loss of flagella/motor and calcium domain encoding genes. Our phylogenomic data support multiple origins of downy mildews from hemibiotrophic progenitors and suggest that common gene losses in these downy mildews may be of genes involved in the necrotrophic stages of Phytophthora spp. CONCLUSIONS: We present a high-quality draft genome of Peronospora effusa that will serve as a reference for Peronospora spp. We identified several Pfam domains as under-represented in the downy mildews consistent with the loss of zoosporegenesis and necrotrophy. Phylogenomics provides further support for a polyphyletic origin of downy mildews.

Identification of water use efficiency related genes in 'Garnem' almond-peach rootstock using time-course transcriptome analysis.

Drought is one of the main abiotic stresses with far-reaching ecological and socioeconomic impacts, especially in perennial food crops such as Prunus. There is an urgent need to identify drought resilient rootstocks that can adapt to changes in water availability. In this study, we tested the hypothesis that PEG-induced water limitation stress will simulate drought conditions and drought-related genes, including transcription factors (TFs), will be differentially expressed in response to this stress. 'Garnem' genotype, an almond × peach hybrid [P. amygdalus Batsch, syn P. dulcis (Mill.) x P. persica (L.) Batsch] was exposed to PEG-6000 solution, and a time-course transcriptome analysis of drought-stressed roots was performed at 0, 2 and 24 h time points post-stress. Transcriptome analysis resulted in the identification of 12,693 unique differentially expressed contigs (DECs) at the 2 h time point, and 7,705 unique DECs at the 24 h time point after initiation of the drought treatment. Interestingly, three drought-induced genes, directly related to water use efficiency (WUE) namely, ERF023 TF; LRR receptor-like serine/threonine-kinase ERECTA; and NF-YB3 TF, were found induced under stress. The RNAseq results were validated with quantitative RT-PCR analysis of eighteen randomly selected differentially expressed contigs (DECs). Pathway analysis in the present study provides valuable information regarding metabolic events that occur during stress-induced signalling in 'Garnem' roots. This information is expected to be useful in understanding the potential mechanisms underlying drought stress responses and drought adaptation strategies in Prunus species.

Metabolic Reprogramming in Leaf Lettuce Grown Under Different Light Quality and Intensity Conditions Using Narrow-Band LEDs.

Light-emitting diodes (LEDs) are an artificial light source used in closed-type plant factories and provide a promising solution for a year-round supply of green leafy vegetables, such as lettuce (Lactuca sativa L.). Obtaining high-quality seedlings using controlled irradiation from LEDs is critical, as the seedling health affects the growth and yield of leaf lettuce after transplantation. Because key molecular pathways underlying plant responses to a specific light quality and intensity remain poorly characterised, we used a multi-omics-based approach to evaluate the metabolic and transcriptional reprogramming of leaf lettuce seedlings grown under narrow-band LED lighting. Four types of monochromatic LEDs (one blue, two green and one red) and white fluorescent light (control) were used at low and high intensities (100 and 300 µmol·m-2·s-1, respectively). Multi-platform mass spectrometry-based metabolomics and RNA-Seq were used to determine changes in the metabolome and transcriptome of lettuce plants in response to different light qualities and intensities. Metabolic pathway analysis revealed distinct regulatory mechanisms involved in flavonoid and phenylpropanoid biosynthetic pathways under blue and green wavelengths. Taken together, these data suggest that the energy transmitted by green light is effective in creating a balance between biomass production and the production of secondary metabolites involved in plant defence.

A Conceptual Model for Youth-Led Programs as a Promising Approach to Early Childhood Care and Education.

The international community has set forth global targets that include calls for universal access to high-quality early childhood care and education (ECCE), as indicated in the United Nations' Sustainable Development Goals. One major impediment to achieving this target is the lack of a skilled workforce. In this paper, we argue the case for leveraging youth as an untapped resource for supplying the workforce the ECCE system needs. Youth comprise a large proportion of the global population, and historically, although youth experience higher unemployment rates than their adult counterparts, youth are important agents of social awareness, social transformation, and community mobilization in multiple global contexts. We provide a conceptual model based on developmental theories and program examples to leverage the discourse of youth-led ECCE programs as a viable option to address workforce gaps while benefiting both young children and youth.

Genome assembly with in vitro proximity ligation data and whole-genome triplication in lettuce.

Lettuce (Lactuca sativa) is a major crop and a member of the large, highly successful Compositae family of flowering plants. Here we present a reference assembly for the species and family. This was generated using whole-genome shotgun Illumina reads plus in vitro proximity ligation data to create large superscaffolds; it was validated genetically and superscaffolds were oriented in genetic bins ordered along nine chromosomal pseudomolecules. We identify several genomic features that may have contributed to the success of the family, including genes encoding Cycloidea-like transcription factors, kinases, enzymes involved in rubber biosynthesis and disease resistance proteins that are expanded in the genome. We characterize 21 novel microRNAs, one of which may trigger phasiRNAs from numerous kinase transcripts. We provide evidence for a whole-genome triplication event specific but basal to the Compositae. We detect 26% of the genome in triplicated regions containing 30% of all genes that are enriched for regulatory sequences and depleted for genes involved in defence.

Early Childhood Mental Health Consultation: Results of a Statewide Random-Controlled Evaluation.

OBJECTIVE: Despite recent federal recommendations calling for increased funding for early childhood mental health consultation (ECMHC) as a means to decrease preschool expulsions, no randomized-controlled evaluations of this form of intervention have been reported in the scientific literature. This study is the first attempt to isolate the effects of ECMHC for enhancing classroom quality, decreasing teacher-rated behavior problems, and decreasing the likelihood of expulsion in targeted children in early childhood classrooms. METHOD: The sample consisted of 176 target children (3-4 years old) and 88 preschool classrooms and teachers randomly assigned to receive ECMHC through Connecticut's statewide Early Childhood Consultation Partnership (ECCP) or waitlist control treatment. Before randomization, teachers selected 2 target children in each classroom whose behaviors most prompted the request for ECCP. Evaluation measurements were collected before and after treatment, and child behavior and social skills and overall quality of the childcare environment were assessed. Hierarchical linear modeling was used to evaluate the effectiveness of ECCP and to account for the nested structure of the study design. RESULTS: Children who received ECCP had significantly lower ratings of hyperactivity, restlessness, externalizing behaviors, problem behaviors, and total problems compared with children in the control group even after controlling for gender and pretest scores. No effects were found on likelihood of expulsion and quality of childcare environment. CONCLUSION: ECCP resulted in significant decreases across several domains of teacher-rated externalizing and problem behaviors and is a viable and potentially cost-effective means for infusing mental health services into early childhood settings. Clinical and policy implications for ECMHC are discussed.

The genome sequence of the outbreeding globe artichoke constructed de novo incorporating a phase-aware low-pass sequencing strategy of F1 progeny.

Globe artichoke (Cynara cardunculus var. scolymus) is an out-crossing, perennial, multi-use crop species that is grown worldwide and belongs to the Compositae, one of the most successful Angiosperm families. We describe the first genome sequence of globe artichoke. The assembly, comprising of 13,588 scaffolds covering 725 of the 1,084 Mb genome, was generated using ~133-fold Illumina sequencing data and encodes 26,889 predicted genes. Re-sequencing (30×) of globe artichoke and cultivated cardoon (C. cardunculus var. altilis) parental genotypes and low-coverage (0.5 to 1×) genotyping-by-sequencing of 163 F1 individuals resulted in 73% of the assembled genome being anchored in 2,178 genetic bins ordered along 17 chromosomal pseudomolecules. This was achieved using a novel pipeline, SOILoCo (Scaffold Ordering by Imputation with Low Coverage), to detect heterozygous regions and assign parental haplotypes with low sequencing read depth and of unknown phase. SOILoCo provides a powerful tool for de novo genome analysis of outcrossing species. Our data will enable genome-scale analyses of evolutionary processes among crops, weeds, and wild species within and beyond the Compositae, and will facilitate the identification of economically important genes from related species.

Genome-Wide Architecture of Disease Resistance Genes in Lettuce.

Genome-wide motif searches identified 1134 genes in the lettuce reference genome of cv. Salinas that are potentially involved in pathogen recognition, of which 385 were predicted to encode nucleotide binding-leucine rich repeat receptor (NLR) proteins. Using a maximum-likelihood approach, we grouped the NLRs into 25 multigene families and 17 singletons. Forty-one percent of these NLR-encoding genes belong to three families, the largest being RGC16 with 62 genes in cv. Salinas. The majority of NLR-encoding genes are located in five major resistance clusters (MRCs) on chromosomes 1, 2, 3, 4, and 8 and cosegregate with multiple disease resistance phenotypes. Most MRCs contain primarily members of a single NLR gene family but a few are more complex. MRC2 spans 73 Mb and contains 61 NLRs of six different gene families that cosegregate with nine disease resistance phenotypes. MRC3, which is 25 Mb, contains 22 RGC21 genes and colocates with Dm13. A library of 33 transgenic RNA interference tester stocks was generated for functional analysis of NLR-encoding genes that cosegregated with disease resistance phenotypes in each of the MRCs. Members of four NLR-encoding families, RGC1, RGC2, RGC21, and RGC12 were shown to be required for 16 disease resistance phenotypes in lettuce. The general composition of MRCs is conserved across different genotypes; however, the specific repertoire of NLR-encoding genes varied particularly of the rapidly evolving Type I genes. These tester stocks are valuable resources for future analyses of additional resistance phenotypes.

Identification of Genetic Loci Associated with Quality Traits in Almond via Association Mapping.

To design an appropriate association study, we need to understand population structure and the structure of linkage disequilibrium within and among populations as well as in different regions of the genome in an organism. In this study, we have used a total of 98 almond accessions, from five continents located and maintained at the Centro de Investigación y Tecnología Agroalimentaria de Aragón (CITA; Spain), and 40 microsatellite markers. Population structure analysis performed in 'Structure' grouped the accessions into two principal groups; the Mediterranean (Western-Europe) and the non-Mediterranean, with K = 3, being the best fit for our data. There was a strong subpopulation structure with linkage disequilibrium decaying with increasing genetic distance resulting in lower levels of linkage disequilibrium between more distant markers. A significant impact of population structure on linkage disequilibrium in the almond cultivar groups was observed. The mean r2 value for all intra-chromosomal loci pairs was 0.040, whereas, the r2 for the inter-chromosomal loci pairs was 0.036. For analysis of association between the markers and phenotypic traits, five models comprising both general linear models and mixed linear models were selected to test the marker trait associations. The mixed linear model (MLM) approach using co-ancestry values from population structure and kinship estimates (K model) as covariates identified a maximum of 16 significant associations for chemical traits and 12 for physical traits. This study reports for the first time the use of association mapping for determining marker-locus trait associations in a world-wide almond germplasm collection. It is likely that association mapping will have the most immediate and largest impact on the tier of crops such as almond with the greatest economic value.