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Spinach (Spinacia oleracea L.) is an important vegetable worldwide with high nutritional and health-promoting compounds. Bolting is an important trait to consider to grow spinach in different seasons and regions. Plant height and leaf erectness are important traits for machine harvesting. Breeding slow bolting, taller, and more erect spinach cultivars is needed for improved spinach production. A total of 288 United States Department of Agriculture (USDA) spinach accessions were used as the association panel in this research. Single-nucleotide polymorphisms (SNPs) discovered through genotyping by sequencing (GBS) were used for genotyping. Two structured populations and the admixtures were inferred for the 288 spinach accession panel using STRUCTURE and MEGA. Association mapping was conducted using single-marker regression (SMR) in QGene, and general linear model (GLM) and mixed linear model (MLM) built in TASSEL. Three SNP markers, AYZV02001321_398, AYZV02041012_1060, and AYZV02118171_95 were identified to be associated with bolting. Eight SNP markers, AYZV02014270_540, AYZV02250508_2162, AYZV02091523_19842, AYZV02141794_376, AYZV02077023_64, AYZV02210662_2532, AYZV02153224_2197, and AYZV02003975_248 were found to be associated with plant height. Four SNP markers, AYZV02188832_229, AYZV02219088_79, AYZV02030116_256, and AYZV02129827_197 were associated with erectness. These SNP markers may provide breeders with a tool in spinach molecular breeding to select spinach bolting, plant height, and erectness through marker-assisted selection (MAS).

Breeding heat-tolerant spinach is an important project to meet the demand of increasing spinach production in heat conditions. Seed germination is the early stage to test, screen, and develop heat-tolerant spinach genotypes. The objective of this research was to determine temperature effect on the seed germination percentage and to select heat-tolerant spinach genotypes. A total of nine spinach genotypes were used in this research. The germination experiment was conducted using seven temperatures: 10, 15, 20, 25, 30, 32, and 35 °C under growth chambers. The temperature trials were conducted using completely randomized design (CRD) with three replicates. Spinach seed germination percentage varied among the nine spinach genotypes under the seven temperatures, indicating that genetic variation for heat tolerance existed in the nine spinach genotypes. ‘Donkey’, ‘Marabu’, and ‘Raccoon’ showed higher seed germination percentage with over 70% at 30 and 32 °C, indicating the three spinach genotypes had heat tolerance for germination. However, all spinach genotypes except ‘Ozarka II’ dropped their germination percentages sharply to less than 30%; ‘Ozarka II’ had 63% germination under 35 °C, indicating it is a good source of heat tolerance for seed germination. The higher germination percentages above 30 °C of ‘Ozarka II’, ‘Donkey’, ‘Marabu’, and ‘Raccoon’ may indicate their potential as donors of heat-tolerant traits in spinach breeding program.

Fusarium wilt of tomato (Solanum lycopersicum), caused by fungal pathogen Fusarium oxysporum f. sp. lycopersici (Fol), is one of the most important diseases in tomato production. Three races of the pathogen are described, and race-specific resistance genes have been applied in commercial tomato cultivars for controlling the disease. Race 3 (Fol3) threatens tomato production in many regions around the world, and novel resistance resources could expand the diversity and durability of Fol resistance. The wild tomato species, Solanum pennellii, is reported to harbor broad resistance to Fol and was the source of two known Fol3 resistance genes. In this study, we evaluated 42 S. pennellii accessions for resistance to each fusarium wilt race. F₁ plants, developed from crossing each accession with the Fol3 susceptible line ‘Suncoast’, were evaluated for Fol3 resistance, and BC₁F₁ plants were screened to determine the likelihood that Fol3 resistance was based on a novel locus (loci). Nearly all accessions showed resistance to Fol3, and many accessions were resistant to all races. Evaluation of F₁ plants indicated a dominant resistance effect to Fol3 from most accessions. Genetic analysis indicated 24 accessions are expected to contain one or more novel Fol3 resistance loci other than an allele near the I-3 locus. To investigate genetic structure of the S. pennellii accessions used in this study, we genotyped all 42 accessions using genotyping by sequencing. Approximately 20% of the single nucleotide polymorphism (SNP) loci were heterozygous across accessions, likely due to the outcrossing nature of the species. Genetic structure analysis at 49,120 unique SNP loci across accessions identified small but obvious genetic differentiations.