Development of a differential panel to identify <i>Peronospora belbahrii</i> races in sweet basil ( <i>Ocimum basilicum</i> )

bioRxiv (Cold Spring Harbor Laboratory) · 2025-09-20

Abstract First reported in the United States in 2007, downy mildew of sweet basil ( Ocimum basilicum ), caused by the oomycete pathogen Peronospora belbahrii , has become a major challenge in global basil production. Downy mildew-resistant cultivars have been developed and commercially available since 2018, but observations of isolates overcoming resistance were reported after each new introduction. The rapid development of pathogens overcoming genetic resistance suggests the evolution of new races under selective pressure. In this study, we report on the development of a differential panel of distinct basil cultivars with varying and differential sources of genetic resistance tested against P. belbahrii strains obtained from geographically diverse multi-year collections from basil-producing locations in the US, Israel, and Italy. Screening multiple P. belbahrii isolates revealed three distinct virulence profiles that distinguished race 0, race 1, and race 2. Races 1 and 2 were defined by virulence in cultivars with single gene resistance loci Pb1 and Pb2 , respectively. Evaluation of cultivars with quantitative resistance revealed more variation in susceptibility or partial resistance, suggesting “broad spectrum” (or race-nonspecific) resistance. With continued isolate collection and screening efforts, the denomination of P. belbahrii races may be further expanded, and newly developed resistant cultivars can be added to the proposed panel to definitively evaluate novel P. belbahrii strains. This study lays the groundwork to further explore dynamics of race evolution and mechanisms of resistance breakdown, which will be essential for discovering new sources of resistance for controlling basil downy mildew.

A Rapid Screening Approach to Identify Resistance to Basil Bacterial Leaf Spot (Pseudomonas cichorii)

HortScience · 2025-02-18 · 1 citations

Basil ( Ocimum spp.) is among the most economically important culinary herbs grown worldwide. Ocimum basilicum includes both the European style sweet basil and the distinct Thai basil. Field, greenhouse, and indoor production practices involve growing dense compact stands that facilitate ideal conditions for the development of significant foliar diseases. One such disease, which has increased in prevalence and severity over the past decade throughout basil production regions in the United States and Europe, is bacterial leaf spot (BLS) caused by the pathogen Pseudomonas cichorii , a common bacterial pathogen with a broad host range including both wild plant species and commercial crops. Under favorable conditions, BLS is capable of causing significant losses before harvest, with growers currently having few economically viable chemical controls available for the disease. At present, no known resistance to BLS exists in commercially available cultivars. This study establishes a rapid pathogenicity screening assay for identification of potential BLS resistant germplasm within the O. basilicum and broader Ocimum genus for use in breeding genetically resistant lines. Three basil accessions, ‘Lettuce Leaf’ ( O. basilicum ), ‘Mrs. Burns’ Lemon’ ( O. africanum ), and the coded Rutgers’ ‘RUGBX 88’ ( Ocimum spp.), were inoculated with P. cichorii at 10 8 CFUs and screened for disease severity at the cotyledon, first true leaf, second true leaf, and mature growth stage (four to five nodes). Disease severity scores (0 to 5) were assessed daily from 3 to 6 days post-inoculation (DPI) to determine the best growth stage for rapid screening purposes. Disease severity scores at the cotyledon and first true leaf stage displayed significant variation from mature plants while there were no significant differences (Dunn’s test, α = 0.05) in ratings between the second true leaf stage and maturity for all three accessions; the second true leaf growth stage was then selected to screen a collection of commercial basil cultivars for BLS resistance. Pathogenicity assays at the second true leaf stage revealed substantial variation in disease severity scores with the lowest being 2.28 (‘Queen of Sheba’) and the highest being 4.65 (‘Siam Queen’) across all lines tested. This methodology demonstrates the screening of basils at the second true leaf growth stage can readily be applied to Ocimum spp. Germplasm collections for the identification of potential BLS-resistant lines for incorporation into breeding programs.

A Review of Elicitation Studies from Nepeta and Related Species

University of Massachusetts (UMass) Amherst · 2025-12-28

Exploring the Epigenetic and Metabolic Pathways for Antioxidant and Anti-Inflammatory Potentials of Tart Cherry Juice Concentrate

Current Pharmacology Reports · 2025-07-26 · 2 citations

) has high antioxidant and anti-inflammatory potentials due to its rich bioactive components like anthocyanins, polyphenols, vitamins, beta-carotene, ellagic acid, and chlorogenic acid. Oxidative damage and inflammation are underlying reasons to chronic disease pathogenesis. Oxidative stress usually caused by the imbalance between antioxidants and pro-oxidants. Additionally, a chronic inflammatory state is typically modulated by oxidative stress. Inflammation plays a critical role in chronic health conditions, such as cardiovascular diseases, hypertension, insulin resistance, arthritis and cancer. Numerous studies indicate that there is a strong relationship between TC and the inhibition of inflammation and oxidative damage by regulating different epigenetic and metabolic pathways. In this review, the recent developments of TC components and their metabolites on inflammatory and oxidative damages will be discussed, and the challenges and limitations to better support future research, including clinical trials to confirm these findings.

Cold Plasma Treatment of Sweet Basil Seeds and Nutrient Water in Hydroponics: Impact on Growth and Quality

Journal of Food Science · 2025-05-01

This study investigated the combined effect of two plasma treatments during hydroponic growing of sweet basil plants. Air-based cold plasma was applied to basil seeds using a Plasmajet. Also, plasma-activated water (PAW) was produced by using a submerged gliding arc plasmatron system followed by mixing the PAW with a nutrient solution (NS) to make plasma-activated NS (PANS). Basil plants from untreated and plasma-treated seeds were grown hydroponically using NS and PANS in a greenhouse in an ebb-and-flow system. Basil plants were harvested after 21 days and analyzed for their dry tissue mass, growth parameters (plant height, number of branches and nodes, root length, and leaf index), quality (color, texture), and microbiology (total plate count). The combination of plasma treatment of seeds followed by growing the plants using PANS (treated group) resulted in higher plant height, longer root length, greater number of branches, bigger leaves, and higher zinc content in leaves in comparison to plants grown from untreated seeds and with NS (control group). Plasma treatment did not significantly affect moisture content, number of nodes, dry weight, wet weight, greenness, texture, aroma content, and sensory attributes of basil leaves. However, sensory results showed increased basil flavor, aroma, and bitterness in the tomato basil salad made with PANS-treated basil, compared to tomato basil salad made with NS-treated basil. This work revealed that the plasma treatment of the basil seeds combined with PANS could be effective to enhance the growth of sweet basil plants and increase the aroma and flavor of this culinary herb.

Relationship between sensory perceptions and volatile and phenolic compounds of fresh basil ( <i>Ocimum basilicum</i>  L.) evaluated by multivariate statistics

Journal of Food Science · 2025-04-01 · 1 citations

Sensory and phytochemical analyses were conducted on sweet basil (Ocimum basilicum L.) to investigate the impact of volatile and phenolic compounds on aroma, taste, and flavor by mouth. A trained panel evaluated seven accessions, including 'Aroma 2', 'Nufar', 'CB19', and four breeding lines developed by Rutgers for downy mildew resistance (DMR). The basils selected for this study displayed unique sensory profiles that were chemically characterized with 21 volatile and 15 phenolic compounds using GC/MS and LC/MS, respectively. Principal component analysis revealed a two-factor model. Factor 1 described cinnamon, floral, ginger, lemon, and musty aromas, clustering with eucalyptol and many minor aromatic compounds. 'Rutgers Thunderstruck-DMR' closely aligned with these attributes. Factor 2 described an axis with clove aroma/flavor and bitter taste on one end and anise and sweet aroma/taste on the opposite end. Anise aroma/flavor was closely associated with methyl chavicol and sweet aroma/flavor. Eugenol and several phenolic acids clustered near bitter taste. However, not all phenolic acids contributed to bitterness or astringency, suggesting diverse roles in sensory perception. 'Aroma 2', 'Rutgers Passion DMR', and 'Rutgers Obsession DMR' were aligned with the clove/spicy/bitter pole of Factor 2, whereas 'CB19' was oppositely aligned with the anise/sweet pole. 'Nufar' and 'Rutgers Devotion DMR' occupied the center of the plot and were characterized as moderate in their sensory/phytochemical profiles. In conclusion, this study reveals that new varieties can be distinguished by their sensory/phytochemical profiles and compared to commercial cultivars. Further, the inclusion of phenolic compounds led to more precise sensory/phytochemical descriptions of these varieties. PRACTICAL APPLICATION: This research provides valuable insights into the aroma, flavor, and underlying phytochemistry of fresh basil, which can help improve its taste and quality for culinary use. Sensory scientists and breeders can use the tools presented in this study as a means of selecting basil varieties to identify 'off types' and enhance aroma and flavor profiles.

Predicting the resistance of basil entries to downy mildew based on their genetics, pathogen race, growth stage, and environmental conditions

Planta · 2025-05-29 · 2 citations

Abstract Main conclusion A model predicting the level of resistance of basil to downy mildew was developed. The model integrates plant age, genetic background, sporulation, disease intensity, pathogen races, and environmental data at an early stage of disease. These results can be used to select and develop new basil cultivars and accelerate the time needed in breeding for basil downy mildew resistance. Abstract Basil downy mildew (BDM) caused by the oomycete Peronospora belbahrii emerged as a global threat, rapidly becoming the most devastating disease of sweet basil ( Ocimum basilicum ) and other Ocimum spp. worldwide. Despite advancements in understanding its biology and epidemiology, and the availability of approved fungicides and management strategies, BDM remains economically destructive and an ongoing risk to basil production worldwide. Recently, the development and introduction of resistant cultivars have emerged as crucial tools in BDM management and the emergence of new BDM races creates new challenges to controlling this disease. The present study aimed to provide growers and breeders with insights into the survival capabilities of resistant basil cultivars under varying genetic backgrounds, pathogen races, growth stages, and various environmental conditions. Through a series of lab and field experiments, we evaluated the response of multiple resistant sources and their lineages to various isolates of P. belbahrii across different locations, using multiple indices to assess their resistance. Entries carrying the R genes Pb1/Pb2 exhibited complete resistance across all races, growth stages, and environmental conditions. Those harboring the R-gene Pb2 showed similar resistance levels, with minor variability due to growth stage. Responses of Pb1 plants varied with pathogen race, displaying full resistance to race 0 at all growth stages but displaying susceptibility to race 1. Plant cultivars possessing MRI resistance genes and their recombinant inbred lines (RIL’s) exhibited variable responses to pathogen attacks, ranging from high tolerance to complete susceptibility. Some MRI RIL’s showed high resistance similar to Pb2 entries. Pb0 cultivars and 'Eleonora' (unknown background) were susceptible to all races and growth stages in all experiments. Comprehensive analysis across all genetic backgrounds revealed a significant correlation ( R = 0.73) between disease intensity (D.I) at the seedling stage under controlled conditions and D.I in adult plants under field conditions. Principal Component Analysis (PCA) across six experiments indicated that the primary components influencing disease outcomes were the accession, race, and growth stage, explaining 65%, 22%, and 7% of the variability, respectively. A prediction model based on the statistical parameters residual (%) and root-mean-square error (RMSE) demonstrated strong predictability, particularly regarding pathogen sporulation and daily disease development rates. The model predicted resistance probabilities with R 2 values of 0.81, 0.91, and 0.93 at the second, third, and final disease score readings, respectively, significantly earlier (~ 14–21 days post-infection) than traditional assessments (~ 42 days). These findings demonstrate that resistance in basil entries against current pathogen races can be effectively assessed within weeks of disease onset, facilitating more timely and informed management decisions for growers and providing an important tool for plant breeders in search of improved BDM resistance.

Identification of Novel Basil Downy Mildew Resistance Genes Using De Novo Comparative Transcriptomics

Phytopathology · 2025-03-14

Sweet basil ( Ocimum basilicum) production is threatened by the oomycete pathogen Peronospora belbahrii, causing basil downy mildew (BDM). BDM-resistant cultivar ‘Mrihani’ (MRI) was identified in a germplasm screen and bred with BDM-susceptible ‘Newton’ (SB22) to produce resistant cultivars, but the molecular mechanisms conferring resistance in MRI and the progeny remained unknown. A comparative transcriptomic approach was used to identify candidate resistance genes and potential mechanisms for BDM resistance. To differentiate the host–pathogen interactions in resistant and susceptible plants, RNA samples from BDM-infected MRI and SB22 plants were harvested at four time points during the first 3 days of infection, with mock-inoculated controls for both genotypes. Three categories of genes uniquely transcribed in the resistant MRI upon pathogen challenge were identified: nucleotide-binding leucine-rich repeat proteins (NLRs), multifunctional receptor-like kinases (RLKs), and secondary metabolic enzymes. Validation of the top resistance candidate NLR gene confirmed its unique presence in MRI and two of four resistant MRI × SB22 F 2 progeny. In MRI, pathogen challenge also induced differential regulation in members of the salicylic acid synthesis pathway, suggesting its role in BDM resistance. Overall, our study demonstrates the utility of de novo comparative transcriptomics to identify resistance genes and mechanisms in non-model crops.

Development of a scalable, high-anthocyanin and low-acidity natural red food colorant from Hibiscus sabdariffa L.

Food Chemistry · 2024-08-05 · 10 citations

Regional distribution of cellular of molecular pathways in a mouse model of Gulf War illness by Single-Cell RNA Sequencing Analysis

Research Square · 2024-08-05