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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. 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.

Summary In many aromatic plants including spearmint (Mentha spicata), the sites of secondary metabolite production are tiny specialized structures called peltate glandular trichomes (PGT). Having high commercial values, these secondary metabolites are exploited largely as flavours, fragrances and pharmaceuticals. But, knowledge about transcription factors (TFs) that regulate secondary metabolism in PGT remains elusive. Understanding the role of TFs in secondary metabolism pathway will aid in metabolic engineering for increased yield of secondary metabolites and also the development of new production techniques for valuable metabolites. Here, we isolated and functionally characterized a novel MsYABBY5 gene that is preferentially expressed in PGT of spearmint. We generated transgenic plants in which MsYABBY5 was either overexpressed or silenced using RNA interference (RNAi). Analysis of the transgenic lines showed that the reduced expression of MsYABBY5 led to increased levels of terpenes and that overexpression decreased terpene levels. Additionally, ectopic expression of MsYABBY5 in Ocimum basilicum and Nicotiana sylvestris decreased secondary metabolite production in them, suggesting that the encoded transcription factor is probably a repressor of secondary metabolism.

Sweet basil (Ocimum basilicum) plants produce its characteristic phenylpropene-rich essential oil in specialized structures known as peltate glandular trichomes (PGTs). Eugenol and chavicol are the major phenylpropenes produced by sweet basil varieties whose synthetic pathways are not fully elucidated. Eugenol is derived from coniferyl acetate by a reaction catalysed by eugenol synthase. An acyltransferase is proposed to convert coniferyl alcohol to coniferyl acetate which is the first committed step towards eugenol synthesis. Here, we perform a comparative next-generation transcriptome sequencing of different tissues of sweet basil, namely PGT, leaf, leaf stripped of PGTs (leaf–PGT), and roots, to identify differentially expressed transcripts specific to PGT. From these data, we identified a PGT-enriched BAHD acyltransferase gene ObCAAT1 and functionally characterized it. In vitro coupled reaction of ObCAAT1 with eugenol synthase in the presence of coniferyl alcohol resulted in eugenol production. Analysis of ObCAAT1-RNAi transgenic lines showed decreased levels of eugenol and accumulation of coniferyl alcohol and its derivatives. Coniferyl alcohol acts as a common substrate for phenylpropene and lignin biosynthesis. No differences were found in total lignin content of PGTs and leaves of transgenic lines, indicating that phenylpropene biosynthesis is not coupled to lignification in sweet basil.

Sweet basil (Ocimum basilicum) leaves are rich in bioactive compounds that present therapeutic benefits for human health. Ultrasonic-assisted extraction (UAE) is frequently used to obtain phenolic compounds from plants/herbal sources. However, few works have developed multi-variable studies to find the optimal conditions to extract the maximum amount of compounds, especially when applied to UAE via a sonotrode. The purpose of this work was to perform a multi-variable study by employing a Box–Behnken design to collect the highest active compound content from Ocimum basilicum leaves. The efficacy of the design was endorsed by ANOVA. The studied parameters for UAE via a sonotrode were the ethanol/water ratio, amplitude, and time. The analyzed responses were the rosmarinic acid, the sum of phenolic acids, and the sum of phenolic compounds content. The optimal conditions were found to be 50% ethanol/water, 50% amplitude, and 5 min. Twenty bioactive compounds were identified by HPLC-ESI-TOF-MS when the extract was collected by applying the optimal conditions. Ocimum basilicum may be appreciated as a valuable source of important bioactive substances for pharmaceutical use.

The medicinal plant sweet basil (Ocimum basilicum) accumulates bioactive ursane- and oleanane-type pentacyclic triterpenes (PCTs), ursolic acid and oleanolic acid, respectively, in a spatio-temporal manner; however, the biosynthetic enzymes and their contributions towards PCT biosynthesis remain to be elucidated. Two CYP716A subfamily cytochrome P450 monooxygenases (CYP716A252 and CYP716A253) are identified from a methyl jasmonate-responsive expression sequence tag collection and functionally characterized, employing yeast (Saccharomyces cerevisiae) expression platform and adapting virus-induced gene silencing (VIGS) in sweet basil. CYP716A252 and CYP716A253 catalyzed sequential three-step oxidation at the C-28 position of α-amyrin and β-amyrin to produce ursolic acid and oleanolic acid, respectively. Although CYP716A253 was more efficient than CYP716A252 for amyrin C-28 oxidation in yeast, VIGS revealed essential roles for both of these CYP716As in constitutive biosynthesis of ursolic acid and oleanolic acid in sweet basil leaves. However, CYP716A253 played a major role in elicitor-induced biosynthesis of ursolic acid and oleanolic acid. Overall, the results suggest similar as well as distinct roles of CYP716A252 and CYP716A253 for the spatio-temporal biosynthesis of PCTs. CYP716A252 and CYP716A253 might be useful for the alternative and sustainable production of PCTs in microbial host, besides increasing plant metabolite content through genetic modification.

Production of a volatile phenylpropene; eugenol in sweet basil is mostly associated with peltate glandular trichomes (PGTs) found aerially. Currently only one eugenol synthase (EGS), ObEGS1 which belongs to PIP family is identified from sweet basil PGTs. Reports of the presence of eugenol in roots led us to analyse other EGSs in roots. We screened for all the PIP family reductase transcripts from the RNA-Seq data. In vivo functional characterization of all the genes in E. coli showed their ability to produce eugenol and were termed as ObEGS2-8. Among all, ObEGS1 displayed highest expression in PGTs and ObEGS4 in roots. Further, eugenol was produced only in the roots of soil-grown plants, but not in roots of aseptically-grown plants. Interestingly, eugenol production could be induced in roots of aseptically-grown plants under elicitation suggesting that eugenol production might occur as a result of environmental cues in roots. The presence of ObEGS4 transcript and protein in aseptically-grown plants indicated towards post-translational modifications (PTMs) of ObEGS4. Bioinformatics analysis showed possibility of phosphorylation in ObEGS4 which was further confirmed by in vitro experiment. Our study reveals the presence of multiple eugenol synthases in sweet basil and provides new insights into their diversity and tissue specific regulation.

Background Sweet basil ( Ocimum basilicum ) is one of the most significant aromatic plants in Turkiye. Recently, a new pathogen induced symptoms were discovered and identified as basil downy mildew caused by Peronospora belbahrii Thines. The pathogen has been introduced into the country and it has quickly become the most damaging disease in basil cultivation. The purpose of this study was to investigate the molecular and morphological properties of the causal organism of downy mildew observed on sweet basil and determine the disease incidence and prevalence in Antalya province. Methods and results According to morphological characteristics (conidia, conidiophores) disease was determined as downy mildew caused by P. belbahrii . Pathogenicity tests were performed by spraying with a sporangial suspension of P. belbahrii (1 × 10 5 sporangia/mL). After 1 week, all inoculated plants exhibited characteristic downy mildew symptoms on their leaves, whereas non-inoculated control plants remained disease-free. All molecular analyses involving the internal transcribed spacer region were amplified using Nested PCR with primer pairs ITS4 and ITS6 for the first round and ITS4 and DC6 for the second round. Resulting sequences of all the nested PCR products had 99% similarity with P. belbahrii isolates. Disease incidence was 22.4–70.2% of sweet basil cultivation area in Antalya province. Conclusions Based on the molecular analysis, morphological characteristics and pathogenicity tests the pathogen was identified as P. belbahrii . To our knowledge, this is the first report of downy mildew caused by P. belbahrii on sweet basil in Turkiye.

This study focused on the effectiveness of neutral electrolyzed water (NEW) in inactivating coliforms on sweet basil, a fresh‐cut vegetable consumed, and estimating the human health risks related to the consumption of untreated sweet basil. The sweet basil samples contaminated with coliforms were treated with NEW to evaluate its effectiveness in inactivation. The hazard quotients (HQs) for untreated and treated sweet basil were then calculated based on the estimated daily intake and the toxicological reference values for coliforms. The results demonstrated that NEW was effective in reducing the coliform counts on sweet basil. The ranges of the total and fecal coliform removal efficiency were 62.31%–100% and 40.86%–100%, respectively. Moreover, HQ calculations indicated that consumption of untreated sweet basil had a higher risk of coliform exposure compared with treated sweet basil. On the basis of the results, NEW greatly reduced the risk of gastroenteritis in children (HQ decreased from 558,000 to 27.4). In other words, this disinfection solution reduced the probability of risk by 232,500 times. The application of NEW promises to reduce the microbial load on freshly chopped vegetables, such as sweet basil, making them safer for consumption, especially for children. Electrolyzed water effectively reduces coliform contamination on sweet basil, significantly decreasing health risks and potential gastroenteritis in children, thereby enhancing food safety for fresh produce consumption.

Sweet basil ( Ocimum basilicum L.) downy mildew disease (DM) caused by Peronospora belbahrii is a worldwide threat to the basil industry due to the lack of natural genetic resistance in sweet basil germplasm collections. In this study, we used CRISPR-gene editing to modify the sweet basil DM susceptibility gene homoserine kinase ( ObHSK ). Gene-edited plants challenged with P. belbahrii displayed a significantly reduced susceptibility to DM, based on phenotypic disease indices and on in planta pathogen load. These results suggest that ObHSK plays a role in conditioning DM susceptibility, similar to that observed for the AtHSK gene in Arabidopsis. These results demonstrate the utility of CRISPR-gene editing in enhancing DM resistance and contributing to sweet basil breeding programs.

Experiment was conducted in fields of Agriculture College, Al-Muthanna University, during the growing season 2020, to study the response of sweet basil ( Ocimum basilicum L.) to spraying three concentrations of aspartic acid (0, 75 and 150 mg.L −1 ) and with three concentrations of glutamic acid (0, 75 and 150 mg.L −1 ), and their impact on its growth and essential oil content. Results showed that the basil plants that have been sprayed with aspartic acid at a concentration (150 mg.L −1 ) significantly superior in plant height, fresh and dry weight of shoot, percentage and yield of volatile oil (45.61cm, 19.70 gm.plant −1 , 1.80 gm.plant −1 , 1.75 % and 31.48 μL.plant −1 ) respectively. Results also showed the significant effect of spraying glutamic acid at a concentration (150 mg.L −1 ), which gave highest values in plant height, fresh and dry weight of shoot, percentage and yield of volatile oil (48.67 cm., 20.28 gm.plant −1 , 1.83 gm.plant −1 , 1.56 % and 29.08 μL.plant −1 ) respectively.