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 commercially available since 2018. However, new pathogenic races that overcome host resistance were observed after each new cultivar introduction, suggesting rapid pathogen evolution under selective pressure. To track the race structure and to monitor the shift of pathogen populations, we established a differential panel of distinct basil cultivars that carry varying sources of genetic resistance. Testing against P. belbahrii strains obtained from geographically diverse multi-year collections from basil-producing locations in the US, Israel, and Italy, this differential panel revealed three distinct virulence profiles that distinguish race 0, race 1, and race 2. Race 0 isolates are avirulent on cultivars with resistance loci Pb1 and Pb2, while races 1 and 2 were defined by virulence in cultivars with loci Pb1 and Pb2, respectively. Compared to major gene resistance, evaluation of cultivars with quantitative disease resistance revealed more variation in susceptibility (or intermediate resistance), suggesting race-nonspecific resistance and highlighting the potential durability of utilizing diverse sources of resistance in future breeding approaches. With the dynamic nature of the pathogen and the continued efforts in adding disease resistant basil cultivars to meet the market demands, the denomination of P. belbahrii races is likely to expand, and this differential panel will continue to develop. Most importantly, 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.

Basil (Ocimum basilicum) is one of the most widely grown herb crops for fresh consumption, processing, and essential oil production. These markets are reliant upon high-quality, pathogen-free material, as disease renders fresh material unsellable and may alter taste and essential oil profiles for industrial producers. Meeting high-quality standards has become increasingly difficult with the introduction of basil downy mildew caused by Peronospora belbahrii into the United States and globally. Basil downy mildew is a highly destructive foliar disease of basil resulting in chlorosis, large lesions, gray-black spores, and plant death. Fungicides have shown variable efficacy between field seasons, are expensive, and require diligent and repeated applications for complete control. Repeated applications of high-risk fungicides provide selective pressure for pathogen evolution, exemplified by the appearance of mefenoxam-resistant populations of P. belbahrii. Resistant sweet basil varieties, though initially successful, have begun to break down under rapid pathogen race differentiation. This adaptability makes understanding the population genetics of the pathogen critical. This study, utilizing simple sequence repeats, examined the genetic diversity of 92 P. belbahrii isolates collected during 2018 to 2024 from Israel, Italy, Hawaii, Florida, Kansas, and the U.S. Northeast. Genetic diversity statistics indicate a highly heterozygous, largely non-clonal population structure in both the United States and Israel. These two populations appear to be at least partially genetically distinct and indicate differentiation along geographic lines. Significant genetic differences were also detected between race 0 and race 1, though a distinct set of classifying markers was not found.

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

Downy mildew caused by the oomycete Pseudoperonospora cubensis is a devastating disease of cucurbits. Cucumis species are attacked by pathotype 3 (clade 2) of the pathogen, while Cucurbita species are attacked by pathotype 6 (clade 1). The Sikkim-type cucumbers PI 197088 and PI 330628 express high levels of resistance against both pathotypes (clades) of the pathogen but no green-fruit cucumber cultivars resistant to the disease are available on the market. Here we report on several non-Sikkim accessions of cucumber that show resistance against downy mildew in four consecutive seasons. Mean % foliage attacked with downy mildew in the susceptible controls Ilan and SMR-18 was 93% and 71%, respectively, as against 0.2% and 1.8% in the Sikkim-type resistant controls PI 197088 and PI 330628, respectively. Twenty-four green fruit accessions were significantly more resistant than the susceptible cucumber controls. Five accessions showed less than 10% infected leaf area with downy mildew as follows: PI 432870—5%, PI 390266—7.5%, PI 418964—8.5%, PI 390258—8.8%, and G12—10%. PI 390258 and PI 390266 were susceptible to race 1 of powdery mildew but resistant to race 2, whereas PI 418964 was resistant to both races. These accessions may be used in breeding programs to accelerate the production of green-fruit, disease-resistant cucumbers.

Downy mildew, caused by the oomycete Pseudoperonospora cubensis, is the most destructive foliar disease of cucumbers. While partially resistant slicer cultivars (with spined fruits) are commercially available, no resistant Beit Alpha cultivars (characterized by smooth, dark green fruit) have been developed to date. Here, we report the successful breeding of downy mildew-resistant Beit Alpha cucumber lines. Resistance was transferred from the wild Sikkim cucumber accessions PI 197088 and PI 330628 (characterized by round fruit, with heavily netted brown rind). The resistance and fruit phenotype were restored through backcrosses to elite commercial susceptible cultivars. Due to the recessive nature of the resistance genes and their distribution across multiple chromosomes, the breeding program required multiple backcrosses and stringent selections for both resistance and fruit type.

Powdery mildew incited by the fungus Erysiphe necator is a destructive disease of grapes in Israel and elsewhere, attacking green parts of the vine and reducing yield and wine quality. Demethylation inhibitors (DMI) and quinone outside inhibitors (QoI) fungicides are frequently used to control the disease. However, starting in 2005 and 2007, respectively, we observed reduced control efficacy of DMI and QoI fungicides in Israel. The resistance of E. necator to DMI or QoI has not been phenotypically described or genetically characterized in the Middle Eastern region, and the seasonal dynamics of resistance have been under-studied worldwide. Field experiments performed during 2017 and 2018 in the Judean-foothills and Upper Galilee regions, showed reduced efficacy of both fungicides. Sensitivity of E. necator to the fungicides was determined in grape leaf disks bioassays. Isolates collected from sprayed plots exhibited EC50 values of 100-1000 and 2-8 mu g/mL for QoI and DMI, respectively, while isolates collected from non-sprayed vines showed EC50 values of 0.5-1.6 and 0.04-1.8 mu g/mL, respectively. Resistant isolates carried the genetic mutations to DMI (Y136F) and QoI (G143A). We conclude that the recently reduced control efficacy of the disease in Israeli vineyards resulted from fungicide resistance. Seasonal dynamics of DMI and QoI mutant isolates in the vineyards were different. The proportion of QoI mutant isolates increased and became dominant by mid and late season, while DMI mutant isolates dominated mid-season, and DMI-wild-type isolates dominated at the beginning and end of the season when selection pressure was low.

The fungicides oxathiapiprolin, benthiavalicarb, and their mixture (Zorvec Endavia) provided excellent protection for tomato fruits against Phytophthora infestans when applied directly to the fruits or to the fruit stem scar. High levels of protection were also recorded when the fungicides were applied to the root system of fruit-bearing plants grown in a greenhouse. The objective of this study was to follow the translocation of oxathiapiprolin and benthiavalicarb into the fruits of tomato. We discovered that while soil drenching conferred strong protection to leaves, it failed to provide good protection for the fruits. Similarly, a fungicidal spray applied to plants while their fruits were bagged during spraying provided full protection to the leaves but failed to protect the fruits. These results indicate differential systemic translocation of the fungicides to leaves versus fruits. LC–MS/MS analyses revealed translocation of oxathiapiprolin and benthiavalicarb to leaves but not to fruits in soil-treated plants. Thus, while fruits may be less protected, they may also pose a lower risk of pesticide residues to consumers. This is the first study to compare fruit versus leaf infection and demonstrate differential systemic translocation of systemic fungicides to leaves versus fruits.

Potatoes are grown in Israel twice a year, in autumn and spring, contributing over $300 million to the state's economy in 2022. In both seasons late blight caused by the oomycete Phytophthora infestans is a major threat to yields. Fungicides are the most important means to control P. infestans. The classical fungicides mancozeb and chlorothalonil were banned by the regulator while mefenoxam, cymoxanil and infinito, suffer of reduced field efficacy. The new OSBPI fungicide oxathiapiprolin solo provides excellent control of the disease by foliar or soil applications but its proneness to resistance development enforces its application in mixtures with fungicides with a different mode of action. In three field trials done in Israel during 2021-2023, oxathiapiprolin solo and seven oxathiapiprolin-premixed fungicides were applied to potato crops Sifra or VR808 at early season. Plants were thereafter inoculated with mixed genotypes of P. infestans, sensitive and resistant to mefenoxam, and disease progress was monitored along 35 days after inoculation. All oxathiapiprolin products provided excellent control of the disease all along the season, significantly better than the fungicides mancozeb, mefenoxam, cymoxanil, ranman or infinito. Disease control was dependent on the dose applied, the proportion of oxathiapiprolin in the mixture, the partner fungicide, and the experiment. At the recommended dose of 0.1 % (50 g/ha in 500 L), the mixtures with mefenoxam or mandipropamid were more effective than the mixtures with chlorothalonil or azoxystrobin. At 0.2 %, all seven mixtures were highly effective all along the season. Tuber yields were significantly higher in plots treated with oxathiapiprolin mixtures as compared with control fungicide-free plots. Monitoring assays done along the season failed to detect oxathiapiprolin-insensitive mutants of P. infestans in all three trials, including plots treated with 0.2 % oxathiapiprolin solo (MIC = 0.3 ppm ai). We conclude that a single preventive application of oxathiapiprolin-based fungicides to potato crops at early season can provide effective control of late blight under heavy pressure of P.infestans for as long as 5 weeks without selecting for insensitive mutants.

Late blight, caused by the oomycete Phytophthora infestans, is a devastating disease of potato worldwide. In Israel, potatoes are grown twice a year, in autumn and spring, with late blight causing extensive damage in both seasons. While tuber seeds for the autumn planting are produced locally, seed tubers for the spring planting are imported from Europe due to dormancy of local tubers. Here, we demonstrate that seed tubers imported from Europe for the spring season carry asymptomatic infection with EU genotypes of P. infestans, which alters the population structure of the pathogen each spring. The proportion of imported tubers carrying asymptomatic infections ranged between 1.2 and 3.75%, varying by year and cultivar. Asymptomatic tubers produced late blight-infected sprouts about one month after planting. The sporangia produced on these sprouts served as primary inoculum, causing intensive foliage attacks on neighboring plants. When sprout-infected plants were uprooted and the mother tuber was washed, sliced, and placed in moistened dishes at 18 °C, profuse sporulation of P. infestans developed on the slices’ surfaces within 1–2 days. The dominant genotype of P. infestans in the autumn season in Israel is 23A1, but genotypes in the following spring season changed to include 13A2 or 36A2. Surprisingly, genotype 43A1, which might be resistant to CAA and OSBPI fungicides and appeared in Europe in 2022, emerged in Israel in spring 2024. The immigrating genotypes do not persist in the country, allowing 23A1 to regain predominance in the following autumn. Long-term monitoring data suggest that the population structure of P. infestans changes yearly but temporarily due to the import of new genotypes from Europe.

SUMMARYLate blight caused by the oomycete Phytophthora infestans is a most devastating disease of potatoes (Solanum tuberosum). Its early detection is crucial for suppressing disease spread. Necrotic lesions are normally seen in leaves at 4 days post‐inoculation (dpi) when colonized cells are dead, but early detection of the initial biotrophic growth stage, when the pathogen feeds on living cells, is challenging. Here, the biotrophic growth phase of P. infestans was detected by whole‐plant redox imaging of potato plants expressing chloroplast‐targeted reduction–oxidation sensitive green fluorescent protein (chl‐roGFP2). Clear spots on potato leaves with a lower chl‐roGFP2 oxidation state were detected as early as 2 dpi, before any visual symptoms were recorded. These spots were particularly evident during light‐to‐dark transitions, and reflected the mislocalization of chl‐roGFP2 outside the chloroplasts. Image analysis based on machine learning enabled systematic identification and quantification of spots, and unbiased classification of infected and uninfected leaves in inoculated plants. Comparing redox with chlorophyll fluorescence imaging showed that infected leaf areas that exhibit mislocalized chl‐roGFP2 also showed reduced non‐photochemical quenching and enhanced quantum PSII yield (ΦPSII) compared with the surrounding leaf areas. The data suggest that mislocalization of chloroplast‐targeted proteins is an efficient marker of late blight infection, and demonstrate how it can be utilized for non‐destructive monitoring of the disease biotrophic stage using whole‐plant redox imaging.

AbstractBACKGROUNDOxathiapiprolin (OXPT; FRAC code 49) is a new piperidinyl‐thiazole isooxazoline anti‐oomycete fungicide that targets oxysterol‐binding proteins. The fungicide is known to translocate acropetally from root to shoot to protect plants against fungal attack.RESULTSOXPT is ambimobile. It can also translocate basipetally from shoot to root. OXPT exhibits an unprecedented capacity for trans‐plant protection. When two tomato plants are grown in one pot, and one is treated with OXPT (on the stem, leaves or apex), while the other plant and soil surface are adequately covered, both plants become protected against late blight caused by Phytophthora infestans.CONCLUSIONTrans‐plant systemic protection induced by OXPT involves translocation of the fungicide from the shoot of the treated plant to its root, exudation into the soil and uptake by the root of the neighboring untreated plant to protect it against the disease. Liquid chromatography–tandem mass spectrometry analyses confirmed the occurrence of OXPT in root exudates of OXPT‐treated tomato plants in quantities sufficient to protect detached tomato leaves and intact plants against P. infestans. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Mancozeb (MZ) is a broadly used fungicide for the control of plant diseases, including late blight in potatoes caused by the oomycete Phytophthora infestans (Mont.) De Bary. MZ has been banned for agricultural use by the European Union as of January 2022 due to its hazards to humans and the environment. In a search for replacement fungicides, twenty-seven registered anti-oomycete fungicidal preparations were evaluated for their ability to mitigate the threat of this disease. Fourteen fungicides provided good control (≥75%) of late blight in potted potato and tomato plants in growth chambers. However, in Tunnel Experiment 1, only three fungicides provided effective control of P. infestans in potatoes: Cyazofamid (Ranman, a QiI inhibitor), Mandipropamid (Revus, a CAA inhibitor), and Oxathiapiprolin + Benthiavalicarb (Zorvek Endavia, an OSBP inhibitor + CAA inhibitor). In Tunnel Experiment 2, these three fungicides were applied at the recommended doses at 7-, 9-, and 21-day intervals, respectively, totaling 6, 4, and 2 sprays during the season. At 39 days post-inoculation (dpi), control efficacy increased in the following order: Zorvec Endavia > Ranman > Revus > Mancozeb. Two sprays of Zorvec Endavia were significantly more effective in controlling the blight than six sprays of Ranman or four sprays of Revus. We, therefore, recommend using these three fungicides as replacements for mancozeb for the control of late blight in potatoes. A spray program that alternates between these three fungicides may be effective in controlling the disease and also in avoiding the build-up of resistance in P. infestans to mandipropamid and oxathiapiprolin.

Powdery mildew caused by the fungus Erysiphe necator is a major grape disease worldwide. It attacks foliage and berries and reduces yield and wine quality. Fungicides are mainly used for combating the disease. Fungicide resistance and the global requisite to reduce pesticide deployment encourage the use of environment-friendly alternatives for disease management. Our field experiments showed that the foliar application of the potassium phosphate fertilizer Top-KP+ (1-50-33 NPK) reduced disease incidence on leaves and clusters by 15–65% and severity by 75–90%, compared to untreated vines. Top-KP+ mixed with Nanovatz (containing the micronutrients boron (B) and zinc (Zn)) or with TruPhos Platinum (a mixture containing N, P2O5, K2O, Zn, B, Mg, Fe, Mn, Cu, Mo, and CO) further reduced disease incidence by 30–90% and disease severity by 85–95%. These fertilizers were as effective as the fungicide tebuconazole. Tank mixtures of fertilizers and tebuconazole further enhanced control efficacy in the vineyards. The modes of action of fertilizers in disease control were elucidated via tests with grape seedlings, microscopy, and berry metabolomics. Fertilizers applied preventively to the foliage of grape seedlings inhibited powdery mildew development. Application onto existing mildew colonies plasmolyzed mycelia and conidia and arrested the development of the disease. Berries treated with fertilizers or with a fungicide showed a significant increase in anti-fungal and antioxidant metabolites. Twenty-two metabolites, including non-protein amino acids and carbohydrates, known for their anti-fungal and bioactive effects, were significantly upregulated in grapes treated with fertilizers as compared to grapes treated with a fungicide, suggesting possible indirect activity against the pathogen. Esters and organic acids that contribute to wine quality were also upregulated. We conclude that integrating macro and micronutrients in spray programs in commercial vineyards shall control powdery mildew, reduce fungicide deployment, delay the buildup of fungicide resistance, and may improve wine quality.

Precision irrigation can affect orchard water status and water productivity (WP). It is hypothesized that crop water status-based irrigation at the subfield scale can maintain tree water status according to targets, thereby increasing WP. Our objectives were to define a spatiotemporal decision support protocol for variable rate drip irrigation (SDSP-VRDI) in a well-watered peach orchard and to evaluate protocol efficiency on a subfield scale. Research was initiated during 2017 in a uniformly irrigated commercial peach orchard. In 2018, half the orchard was converted to SDSP-VRDI utilizing a model developed to study the relationship between stem water potential (SWP) and thermal image-based crop water stress index (CWSI). In 2019, the orchard's south subplot continued to be irrigated uniformly while its north subplot was managed according to SDSP-VRDI during the primary stage of fruit growth and the period of peak irrigation (stage III). The SDSP-VRDI included seven steps including calculation of the CWSI per management cell (MC) using thermal imagery. The CWSI was used to estimate SWP that was compared to a specified target range driving irrigation applied per MC based on FAO-56. The target range was reached in most MCs by applying MC-specific irrigation. Some specific MCs responded well to higher amounts of irrigation while others did not, as evident from relative yield, WP, and water cost efficiency data. Management downscaling from field to subfield scale appears to be beneficial and could advance precision irrigation management of complex orchard systems.

Precision drip irrigation of horticultural crops is receiving interest, mostly in applications in large orchards and vineyards where spatial variability results in costs to yields, quality and water productivity. We review the issues and status of precision and variable rate drip irrigation and summarize advancements and issues regarding opportunity to consider spatial irrigation management in orchards and vineyards. Topics discussed include: the conflict between "smart" and "precise" irrigation; challenges and advancement in variable-rate drip irrigation application technologies and; the use of data, including that acquired from sensors and remote sensing, for both the delineation of management zones and decision making for irrigation scheduling within zones. Prospects for future work and progress for drip irrigated horticultural application of precision water management include variable rate dripper technologies, utilization of big data from sensors and remote sensing, and unique multivariate data processing including spatial-temporal modeling.

Wide assimilation of precision agriculture among farmers is currently dependent on the ability to demonstrate its efficiency at the field-scale. Yet, most experiments that compare variable-rate vs uniform application (VRA and UA) are performed in strips, concentrated in a small portion of the field with limited extrapolation to the field scale. A spatiotemporal normalized ratio (STNR) methodology is proposed to evaluate the impact of VRA compared with UA for on-farm trials at the field scale. It incorporates a base year in which the whole plot is managed with UA and consecutive years in which half of the plot is managed with UA and the other half is managed with VRA. Additionally, a novel normalized relative comparison index (NRCI) is presented where the ratios of VRA/UA sub-plots are compared between a base year and a consecutive year, for any measured parameter. The NRCI determines the impact of VRA on variability using statistical measures of dispersion (variability measures) and on performance with statistical measures of central tendency (performance measures). Variability measures with NRCI values lower or higher than 1 indicate VRA management decreased or increased variability. Performance measures with NRCI lower or higher than 1 indicate subplot impairment or improvement, respectively due to VRA management. The methodology was demonstrated on a commercial drip irrigated peach orchard and a wine grape vineyard. NRCI results showed that VRA drip irrigation reduced water status in-field variability but did not necessarily increase yield. The benefits and limitations of the proposed design are discussed.

Current irrigation management zones (IMZs) for variable rate irrigation (VRI) systems are static. They are delineated in the beginning of the season and used thereafter. However, recent research has shown that IMZ boundaries are transient and change with time during the growing season. The primary goal of this study was to explore the potential of using vegetation indices (VIs) developed from unmanned aerial vehicle (UAV) and satellite images to predict cotton physiological parameters that can be used to delineate in-season boundaries of IMZs. A 2 year study was conducted in a 38 ha commercial cotton field in southwestern Georgia, USA. Throughout the two growing seasons, VIs were calculated from UAV, PlanetScope, and Sentinel-2 images. Predawn leaf water potential (LWP PD ) and plant height were measured at 37 locations in the field on the same day as the flights and correlated with UAV and satellite based-VIs. GNDVI (Green normalized difference vegetation index) was the best predictor of plant height with correlation values of 0.72 (p < .0001) and 0.84 (p < .0001) for 2019 and 2020, respectively. A secondary goal was to compare the performance of dynamic VRI (DVRI) to conventional irrigation. The field was divided into alternating parallel conventional, and DVRI strips to compare the two scheduling methods. The conventional strips were irrigated using the farmer’s standard method and individual IMZs within the DVRI strips were irrigated based on soil water tension (SWT) measured with a wireless soil moisture sensor network. LWP and SWT measurements correlated well. IMZs were initially delineated using soil texture, apparent soil electrical conductivity (ECa), and yield maps and satellite images from previous years and were modified in-season to reflect patterns observed in the plant height maps. In 2020, the DVRI system prescribed an average irrigation amount of 50.8 mm while conventional irrigation applied an average of 58.4 mm. Average yields for DVRI and conventional were 1248 and 1191 kg ha −1 , respectively. The DVRI system resulted in average yield 4.6% higher than conventional irrigation, while applying 14.0% less water. Despite the lower water application by the DRVI system, the performance comparison between the DRVI and the conventional irrigation was not conclusive.

A methodology to compare field-scale uniform application (UA) and variable rate application (VRA) to evaluate precision management is defined. The methodology includes a relative comparison index (RCI) where the ratio between VRA and UA plots is compared in a base-year and additional season for any measured parameter. VRA irrigation decreased the variability of stem water potential (SWP), yield and water productivity (WP) (RCI1). The methodology has the potential to enrich the current VRA toolbox.