Podosphaera Xanthii Research Articles

Proteome Profiling of Cucurbita pepo Phyllosphere After Infection by Podosphaera xanthii and Application of Reynoutria sachalinensis Extract

Podosphaera xanthii is the main causal agent of powdery mildew (PM) disease for Cucurbita pepo. Disease control is attained principally by applications of chemical fungicides, along with parallel use of tolerant crop varieties and alternate application of elicitors to control development of disease resistance. To get insight into C. pepo molecular responses to P. xanthii infection and elicitor treatment we studied the proteomic profile differences at the phyllosphere of a zucchini cultivar susceptible to PM, at the onset of P. xanthii (PX) infection and after application of Reynoutria sachalinensis (RS) plant extract, respectively, using a nano-LC-HRMS/MS, Q-Exactive-Orbitrap approach. Analysis of peptide sequences regarding four treatment groups (Control; PX; RS; and RSPX (PX-infected priorly treated with RS)) resulted in 2070 CuGenDB annotations. Three comparisons (treatments vs. Control) encompassed most of the Differentially Expressed Proteins (DEPs). In these three comparisons, KEGG and Gene Ontology functional analyses highlighted unique differentially enriched pathways—some of which included highly expressed proteins—in PX-related (proteasome, pentose phosphate pathway, and carbon fixation), RS-related (biosynthesis of secondary metabolites, flavonoids, and starch and sucrose metabolism), and RSPX-related (pyruvate metabolism and polycomb repressive complex) comparisons, respectively, suggesting distinct mechanisms of early plant responses modulated by PX and RS. Furthermore, in four out of six comparisons the thiamine metabolism pathway was found to be enriched, suggesting a pivotal role in PX-induced responses.

Specialty Melons Grown under High Tunnel Conditions Yield Good to Excellent Internal Quality

Interest in local foods, especially locally grown fruit, is increasing. High tunnel vegetable growers are strategically poised to meet this demand by growing specialty melons (Cucumis melo). Although specialty melons are commonly grown in high tunnels in other parts of the world, it is an uncommon practice in the midwestern United States. The objectives of this study were to evaluate 10 specialty melon cultivars for high tunnel production and measure fruit yield and internal quality. Fruit of the cultivar Eden’s Gem yielded the greatest number of marketable fruits per plant; however, these melons are small and have a loose cavity. Fruit of the cultivars Honey Orange and Divergent yielded the largest marketable fruit per plant with tighter cavities; however, the cavities were large. All cultivars had good to excellent internal quality in terms of sugar content. The production of specialty melons in the high tunnel was successful, resulting in the production of melons with good to excellent internal quality, and several yielded three to four marketable fruit per plant. Implementing a strong pest management plan for cucumber beetle (Diabrotica undecimpunctata howardi) and powdery mildew (Erysiphe cichoracearum, Sphaerotheca fuliginea) is recommended to prevent yield loss, especially in locations such as the Midwest, where cucumber beetles often vector bacterial wilt (Erwinia tracheiphila).

The mutant STAY-GREEN (Cssgr) in cucumber interacts with the CSEP30 protein to elicit a defense response against Podosphaera xanthii.

The online version contains supplementary material available at 10.1007/s11032-024-01504-6.

Fungicidal Activity of Novel 6-Isothiazol-5-ylpyrimidin-4-amine-Containing Compounds Targeting Complex I Reduced Nicotinamide Adenine Dinucleotide Oxidoreductase.

To discover novel inhibitors of the complex I reduced nicotinamide adenine dinucleotide (NADH) oxidoreductase as fungicides, a series of 6-isothiazol-5-ylpyrimidin-4-amine-containing compounds were designed using a computer-aided pesticide design method and splicing of substructures from diflumetorim and isotianil. In vitro fungicidal bioassays indicated that compounds T17-T24 showed high inhibitory activity against Rhizoctonia solani with an effective concentration (EC50) value falling between 2.20 and 23.85 μg/mL, which were more active than or equivalent to the lead diflumetorim with its EC50 of 19.80 μg/mL. In vivo antifungal bioassays demonstrated that, at a concentration of 200 μg/mL, T7 and T21 showed higher inhibition against Pseudoperonospora cubensis than all other compounds, while T23 exhibited the highest inhibition against Sphaerotheca fuliginea. T23 showed an approximately twofold lower inhibition potency against R. solani complex I NADH oxidoreductase than diflumetorim. Molecular docking and transcriptomic analyses indicated that T23 and diflumetorim both might share the same mode of action, targeting NADH oxidoreductase. T23 as a good fungicidal candidate against R. solani is worthy of further investigation.

Phospholipid production and signaling by a plant defense inducer against Podosphaera xanthii is genotype-dependent.

Biotrophic phytopathogenic fungi such as Podosphaera xanthii have evolved sophisticated mechanisms to adapt to various environments causing powdery mildews leading to substantial yield losses. Today, due to known adverse effects of pesticides, development of alternative control means is crucial and can be achieved by combining plant protection products with resistant genotypes. Using plant defense inducers, natural molecules that stimulate plant immune system mimicking pathogen attack is sustainable, but information about their mode of action in different hosts or host genotypes is extremely limited. Reynoutria sachalinensis extract, a known plant defense inducer, especially through the Salicylic acid pathway in Cucurbitaceae crops against P. xanthii, was employed to analyze the signaling cascade of defense activation. Here, we demonstrate that R. sachalinensis extract enhances phospholipid production and signaling in a Susceptible to P. xanthii courgette genotype, while limited response is observed in an Intermediate Resistance genotype due to genetic resistance. Functional enrichment and cluster analysis of the upregulated expressed genes revealed that inducer application promoted mainly lipid- and membrane-related pathways in the Susceptible genotype. On the contrary, the Intermediate Resistance genotype exhibited elevated broad spectrum defense pathways at control conditions, while inducer application did not promote any significant changes. This outcome was obvious and at the metabolite level. Main factor distinguishing the Intermediate Resistance form the Susceptible genotype was the epigenetic regulated increased expression of a G3P acyltransferase catalyzing phospholipid production. Our study provides evidence on phospholipid-based signaling after plant defense inducer treatment, and the selective role of plant's genetic background.

Fine mapping and identification of candidate genes associated with powdery mildew resistance in melon (Cucumis melo L.).

Powdery mildew (PM), a common disease of many major crop species, including melon (Cucumis melo L.), affects plant growth and fruit quality and seriously reduces production. Using a combined morphological and molecular approach, we attribute the PM pathogen that naturally occurs in melon to Podosphaera xanthii, and specifically to physiological race 1. An investigation into the genetic basis of PM resistance in melon using the resistant accession 'PI 164637' and susceptible counterpart 'HDZ' reveals dominant inheritance of PM resistance at the seedling stage, supported by F2 and backcross population segregation ratios. Adult plant assessments indicate a major gene with an additive effect for PM resistance. Bulk segregant analysis coupled with high-throughput sequencing identified a significant quantitative trait locus on chromosome 6 that is associated with PM resistance. Genetic mapping narrowed down the candidate region to 63.5kb using InDel molecular markers, harboring 12 candidate genes. The marker chr06_indel_5 047 127 demonstrated high accuracy in screening PM resistance in an F2 segregating population and 30 inbred lines as natural populations. Functional annotation and expression analysis of candidate genes revealed that MYB transcription factor MELO3C006700, GATA transcription factor MELO3C028829 and heparanase-like protein MELO3C006697 are promising candidate genes for PM resistance in melon. The genetic architecture underlying this resistance in melon offers valuable insights for breeding programs, and the identified markers, especially chr06_indel_5 047 127, may enable practical applications for marker-assisted selection in developing PM-resistant melon varieties.

Powdery Mildew of Xanthium strumarium Caused by Podosphaera xanthii in central China.

Xanthium strumarium, known as cocklebur, is an annual herb and has been used in traditional Chinese medicine. In October 2020, powdery mildew-like disease signs and symptoms were observed on X. strumarium grown in a crop field, Xinxiang city, Henan Province, China (35.36076° N, 113.93467° E). The specimen (PX-XS2023) was stored in Xinxiang Key Laboratory of Plant Stress Biology. White colonies in irregular or coalesced circular shaped-lesions were abundant on both ad- and abaxial surfaces of leaves and covered up to 99 % of the leaf area. Some of the infected leaves were senesced. More than 70 % of plants (n = 130) exhibited these signs and symptoms. Conidiophores were straight or slightly curved, 55 to 160 × 11 to 13 μm composed of foot-cells, shorter cells and conidia. Conidia were ellipsoid to oval, 29 to 40 × 14 to 20 μm (n = 50), with a length/width ration of 2.0 to 2.5, containing fibrosin bodies. Dark brown to black chasmothecia were found on infected leaves. The appendages were mycelium-shaped and at the base of scattered or gregarious chasmothecia (n = 50, 70 to 120 μm in diameter). Asci were 55 to 80 × 50 to 65 μm (n=30). These morphological characteristics were consistent with those of Podosphaera xanthii (Braun and Cook 2012). The internal transcribed spacer (ITS) region and Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) region of the fungus (PX-XS2023) were amplified and sequenced with primers ITS1/ITS4 (White et al. 1990) and GAPDH1/GAPDH3R (Bradshaw et al. 2022) according to a previously reported method (Zhu et al. 2022). The resulting sequences were respectively deposited into GenBank (Accession No. MW300956 and PP236083). BLASTn analysis indicated that the sequences were respectively 99.82 % (564/565) and 100% (272/272) identical to P. xanthii (MT260063 and ON075658). The phylogenetic analysis indicated that the strain PX-XS2023 and P. xanthii were clustered into a same branch. Therefore, the causal agent of powdery mildew on X. strumarium was P. xanthii. To conduct pathogenicity assays, mature leaves of five healthy X. strumarium (height in 50 centimeters) were inoculated with fungal conidia by gently pressing surfaces of infested leaves onto leaves of healthy plants (Zhu et al. 2020). Five untreated plants served as controls. The controls and inoculated plants were separately maintained in greenhouses (humidity, 60%; light/dark, 16 h/8 h; temperature, 18°C). Eight days post-inoculation, signs of powdery mildew were detectable on inoculated plants, however, the controls were asymptomatic. Thus, the fungal pathogen was morphologically and molecularly identified and confirmed as P. xanthii. This powdery mildew caused by P. xanthii was previously reported on X. strumarium in Korea, Russia and India (Farr and Rossman, 2021). In addition, P. xanthii was recorded on X. strumarium in Xinjiang Province, China (Tai 1979). However, this is the first report of P. xanthii on X. strumarium in central China, where is around 3000 km away from Xinjiang Province with geographically differences. The sudden presence of powdery mildew caused by P. xanthii may adversely affect plant health and thus reduce medical value of X. strumarium. Therefore, the identification and confirmation of P. xanthii infecting X. strumarium enhance the knowledge on the hosts of this pathogen in China and will provide fundamental information for disease control in the future.

First report of powdery mildew on Impatiens balsamina caused by Podosphaera xanthii in the USA

First report of powdery mildew on Impatiens balsamina caused by Podosphaera xanthii in the USA

Podosphaera xanthii Causing Powdery Mildew on Salvia farinacea in Central China.

Salvia farinacea, commonly referred as mealycup sage, is a perennial herbaceous plant belonging to the Salvia genus of the Lamiaceae family. It originates from the Mediterranean region, North America, and Europe and is globally cultivated due to its appealing and captivating flowers. Moreover, mealycup sage is utilized as traditional Chinese medicinal plant for treatment of cardiovascular diseases (Li et al. 2018). In October 2023, powdery mildew-like symptoms were observed on Salvia farinacea plants cultivated in a garden located in Xinxiang City, Henan Province, China (113.93, 35.29). The leaves were covered with white and thin masses of mycelia, conidiophores and conidia of the fungus. About 100 plants were checked and 90 % were infected. There were a large number of white colonies with irregular or continuous round lesions on the adaxial and abaxial surfaces of the leaves, covering approximately 80% of the leaf area. The slightly or straight curved conidiophores (n = 30) were 46 to 145× 8 to 11 μm in size and consisted of foot cells, shorter cells and conidia. The ellipsoidal to oval conidia (n = 30), containing fibrosin bodies, were 24 to 35 × 12 to 19 μm in size and had a length/width ratio of 1.8 to 2.1. No chasmothecia were observed on leaves. These morphological features were consistent with those of Podosphaera xanthii (Braun and Cook 2012). Following the previously described method (White et al. 1990; Bradshaw et al. 2022; Zhu et al. 2022a), the sequences of ITS and Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) regions were amplified with specific primers ITS1/ITS4 (ITS1 5'-TCCGTAGGTGAACCTGCGG-3' ; ITS4 5'-TCCTCCGCTTATTGATATGC-3') and PMGAPDH1/PMGAPDH3R (PMGAPDH1 5'-GGAATGGCTATGCGTGTACC-3'; PMGAPDH3R 5'-CCCCATTCGTTGTCGTACCATG-3'), and the resulting sequences were uploaded in GenBank (Accession No. OR761885 and PP236082, respectively). BLASTn analysis showed that the sequence shared 560/565 (99%) and 272/272 (100%) homology with P. xanthii (MW301281) on Impatiens balsamina (Zhu et al. 2022b) and with P. xanthii (ON075658) on Cucumis melo (Bradshaw et al. 2022), respectively. The phylogenetic analysis clearly illustrated that the collected isolate of P. xanthii clustered in the same clade. The pathogenicity was tested according to the method previously described (Zhu et al. 2021). The fungus was inoculated onto the leaf surfaces of three healthy plants by blowing conidia from infected leaves with pressurized air. Non-inoculated plants were treated as control. Both the control and inoculated plants were separately placed in growth chambers under 60% humidity; light/dark, 16 h/8 h; and a temperature of 18°C. After a period of 12-15 days, the leaves of the inoculated plants exhibited signs of powdery mildew, whereas the control group remained unaffected. Therefore, the fungal pathogen was identified and confirmed as P. xanthii (isolate PXSF202310). Previously, P. xanthii was reported on Impatiens balsamina and S. farinacea from China and Korea (Zhu et al. 2021; Choi et al. 2022). As far as we know, this is the first documentation of P. xanthii on S. farinacea in central China. The presence of P. xanthii can lead to a deterioration in plant health and stunted growth, thereby negatively impacting both the decorative and medicinal value of S. farinacea. The recognition of P. xanthii on S. farinacea enhances our comprehension of this pathogen hosts and provides fundamental information for forthcoming disease control studies.

Susceptibility of Zucchini Cultivars to Powdery Mildew (Podosphaera xanthii) Under High- and Low-Nitrogen Regimes

Powdery mildew, primarily caused by Podosphaera xanthii, threatens cucurbit crop yield and longevity. Fungicides and resistant cultivars cannot fully manage or prevent the disease. Previous work has shown that powdery mildew incidence and severity can increase under high soil nitrogen. This study was conducted in Kentucky to determine disease severity and yield using a split plot design with nitrogen fertility (high: 140 kg/ha; low: 84 kg/ha) and zucchini cultivar (Cash Machine, Cue Ball, Desert, Dunja, Eight Ball, Emerald Delight, Golden Glory, Mexicana, and Spineless Perfection) as the main plot and subplot factors, respectively. In year 1, powdery mildew severity was significantly higher in high soil nitrogen and varied significantly among cultivars. Yield was significantly lower in high soil nitrogen. Significant differences in fruit count, but not fruit weight, were observed among the cultivars. In year 2, nitrogen did not significantly affect disease severity, but fruit weight and count were significantly lower in the high soil nitrogen treatment. Golden Glory had significantly higher powdery mildew severity, while Mexicana and Eight Ball had significantly lower severity compared to all other cultivars. Spineless Perfection had the highest fruit weight and was significantly higher than all other cultivars except for Cue Ball and Eight Ball. Golden Glory had the highest fruit count and was significantly higher than all others except for Dunja. Nitrogen did not consistently affect disease severity throughout the study. The effects of powdery mildew on yield should be explored further, as heavily diseased plants did not always have low yield.

First Report of Powdery Mildew Caused by Podosphaera xanthii on Sphagneticola trilobata in Hainan Province, China.

Sphagneticola trilobata (L.) Pruski is a perennial creeping herb of the Asteraceae family, which is native to South America. It was introduced into Southern China as a groundcover in the 1970s (Zhang et al. 2023). Now it is mainly used for folk medicine to treat various kinds of inflammatory, incuding joint pain, rheumatic diseases, arthritis, in addition to treating persistent wounds, ulcers, and edemas (Gonçalves et al. 2022). In February and November 2023, powdery mildew symptoms were observed on 60% of S. trilobata plants on the Hainan Medical University campus (19° 58' 53″ N; 110° 19' 47″ E) in Haikou, Hainan Province, China. Powdery mildew colonies covered the leaf surfaces and stems of affected plants, causing discoloration and defoliation. Mycelia were superficial and hyphal appressoria were nipple-shaped. Conidiophores (n =30) were unbranched, cylindrical, 74 to 161 × 10 to 14 µm, and produced three to five immature conidia in chains with a crenate outline. Foot cells (n =30) were cylindrical, straight or sometimes curved at the base, and 27 to 56 µm long. Conidia (n =100) were ellipsoid-ovoid to doliiform, 17 to 30 ×14 to 28 µm (length/width ratio = 1.1 to 1.9), with well-developed fibrosin bodies, and produced germ tubes from the lateral position. Based on these morphological characteristics, the pathogen was provisionally identified as Podosphaera xanthii (Braun and Cook 2012). The teleomorph was not observed. A specimen was deposited in the Hainan Medical University Plant Pathology Herbarium as HMST-23. To confirm the genus identification and ascertain a putative species, genomic DNA was extracted from mycelium, conidiophores, and conidia using a fungal DNA kit (Omega Bio-Tek, USA). The rDNA internal transcribed spacer (ITS) region was amplified with primers ITS1/ITS4 (White et al. 1990) and sequenced directly. The resulting 577-bp sequence was deposited in GenBank (accession no. OR784549). A BLASTn search in GenBank of this sequence showed 100% similarity with the ITS sequences of P. xanthii isolates from China (MT260063, MN203658, OP765400, and MT739423), Thailand (LC270780), and Vietnam (KM260731, KM260730, and KR779870). Additionally, the 28S rDNA region was amplified using the primer pairs NL1 and NL4 (O´Donnell 1993; accession no. OR784550). This region shared 100% similarity with P. xanthii isolates (LC371334, LC270782, AB936277, and OP765401) as well. Powdery mildew from Hainan sample belonged to the P. xanthii group with strong bootstrap values support 99% in maximum likelihood phylogenetic tree based on ITS and 28S gene sequences. To confirm pathogenicity, five healthy potted plants of S. trilobata were inoculated by gently pressing a powdery mildew-infected leaf onto 15 young leaves. Five non-inoculated plants served as controls. All plants were maintained in a greenhouse at 24 to 30°C, 70% relative humidity, with a 16-h photoperiod. After 7 days, inoculated leaves showed powdery mildew symptoms whereas no symptoms were observed on control plants. The fungal colonies observed on inoculated plants were morphologically identical to those found on the originally infected leaves collected from Hainan Province. Based on the morphological characteristics and molecular identification, the fungus was identified as P. xanthii. In different countries and regions, P. xanthii has been previously reported on S. trilobata in Taiwan (Yeh et al. 2021). To our knowledge, this is the first record of P. xanthii infecting S. trilobata in Hainan Province, China. S. trilobata is often planted as an ornamental plant on both sides of the road, and we are concerned that it may serve as a new host, spreading this pathogen to other economic crops.

CmPIF8-CmERF27-CmACS10-mediated ethylene biosynthesis modulates red light-induced powdery mildew resistance in oriental melon.

Powdery mildew is a serious fungal disease in protected melon cultivation that affects the growth, development and production of melon plants. Previous studies have shown that red light can improve oriental melon seedlings resistance to powdery mildew. Here, after inoculation with Podosphaera xanthii, an obligate fungal pathogen eliciting powdery mildew, we found that red light pretreatment increased ethylene production and this improved the resistance of melon seedlings to powdery mildew, and the ethylene biosynthesis gene CmACS10 played an important role in this process. By analysing the CmACS10 promoter, screening yeast one-hybrid library, it was found that CmERF27 positively regulated the expression of CmACS10, increased powdery mildew resistanceand interacted with PHYTOCHROME INTERACTING FACTOR8 (CmPIF8) at the protein level to participate in the regulation of ethylene biosynthesis to respond to the red light-induced resistance to P. xanthii, Furthermore, CmPIF8 also directly targeted the promoter of CmACS10, negatively participated in this process. In summary, this study revealed the specific mechanism by which the CmPIF8-CmERF27-CmACS10 module regulates red light-induced ethylene biosynthesis to resist P. xanthii infection, elucidate the interaction between light and plant hormones under biological stress, provide a reference and genetic resources for breeding of disease-resistant melon plants.

Ficus carica Linn leaves extract induces cucumber resistance to Podosphaera xanthii by inhibiting conidia and regulating enzyme activity

Cucumbers (Cucumis sativus L.) are highly susceptible to infection by powdery mildew (PM), resulting in a deterioration of cucumber quality. The utilization of chemical control measures can effectively control cucumber PM; however, it may potentially give rise to issues such as environmental pollution, compromised safety, and drug resistance. The urgent need for a green, secure, and efficient strategy to manage cucumber PM necessitates attention. The predominant fungal pathogen causing PM in cucumbers is Podosphaera xanthii (P. xanthii) in this study. The preventive and control efficacy of Ficus carica Linn leaf extract (FLE) against P. xanthii was investigated for the first time. The preventive experiments entail pre-infection spraying of FLE prior to the occurrence of P. xanthii, while the curative experiments involve post-outbreak spraying of FLE. After comprehensive consideration, the optimal approach was determined to be spraying the front of cucumber leaves with a concentration of 0.04 mg/mL FLE in order to effectively control P. xanthii in leaf disc bioassay. The lowest superposition rate from FLE and trisodium phosphate dodecahydrate was 12.86 %, indicating that the impact of FLE on the respiratory metabolism of P. xanthii conidia primarily operates through the hexose monophosphate pathway (HMP). The growth of P. xanthii conidia and mycelium can be inhibited or delayed by FLE. The application of FLE can effectively mitigated chlorophyll loss, suppressed the activities of peroxidase (POD) and polyphenol oxidase (PPO), as well as enhanced the activities of phenylalanine ammonia lyase (PAL), chitinase, and β- 1,3-glucanase. Furthermore, three representative enzyme genes, PAL, POD, and chitinase, were chosen for the purpose of validation. The results suggested that FLE has the ability to modulate the expression of relevant enzyme genes, with peak effects observed after 3–4 days of treatment. The findings offer theoretical support for the advancement of novel botanical pesticides aimed at controlling crop diseases.

Cucumber (Cucumis sativus L.) translationally controlled tumor protein interacts with CsRab11A and promotes activation of target of rapamycin in response to Podosphaera xanthii.

The target of rapamycin (TOR) kinase serves as a central regulator that integrates nutrient and energy signals to orchestrate cellular and organismal physiology in both animals and plants. Despite significant advancements having been made in understanding the molecular and cellular functions of plant TOR kinases, the upstream regulators that modulate TOR activity are not yet fully elucidated. In animals, the translationally controlled tumor protein (TCTP) is recognized as a key player in TOR signaling. This study reveals that two TCTP isoforms from Cucumis sativus, when introduced into Arabidopsis, are instrumental in balancing growth and defense mechanisms against the fungal pathogen Golovinomyces cichoracearum. We hypothesize that plant TCTPs act as upstream regulators of TOR in response to powdery mildew caused by Podosphaera xanthii in Cucumis. Our research further uncovers a stable interaction between CsTCTP and a small GTPase, CsRab11A. Transient transformation assays indicate that CsRab11A is involved in the defense against P. xanthii and promotes the activation of TOR signaling through CsTCTP. Moreover, our findings demonstrate that the critical role of TOR in plant disease resistance is contingent upon its regulated activity; pretreatment with a TOR inhibitor (AZD-8055) enhances cucumber plant resistance to P. xanthii, while pretreatment with a TOR activator (MHY-1485) increases susceptibility. These results suggest a sophisticated adaptive response mechanism in which upstream regulators, CsTCTP and CsRab11A, coordinate to modulate TOR function in response to P. xanthii, highlighting a novel aspect of plant-pathogen interactions.

First Report of Powdery Mildew Caused by Podosphaera xanthii on Youngia japonica subsp. elstonii in Hainan Province, China.

Youngia japonica (L.) DC. is a polymorphic annual herb of the Asteraceae family. Although this plant originated in Asia, it is now world-widely distributed. In China, Y. japonica is used for edible or folk medicine to treat viral infections and various kinds of inflammation (Yu et al. 2021). As a traditional Chinese medicinal herb, Y. japonica used for the treatment of inflammatory diseases, such as angina, leucorrhea, mastitis, conjunctivitis, and rheumatoid arthritis (Chen et al. 2006). During the spring of 2023, powdery mildew symptoms were observed on 60% of Y. japonica subsp. elstonii plants in a greenhouse on the Hainan Medical University campus (19° 58' 53″ N; 110° 19' 47″ E) in Haikou, Hainan Province, China. Powdery mildew colonies covered the leaf surfaces and stems of affected plants, causing discoloration and defoliation. Mycelia were superficial and hyphal appressoria were nipple-shaped. Conidiophores (n =30) were unbranched, cylindrical, 99 to 166 × 11 to 16 µm, and produced three to five immature conidia in chains with a crenate outline. Foot cells (n =30) were cylindrical, straight or sometimes curved at the base, and 35 to 61 µm long. Conidia (n =100) were ellipsoid-ovoid to doliiform, 21 to 40 ×13 to 21 µm (length/width ratio = 1.4 to 2.3), with well-developed fibrosin bodies, and produced germ tubes from the lateral position. Based on these morphological characteristics, the pathogen was provisionally identified as Podosphaera xanthii (Braun and Cook 2012). The teleomorph was not observed. A specimen was deposited in the Hainan Medical University Plant Pathology Herbarium as HMYJ-23. To confirm the genus identification and ascertain a putative species, genomic DNA was extracted from mycelium, conidiophores, and conidia using a fungal DNA kit (Omega Bio-Tek, USA). The rDNA internal transcribed spacer (ITS) region was amplified with primers ITS1/ITS4 (White et al. 1990) and sequenced directly. The resulting 575-bp sequence was deposited in GenBank (accession no. OR229712). A BLASTn search in GenBank of this sequence showed 99% similarity with the ITS sequences of P. xanthii isolates from China (MT260063, OP765400, MW422608, and MT739423), Thailand (LC270778, LC270779, and LC270780), and Argentina (AB525914). Additionally, the 613-bp 28S rDNA region was amplified using the primer pairs NL1 and NL4 (O'Donnell 1993; accession no. OR240257). This region shared 100% similarity with P. xanthii isolates (MK357436, LC371333, LC270780, OP765401, and AB936277) as well. To confirm pathogenicity, five healthy potted plants of Y. japonica subsp. elstonii were inoculated by gently pressing a powdery mildew-infected leaf onto the young leaves. Five non-inoculated plants served as controls. All plants were maintained in a greenhouse at 24 to 30°C, 70% relative humidity, with a 16-h photoperiod. After 7 days, inoculated leaves showed powdery mildew symptoms whereas no symptoms were observed on control plants. The fungal colonies observed on inoculated plants were morphologically identical to those found on the originally infected leaves collected from Hainan Province. Based on the morphological characteristics and molecular identification, the fungus was identified as P. xanthii. To our knowledge, this is the first record of P. xanthii infecting Y. japonica subsp. elstonii in Hainan province, China. We are concerned that the pathogen could become a threat to the widespread planting of Y. japonica subsp. elstonii in the future.

Chemical and nutritional management of powdery mildew caused by Sphaerotheca fuliginea on pumpkin vines

Pumpkin is a popular vegetable crop in Pakistan and India which is grown in rainy season. Numerous biotic and abiotic factors have an impact on this crop. Sphaerotheaca fuliginea is one of the biotic agents that poses a major risk to the crop, leading to significant losses in both quantity and quality. Applying nutritional supplements to strengthen resistance against pumpkin powdery mildew infection is an economical and ecologically sustainable approach to managing the disease. Three treatments including 1% potassium monophosphate, 1% potassium silicate, and their combination (1:1) given in the field have been tested in order to control the disease. The spraying procedure used before the inoculation revealed that the disease was infected. A maximum 49% decrease in disease was achieved in the control group when potassium silicate and mono potassium phosphate were combined. The distinctive effects of 1% potassium silicate and 1% potassium phosphate mono shown, for comparison control, a 43% and 39% lower incidence of disease, respectively. In the field, tests were conducted to determine the efficacy of three fungicide combinations: Bravo (chlorothainal), score (Difenaconzole), and Bravo + score. The standard concentration of each combination was tested against S. fuliginea. The disease control was reduced by 61% when the two fungicides were combined (Bravo+ score). Compared to the control, the partition effect score and Bravo produced a 56% and 54% reduction in disease, respectively. By choosing an appropriate formulation and application technique of nutritional supplements can be effectively used in inhibiting the growth of S. fuliginea.

First Report of Powdery Mildew Caused by Podosphaera xanthii on Acalypha indica in China.

Acalypha indica L. is an annual erect herb of the Euphorbiaceae family. This plant is found widely in the tropics and parts of Africa and Asia (Chakraborty et al. 2023). In China, A. indica is a vegetable and also used as a folk medicine due to its antipyretic and hemostatic, antibacterial and anti-inflammatory properties. In February 2022 and 2023, powdery mildew symptoms were observed on 70% of A. indica plants on the Hainan Medical University campus (19° 58' 53″ N; 110° 19' 47″ E) in Haikou, Hainan Province, China. Powdery mildew colonies covered the leaf surfaces and stems of affected plants, causing discoloration and defoliation. Mycelia were superficial and hyphal appressoria were nipple-shaped. Conidiophores (n =30) were unbranched, cylindrical, 66 to 150 × 10 to 15 µm, and produced three to five immature conidia in chains with a crenate outline. Foot cells (n =30) were cylindrical, straight or sometimes curved at the base, and 31 to 59 µm long. Conidia (n =100) were ellipsoid-ovoid to doliiform, 20 to 33 ×12 to 20 µm (length/width ratio = 1.3 to 2.4), with well-developed fibrosin bodies, and produced germ tubes from the lateral position. Based on these morphological characteristics, the pathogen was provisionally identified as Podosphaera xanthii (Braun and Cook 2012). The teleomorph was not observed. A specimen was deposited in the Hainan Medical University Plant Pathology Herbarium as HMAI-23. To confirm the genus identification and ascertain a putative species, genomic DNA was extracted from mycelium, conidiophores, and conidia using a fungal DNA kit (Omega Bio-Tek, USA). The rDNA internal transcribed spacer (ITS) region was amplified with primers ITS1/ITS4 (White et al. 1990) and sequenced directly. The resulting 575-bp sequence was deposited in GenBank (accession no. OR775733). A BLASTn search in GenBank of this sequence showed 99% similarity with the ITS sequences of P. xanthii on plants of Fabaceae, Malvaceae and Cucurbitaceae family from China (MH143485, MT242593, MK439611 and MH143483), Thailand (LC270779 and LC270778), Korea (MG754404), Vietnam (KM260704), and Puerto Rico (OP882310). Additionally, the 28S rDNA region was amplified using the primer pairs NL1 and NL4 (O´Donnell 1993; accession no. OR784547). This region shared 99% similarity with P. xanthii isolates (LC371333, LC270780, AB936277, and OP765401) as well. To confirm pathogenicity, five healthy potted plants of A. indica were inoculated by gently pressing a powdery mildew-infected leaf onto 15 young leaves. Five non-inoculated plants served as controls. All plants were maintained in a greenhouse at 24 to 30°C, 70% relative humidity, with a 16-h photoperiod. After 7 days, inoculated leaves showed powdery mildew symptoms whereas no symptoms were observed on control plants. The fungal colonies observed on inoculated plants were morphologically identical to those found on the originally infected leaves collected from Hainan Province. Based on the morphological characteristics and molecular identification, the fungus was identified as P. xanthii. In different countries and regions, P. xanthii has been previously reported on A. indica from Sudan and India (Amano 1986). To our knowledge, this is the first record of P. xanthii infecting A. indica in China. We are concerned that the pathogen could become a threat to the widespread planting of A. indica in the future.

Status, Gaps and Perspectives of Powdery Mildew Resistance Research and Breeding in Cucurbits

Cucurbitaceae, the gourd family of flowering plants, is a very large and diverse family, the order Cucurbitales, contains 95 genera and 950–980 species of food and ornamental plants, and wild and weedy species mostly with high genetic diversity. This review is focused on the most important cucurbit crops (Cucumis sativus, Cucumis melo, Cucurbita spp., Citrullus lanatus, Momordica charantia, Lagenaria siceraria, and Luffa acutangula) and some their wild relatives as hosts of cucurbit powdery mildews (CPM). Powdery mildews (PM) (Ascomycota, Erysiphales) are one of the most frequently encountered and easily visible groups of plant pathogenic fungi with > 900 species. They are obligate biotrophs, they colonize above-ground plant tissues, mostly leaves, though they may also colonize stems, petioles, flowers and fruits, and they are usually debilitators, not killers. These parasitic fungi have been problematic on cucurbits for a long time world-wide, causing serious economic losses in yield and quality. All economically important cucurbit crops host CPM. Seven PM species with different taxonomic positions, host ranges, geographic distributions and ecological requirements are known on cucurbits. CPM species taxonomy and denomination rapidly changed during last few decades through detailed analyses and clarifications. At least three PM species frequently parasitize cucurbits: the endoparasite Leveillula taurica (Lt) with marginal economic importance; and two ectoparasitic species, Golovinomyces orontii (Go), and Podosphaera xanthii (Px), which are economically important world-wide. The two pathogens differ in ecological requirements and distribution, though they may occur together in mixed infections. They are highly variable at the population level for virulence, race identities, and fast adaptation of pathogens. Cucurbit-CPM species interactions are diverse and complicated, and differ between hosts and their respective pathogen genera and species. Here we present a critical overview of obstacles, gaps and recent progress in these matters for six cucurbit genera with respect to resistance resources, genetics of resistance, genetic mapping and development of molecular markers, physiology and mechanisms of resistance, developments in mlo-mediated resistance, patents, and CPM resistance breeding.

First report of Powdery Mildew Caused by Podosphaera xanthii on Siraitia grosvenorii in Guizhou, China.

Swingle (Siraitia grosvenorii), a member of the Cucurbitaceae family, stands out as a distinctive plant with both economic and medicinal significance. In October 2023, severe powdery mildew were observed on S. grosvenorii in Guiyang City (26.50°N; 106.66°E), Guizhou Province, China. About 80 % of the plants in the greenhouse showed powdery mildew symptoms. Three infected plant samples were selected for morphological and molecular analysis (GZAAS 23-0801, GZAAS 23-0802 and GZAAS 23-0803). The voucher specimens are deposited in the Key Laboratory of Agricultural Biotechnology of Guizhou Province. The symptoms initially manifested as irregular to nearly circular, small yellow spots, with distinct depressions as well as surfaces covered in white mycelium. Over time, these spots gradually expanded and merged patches. In the final stages, the entire leaves turned into yellow and withered. Microscopic observations showed that fungal hyphae were septate, branched, and flexuous to straight and 5 to 9 µm wide, and appressoria were indistinct to slightly nipple-shaped. Conidia were hyaline and ellipsoid to oval with fibrosin bodies and measured 31 to 43 × 18 to 24 μm (n = 50) with a length/width ratio of 1.3 to 2.3. Conidiophores were unbranched, straight, 120 to 268 × 14 to 22 µm (n = 30), producing two to five immature conidia in chains. Foot cells of conidiophores were cylindrical, 39 to 84 × 8 to 14 μm (n = 30), followed by one to three short cells. Short cells were cylindrical, 12 to 32 × 8 to 15 μm (n = 50). The morphological characteristics were identical with the previous description of Podosphaera xanthii (Braun and Cook, 2012). Total DNA was extracted from conidia and mycelia by the Chelex method (Walsh et al., 1991). The ribosomal DNA internal transcribed spacer (ITS) and nuclear ribosomal large subunit (LSU) were amplified by using the primers ITS1/ITS4 (White et al., 1990) and LSU1/LSU2 (Scholin et al., 1994), respectively. The ITS (OR825802, OR825803 and OR825804, respectively) and LSU (OR825805, OR825806 and OR825807, respectively) sequences of three isolates, were deposited in GenBank. The BLAST results revealed that both the ITS and LSU region sequence were 100% identical to those of P. xanthii (ITS: MF043939, MG754404 and KJ698669; LSU: OQ061319, AB936277and OP218411). Phylogenetic analyses of ITS and LSU sequences showed that our three isolates were clustered with P. xanthii (KX842351, LC270782 and LC270779) with high statistical support (ML/MP/BI: 100%/97%/1.00). Combined with their morphological characteristics, these three isolates were identified as P. xanthii. Pathogenicity tests were performed by gently brushing conidia onto the leaves of five healthy S. grosvenorii plants. Five non-inoculated plants were used as the control. All plants were maintained in a greenhouse at 25 ± 2°C. One week after inoculation, similar symptoms were observed in the inoculated plants, whereas no symptoms occurred on the control plants. By microscopic observation, the fungus on the inoculated plants was morphologically identical to those on originally diseased plants. Powdery mildew caused by P. xanthii has been reported on Vernonia cinerea (Wu et al., 2023), Vigna unguiculata (Zhang et al., 2023), Cucumis melo (Meesam et al., 2023). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on S. grosvenorii in Guizhou, China. The occurrence of powdery mildew on S. grosvenorii may pose a potential threat to its large-scale cultivation. The pathogen could become a threat to other Cucurbitaceae members in the future.

Effect of Weather Parameters on Development of Powdery Mildew of Ber (Ziziphus mauritiana) Caused by Oidium erysiphoides

India’s one of the most popular fruits is the ber (Ziziphus mauritiana Lamk.). Ziziphus mauritiana is sometimes referred to as Indian plum or desert apple. Oidium erysiphoides f. sp. Ziziphi, which causes powdery mildew of ber, is more common and a threat in northern states. The white powdery coating on leaves and fruits affects the photosynthesis and growth & development, respectively. This disease results in 50-60% loss in fruit yield and reduces market value of the produce. In the present study, the effect of abiotic environmental elements such as temperature, relative humidity, wind speed, and others were observed and they had a significant impact on the progression of powdery mildew disease. In the study, which was carried out on two ber cultivars viz., Gola and Kaithali, the disease progression on both cultivars showed a significantly negative correlation with maximum (Tmax) and minimum temperature (Tmin) and a significantly positive correlation with morning (RHm) and evening relative humidity (RHe). The favourable weather variables were observed viz., Tmax above 20.3 °C, Tmin around 9.9 °C and RHm was more than 80%. The ber cultivar Gola was more susceptible to disease development than Kaithali, with Gola having the highest disease intensity.