Rust Spores Research Articles

Advancing crop disease early warning in South Asia by complementing expert surveys with internet media scraping

AbstractWheat contributes one‐fifth of the global food supply with an estimated 29% of global production in low and lower‐middle income countries. As production expands across southern Asia, yields are often negatively impacted by outbreaks of fungal rust diseases. A wheat rust early warning and advisory system comprising surveillance, near real‐time disease risk forecasts and advisory dissemination has been established in two target countries in South Asia, including Nepal and Bangladesh. However, as wheat rust spores can be aerially transmitted over long distances, near real‐time estimates of disease incidence are required from sources of infection in neighbouring regions. To address this challenge, we developed and tested a novel algorithm to generate proxy observations of infection sources using online media reports in two neighbouring countries, India and Pakistan. Media sampling could provide an effective alternative where data from ground surveys are not readily available in near real‐time. Our results show that west Nepal was exposed to a substantial inoculum pressure from aerially dispersed stripe rust spores originating from India and Pakistan. There were no outbreaks of stripe rust disease in Bangladesh with only very low levels of cross‐border dispersion and generally unfavourable environmental conditions for infection. We further describe how proxy observations informed farmer decision‐making in near real‐time in Nepal and filled a knowledge gap in identifying early sources of infection for a major outbreak of stripe rust during 2020 in Nepal. Our results highlight the importance of international cooperation in mitigating transboundary plant pathogens.

Case of Willow Rust Spores (Melampsora Spp.) Collected by Honey Bees

Abstract Honey bee workers (Apis mellifera L.) collect nectar, honeydew and pollen from plants in orderto provide the colony with, among others, carbohydrates and protein. Whenever these sources are unavailable in the environment, bees turn to alternatives. An example of this are fungi spores collected accidentally or on purpose. This last phenomenon is the aim of this study, in which we have shown that worker bees can collect willow rust (Melampsora spp.) spores. We observed as the bees obtained spores and placed them in pollen baskets. The presence of spores was demonstrated with the use of a scanning electron microscope (SEM). This observation indicates that the honey bee may use alternative sources as a potential supplement. There are few studies in this field and it requires a deeper analysis.

Coherent spore dispersion via drop-leaf interaction.

The dispersion of plant pathogens, such as rust spores, is responsible for more than 20% of global crop yield loss annually. However, the release mechanism of pathogens from flexible plant surfaces into the canopy is not well understood. In this study, we investigated the interplay between leaf elasticity and rainfall, revealing how a flexible leaf structure can generate a lateral flow stream, with embedded coherent structures that enhance transport. We first modeled the linear coupling between drop momentum, leaf vibration, and the stream flux from leaf surfaces. With Lagrangian diagnostics, we further mapped out the nested coherent structures around the fluttering profile, providing a dynamical description for local spore delivery. We hope the mechanistic details extracted here can facilitate the construction of physically informed analytical models for local crop disease management.

Uromyces savulescui on statice (Limonium sinuatum) in the Americas and reevaluation of its reported geographic range.

Limonium sinuatum (Plumbaginaceae) is the most commonly cultivated recognizable cut flower crop in the genus Limonium. It is known by several common names including statice and sea lavender, due to its lilac-colored flowers and the fact that it naturally inhabits mainly coastal areas (Mellesse et al, 2013). Limonium sinuatum is native to the Mediterranean, although as a popular garden plant, has been naturalized in other parts of the world including coastal areas of California (USDA NRCS 2020). Cultivated L. sinuatum is used in fresh and dry flower arrangements in the Americas, comprising approximately 20% of the floriculture cultivated area in Ecuador (Vega and Morales 2011; Abascal Cañas 2017). In December 2014, L. sinuatum plants in the public park "Baños del Inca" in Cajamarca, Peru (S 7 9'46"; W 78 27'53"), were found infected with a rust disease. The plants were scattered in the park but infection incidence was 100% as individual plants were all found to be infected (Fig 1). Based on the percentage of symptomatic areas, including the yellow halos around pustules, calculated with ImageJ (Collins, 2007) from field photographs, the disease severity was estimated to be 58.9% in average, ranging from 19.8% up to 90.0%. Uredinia were present on both sides of the leaves as well as on stems and were roundish, oblong, pulverulent, and cinnamon brown in color; urediniospores 25.5 to 35.0 × 22.5 to 31.0 µm, were globoid to ellipsoid; urediniospore walls were cinnamon-brown, 2.5 to 3.0 µm thick, densely verrucose, with 2 to 3 equatorial germ pores. Few telia were present on leaves; these were scattered roundish or oblong, and greyish in color; teliospores 26.5 to 41.0 × 16.0 to 25.0 µm, were ellipsoid to obovoid, mostly attenuated at the apex; teliospore walls were colorless, 2-3 µm thick at sides, and up to 10 µm thick at apex. Teliospores readily germinated in sori producing basidia and basidiospores (Fig. 2). The rust features and dimensions of rust spores are consistent with available descriptions of Uromyces savulescui Rayss (Guyot 1951; Vakalounakis and Malathrakis 1987). To confirm identity, a 576 bp region of the 28S subunit of the ribosomal DNA repeat was sequenced following previously published protocols and primers (Aime 2006, Aime et al. 2018). The resulting sequence (GenBank Accession No. OR291160) shared 99.83% (573/574 bp) identity with a sequence deposited as Uromyces limonii (DC.) Lev. (accession KY764194, BPI910295, Demers et al. unpublished) from L. sinuatum in Ethiopia. However, U. limonii produces orange uredinia, thin-walled yellow-orange urediniospores, teliospores with mostly light chestnut brown wall and infects different hosts (Savile and Conners 1951). It is likely that KY764194 represents a misannotated record of U. savulescui. While Koch's postulates can be a useful tool for establishing causality in certain infectious diseases, their use may be limited when it comes to rust diseases based on old herbarium specimens. In our case, due to the age of the specimen, which is almost nine years old, various other methods were employed to identify the pathogen. These methods included microscopic examination for morphological criteria of the urediniospores and teliospores, as well as molecular techniques like 28S rDNA sequencing. Rust disease on L. sinuatum has been previously reported in Ecuador but the causal agent was identified as a Puccinia sp. and reported that the rust was able to destroy entire plots in humid conditions (Vega and Morales 2011). Whether this report also represent U. savulescui is not certain, but given that the urediniospores of Puccinia species are generally 2-celled, it is unlikely. García-Hernández et al. (2008) reported U. limonii on Limonium spp. from Chile, and Coca (2020) also reported U. limonii on Limonium sp., from Bolivia. However, judging from the photomicrographs (Coca 2020), the rust in the latter report is definitely U. savulescui and not U. limonii. Uromyces savulescui has been previously reported from the Mediterranean region and the Canary Islands (Vakalounakis and Malathrakis 1987). To our knowledge there is no report of this rust in the Americas, excepting the probable misidentifications already listed herein. The specimen has been deposited in the Arthur Fungarium at Purdue University as PURN15037.

Puccinia Spore Concentrations in Relation to Weather Factors and Phenological Development of a Wheat Crop in Northwestern Spain

Rust is one of the main diseases affecting wheat crops in Spain, causing significant yield and quality losses. Research on its identification and quantification in the air is a worldwide priority due to the importance of this crop as a source of food and feed. The objective of this study is to determine the temporal variation of airborne spores of Puccinia and their relationship with meteorological variables and the phenological development of a wheat crop in Northwestern Spain during two growing seasons. The study was conducted in A Limia, Ourense, located in Northwestern Spain, during the wheat growing seasons of 2021 and 2022. The Lanzoni VPPS 2010 spore trap was used to collect airborne spores, which were identified using optical microscopy. The wheat growing season was less than 95 days during both years, and wheat rust spores were detected during all phenological stages of the crop. Concentrations were higher than 100 spores/m3 from the booting stage to senescence, mainly in 2021. Statistical analyses showed that temperature was the meteorological variable that most influenced Puccinia concentrations in the air in both years. The modification of a prediction model proposed by other authors for wheat rust, which takes into account mean temperature (10–25 °C), dew point temperature (<5 °C), and nighttime temperature (10–20 °C), allowed us to tentatively predict the increase in Puccinia concentrations in the year 2022 when these conditions occurred for four or five consecutive days. This research is the first in Spain to report the presence of rust-causing Puccinia spores in the air during all phenological stages of the wheat crop and provides useful information for designing management strategies, considering temperature values.

Electrospinning polyethylene terephthalate glycol

Polyethylene terephthalate glycol (PETG) is a difficult-to-spin material, and no previous papers have reported the correct conditions to create PETG meshes. To address this issue, a preliminary study on the solubility and electrospinnability of PETG using a range of solvent system was conducted and a Teas graph was established to select the ideal solvent system. Based on these preliminary results, electrospun PETG fibers were produced using a highly volatile binary solvent system consisting of dichloromethane (DCM) and trifluoroacetic acid (TFA). Produced meshes were extensively characterized, and the results demonstrated for the first time the ability of electrospun PETG meshes to support the inoculation and germination of yellow rust spores, thus confirming that PETG is an ideal material to be used for the fabrication of agriculture biosensors. The results also showed that the best solvent split was 85/15 (DCM/TFA).

Mite fauna on Dittrichia species (Asteraceae) in Syrian costal region: new records and primary observations on the behavior of Typhloseiella isotricha (Athias-Henriot) (Meostigmata: Phytoseiidae)

Surveys of mite fauna on Dittrichia viscosa and D. graveolens (Asteraceae) were conducted at multiple locations in Tartous and Latakia governorates, Syria, in 2021 and 2022. A total of 13 mite species belonging to seven families (Acaridae, Camerobiidae, Erythraeidae, Phytoseiidae, Raphignathidae, Tenuipalpidae, and Tetranychidae) were collected. Among them, Erythraeus (Zaracarus) passidonicus (Erythraeidae), Raphignathus collegiatus (Raphignathidae), and Brevipalpus rotai (Tenuipalpidae) are recorded for the first time in Syria. The most abundant family observed on Dittrichia species was Phytoseiidae with four species representing about 86% of total collected mite specimens. Among them, Typhloseiella isotricha was the dominant species. It was mainly observed on big leaves of D. viscosa, highly infected by the rust spots of Coleosporium inulae. Results suggest that rust spores could be a potential food for this predator.

Three‐way fungal interactions affect the potential biological control of Himalayan balsam, Impatiens glandulifera

AbstractHimalayan balsam (Impatiens glandulifera) is one of the most invasive weeds across Europe. The rust fungus, Puccinia komarovii var. glanduliferae has been introduced as a biological control agent, but success has been patchy. Here, we investigated whether mycorrhizal and endophytic fungi can affect rust efficacy and plant growth. Over three experiments, we found that AM fungi and the rust alone or together consistently reduced plant growth, but this depended on the identity of species in the AM inoculum. Meanwhile, AM fungi increased infection frequency of the endophyte Colletotrichum acutatum. Rust inoculation had no detrimental effects on mycorrhizal colonisation or C. acutatum infection, but the latter two fungi reduced rust sporulation. However, plant size was reduced when all three fungal types were present, suggesting that a combined fungal inoculum offers a promising approach for the control of this weed.

Genetic sources of resistance bread winter wheat to leaf (brown) rust and their value in juvenile stage of growing

Actuality of the topic. With the growth of prices for fungicides, the ecological crisis of the biosphere, the absence of a wide range of donors, and with the constant variability of the pathogen, resistance of bread winter wheat plants is lost, therefore, it is important to search for new effective sources of resistance and involve them in breeding work for resistance to leaf rust. The purpose of the research is to compare genotypes of different ecological and geographical origin and to determine the best genetic sources of resistance to brown rust for their effective use in breeding. Methods. The experiment was carried out in laboratory conditions; Bread winter wheat samples were contaminated with leaf (brown) rust spores in the juvenile stage of growing. Research results. Among the four analyzed genetic sources of resistance of different ecological and geographical origins, the best were the representative genotypes from other breeding institutions of Ukraine. According to the average indicator of resistance, their average level of resistance was at the level of 6.5 points on a 9-point scale, and genotypes of Western European origin – 5.2 points, genotypes of selection from SGI–NCSS and CIMMYT-ICARDA - Turkey had the worst score – 4.6 and 3.4 points. Summary. The fact that bread winter wheat genotypes from other breeding institutions of Ukraine and Western European origin are the best can be explained by the formation of these genotypes in optimal conditions for the development of leaf (brown) rust, which served as a natural infectious background for selection for resistance to this trait. However, among genetic sources with low resistance, there are samples with increased resistance, which, in combination with other adaptive traits, can be successfully used in the selection of bread winter wheat for resistance to leaf (brown) rust for the south of Ukraine. Keywords: bread winter wheat, leaf (brown) rust, sources of resistance, genotypes-representatives, resistance

Multi-Layer Biosensor for Pre-Symptomatic Detection of Puccinia strifformis, the Causal Agent of Yellow Rust.

The yellow rust of wheat (caused by Puccinia striiformis f. sp. tritici) is a devastating fungal infection that is responsible for significant wheat yield losses. The main challenge with the detection of this disease is that it can only be visually detected on the leaf surface between 7 and 10 days after infection, and by this point, counter measures such as the use of fungicides are generally less effective. The hypothesis of this study is to develop and use a compact electrochemical-based biosensor for the early detection of P. striiformis, thus enabling fast countermeasures to be taken. The biosensor that was developed consists of three layers. The first layer mimics the wheat leaf surface morphology. The second layer consists of a sucrose/agar mixture that acts as a substrate and contains a wheat-derived terpene volatile organic compound that stimulates the germination and growth of the spores of the yellow rust pathogen P. s. f. sp. tritici. The third layer consists of a nonenzymatic glucose sensor that produces a signal once invertase is produced by P. striiformis, which comes into contact with the second layer, thereby converting sucrose to glucose. The results show the proof that this innovative biosensor can enable the detection of yellow rust spores in 72 h.

EFFECT OF SALICYLIC ACID AND OXALIC ACID ON THE RESISTANCE TO WHEAT RUST DISEASE (BASIDIOMYCETES, UREDINALES, PUCCINIA)

Wheat rust pathogens belong to genus Puccinia, family Pucciniaceae, order Uredinales and class Basidiomycetes. During epiphytosis, the fungus causes significant damage to crops, disrupts assimilation processes in plants and reduces photosynthesis. Spring soft wheat Arai variety was tested for rust resistance. In this study, we used different concentrations of salicylic acid and oxalic acid. We treated the wheat seeds and seedlings with different concentrated acids. In the context of the artificial epidemic, during the rooting, dulling and germination stages of wheat development, we were infected with spores of yellow rust (Puccinia striiformis f.sp. tritici), brown rust (Ruccinia tritici Erikss) and stem rust (Puccinia graminis Pers. F. Sp. Tritici). We tested the effect of different concentrations of salicylic acid and oxalic acid on wheat rust disease.. The results of the study showed that the seeds were found to be moderately resistant to yellow rust of wheat treated with concentrated acid 0.25 mM SA + 0.1 mM OA (1) and 0.25 mM SA + 0.2 mM OA (3). 0.5 mM SA + 0.2 mM OA (2) was immunocompromised to brown rust when treated with concentrated acid spray. In organic agriculture, the chemical control of deafness in wheat leads to environmental pollution, in addition is not economically viable and a realistic way to combat it. Therefore, we need to look for effective ways for disease control. The data obtained in the study allow to fight against yellow rust and brown rust of wheat.

Genomic characterization of Puccinia triticina using molecular marker technology.

Leaf rust, caused by Puccinia triticina, is the most common rust disease of wheat. The fungus is an obligate parasite capable of producing infectious urediniospores. To study the genetic structure of the leaf rust population 20 RAPD primers were evaluated on 15 isolates samples collected in Pakistan. A total of 105 RAPD fragments were amplified with an average of 7 fragments per primer. The number of amplified fragments varied from 1 to 12. GL Decamer L-07 and GL Decamer L-01 amplified the highest number of bands (twelve) and primer GL Decamer A-03 amplified the lowest number of bands i.e one. Results showed that almost all investigated isolates were genetically different that confirms high genetic diversity within the leaf rust population. Rust spores can follow the migration pattern in short and long distances to neighbor areas. Results indicated that the greatest variability was revealed by 74.9% of genetic differentiation within leaf rust populations. These results suggested that each population was not completely identical and high gene flow has occurred among the leaf rust population of different areas. The highest differentiation and genetic distance among the Pakistani leaf rust populations were detected between the leaf rust population in NARC isolate (NARC-4) and AARI-11and the highest similarity was observed between NARC isolates (NARC-4) and (NARC-5). The present study showed the leaf rust population in Pakistan is highly dynamic and variable.

Temporal sporulation of Thekopsora areolata and Chrysomyxa spp. in Finnish Norway spruce seed orchards

Cone rusts Thekopsora areolata and Chrysomyxa pirolata are widely distributed in northern hemisphere. In Fennoscandia, these rusts cause severe damage and great economical losses especially in seed orchards specialized to produce high quality seeds. The aim of this study was to investigate sporulation of cone rusts and factors affecting epidemics to develop new control practices against these rusts. Natural sporulation of T. areolata was investigated in Finnish Norway spruce seed orchards on Prunus padus and the effect of environmental variables on rust sporulation in 2018–19. A sample of Prunus leaves was collected from which the coverage and number of T. areolata pustules were estimated. The frequency of cones with cone rusts, T. areolata, Chrysomyxa pirolata and C. ledi, was also estimated in Picea abies cones and the sporulation of C. pirolata on Pyrola sp. leaves in the seed orchards. The T. areolata incidence on Prunus was modelled with temperature sum, rainfall, seed orchard and time of estimation.The T. areolata disease incidence was low (<30%) in seed orchards in 2018, but it exceeded 100% in 2019. T. areolata pustules covered less than 10% of the leaves in 2018 and 10–40% in 2019. An ascomycete, Phloeosporella padi, was common in all Prunus leaves in 2018–19. Low rainfall in May-June explained the low disease rate on Prunus in 2018, while high rainfall explained the high disease rate in May-June in 2019. Cumulative rainfall, temperature sum, time and their interactions were all significant variables in a disease model explaining the disease incidence, while seed orchard was a non-significant variable. Cone rust frequency was low in P. abies cones in the seed orchards in 2019. Telia with basidia of C. pirolata were rare in May-June on Pyrola due to low rainfall in 2018, but frequent due to high rainfall in 2019. Rust control of T. areolata is recommended to concentrate on Prunus to reduce the number of overwintering diseased leaves in the seed orchards. Old infected cones should be removed from seed orchards to reduce aeciospore dissemination to Prunus in May-June. Control of C. pirolata is recommended to concentrate on Pyrola in early May.

A new spectral index for the quantitative identification of yellow rust using fungal spore information

ABSTRACT Yellow rust (Puccinia striiformis f. sp. Tritici) is a frequently occurring fungal disease of winter wheat (Triticum aestivum L.). During yellow rust infestation, fungal spores appear on the surface of the leaves as yellow and narrow stripes parallel to the leaf veins. We analyzed the effect of the fungal spores on the spectra of the diseased leaves to find a band sensitive to yellow rust and established a new vegetation index called the yellow rust spore index (YRSI). The estimation accuracy and stability were evaluated using two years of leaf spectral data, and the results were compared with eight indices commonly used for yellow rust detection. The results showed that the use of the YRSI ranked first for estimating the disease ratio for the 2017 spectral data (R2 = 0.710, RMSE = 0.097) and outperformed the published indices (R2 = 0.587, RMSE = 0.120) for the validation using the 2002 spectral data. The random forest (RF), k-nearest neighbor (KNN), and support vector machine (SVM) algorithms were used to test the discrimination ability of the YRSI and the eight commonly used indices using a mixed dataset of yellow-rust-infested, healthy, and aphid–infested wheat spectral data. The YRSI provided the best performance.

Elucidating the interactions between the rust Hemileia vastatrix and a Calonectria mycoparasite and the coffee plant

SummaryCalonectria hemileiae, a fungus associated with pustules of the coffee leaf rust (CLR, Hemileia vastatrix) in Brazil, was tested in vitro and in planta to assess its biocontrol potential. The fungus inhibited the germination of rust spores by over 80%. CLR severity was reduced by 93% when Calonectria was applied to coffee leaf discs inoculated with H. vastatrix, whilst a reduction of 70-90% was obtained for in planta experiments. Mycoparasitism was demonstrated through the fulfillment of Koch's postulates. Elucidation of the biochemical interaction between Calonectria and Hemileia on coffee plants indicated that the mycoparasite was able to increase plant resistance to rust infection. Coffee plants sprayed with Calonectria alone showed greater levels of chitinase, β-1,3-glucanase, ascorbate peroxidase and peroxidase. Although effective in controlling the rust, fungicide applications damaged coffee photosynthesis, whereas no harm was caused by Calonectria. We conclude that C. hemileiae shows promise as a biocontrol agent of CLR.

A low cost method for early detection of airborne Puccinia rust spores using glass slides and foldscope in the sugarcane field

The rust pathogens (Puccinia spp.) affect many cereals, pulses and sugar crops causing a major threat to crop production and productivity throughout the world. The sugarcane crop is being affected by Puccinia melanocephala and P. kuehnii causing brown and orange rust respectively. Sugarcane rust is an important constraint in popularizing the new and high potential varieties due to its appearance on the foliage. Under the changing climatic conditions many popular cultivars are showing rust infection from mild to severe form depending on the weather conditions during the crop seasons. Being an obligate pathogen, the rust is present on sugarcane throughout the year but the appearance and severity is highly influenced by the weather parameters such as temperature, relative humidity and the physiological maturity of the crop. Trapping the uredospores using Vaseline coated microscopic glass slides helped to determine the inoculum load at various time intervals in the air. The uredospores can be observed with the help of Foldscope, which broadens the scope of detection of uredospores without depending on the compound microscope in remote areas. By connecting with the mobile phone, the spores can be photographed and digital pictures can be shared for further confirmation. The frequency and quantity of the uredospores trapped will help in quantifying the spores in the field for management of sugarcane rust well in advance before the appearance of the symptoms in hot spot areas. This simple tool will be a boon for detection of rust spores in the field during the latent period before the appearance of the symptoms thus enabling management of rust in time.

Rapid Collection and Aptamer-Based Sensitive Electrochemical Detection of Soybean Rust Fungi Airborne Urediniospores

Plants are the central source of food for humans around the world. Unfortunately, plants can be negatively affected by diverse kinds of diseases that are responsible for major economic losses worldwide. Thus, monitoring plant health and early detection of pathogens are essential to reduce disease spread and facilitate effective management practices. Various detection approaches are currently practiced. These methods mainly include visual inspection and laboratory tests. Nonetheless, these methods are labor-intensive, time-consuming, expensive, and inefficient in the early stages of infection. Thus, it is extremely important to detect diseases at the early stages of the epidemic. Here, we would like to present a fast, sensitive, and reliable electrochemical sensing platform for the detection of airborne soybean rust spores. The suspected airborne soybean rust spores are first collected and trapped inside a carbon 3D electrode matrix by high-capacity air-sampling means. Then, a specific biotinylated aptamer, suitable to target specific sites of soybean rust spores is applied. This aptamer agent binds to the surface of the collected spores on the electrode. Finally, spore-bound aptamer units are incubated with a streptavidin–alkaline phosphatase agent leading to the enzymatic formation of p-nitrophenol, which is characterized by its unique electrochemical properties. Our method allows for the rapid (ca. 2 min), selective, and sensitive collection and detection of soybean rust spores (down to the limit of 100–200 collected spores per cm2 of electrode area). This method could be further optimized for its sensitivity and applied to the future multiplex early detection of various airborne plant diseases.

Efecto Bioprotector de Micorrizas Arbusculares en la Reducción de Roya (Hemileia vastatrix) en la Región San Martín

La roya es un problema generalizado que ha afectado a diferentes países de América Latina, generando pérdidas económicas en los productores cafetaleros. Se evaluó el efecto de los hongos micorrízicos arbusculares (HMA), sobre la presencia de roya (Hemileia vastatrix) en plantas de café. Se empleó un Diseño Completamente al Azar con dos factores: fuentes de inóculo HMA e Inoculación de roya, incluyendo tratamiento testigos (absoluto e infestado); se usó como sustrato tierra agrícola y arena (2:1); se inoculó plantas de café con 1 500 esporas de HMA procedente de Rioja, Lamas, Dorado y Huallaga, posteriormente se inóculo con esporas de roya; se evaluaron altura de planta, área foliar, biomasa seca y aérea, incidencia, severidad, colonización micorrízica y longitud de micelio extraradical. Los resultados mostraron que los tratamientos inoculados con HMA presentaron mejoras incrementos en morfología, micorrización y menor incidencia y severidad a roya.

Distinct Transcriptomic Reprogramming in the Wheat Stripe Rust Fungus During the Initial Infection of Wheat and Barberry.

Puccinia striiformis f. sp. tritici is the causal agent of wheat stripe rust that causes severe yield losses all over the world. As a macrocyclic heteroecious rust fungus, it is able to infect two unrelated host plants, wheat and barberry. Its urediniospores infect wheat and cause disease epidemic, while its basidiospores parasitize barberry to fulfill the sexual reproduction. This complex life cycle poses interesting questions on the different mechanisms of pathogenesis underlying the infection of the two different hosts. In the present study, transcriptomes of P. striiformis f. sp. tritici during the initial infection of wheat and barberry leaves were qualitatively and quantitatively compared. As a result, 142 wheat-specifically expressed genes (WEGs) were identified, which was far less than the 2,677 barberry-specifically expressed genes (BEGs). A larger proportion of evolutionarily conserved genes were observed in BEGs than that in WEGs, implying a longer history of the interaction between P. striiformis f. sp. tritici and barberry. Additionally, P. striiformis f. sp. tritici differentially expressed genes (DEGs) between wheat at 1 and 2 days postinoculation (dpi) and barberry at 3 and 4 dpi were identified by quantitative analysis. Gene Ontology analysis of these DEGs and expression patterns of P. striiformis f. sp. tritici pathogenic genes, including those encoding candidate secreted effectors, cell wall-degrading enzymes, and nutrient transporters, demonstrated that urediniospores and basidiospores exploited distinct strategies to overcome host defense systems. These results represent the first analysis of the P. striiformis f. sp. tritici transcriptome in barberry and contribute to a better understanding of the evolutionary processes and strategies of different types of rust spores during the infection process on different hosts.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Dynamics of splashed droplets impacting wheat leaves treated with a fungicide.

Wheat is threatened by diseases such as leaf rust. One significant mechanism of disease spread is the liberation and dispersal of rust spores due to rainsplash. However, it is unclear to what extent the spore-laden splashed droplets can transmit the disease to neighbouring leaves. Here, we show that splashed droplets either bounce or stick, depending on the orientation of the leaf and whether the surface of the leaf has been treated with a fungicide. A scaling model revealed that bouncing was enabled when the droplet's kinetic energy exceeded its pinning energy to the surface. Our findings indicate that, ironically, the application of fungicide to protect a wheat plant may also facilitate pathogen spread and infection by making leaves sticky to spore-laden droplets.