Rust Infection Research Articles

Diversidad endomicorrícica en plantas de café (Coffea arabica L.) infestadas con roya (Hemileia vastatrix)

El café (Coffea arabica L.) es uno de los productos agrícolas más importantes en el mundo, ya que más de 56 países se dedican a su cultivo y es el principal commodity agrícola desde el periodo 1962-1989; y la roya anaranjada del cafeto (Hemileia vastatrix Berkeley & Broome) es la enfermedad más devastadora de este cultivo. En Centroamérica, las pérdidas causadas por este patógeno fueron de hasta el 50 % en el ciclo productivo 2011-2012. La producción de café en el estado de Veracruz decreció 8 % desde el 2011 debido a infestaciones por roya, en consecuencia se han realizado investigaciones sobre microorganismos benéficos que brinden tolerancia hacia el patógeno, cuya obtención y aplicación no represente riesgo de deterioro del recurso suelo. En este sentido, las endomicorrizas cumplen con dichos requisitos, sin embargo es necesario conocer la diversidad y condiciones de asociación con la especie agrícola de interés para que el manejo sea efectivo. Por ello el objetivo fue caracterizar poblaciones endomicorrícicas presentes en plantas de café (Coffea arabica L.) variedad Typica con y sin signos de infección por roya en Ixhuatlán del café, Veracruz. Se identificaron 37 especies que corresponden a 14 géneros de endomicorrizas, siendo los más comunes Acaulospora y Rhizophagus, este último es el más frecuente en plantas sin signos de infección por roya. También se encontró mayor porcentaje de colonización en raíz y densidad de esporas en plantas sin signos de infección (7.70 % y 661.68 esporas/100 g de suelo, respectivamente) pero el índice de diversidad de Shannon (H) y el de Simpson (D) no señalan que las poblaciones endomicorrícicas encontradas sean diversas. Estos resultados muestran que las plantas que interaccionan en simbiosis con micorrizas son capaces de tolerar mejor el estrés biótico y abiótico, además la prevalencia de ciertos géneros endomicorrícicos en plantas de café con características fisiológicas particulares da pauta para profundizar en el estudio de la simbiosis diferencial establecida entre plantas y microorganismos.

Study on stripe rust (Puccinia striiformis) effect on grain filling and seed morphology building of special winter wheat germplasm Huixianhong.

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an airborne fungal disease which always destructs leaf and leads to stagnation of grain filling, decreasing of kernel weight, thin seed and yield loss. Winter wheat Huixianhong is a special germplasm with special characteristics of tolerance or resistance against stripe rust. In order to understand the effect on Huixianhong from stripe rust, we designed two kinds of treatment, inoculation of stripe rust fungi (IH) and artificial immune by bactericide (CK) to study the dynamic of disease process, the grain filling and the thousand-kernel weight (TKW). Our results showed that the incubation period of Hongxinahui was 13.5 days. The prevalence increased from 32.9% at 15 days after jointing to 80.0% at 9 days after booting, and reached to 97.0% at the heading stage. The infection type (IT) was 7 to 9 at the beginning of anthesis. The severity, leaf withered area ratio and disease index at the 15th day after anthesis were 67.17%, 98.17% and 0.6717, respectively. The IH maximum increasing rate of leaf necrosis and chlorosis area was from heading beginning stage to anthesis beginning stage, which increased from 18.66 mm2·d-1 to 21.04 mm2·d-1. The maximum rate of grain filling was 1.25 mg·d-1 at the 18th day after anthesis, which was earlier than that of CK by 3.3 days. The IH thousand-kernel weight Loss (TKWL) was more than that of CK by 6.19%, the stage of heading and amature were 3.0 days and 4.5 days earlier than CK, respectively. The stripe rust infection seriously destructed the photosynthetic function of leaf at the earlier stage of grain filling, i.e. at the beginning of anthesis, which led to the most important biomass loss and the grain filling rate decrease. As far as stripe rust is concerned, Huixianhong is a high susceptible, easily been infected, seriously showing symptoms and most quickly epidemic type but can successfully complete grain filling in high quality. It is a very useful germplasm for creating and selecting special breeding materials against stripe rust.

Additive Manufacturing of Devices Used for Collection and Application of Cereal Rust Urediniospores.

Optimized inoculation procedures are an important consideration in achieving repeatable plant infection when working with biotrophic rust fungi. Several plant pathology laboratories specializing in rust research employ a system where the collection and application of fungal spores are accomplished using an exchangeable gelatin capsule. Urediniospores are collected from erumpent pustules on plant surfaces into a capsule fitted to a cyclone collector controlled by a vacuum pump. By adding light mineral oil to the same capsule, the spore suspension is then sprayed onto plants by means of a dedicated atomizer (inoculator) connected to an air pressure source. Although devices are not commercially available, modern day technologies provide an opportunity to efficiently design and manufacture collectors and inoculators. Using a process called Additive Manufacturing (AM), also known as “3D printing,” the bodies of a collector and inoculator were digitally designed and then laser-sintered in nylon. Depending on availability, copper or aluminum tubes were fitted to the bodies of both devices afterward to either facilitate directed collection of spores from rust pustules on plant surfaces or act as a siphon tube to deliver the spore suspension contained in the capsule. No statistical differences were found between AM and metal inoculators for spray delivery time or spore deposition per unit area. In replicated collection and inoculation tests of wheat seedlings with urediniospore bulks or single pustule collections of Puccinia triticina and P. graminis f. sp. tritici, the causal organisms of leaf rust and stem rust, consistent and satisfactory infection levels were achieved. Immersing used devices in acetone for 60 s followed by a 2 h heat treatment at 75°C produced no contaminant infection in follow-up tests.

Detecting advanced stages of winter wheat yellow rust and aphid infection using RapidEye data in North China Plain

Yellow rust (Puccinia striiformis f. sp. Tritici) and aphid (Sitobion avenae F.) are two major biotic factors threatening winter wheat growth in the main growing region in northern China. The goal of this study was to develop a remote sensing based approach to reliably detect and discriminate yellow rust and aphid infection. The study was conducted in the North China Plain in 2017 based on RapidEye satellite images using three supervised classification algorithms, the maximum-likelihood classifier, the support vector machine, and the random forest. An overall accuracy of above 60% for aphid and above 70% for yellow rust can be achieved using a single image (May 7 or 10, 2017) with any of the three algorithms. With multi-temporal images, the overall accuracies both increased for aphid and yellow rust (above 70% and above 78%). Using the image acquired on 23 May 2017, joint infections by yellow rust and aphid can be detected with satisfaction (>73% overall accuracy), although confusion exists between the two infections. This study demonstrates that winter wheat disease/pest infection can be detected with remote sensing technologies, providing decision support to farmers, insurance companies, and government organizations in the agriculture sector.

Puccinia sambuci Infection of American Elderberry Plants

Elderberry rust (Puccinia sambuci Schwein.) Arthur (=P. bolleyana) (Arthur, 1921) disease is frequently found in commercial American elderberry (Sambucus nigra L. subsp. canadensis L.) plantings when an alternate host, Carex sp., is present. To evaluate potential infection periods of P. sambuci on elderberry plants, micrometeorological conditions were monitored. Rust symptoms were observed on elderberry on 5 Apr. 2016, and conditions favorable for possible infection were 9 to 18 °C, ≥3 hours of continuous leaf wetness, and ≥85% relative humidity. Studies were also conducted to ascertain whether P. sambuci with varying pustule numbers affects fruiting, berry puree quality, or vegetative growth. Fruit yield was reduced by 31% when potted ‘Bob Gordon’ elderberry averaged six rust pustules per plant compared with noninfected plants. In another experiment, field-grown ‘Wyldewood’ plants averaging 137 rust pustules/cane at harvest had 47% less fruit weight on canes than uninfected canes. Titratable acidity of fruit puree from plants was lower when plants had either 690 rust pustules/plant or 137/pustules/cane, but soluble solids and pH of puree were unaffected by P. sambuci infection. The effect of rust infection on vegetative growth of elderberry plants also varied with pustule numbers. With a low infection level (six pustules per plant), P. sambuci did not induce premature leaf loss on ‘Bob Gordon’ plants or adversely affect shoot dry weight at the end of the growing season. When P. sambuci infection on ‘Wyldewood’ plants was more severe (137 pustules/cane), greater leaf loss occurred on infected canes than on uninfected canes. At very high infection levels (690 pustules/plant), ‘Bob Gordon’ plant dry weight was reduced. Because of the potential for fruit yield loss on elderberry plants, control of P. sambuci at relatively low infection levels on this plant may be warranted. Strategies that eliminate or suppress the alternate host would likely reduce the P. sambuci inoculum and limit the potential for elderberry plant infection.

Defoliation of wild native box trees (Buxus sempervirens): Does box rust (Puccinia buxi) infection influence herbivory, survival and growth of the invasive Cydalima perspectalis?

AbstractThe invasive box‐tree moth Cydalima perspectalis causes damage to horticultural box trees (Buxus spp.) in private gardens and parks in Europe and defoliation of large areas of European native box trees Buxus sempervirens, which grow in the understorey of deciduous forests. In some parts of their distribution area, wild native box trees are infected by the box rust Puccinia buxi, a fungus which does not occur in the native range of C. perspectalis. We examined whether the infection of P. buxi deters grazing by C. perspectalis in 31 wild box‐tree stands in forests in north‐western Switzerland and south‐western Germany. On average, 82.4% of the box trees were infested by P. buxi (among‐site variation 20%–100%), or 18.5% of their leaves. Linear mixed‐effect (LME) models revealed that the percentage of rust‐infected leaves was influenced by the local box‐tree density and the slope aspect of the forest site. 9.5% of the leaves showed grazing damage by C. perspectalis. LME showed that the percentage of leaves with grazing damage was affected by the elevation of the site and the percentage of rust‐infected leaves. The effect of box rust infection on food choice and larval performance (survival and growth rate) was examined in two experiments. In food‐choice tests, larvae of C. perspectalis did not show any preference for uninfected or rust‐infected box‐tree leaves and consumed similar amounts of leaf tissue of either type. However, when larvae were reared on leaves with three different degrees of P. buxi‐infection (and uninfected leaves as control), both survival and growth rate decreased with increasing degree of rust infection. This indicates that larval performance of C. perspectalis is reduced by the box rust. In the case of an outbreak of C. perspectalis, however, larvae may indiscriminately defoliate wild box trees.

Genome-wide mapping of adult plant stripe rust resistance in wheat cultivar Toni

Two adult plant stripe rust resistance QTL, QYrto.swust-3AS and QYrto.swust-3BS, were identified and mapped in common wheat cultivar Toni. The two QTL were located to corresponding positions in the wheat physical map position based on flanking SNP markers. Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most important foliar diseases of wheat. Characterization and utilization of resistance genes are the most effective, economic and environmental-friendly way to control the disease. The wheat cultivar Toni resistant at the adult plant stage to predominant Chinese Pst races was crossed with the susceptible genotype Mingxian 169. A recombinant inbred line population comprising 171 lines was tested in the field at three locations in the 2016 and 2017 crop seasons. The Affymetrix Axiom® 35K single-nucleotide polymorphism (SNP) Wheat Breeder's Genotyping Array was used to map quantitative trait loci (QTL) for adult plant resistance to stripe rust. Inclusive composite interval mapping identified stable QTL QYrto.swust-3AS and QYrto.swust-3BS that explained 31.6-48.2% and 21.9-56.3% of the variation in stripe rust severity and infection type, respectively. The two QTL regions were anchored to the wheat IWGSC Ref Seq v1.0 sequence. QYrto.swust-3AS was localized to a 2.22-Mb interval flanked by SNP markers AX-95240191 and AX-94828890. Among 65 HC (high confidence) annotated genes in this region, 11 (16.9%) contained NB-ARC domains and 9 (13.8%) contained protein kinase domains and thus could contribute to disease resistance. QYrto.swust-3BS was localized to a 4.77-Mb interval flanked by SNP markers AX-94509749 and AX-94998050. One hundred and thirty three HC genes are annotated in this region. Among them, 14 (10.5%) protein kinase domain genes may contribute to disease resistance. The linked markers should be useful for marker-assisted selection in breeding for resistance.

English

Stem rust (Puccinia graminis f. sp. tritici) is one of the three rust diseases that infect triticale (X. Triticosecale Wittmack). Twenty-six triticale genotypes were evaluated for adult plant resistance (APR) to stem rust (Sr) infection in the greenhouse in a Randomized Complete Block Design (RCBD). R-TR (resistant –trace or minimal uredinia) reactions were observed on 6 genotypes EUT046, EUT59, EUT090, EUT093, 118 and EUT139 at adult plant stage. Reactions of 5RMR (5% disease severity with resistant-moderately resistant reactions) were observed on EUT001, EUT034, EUT035, EUT123 and EUT124. Four of the genotypes evaluated showed moderately resistant (MR) reactions with severity ranging from 10 MR to 15 MR. Effects due to genotype, stage and genotype × stage interactions were significant (p<0.001) for length, width and area of spore. The mean length of spore increased from 0.75 mm at 17 days to 2.65 mm at 35 days after inoculation (DAI). The mean area of spore ranged from 0.27 to 1.33 mm2 between the 17 and 35 DAI. The slowest development (0.003 mm2 day-1, 0.006 mm2 day-1 and 0.009 mm2 day-1) of Sr spore was observed between 17-20 DAI for EUT035, EUT123 and EUT034, respectively. Triticale genotypes were also significantly (p<0.001) different for the latent period, AUDPC, number and weight of grains per spike. The mean latent period ranged from 10.00 days for EUT004 to 22.66 days for EUT001 and EUT087. Triticale genotypes that showed high level of APR were identified and can be used as sources of resistance in triticale breeding programs against stem rust. Key words: Adult Plant Resistance, Stem rust, Resistant, Triticale genotypes.

АГРОЭКОЛОГИЧЕСКИЕ АСПЕКТЫ РАЗВИТИЯ PUCCINIA DISPERSA ERIKS. И PUCCINIA GRAMINIS PERS. НА ПОСЕВАХ ОЗИМОЙ РЖИ В КИРОВСКОЙ ОБЛАСТИ

The article is devoted to the analysis of the results of winter rye selection in the Research Center of the North-East for more than half a century of research. The dynamics of the degree of damage by brown and stem rust and the immune status of 9 varieties created at the institute in different periods (Vyatka 2, zoned in 1950; Dymka, 1993; Kirovskaya 89, 1993; Falenskaya 4, 1999; Snezhana, 2004; Rushnik, 2008; Flora, 2010; Grafinya, 2015; Kiprez - has been in state testing since 2017), and with different conditions of climatic factors. Taking into account the selection methods and the source material used in the work, as well as the year of inclusion of varieties in the State Register, they were divided into 3 stages of selection and variety change, 3 varieties in each. The study of the gene pool took place in 2010-2018 in the nursery of the competitive test with the natural infectious load of pathogens. The degree of damage to indicator (susceptible) varieties of brown rust averaged 41.4%, stem - 71.3%, which in terms of hardness corresponds to an average and strong infectious background. A reliable (at P ≥095) decrease in the degree of plant damage by stem rust was revealed with an increase in precipitation during the period of “bloom - milky-wax ripeness” (r = -0.68). At the same time, a closer relationship (r = - 0.74) for the varieties of the third stage of selection than for the varieties of the first and second stages is r = -0.62 and 0.66, respectively. The effect of temperature on the pathogenesis of both types of rust is insignificant, although it has a negative value. In the plant-microbial relationship Secale cereale-Puccinia dispersa, the effect of environmental factors is mostly insignificant, except for the effect of temperature on the development of brown rust in varieties of the second stage of selection (r = -0.51). Among the studied gene pool, only the Snezhana variety is characterized as resistant to leaf rust with a degree of damage ranging from 4.0 to 20.0%, and Vyatka 2 is moderately resistant to stem rust (20.0-35.0%). This trait in the Snezhana variety can be determined by the presence in its genome of the complex resistance donor Rossul (Lr4 and Sr1) from the VIR collection, and in the Vyatka 2 variety - by the recessive-polygenic type of short-stemming and intensive growth during the critical periods of the P. graminis pathogenesis. Close to them in terms of immune status is the Kirovskaya 89 variety, created with the participation of the Russian donor (RPd is an unidentified brown rust resistance gene). To date, in a series of successive stages of breeding, there is no significant progress in increasing the rust resistance of winter rye varieties. However, given the increase in rust infection, it is necessary to expand the immunological studies and strengthen the breeding work in this direction.

Antioxidant defense against rust infection in the leaf tissue of Malus crabapple

Plant tissues and cells can sense and transmit stress signals, change their morphological structures, alter protein and gene expression, and activate metabolic pathways to adapt to stressful environments. However, the internal and external resistance mechanisms related to antioxidation in local tissues or cells suffering from biotic stress remain unclear. We studied the response of Malus crabapple leaves to cedar-apple rust infection, and the results revealed that significant color changes and flavonoid compound accumulation (especially anthocyanins) occurred in the rust-infected tissue (RIT), whereas no significant color changes and only flavonol and flavanone accumulation occurred in the non-infected tissue (NIT). There was an up-regulation of expression of the key structural genes and MYBs related to anthocyanins biosynthesis in the RIT, while its expression related to flavonol and flavanone biosynthesis was up-regulated in the NIT. Moreover, the accumulation of glucose, sucrose, and sorbitol among the tested carbohydrates was successively induced at higher levels in the RIT and NIT. Importantly, rust infection increased the contents of jasmonate (JA), abscisic acid (ABA), and ethylene (ETH), and significantly up-regulated related key genes in the RIT and NIT during rust spot expansion. Spearman’s correlation and redundancy analyses indicated that ABA and ETH were potentially involved in oxidative defense responses to rust spot expansion by initiating the transcription of key genes, increasing the sugar supply, and adjusting the osmotic balance.

Characterization of molecular diversity and genome-wide association study of stripe rust resistance at the adult plant stage in Northern Chinese wheat landraces

BackgroundStripe rust is a serious fungal disease of wheat (Triticum aestivum L.) caused by Puccinia striiformis f. sp. tritici (Pst), which results in yield reduction and decreased grain quality. Breeding for genetic resistance to stripe rust is the most cost-effective method to control the disease. In the present study, a genome-wide association study (GWAS) was conducted to identify markers linked to stripe rust resistance genes (or loci) in 93 Northern Chinese wheat landraces, using Diversity Arrays Technology (DArT) and simple sequence repeat (SSR) molecular marker technology based on phenotypic data from two field locations over two growing seasons in China.ResultsSeventeen accessions were verified to display stable and high levels of adult plant resistance (APR) to stripe rust via multi-environment field assessments. Significant correlations among environments and high heritability were observed for stripe rust infection type (IT) and disease severity (DS). Using mixed linear models (MLM) for the GWAS, a total of 32 significantly associated loci (P < 0.001) were detected. In combination with the linkage disequilibrium (LD) decay distance (6.4 cM), 25 quantitative trait loci (QTL) were identified. Based on the integrated map of previously reported genes and QTL, six QTL located on chromosomes 4A, 6A and 7D were mapped far from resistance regions identified previously, and represent potentially novel stripe rust resistance loci at the adult plant stage.ConclusionsThe present findings demonstrated that identification of genes or loci linked to significant markers in wheat by GWAS is feasible. Seventeen elite accessions conferred with stable and high resistance to stripe rust, and six putative newly detected APR loci were identified among the 93 Northern Chinese wheat landraces. The results illustrate the potential for acceleration of molecular breeding of wheat, and also provide novel sources of stripe rust resistance with potential utility in the breeding of improved wheat cultivars.

Point Inoculation Method for Measuring Adult Plant Response of Wheat to Stripe Rust Infection.

Depending on the pathogenicity of the stripe rust fungus Puccinia striiformis f. sp. tritici, the nature of resistance in the wheat host plant, and the environment, a broad range of disease phenotypes can be expressed. Therefore, the phenotyping of partial adult plant stripe rust resistance requires reliable and repeatable procedures, especially under controlled conditions. In this study, the development of a flag leaf point inoculation method, which resulted in a 100% initial infection rate, is reported. Flag leaf inoculations were achieved by placing 6-mm antibiotic test paper discs, dipped into a urediniospore and water suspension and covered with water-proof plastic tape, on the adaxial side of leaves. Results from independent trials allowed for the statistical comparison of stripe rust lesion expansion rate in wheat entries that differ in resistance. The technique is inexpensive, reliable, and applicable to routine screening for adult plant response type, quantitative comparison of stripe rust progress, environmental influences, and pathogenicity of different isolates.

Nitrogen accumulation in grains, remobilization and post-anthesis uptake under tan spot and leaf rust infections on wheat

Nitrogen (N) fluxes involve important processes determining grain yield and quality in wheat (Triticum aestivum L.) and could be affected by major fungal diseases like leaf rust (Puccinia triticina Eriks) and tan spot [Pyrenophora tritici-repentis (Died.) Drechs., anamorph Drechslera tritici-repentis) (Died.) Shoem.]. Although effects of foliar diseases on N accumulation and translocation have already been studied, none of these studies performed inoculations in field conditions. This study aimed to determine the effects of independent inoculations to ensure the predominance of each pathogen of 1) Pyrenophora tritici-repentis (necrotroph) and 2) Puccinia triticina (biotroph) on N accumulation and allocation in wheat crops. Experiments were carried out using a split-split plot design where the main plots were both diseases, subplots were three inoculation treatments and ten cultivars were the sub-subplots. Healthy area duration (HAD), crop growth rate (CGR), N remobilization (NREM), N post-anthesis uptake (NPU), %N in grains and N stored in grains were calculated. The results indicate that the nutrition habit of the pathogens would cause a differential effect on crop N fluxes with more noticeable effects for P.triticina, explained by the retention of N in green tissues, which prevents the normal translocation of N to the grains. Higher rates of N stored in grains, NREM and a negative rate for % N in grains were manifested due to longer extensions in the HAD for leaf rust compared to tan spot. Inoculations with Py.tritici-repentis caused increases in the %N in grains up to 14.9%, while P.triticina reduced it by 9.89%. Both NREM (-30.9%) and N stored in grains (-24.4%) showed significant reductions under increases in the inoculum dose of P.triticina, but not under Py.tritici-repentis infections. Relating HAD and CGR to N accumulation under foliar diseases infections could be an effective tool to improve the modelling of yield and quality losses more accurately.

Seed Availability Does Not Ensure Regeneration in Northern Ecosystems of the Endangered Limber Pine

Research Highlights: When biotic interactions such as disease alter both the seed production capacity of stands, and seedling survivorship, the relative importance of seed availability versus substrate specificity may alter future regeneration opportunities for plant populations. Background and Objectives: We investigated the importance of disease severity, seed availability, and substrate limitation to the regeneration dynamics of the endangered limber pine, Pinus flexilis, in two ecosystems with varying forest composition, and different histories of white pine blister rust infection (WPBR; Cronartium ribicola). Materials and Methods: A total of 17 stands from the montane ecoregion (Alberta, Canada) were sampled for seed production between 2007–2010, seedling density, and age structure. Model selection using an information theoretic approach compared a series of a priori models and their combinations, based on our hypotheses on the role biotic variables play in the regeneration process. Results: Despite higher rates of WPBR infection, 2.3 times more seed was available for avian dispersers in the southern ecosystem. Recent seedling regeneration did not correspond to seed production (83 versus 251 seedlings/ha, in southern versus northern ecosystems, respectively), resulting in a seven-fold difference in seed to seedling ratios between ecosystems. Models suggest that disease and vegetation cover were important factors explaining the absence of regeneration in 79.4% of the plots sampled, while basal area (BA) of live limber pine, rocky substrates, ecosystem, South aspects, and slope enhanced limber pine regeneration. Seedling age structures suggest that recent regeneration is less likely in more diseased landscapes, than it was historically (40% versus 72.8% of seedlings &lt; 20 years old, respectively, in southern versus northern ecosystems). Conclusions: At the northern limits of limber pine’s range, seed availability does not ensure regeneration, suggesting that other environmental or biotic factors hinder regeneration. Regeneration was consistently predicted to be lower in the southern ecosystem than in the northern ecosystem, suggesting that natural regeneration and the potential for population recovery are ecosystem dependent. We recommend that monitoring recent seedlings will aid the identification of biotic and abiotic factors affecting regeneration.

Advances in understanding obligate biotrophy in rust fungi.

Contents Summary 1190 I. Introduction 1190 II. Rust fungi: a diverse and serious threat to agriculture 1191 III. The different facets of rust life cycles and unresolved questions about their evolution 1191 IV. The biology of rust infection 1192 V. Rusts in the genomics era: the ever-expanding list of candidate effector genes 1195 VI. Functional characterization of rust effectors 1197 VII. Putting rusts to sleep: Pucciniales research outlooks 1201 Acknowledgements 1202 References 1202 SUMMARY: Rust fungi (Pucciniales) are the largest group of plant pathogens and represent one of the most devastating threats to agricultural crops worldwide. Despite the economic importance of these highly specialized pathogens, many aspects of their biology remain obscure, largely because rust fungi are obligate biotrophs. The rise of genomics and advances in high-throughput sequencing technology have presented new options for identifying candidate effector genes involved in pathogenicity mechanisms of rust fungi. Transcriptome analysis and integrated bioinformatics tools have led to the identification of key genetic determinants of host susceptibility to infection by rusts. Thousands of genes encoding secreted proteins highly expressed during host infection have been reported for different rust species, which represents significant potential towards understanding rust effector function. Recent high-throughput in planta expression screen approaches (effectoromics) have pushed the field ahead even further towards predicting high-priority effectors and identifying avirulence genes. These new insights into rust effector biology promise to inform future research and spur the development of effective and sustainable strategies for managing rust diseases.

Genetic variation and inheritance in a 9 × 9 diallel in silver birch (Betula pendula)

ABSTRACTA complete diallel cross was made among nine Betula pendula trees growing in a natural population and a trial was planted on agricultural soil at one site. This exceptional trial has provided estimates of genetic parameters that can only be estimated in complete diallels. Traits measured were height and diameter during a period of 37 years, and assessments were made of bud burst, leaf abscission and rust infection at the early ages. All traits showed genetic variation and the variance components of general combining ability (GCA) effects were dominating, with heritability estimates of 0.16 and 0.23 for height and diameter at age six years. The best-growing families could be identified at that age. At age 37 years, when the trial had been thinned twice, the offspring from the highest and lowest ranked parent for growth contributed with 19% and 6% of the total volume of the stand, respectively. The GCA effects were also highly significant for the assessment traits, but with an interaction with year for bud burst. High values of estimates of genetic correlations proved that bud burst, leaf abscission and rust infection are interrelated, and also to some extent with growth traits. Families with an early bud burst were tallest, were less affected by the rust fungus and kept their leaves later in the autumn.

Application of plant extracts as inducers to challenge leaf rust of wheat

Five plant extracts, i.e., henna, Lawsonia inermis; acalypha, Acalypha wilkesiana; chinaberry, Melia azedarach; pomegranate, Punica granatum; and lantana, Lantana camara, were tested as inducers to protect wheat against leaf rust infection caused by Puccinia triticina Eriks. The plant extracts were applied pre-infection on susceptible wheat cultivar "Gemmiza-7" under field conditions during two growing seasons (2016/2017 and 2017/2018). All the tested plant extracts were found to be effective against the leaf rust infection. They significantly reduced the coefficient of infection (ACI) to be ranging 7.50 to 20.00, compared to the non-treated control (ACI = 75.00). Lantana extract was the most effective one (efficiency = 88.88%), which was very close to the fungicide “diniconazole” (efficiency = 89.92%). Henna extract ranked second (80.00%), followed by chinaberry (76.00%), acalypha (72.00%), and pomegranate (68.00%). However, wheat yield components were significantly increased by all the tested treatments, especially lantana extract and the fungicide. Similarly, biochemical analyses revealed a significant increase in the plant contents of chlorophyll a and b, total phenolics, and oxidative enzymes activities (POX and PPO) at all the tested treatments. Results indicated that the tested plant extracts could induce wheat resistance to leaf rust.

Genome-wide Mapping for Stripe Rust Resistance Loci in Common Wheat Cultivar Qinnong 142.

Stripe rust caused by Puccinia striiformis f. sp. tritici threatens worldwide wheat production. Growing resistant cultivars is the best way to control this disease. Chinese wheat cultivar Qinnong 142 (QN142) has a high level of adult-plant resistance to stripe rust. To identify quantitative trait loci (QTLs) related to stripe rust resistance, we developed a recombinant inbred line (RIL) population from a cross between QN142 and susceptible cultivar Avocet S. The parents and 165 F6 RILs were evaluated in terms of their stripe rust infection type and disease severity in replicated field tests with six site-year environments. The parents and RILs were genotyped with single-nucleotide polymorphism (SNP) markers. Four stable QTLs were identified in QN142 and mapped to chromosome arms 1BL, 2AL, 2BL, and 6BS. The 1BL QTL was probably the known resistance gene Yr29, the 2BL QTL was in a resistance gene-rich region, and the 2AL and 6BS QTLs might be new. Kompetitive allele specific polymerase chain reaction markers developed from the SNP markers flanking these QTLs were highly polymorphic in a panel of 150 wheat cultivars and breeding lines. These markers could be used in marker-assisted selection for incorporating the stripe rust resistance QTL into new wheat cultivars.

Changeability in Stripe Rust Infection and Grain Yield of Wheat Associated to Climatic Conditions

STRIPE rust infection caused by Pucciniastrii formis f. sp. tritici was investigated in ten Egyptian wheat cultivars under field conditions during two seasons (2016/17 and 2017/18) at two locations (Sakha and Sids) differ climatologically in Egypt. Variable levels of rust infection followed by a significant reduction in grain weight were recorded at both locations. Stripe rust infections for Sids location (20S - 90S) were higher than those of Sakha location (TrMS - 70S). Average coefficient of infection (ACI) and grain weight loss for Sids location, reaching 90 ACI (Gemmeiza-11) and 23.12% (Giza-160), were higher than those of Sakha location up to 70 ACI and 16.72% in Giza-160. Grain weight loss was strongly associated with ACI among cultivars for both locations, recording r=0.9044 for Sakha location and r=0.8866 for Sids location. Climatic variations were recorded at both locations during the first four months of 2017 and 2018. Rainfall and relative humidity for Sakha location were higher than those of Sids location while wind speed for Sids location was higher than that of Sakha location. Temperatures were relatively close at both locations. ACI values for Sids location were higher than those of Sakha location, revealing correlation with climatic factors. This suggests that wind speed may play an important role in dispersal while relatively heavy rainfall may have opposing effects. The temperature was the main limiting factor for stripe rust infection (negatively associated), followed by relative humidity (positively associated). Our discovery represents a powerful tool for predicting disease infection and management.

First Report of Rust Caused by Aecial Stage of Puccinia klugkistiana on Ligustrum japonicum in Korea

Ligustrum japonicum Thunb. (Oleraceae), called Japanese privet or waxleaf privet, is native to Japan and southern Korea. Owing to its attractive evergreen foliage, it is widely cultivated in other regions with warm temperate climates. This shrub is also naturalized in California and in the southeastern United States from Texas to Virginia (https://www.invasiveplantatlas.org/). In June 2016, hundreds of L. japonicum shrubs were found affected by a rust at a disease incidence of 50% in a public garden in Daegu (35°53′25″N; 128°35′01″E), Korea. Similar symptoms with typical rust pustules on this plant species were also found in Jinju (35°10′46″N; 128°05′48″E), Korea. Examination of an affected plant revealed that orange-yellow rust pustules were formed on the lower leaf surface with corresponding yellowish to chlorotic lesions on the upper surface. Four representative voucher specimens have been deposited in the Korea University herbarium (KUS-F29287, F29290, F29781, and F29797), Seoul, Korea. Morphological characteristics of the aecial stage were as follows. Spermogonia were epiphyllous, aggregated, initially yellow and becoming brown, subepidermal, and flask shaped. Aecia were hypophyllous, densely clustered, on leaves and occasionally also on branches, causing distortion and hypertrophy of the host, cupulate, deeply immersed in host mesophyll, 120 to 200 µm diameter, and yellowish. Peridia were prominent, easily splitting vertically, peridial cells oblong to polygonal, 22 to 36 × 16 to 22 µm, inner wall 4 to 6 µm thick, verrucose, outer wall 6 to 10 µm thick, smooth to finely verrucose. Aeciospores were angularly globose to ellipsoid, densely and minutely verrucose, subhyaline to pale yellowish, 16 to 28 × 16 to 22 µm, walls 1 to 2 µm thick. Morphological characteristics of the collections were in good agreement with the aecial stage of Puccinia klugkistiana (Dietel) J.X. Ji & Kakish. (Hiratsuka et al. 1992; Ji et al. 2017). To confirm the identification, genomic DNA was extracted from aeciospores of two dried herbarium specimens. The internal transcribed spacer (ITS) and large subunit (LSU) regions of rRNA gene were polymerase chain reaction (PCR) amplified using specific primer pairs ITS5u/ITS4rust and universal primers LR0R/LR6 as described by Beenken et al. (2017). PCR products were sequenced and deposited in GenBank (MH644179 and MH644180 for ITS; MH644181 and MH644182 for LSU). No ITS sequence of P. klugkistiana is available in the NCBI database, because this this the first sequence data for ITS of this rust species. LSU sequences from two representative isolates had 100% homology with that of Aecidium klugkistianum (HQ699078) from China. The aecial stage of P. klugkistiana has been reported on eight species/varieties of Ligustrum from East Asia including China, Japan, and Korea (Farr and Rossman 2018; Hiratsuka et al. 1992). In Korea, L. ibota and L. obtusifolium have been recorded as host plants of the aecial stage of P. klugkistiana (Hiratsuka 1942). To our knowledge, this is the first report of the aecial stage of P. klugkistiana on L. japonicum in Korea. Rust infection caused necrotic lesions, greatly detracting from the beauty of the glossy leaves.