Phytophthora Root And Stem Rot Research Articles

Virulence, Aggressiveness, and Fungicide Sensitivity of Phytophthora spp. Associated with Soybean in Illinois.

Phytophthora root and stem rot (PRR), caused by Phytophthora sojae, is one of the most devastating oomycete diseases of soybean in Illinois. Single resistant genes (Rps) are used to manage this pathogen but P. sojae has adapted to Rps, causing failure of resistance in many regions. In addition to P. sojae, recent reports indicate that P. sansomeana could also cause root rot in soybean. Soil samples and symptomatic plants were collected across 40 Illinois counties between 2016 and 2018. P. sojae (77%) was more abundant than P. sansomeana (23%) across Illinois fields. Both species were characterized by virulence, aggressiveness, and fungicide sensitivity. Virulence of all P. sojae isolates was evaluated using the hypocotyl inoculation technique in 13 soybean differentials. Aggressiveness was evaluated in the greenhouse by inoculating a susceptible cultivar and measuring root and shoot dry weight. On average, P. sojae isolates were able to cause disease on six soybean differentials. P. sojae was more aggressive than P. sansomeana. All isolates were sensitive to azoxystrobin, ethaboxam, mefenoxam, and metalaxyl. The characterization of the population of species associated with PRR will inform management decisions for this disease in Illinois.

Phytophthora sojae effector PsAvh113 associates with the soybean transcription factor GmDPB to inhibit catalase-mediated immunity.

Phytophthora species are the most destructive plant pathogens worldwide and the main threat to agricultural and natural ecosystems; however, their pathogenic mechanism remains largely unknown. Here, we show that Avh113 effector is required for the virulence of Phytophthora sojae and is important for development of Phytophthora root and stem rot (PRSR) in soybean (Glycine max). Ectopic expression of PsAvh113 enhanced viral and Phytophthora infection in Nicotiana benthamiana. PsAvh113 directly associated with the soybean transcription factor GmDPB, inducing its degradation by the 26S proteasome. The internal repeat 2 (IR2) motif of PsAvh113 was important for its virulence and interaction with GmDPB, while silencing and overexpression of GmDPB in soybean hairy roots altered the resistance to P. sojae. Upon binding to GmDPB, PsAvh113 decreased the transcription of the downstream gene GmCAT1, which acts as a positive regulator of plant immunity. Furthermore, we revealed that PsAvh113 suppressed the GmCAT1-induced cell death by associating with GmDPB, thereby enhancing plant susceptibility to Phytophthora. Together, our findings reveal a vital role of PsAvh113 in inducing PRSR in soybean and offer a novel insight into the interplay between defence and counter-defence during the P. sojae infection of soybean.

RNA‐seq analysis of soybean (Glycine max) responding to Phytophthora sojae

AbstractPhytophthora sojae is a devastating pathogen of soybean [Glycine max (L.) Merr.] that causes Phytophthora root and stem rot (PRR) on soybean plants worldwide. The pathogen leads to evident differentiation of pathogenicity which brings some difficulties to the control of the disease. Soybean germplasm plays an important role in disease resistance to P. sojae. To understand the role of soybean in the pathogen differentiation of P. sojae, transcriptome sequencing and biological information technology were used to analyse the difference in transcriptional level of soybean response to P. sojae infection by two isolates BB8 and BZ9 with different pathogenicity. A total of 1596 differentially expressed genes (DEGs) were screened from the soybean plants treated with the strong pathogenic isolate BB8 and weak pathogenic isolate BZ9, of which 256 were upregulated and 1340 were downregulated in BZ9 treated samples. Gene Ontology analysis revealed that the highly enriched terms annotated in biological processes were metabolic process, cellular process and single‐organism process. Kyoto Encyclopedia of Genes and Genomes pathways were distributed primarily in metabolism, environmental information processing and cellular processes. Photosynthesis‐antenna proteins, photosynthesis, phenylpropanoid biosynthesis, carbon fixation in photosynthetic organisms, plant hormone signal transduction, flavonoid biosynthesis, carbon metabolism and nitrogen metabolism were the most substantial metabolic pathways. Ten candidate DEGs were selected and their expression levels were detected via fluorescence quantitative polymerase chain reaction. The expression trends were basically consistent with the results of RNA‐seq detection, confirming the reliability of RNA‐seq data. Taken together, this was the report on the transcriptome analysis of soybean in response to P. sojae using high‐throughput sequencing. A number of DEGs and pathways were discovered, which provided valuable information for obtaining high‐quality soybean resistance resources.

Progress and prospectus in genetics and genomics of Phytophthora root and stem rot resistance in soybean (Glycine max L.)

Soybean is one of the largest sources of protein and oil in the world and is also considered a "super crop" due to several industrial advantages. However, enhanced acreage and adoption of monoculture practices rendered the crop vulnerable to several diseases. Phytophthora root and stem rot (PRSR) caused by Phytophthora sojae is one of the most prevalent diseases adversely affecting soybean production globally. Deployment of genetic resistance is the most sustainable approach for avoiding yield losses due to this disease. PRSR resistance is complex in nature and difficult to address by conventional breeding alone. Genetic mapping through a cost-effective sequencing platform facilitates identification of candidate genes and associated molecular markers for genetic improvement against PRSR. Furthermore, with the help of novel genomic approaches, identification and functional characterization of Rps (resistance to Phytophthora sojae) have also progressed in the recent past, and more than 30 Rps genes imparting complete resistance to different PRSR pathotypes have been reported. In addition, many genomic regions imparting partial resistance have also been identified. Furthermore, the adoption of emerging approaches like genome editing, genomic-assisted breeding, and genomic selection can assist in the functional characterization of novel genes and their rapid introgression for PRSR resistance. Hence, in the near future, soybean growers will likely witness an increase in production by adopting PRSR-resistant cultivars. This review highlights the progress made in deciphering the genetic architecture of PRSR resistance, genomic advances, and future perspectives for the deployment of PRSR resistance in soybean for the sustainable management of PRSR disease.

Registration of seven disease‐ and pest‐resistant vegetable soybean germplasm lines

AbstractSoybean [Glycine max (L.) Merr.] germplasm lines LB18‐49 (Reg. no. GP‐448, PI 699118), LB18‐52 (Reg. no. GP‐456, PI 699119), LB18‐57 (Reg. no. GP‐455, PI 699120), LB18‐58 (Reg. no. GP‐454, PI 699487), LB18‐65 (Reg. no. GP‐453, PI 699488), LB18‐67 (Reg. no. GP‐452, PI 699489), and LB18‐75 (Reg. no. GP‐451, PI 699121) are large seeded, non‐genetically modified organism soybean lines ranging in maturity from maturity group (MG) 00 through MG IV. Each line contains a single gene for resistance to soybean aphid or Phytophthora root and stem rot (PRSR). LB18‐49 and LB18‐58 have resistance to soybean aphid biotype 3 (Rag1) provided by LD06‐16721. Soybean aphid resistance to biotype 2 (Rag2) was derived from LD08‐12441 for LB18‐65. LD08‐12582 provided Rag2 resistance for LB18‐52 and LB18‐57. ‘Williams 82’ was the source of the PRSR resistance gene, Rps1k, for LB18‐67 and LB18‐75. Large‐seeded cultivars ‘Tohya’ (MG 00), ‘BeSweet 2001’ (MG II), ‘Gardensoy 24’ (MG II), and ‘Gardensoy 41’ (MG IV) served as recurrent parents with pest‐resistant donor lines to develop large‐seeded, pest‐resistant soybean lines in a range of maturity groups. The combined pest resistance and large seed size, in a range of maturities, will be valuable for breeders developing large‐seeded pest‐resistant cultivars.

Effects of wounding and relative humidity on the incidence of Phytophthora root and stem rot in soybean seedlings

Phytophthora root and stem rot (PRSR) caused by Phytophthora sojae is a major constraint in soybean production. The effects of wounding and relative humidity (RH) on PRSR-induced damage, specifically on the mortality and infection rates in soybean seedlings, which have never been experimentally shown, were investigated. Seedlings were inoculated with P. sojae after being wounded in one of four ways (shallow, moderate, deep, or penetrative incision) or left unwounded. Immediately after inoculation, plants were subjected to five different RH treatments: 3-day wet (100% RH), 1-day wet, ambient (approximately 80% RH), 1-day dry (approximately 60% RH), and 3-day dry treatments. All wounded but uninoculated seedlings survived. The mortality rate ranged from 1 to 99% across all wounding treatments. All unwounded seedlings inoculated with the pathogen survived under all RH treatments. The mortality rates of inoculated seedlings with shallow to deep wounding increased with higher RH. The infection rate followed the same pattern as the mortality rate. Furthermore, the ratio of brown tissues in the cross section of seedlings correlated with wounding depth. These findings demonstrate that the degree of wounding is a crucial determinant of PRSR development, and high RH stimulates disease incidence.

Effect of Resistance and Ethaboxam Seed Treatment on the Management of Phytophthora Root Rot in Illinois and Iowa

Phytophthora root and stem rot (PRR) is a limiting factor for soybean production. Seed treatments are used for early-season management, but efficacy can depend on seed selection and the local environment. Ethaboxam is a new fungicide commercially available as a seed treatment to control oomycetes. Field experiments were established in Illinois and Iowa in 2017 and 2018 to evaluate the effect of ethaboxam + metalaxyl on PRR. Experiments included soybean lines with no resistance gene, Rps1c or Rps1k, and different levels of partial resistance. Seed treatments increased soybean stands in all locations and years. Significant yield effects were observed only in two locations that were inoculated with Phytophthora spp. Groups of soybean lines with the same Rps gene responded differently in each location, showing how Rps gene usefulness depends on the field. A comparison of the effect of seed treatment on lines with different levels of partial resistance showed that partial resistance alone cannot always protect against stand losses. Soybean lines with high levels of partial resistance had consistently higher yields than those with low levels of partial resistance across Illinois locations. These results show that ethaboxam seed treatment can protect early-season stands and that selection of cultivars with high levels of partial resistance is important for PRR management.

Enhanced tolerance to Phytophthora root and stem rot by over-expression of the plant antimicrobial peptide CaAMP1 gene in soybean

BackgroundAntimicrobial peptides play important roles in both plant and animal defense systems. Moreover, over-expression of CaAMP1 (Capsicum annuum antimicrobial protein 1), an antimicrobial protein gene isolated from C. annuum leaves infected with Xanthomonas campestris pv. vesicatoria, confers broad-spectrum resistance to hemibiotrophic bacterial and necrotrophic fungal pathogens in Arabidopsis. Phytophthora root and stem rot (PRR), caused by the fungus Phytophthora sojae, is one of the most devastating diseases affecting soybean (Glycine max) production worldwide.ResultsIn this study, CaAMP1 was transformed into soybean by Agrobacterium-mediated genetic transformation. Integration of the foreign gene in the genome of transgenic soybean plants and its expression at the translation level were verified by Southern and western blot analyses, respectively. CaAMP1 over-expression (CaAMP1-OX) lines inoculated with P. sojae race 1 exhibited enhanced and stable PRR tolerance through T2–T4 generations compared with the wild-type Williams 82 plants. Gene expression analyses in the transgenic plants revealed that the expression of salicylic acid-dependent, jasmonic acid-dependent, and plant disease resistance genes (R-genes) were significantly up-regulated after P. sojae inoculation.ConclusionsThese results indicate that CaAMP1 over-expression can significantly enhance PRR tolerance in soybean by eliciting resistance responses mediated by multiple defense signaling pathways. This provides an alternative approach for developing soybean varieties with improved tolerance against soil-borne pathogenic PRR.

A Review and Perspective on Soybean (Glycine maxL.) Breeding for the Resistance toPhytophthora sojaein Korea

Phytophthora root and stem rot (PRR) of soybean is a severe disease that causes significant economic losses in soybean-growing countries. The causal agent, Phytophthora sojae, is a soil-borne oomycete that causes pre- and post-emergence damping-off of soybean in poorly drained soils. PRR has not been a severe problem in South Korea; however, as the cultivation of soybean in paddy fields recently increased, there is a growing interest because the incidence of PRR can be extensively expanded. R-gene mediated resistance is known as the main strategy for the management of this disease. On the other hand, partial resistance has also been known to provide more effective disease management than the Rps (Resistance to Phytophthora sojae) resistance. Responses of domestic soybean cultivars to a few P. sojae isolates were recently reported, while phenotypic distribution of numerous germplasms is mostly unknown. The objectives of this review are to summarize published studies conducted on PRR, to suggest future directions of genetic researches and breeding to the target pathogen. This review will discuss the followings; i) a brief introduction to PRR and the causal agent P. sojae, ii) types of genetic resistance to P. sojae and findings of genes/QTL conditioning to resistance, iii) changes in virulence pathotype of P. sojae populations, and iv) current status and perspective of genetic/genomic researches on the interaction of soybean and P. sojae in the South Korea.

Identification of New Isolates of Phytophthora sojae and the Reactions of Korean Soybean Cultivars Following Hypocotyl Inoculation.

Phytophthora root and stem rot (PRSR) caused by Phytophthora sojae is one of the most destructive diseases of soybean. PRSR recently became an issue as soybean cultivation in paddy fields increased in South Korea. The management of PRSR mainly involves R-gene–mediated resistance, however, little is known about the resistance in Korean cultivars. Major Korean soybean cultivars were investigated for the presence or absence of R-gene–mediated resistance to four P. sojae isolates, two of which were new isolates. Isolate-specific reactions were observed following P. sojae inoculation. Of 21 cultivars, 15–20 cultivars (71.4–95.2%) showed susceptible reaction for each isolate. Ten cultivars were susceptible to all the isolates, and six cultivars were identified to have R-gene–mediated resistance to one or two isolates. The results of this study would provide a framework for the discovery of resistant cultivars, development of new cultivars resistant to P. sojae, and investigation of pathogenic diversity of P. sojae population in South Korea.

An Improved Method for the Identification of Soybean Resistance to Phytophthora sojae Applied to Germplasm Resources from the Huanghuaihai and Dongbei Regions of China.

Phytophthora root and stem rot (PRR) caused by Phytophthora sojae is a destructive disease afflicting soybean. The use of resistant cultivars is the most effective method to combat PRR. PRR resistance was assessed in 223 soybean cultivars from Huanghuaihai and Dongbei, major soybean-producing regions in east central and northeastern China. To evaluate levels of soybean resistance to P. sojae, we used eight representative P. sojae isolates and a modified etiolated hypocotyl-slit inoculation method. The cultivars Wandou21020, Xu9302-A, Kedou10, and Lidi055 showed resistance to all eight isolates; 14 cultivars showed intermediate resistance to all eight P. sojae isolates, and 53 cultivars were resistant to seven isolates. Thirty-three cultivars (15%) were susceptible only to the highly virulent PsJS2 isolate, which is consistent with the reactions of the Chapman differential line that carries Rps3a. The diverse reaction patterns seen in germplasm from different regions (provinces/cities) in this study reflect the variety of PRR-resistant soybean sources in China. Our research indicates that sources of P. sojae resistance are present in the major soybean production areas of China. This study provides useful information for soybean breeding programs.

Introduction of the harpinXooc-encoding gene hrf2 in soybean enhances resistance against the oomycete pathogen Phytophthora sojae.

Phytophthora root and stem rot (PRR) caused by an oomycete pathogen Phytophthora sojae is one of the most devastating and widespread diseases throughout soybean-producing regions worldwide. The diversity and variability of P. sojae races make effective control of the pathogen challenging. Here, we introduced an elicitor of plant defense response, the harpinXooc-encoding hrf2 gene from the rice bacterial pathogen Xanthomonas oryzae pv. oryzicola into soybean and evaluated resistance to P. sojae infection. Molecular analysis confirmed the integration and expression of hrf2 in the transgenic soybean. After inoculation with P. sojae, non-transformed control (NC) plants exhibited typical PRR symptoms, including necrotic and wilting leaves, and plant death, whereas most of the transgenic plants showed slightly chlorotic leaves and developed normally. Through T3 to T5 generations, the transgenic events displayed milder disease symptoms and had higher survival rates compared to NC plants, indicating enhanced and stable resistance to P. sojae infection, whereas without P. sojae inoculation, no significant differences in agronomic traits were observed between the transgenic and non-transformed plants. Moreover, after inoculation with P. sojae, significant upregulation of a set of plant defense-related genes, including salicylic acid- and jasmonic acid-dependent and hypersensitive response-related genes was observed in the transgenic plants. Our results indicate that hrf2 expression in transgenic soybean significantly enhanced resistance to P. sojae by eliciting multiple defense responses mediated by different signaling pathways. The potential functional role of the hrf2 gene in plant defense against P. sojae and other pathogens makes it a promising tool for broadening disease resistance in soybean.

Over-expression of the Pseudomonas syringae harpin-encoding gene hrpZm confers enhanced tolerance to Phytophthora root and stem rot in transgenic soybean.

Phytophthora root and stem rot (PRR) caused by Phytophthora sojae is one of the most devastating diseasesreducing soybean (Glycine max) production all over the world. Harpin proteins in many plant pathogenic bacteria were confirmed to enhance disease and insect resistance in crop plants. Here, a harpin protein-encoding gene hrpZpsta from the P. syringae pv. tabaci strain Psta218 was codon-optimized (renamed hrpZm) and introduced into soybean cultivars Williams 82 and Shennong 9 by Agrobacterium-mediated transformation. Three independent transgenic lines over-expressing hrpZm were obtained and exhibited stable and enhanced tolerance to P. sojae infection in T2-T4 generations compared to the non-transformed (NT) and empty vector (EV)-transformed plants. Quantitative real-time PCR (qRT-PCR) analysis revealed that the expression of salicylic acid-dependent genes PR1, PR12, and PAL, jasmonic acid-dependent gene PPO, and hypersensitive response (HR)-related genes GmNPR1 and RAR was significantly up-regulated after P. sojae inoculation. Moreover, the activities of defense-related enzymes such as phenylalanine ammonia lyase (PAL), polyphenoloxidase (PPO), peroxidase, and superoxide dismutase also increased significantly in the transgenic lines compared to the NT and EV-transformed plants after inoculation. Our results suggest that over-expression of the hrpZm gene significantly enhances PRR tolerance in soybean by eliciting resistance responses mediated by multiple defense signaling pathways, thus providing an alternative approach for development of soybean varieties with improved tolerance against the soil-borne pathogen PRR.

Phenotypic evaluation and genetic dissection of resistance to Phytophthora sojae in the Chinese soybean mini core collection.

BackgroundPhytophthora root and stem rot (PRR) caused by Phytophthora sojae is one of the most serious diseases affecting soybean (Glycine max (L.) Merr.) production all over the world. The most economical and environmentally-friendly way to control the disease is the exploration and utilization of resistant varieties.ResultsWe screened a soybean mini core collection composed of 224 germplasm accessions for resistance against eleven P. sojae isolates. Soybean accessions from the Southern and Huanghuai regions, especially the Hubei, Jiangsu, Sichuan and Fujian provinces, had the most varied and broadest spectrum of resistance. Based on gene postulation, Rps1b, Rps1c, Rps4, Rps7 and novel resistance genes were identified in resistant accessions. Consequently, association mapping of resistance to each isolate was performed with 1,645 single nucleotide polymorphism (SNP) markers. A total of 14 marker-trait associations for Phytophthora resistance were identified. Among them, four were located in known PRR resistance loci intervals, five were located in other disease resistance quantitative trait locus (QTL) regions, and five associations unmasked novel loci for PRR resistance. In addition, we also identified candidate genes related to resistance.ConclusionThis is the first P. sojae resistance evaluation conducted using the Chinese soybean mini core collection, which is a representative sample of Chinese soybean cultivars. The resistance reaction analyses provided an excellent database of resistant resources and genetic variations for future breeding programs. The SNP markers associated with resistance will facilitate marker-assisted selection (MAS) in breeding programs for resistance to PRR, and the candidate genes may be useful for exploring the mechanism underlying P. sojae resistance.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-016-0383-4) contains supplementary material, which is available to authorized users.

Identification and molecular mapping of Rps11, a novel gene conferring resistance to Phytophthora sojae in soybean.

Rps11 confers excellent resistance to predominant Phytophthora sojae isolates capable of defeating major Rps genes deployed into soybean production, representing a novel source of resistance for soybean cultivar enhancement. Phytophthora root and stem rot (PRSR), caused by the soil-borne pathogen Phytophthora sojae, is a devastating disease of soybean [Glycine max (L.) Merr.] throughout the world. Deploying resistant soybean cultivars is the most effective and environmentally friendly approach to managing this disease. The soybean landrace PI 594527 was found to carry excellent resistance to all P. sojae isolates examined, some of which were capable of overcoming the major Rps genesp, such as Rps1-k, Rps1-c, and Rps3-a, predominantly used for soybean protection in the past decades. A mapping population consisting of 58 F2 individuals and 209 F2:3 families derived from a cross between PI 594527 and the susceptible cultivar 'Williams' was used to characterize the inheritance pattern of the resistance to P. soja (Rps) in PI 594527. It was found that the resistance was conferred by a single Rps gene, designated Rps11, which was initially defined as an ~5 Mb genomic region at the beginning of chromosome 7 by bulked segregant analysis (BSA) with a nucleotide polymorphism (SNP) chip comprising 7039 SNP markers. Subsequently, simple sequence repeat (SSR) markers in the defined region were used to genotype the F2:3 mapping population to map Rps11 to a 225.3 kb genomic region flanked by SSR markers BARCSOYSSR_07_0286 and BARCSOYSSR_07_0300, according to the soybean reference genome sequence. Particularly, an SSR marker (i.e., BARCSOYSSR_07_0295) was found to tightly co-segregate with Rps11 in the mapping population and can be effectively used for marker-assisted selection of this gene for development of resistant soybean cultivars.

Molecular mapping of two genes conferring resistance to Phytophthora sojae in a soybean landrace PI 567139B

Phytophthora root and stem rot (PRR), caused by the soil-borne oomycete pathogen Phytophthora sojae, is one of the most destructive diseases of soybean. PRR can be effectively controlled by race-specific genes conferring resistance to P. sojae (Rps). However, the Rps genes are usually non-durable, as populations of P. sojae are highly diverse and quick to adapt, and can be overcome 8-15years after deployment. Thus, it is important to identify novel Rps genes for development of resistant soybean cultivars. PI 567139B is a soybean landrace carrying excellent resistance to nearly all predominant P. sojae races in Indiana. A mapping population consisting of 245 F2 individuals and 403 F2:3 families was developed from a cross between PI 567139B and the susceptible cultivar 'Williams', and used to dissect the resistance carried by PI 567139B. We found that the resistance in PI 567139B was conferred by two independent Rps genes, designated RpsUN1 and RpsUN2. The former was mapped to a 6.5cM region between SSR markers Satt159 and BARCSOYSSR_03_0250 that spans the Rps1 locus on chromosome 3, while the latter was mapped to a 3.0cM region between BARCSOYSSR_16_1275 and Sat_144, approximately 3.0-3.4cM upstream of Rps2 on chromosome 16. According to the 'Williams 82' reference genome sequence, both regions are highly enriched with NBS-LRR genes. Marker assisted resistance spectrum analyses of these genes with 16 isolates of P. sojae, in combination with the mapping results, suggested that RpsUN1 was likely to be a novel allele at the Rps1 locus, while RpsUN2 was more likely to be a novel Rps gene.

Within-field Pathogenic Diversity of Phytophthora sojae in Commercial Soybean Fields in Iowa

Phytophthora root and stem rot (PRR), caused by the oomycete Phytophthora sojae, is an economically important soybean disease in the north central region of the United States, including Iowa. Previous surveys of the pathogenic diversity of P. sojae in Iowa did not investigate whether multiple pathotypes of the pathogen existed in individual fields. Considering the many pathotypes of P. sojae that have been reported in Iowa, we hypothesized multiple pathotypes could exist within single fields. In the research reported herein, several soil samples were collected systematically from each of two commercial fields with a history of PRR in Iowa, and each soil sample was baited separately for isolates of P. sojae. Numerous pathotypes of P. sojae were detected from both fields. As many as four pathotypes were detected in some soil samples (each consisting of six to eight soil cores), which suggests that a single soybean plant could be subjected to infection by more than one pathotype. This possibility presents important implications in breeding resistant cultivars and in the management of PRR. Accepted for publication 14 July 2009. Published 8 September 2009.