Novel quantitative trait loci for partial resistance to Phytophthora sojae in soybean PI 398841

Phytophthora root and stem rot caused by Phytophthora sojae Kaufmann and Gerdemann is one of the most severe soybean [Glycine max (L.) Merr] diseases in the USA. Partial resistance is as effective in managing this disease as single-gene (Rps gene)-mediated resistance and is more durable. The objective of this study was to identify quantitative trait loci (QTL) associated with partial resistance to P. sojae in PI 398841, which originated from South Korea. A population of 305 F_7:8 recombinant inbred lines derived from a cross of OX20-8 × PI 398841 was used to evaluate partial resistance against P. sojae isolate C2S1 using a tray test. Composite interval mapping using a genome-wide logarithm of odd (LOD) threshold detected three QTL on chromosomes 1, 13, and 18, which individually explained 4–16 % of the phenotypic variance. Seven additional QTL, accounting for 2–3 % of phenotypic variance each, were identified using chromosome-wide LOD thresholds. Seven of the ten QTL for resistance to P. sojae were contributed by PI 398841. Seven QTL co-localized with known Rps genes and previously reported QTL for soil-borne root pathogens, isoflavone, and seed oil. Three QTL on chromosomes 3, 13, and 18 co-localized with known Rps genes, but PI 398841 did not exhibit an Rps gene-mediated resistance response following inoculation with 48 different isolates of P. sojae. PI 398841 is potentially a source of novel genes for improving soybean cultivars for partial resistance to P. sojae.     

Characterization of the Virulence Phenotypes of Heterodera glycines in Minnesota

Knowledge of the virulence phenotypes of soybean cyst nematode, Heterodera glycines populations is important in choosing appropriate sources for breeding resistant cultivars and managing the nematode. We investigated races of 59 H. glycines populations collected from 1997 to 1998 and races and HG Types of 94 populations collected in 2002 from soybean fields across southern and central Minnesota. In the 1997 to 1998 samples, race 3 was predominant and represented 78% of the populations. The remaining populations were 11.9% race 1, 1.7% race 4, 6.8% race 6, and 1.7% race 14. In the 2002 samples, the populations were classified as 15.3% race 1, 77.6% race 3, 2.4% race 5, 3.5% race 6 and 1.2% race 9. Percentage of 1997 to 1998 populations with female indices (FI) higher than 10 were 10.2% on Pickett 71, 3.4% on Peking, 13.6% on PI 88788, 3.4% on PI 90763, 1.7% on PI 209332, and 1.7% on PI 437654. Percentage of 2002 populations with FI >10 was 1.1% on Peking, 17.0% on PI88788, 14.9% on PI 209332, 33.0% on PI 548316, 11.7% on Pickett 71, and 0% on the other three indicators, PI 90763, PI 437654, and PI 89772. The line PI 548316 was relatively susceptible to the Minnesota H. glycines populations and may not be recommended for breeding resistant cultivars in the state. There was no noticeable change of frequencies of virulence phenotypes in response to the use of resistant cultivars during 1997 to 2002 in Minnesota except that FI increased on the PI 209332.     

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 8–15 years 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 F_2:3 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 6.5 cM region between SSR markers Satt159 and BARCSOYSSR_03_0250 that spans the Rps1 locus on chromosome 3, while the latter was mapped to a 3.0 cM region between BARCSOYSSR_16_1275 and Sat_144, approximately 3.0–3.4 cM 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.     

Correlation of Female Indices From Virulence Assays on Inbred Lines and Field Populations of Heterodera glycines

A lack of diversity and durability of resistant soybean varieties complicates management of the soybean cyst nematode (SCN), Heterodera glycines, exemplified by the current overdependence on the PI 88788 source of resistance. Of interest is the effect of adaptation of a SCN population to a source of resistance on its subsequent ability to develop on others. Female indices (FI) from virulence assays (race, HG Type and SCN Type tests) for SCN field populations and inbred lines were analyzed. Female indices on PI 88788, PI 209332 and PI 548316 were highly correlated, as were those of PI 548402, PI 90763, PI 89772 and PI 438489B. Previous studies on resistant SCN-infected soybean roots indicated that the cellular resistance response was similar within these two groups of soybean genotypes. In field populations, highly significant correlations were also found between FI on PI 88788 and PI 548402 and those on PI 89772 and PI 437654. In inbred lines, FI on PI 437654 were correlated with PI 90763 and PI 438489B. To avoid further adaptation, rotation of cultivars with resistance from these groups should be carefully monitored, including those from the most promising source of resistance, PI 437654, such as CystX. In a separate test, 10 soybean varieties developed from CystX were tested against HG Type 0, HG Type 2.5.7 and HG Type 1–7. Female development occurred in all tests but one. Although identification and deployment of unique resistance is needed, management strategies to prevent and detect adaptation should be emphasized.     

Genetics of Soybean-Heterodera glycines Interactions

The soybean cyst nematode, Heterodera glycines, is one of the most economically important pathogens of soybean. Effective management of the nematode is often dependent on the planting of resistant soybean cultivars. During the past 40 years, more than 60 soybean genotypes and plant introductions (PI) have been reported as resistant to H. glycines. About 130 modern soybean cultivars registered in the United States are resistant to certain races of H. glycines. Several resistance genes have been identified and genetically mapped; however, resistance levels in many soybean cultivars are not durable. Some older cultivars are no longer resistant to certain H. glycines populations in many production areas, especially if a soybean monoculture has been practiced. Past soybean registration reports show that all resistant cultivars developed in public institutions from the mid-1960s to the present have been derived from five PIs. This narrow genetic background is fragile. To further complicate the issue, soybean-H. glycines genetic interactions are complex and poorly understood. Studies to identify soybean resistance genes sometimes have overlapped, and the same genes may have been reported several times and designated by different names. Nevertheless, many potential resistance genes in existing germplasm resources have not yet been characterized. Clearly, it is necessary to identify new resistance genes, develop more precise selection methods, and integrate these resistance genes into new cultivars. Rational deployment of resistant cultivars is critical to future sustained soybean production.     

Antibiosis in Soybean Genotypes and the Resistance Levels to Spodoptera eridania (Cramer) (Lepidoptera: Noctuidae)

The southern armyworm (SAW) Spodoptera eridania (Cramer) is one of the most common armyworm species defoliating soybeans. Preliminary screening trials have indicated that some soybean genotypes exhibit resistance to SAW. Therefore, in this study, we evaluated the development of SAW larvae fed on ten soybean genotypes in order to identify genotypes with antibiosis-type resistance. Neonate SAW larvae were daily fed with young leaves collected from plants at the vegetative growth stages V4–V5. Larval development and survival were recorded. Genotypes PI 227687 and PI 227682 delayed larval, pupal, and larva-adult development and yielded larvae with the lowest weight and survival and pupae with the lowest weight. Genotypes IAC 100 and DM 339 also negatively affected larval and pupal development and larval survival but at a lower level. Based on our results, the soybean lines PI 227687 and PI 227682 could be used as sources of genes for soybean breeding programs aiming to develop high yield, SAW-resistant cultivars. Moreover, further trials must be carried out under field conditions to validate if the commercial cultivars IAC 100 and DM 339, which expressed moderate levels of antibiosis-type resistance in the laboratory, are effective in suppressing SAW larvae populations.     

Changes in the Reproduction of Heterodera glycines on Different Lines of Glycine max

Selection for ability of soybean cyst nematode (SCN), Heterodera glycines, to reproduce on soybeans with different sources of resistance divides some SCN race 4 field populations into two distinct subpopulations. These subpopulations reproduce well on ''Bedford'' and plant introduction (PI) 88788 or PI 89772 and PI 90763 but not on both pairs of soybean lines. The ability of these subpopulations to reproduce on the four soybean lines was reversed by changing the soybean line used as a host during a second cycle of selection. When SCN populations previously selected for reproduction on Bedford and PI 88788 were selected for their ability to reproduce on D72-8927 and J74-88, the ability of these populations to reproduce on Bedford and PI 88788 decreased significantly and their ability to reproduce on PI 89772 and PI 90763 increased significantly. Conversely, when SCN populations, previously selected for reproduction on P189772 and P190763, were selected for their ability to reproduce on Bedford, the reproduction of these populations on Bedford increased significantly and reproduction on PI 89772 and PI 90763 decreased significantly. Selection for ability of a SCN race 4 field population to reproduce on soybean lines derived from SCN race 4 resistant PIs resulted in the same division of the field population into two distinct subpopulations. These data substantiate earlier proposals to rotate cultivars with different genes for SCN resistance as a means of managing SCN populations.     

Genetic mapping and development of co-segregating markers of <Emphasis Type="Italic">RpsQ</Emphasis>, which provides resistance to <Emphasis Type="Italic">Phytophthora sojae</Emphasis> in soybean

Key message

The RpsQ Phytophthora resistance locus was finely mapped to a 118-kb region on soybean chromosome 3. A best candidate gene was predicted and three co-segregating gene markers were developed.

Abstract

Phytophthora root rot (PRR), caused by Phytophthora sojae, is a major threat to sustainable soybean production. The use of genetically resistant cultivars is considered the most effective way to control this disease. The Chinese soybean cultivar Qichadou 1 exhibited a broad spectrum resistance, with a distinct resistance phenotype, following inoculation with 36 Chinese P. sojae isolates. Genetic analyses indicated that the disease resistance in Qichadou 1 is controlled by a single dominant gene. This gene locus was designated as RpsQ and mapped to a 118-kb region between BARCSOYSSR_03_0165 and InDel281 on soybean chromosome 3, and co-segregated with Insert11, Insert144 and SNP276. Within this region, there was only one gene Glyma.03g27200 encoding a protein with a typical serine/threonine protein kinase structure, and the expression pattern analysis showed that this gene induced by P. sojae infection, which was suggested as a best candidate gene of RpsQ. Candidate gene specific marker Insert144 was used to distinguish RpsQ from the other known Rps genes on chromosome 3. Identical polymerase chain reaction amplification products were produced for cultivars Qichadou 1 (RpsQ) and Ludou 4 (Rps9). All other cultivars carrying Rps genes on chromosome 3 produced different PCR products, which all lacked a 144-bp fragment present in Qichadou 1 and Ludou 4. The phenotypes of the analyzed cultivars combined with the physical position of the PRR resistance locus, candidate gene analyses, and the candidate gene marker test revealed RpsQ and Rps9 are likely the same gene, and confer resistance to P. sojae.

     

Joint linkage QTL analyses for partial resistance to Phytophthora sojae in soybean using six nested inbred populations with heterogeneous conditions

Partial resistance to Phytophthora sojae in soybean is controlled by multiple quantitative trait loci (QTL). With traditional QTL mapping approaches, power to detect such QTL, frequently of small effect, can be limited by population size. Joint linkage QTL analysis of nested recombinant inbred line (RIL) populations provides improved power to detect QTL through increased population size, recombination, and allelic diversity. However, uniform development and phenotyping of multiple RIL populations can prove difficult. In this study, the effectiveness of joint linkage QTL analysis was evaluated on combinations of two to six nested RIL populations differing in inbreeding generation, phenotypic assay method, and/or marker set used in genotyping. In comparison to linkage analysis in a single population, identification of QTL by joint linkage analysis was only minimally affected by different phenotypic methods used among populations once phenotypic data were standardized. In contrast, genotyping of populations with only partially overlapping sets of markers had a marked negative effect on QTL detection by joint linkage analysis. In total, 16 genetic regions with QTL for partial resistance against P. sojae were identified, including four novel QTL on chromosomes 4, 9, 12, and 16, as well as significant genotype-by-isolate interactions. Resistance alleles from PI 427106 or PI 427105B contributed to a major QTL on chromosome 18, explaining 10–45 % of the phenotypic variance. This case study provides guidance on the application of joint linkage QTL analysis of data collected from populations with heterogeneous assay conditions and a genetic framework for partial resistance to P. sojae.     

Virulence of Phytophthora sojae in the Pampeana Subregion of Argentina from 1998 to 2004

Phytophthora root rot is one of the most serious diseases of soybeans in Argentina. Surveys of commercial fields and trial plots of soybean were conducted throughout the northern Pampeana subregion (Argentina) between 1998 and 2004. A total of 193 isolates of Phytophthora sojae were collected and classified into races or virulence formulae. Among the 173 isolates tested on 8 differentials, 42 different pathotypes were detected, including 18 described races. Races 1, 4, 5, 7, 9, 13, 23 and 24 were found in both plants and soils, whereas races 2, 3, 6, 8, 11, 14, 15, 17, 43 and 44 were only isolated from plants. An additional 19 pathotypes were described from 20 isolates tested in Canada on the expanded set of 14 differential cultivars. Currently, all Rps genes/alleles associated with resistance have been defeated, indicating an increased complexity of virulence within the P. sojae populations in the region. The great increase in virulence complexity found in this study is most likely a result of a long period of continuous production of soybean cultivars with Rps genes and the extensive adoption of the no‐tillage system.     

Genetic mapping of three quantitative trait loci for soybean aphid resistance in PI 567324

Host-plant resistance is an effective method for controlling soybean aphid (Aphis glycines Matsumura), the most damaging insect pest of soybean (Glycine max (L.) Merr.) in North America. Recently, resistant soybean lines have been discovered and at least four aphid resistance genes (Rag1, Rag2, Rag3 and rag4) have been mapped on different soybean chromosomes. However, the evolution of new soybean aphid biotypes capable of defeating host-plant resistance conferred by most single genes demonstrates the need for finding germplasm with multigenic resistance to the aphid. This study was conducted to map quantitative trait loci (QTL) for aphid resistance in PI 567324. We identified two major QTL (QTL_13_1 and QTL_13_2) for aphid resistance on soybean chromosome 13 using 184 recombinant inbred lines from a ‘Wyandot'' × PI 567324 cross. QTL_13_1 was located close to the previously reported Rag2 gene locus, and QTL_13_2 was close to the rag4 locus. A minor QTL (QTL_6_1) was also detected on chromosome 6, where no gene for soybean aphid resistance has been reported so far. These results indicate that PI 567324 possesses oligogenic resistance to the soybean aphid. The molecular markers closely linked to the QTL reported here will be useful for development of cultivars with oligogenic resistance that are expected to provide broader and more durable resistance against soybean aphids compared with cultivars with monogenic resistance.     

Identification and Candidate Gene Analysis of a Novel Phytophthora Resistance Gene Rps10 in a Chinese Soybean Cultivar

Resistance to Phytophthora sojae isolate PsMC1 was evaluated in 102 F_2∶3 families derived from a cross between the resistant soybean cultivar Wandou 15 and the susceptible cultivar Williams and genotyped using simple sequence repeat (SSR) markers. The segregation ratio of resistant, segregating, and susceptible phenotypes in the population suggested that the resistance in Wandou 15 was dominant and monogenic. Twenty-six polymorphic SSR markers were identified on soybean chromosome 17 (Molecular linkage group D2; MLG D2), which were linked to the resistance gene based on bulked segregation analysis (BSA). Markers Sattwd15-24/25 and Sattwd15-47 flanked the resistance gene at a distance of 0.5 cM and 0.8 cM, respectively. Two cosegregating markers, Sattwd15-28 and Sattwd15-32, were also screened in this region. This is the first Rps resistance gene mapped on chromosome 17, which is designated as Rps10. Eight putative genes were found in the mapped region between markers Sattwd15-24/25 and Sattwd15-47. Among them, two candidate genes encoding serine/threonine (Ser/Thr) protein kinases in Wandou 15 and Williams were identified and sequenced. And the differences in genomic sequence and the putative amino acid sequence, respectively, were identified within each candidate gene between Wandou 15 and Williams. This novel gene Rps10 and the linked markers should be useful in developing soybean cultivars with durable resistance to P. sojae.     

Identification of Rotylenchulus reniformis Resistant Glycine Lines

Identification of resistance to reniform nematode (Rotylenchulus reniformis) is the first step in developing resistant soybean (Glycine max) cultivars that will benefit growers in the mid-South region of the United States. This study was conducted to identify soybean (G. max and G. soja) lines with resistance to this pathogen. Sixty-one wild and domestic soybean lines were evaluated in replicated growth chamber tests. Six previously untested soybean lines with useful levels of resistance to reniform nematode were identified in both initial screening and subsequent confirmation tests: released germplasm lines DS4-SCN05 (PI 656647) and DS-880 (PI 659348); accession PI 567516 C; and breeding lines DS97-84-1, 02011-126-1-1-2-1 and 02011-126-1-1-5-1. Eleven previously untested moderately susceptible or susceptible lines were also identified: released germplasm lines D68-0099 (PI 573285) and LG01-5087-5; accessions PI 200538, PI 416937, PI 423941, PI 437697, PI 467312, PI 468916, PI 594692, and PI 603751 A; and cultivar Stafford (PI 508269). Results of previously tested lines evaluated in the current study agreed with published reports 69.6% of the time for resistant lines and 87.5% of the time for susceptible lines. Soybean breeders may benefit from incorporating the newly identified resistant lines into their breeding programs.     

Characterization of Xanthomonas citri pv. glycines Population Genetics and Virulence in a National Survey of Bacterial Pustule Disease in Korea

Xanthomonas citri pv. glycines (Xcg) is a major pathogen of soybean (Glycine max) in South Korea, despite the availability of soybean varieties with some resistance. We conducted a nationwide survey of the incidence and severity of bacterial pustule caused by Xcg. The percentage of infected fields was 7% to 17% between 2015 and 2017. We characterized the diversity of a nationwide collection of 106 Xcg isolates based on avrBs3 banding patterns. The isolates fell into 11 groups, each represented by a type strain; only two of these were similar to isolates collected from 1999 to 2002. The diversity of Xcg strains increased and the dominant strains changed between 1999 and 2017, with three new type strains comprising 44% of the isolates examined in 2012 to 2017. Pathogenicity tests did not show evidence for a shift in the races or aggressiveness of Xcg strains. Korean soybean cultivars, including the widely-grown Daewon cultivar, were susceptible to the 11 new type strains. The cultivar CNS, which carries the rxp resistance gene, was susceptible to most type strains, including two representing 83% of the Korean Xcg strains. In contrast, Williams 82, which also carries rxp, showed resistance to at least five type strains. Collectively, these results suggest that Williams 82 has resistance loci in addition to rxp. The widespread distribution of Xcg, the high virulence of the current endemic strains, and the low resistance of most Korean soybean cultivars collectively favor widespread disease in Korea in years that are favorable to pustule development.     

A Phytophthora sojae Glycoside Hydrolase 12 Protein Is a Major Virulence Factor during Soybean Infection and Is Recognized as a PAMP

We identified a glycoside hydrolase family 12 (GH12) protein, XEG1, produced by the soybean pathogen Phytophthora sojae that exhibits xyloglucanase and β-glucanase activity. It acts as an important virulence factor during P. sojae infection but also acts as a pathogen-associated molecular pattern (PAMP) in soybean (Glycine max) and solanaceous species, where it can trigger defense responses including cell death. GH12 proteins occur widely across microbial taxa, and many of these GH12 proteins induce cell death in Nicotiana benthamiana. The PAMP activity of XEG1 is independent of its xyloglucanase activity. XEG1 can induce plant defense responses in a BAK1-dependent manner. The perception of XEG1 occurs independently of the perception of ethylene-inducing xylanase. XEG1 is strongly induced in P. sojae within 30 min of infection of soybean and then slowly declines. Both silencing and overexpression of XEG1 in P. sojae severely reduced virulence. Many P. sojae RXLR effectors could suppress defense responses induced by XEG1, including several that are expressed within 30 min of infection. Therefore, our data suggest that PsXEG1 contributes to P. sojae virulence, but soybean recognizes PsXEG1 to induce immune responses, which in turn can be suppressed by RXLR effectors. XEG1 thus represents an apoplastic effector that is recognized via the plant’s PAMP recognition machinery.     

Genetic Diversity for Resistance to Heterodera glycines Race 5 in Soybean

Heterodera glycines is a serious pest of soybean in the United States. Plant introductions 90763 and 424595 are reported to be resistant to H. glycines race 5; however their genetic relationship for resistance is unknown. Crosses between these two lines and the susceptible cultivar Essex were studied in the F₁, F₂, and F₃ generations to determine the number of genes involved in inheritance of resistance. The plants were screened using conventional techniques based on the index of parasitism. The data were subjected to analyses using chi-square test to determine goodness of fit between observed and expected genetic ratios. The cross PI 424595 x Essex segregated 1 resistant:63 susceptible in the F₂ generation, which indicated the presence of three recessive genes controlling resistance to race 5. In the cross PI 90763 x Essex, resistance was conditioned by one dominant and two recessive genes. The cross between PI 424595 and PI 90763 segregated into 13 resistant:3 susceptible. The data fit a four-gene model with two recessive and two dominant genes with epistasis. PI 90763 has a dominant gene, whereas PI 424595 has a recessive gene; both share two additional recessive genes for resistance to race 5. This information is important to geneticists and soybean breeders for the development of cultivars resistant to H. glycines.     

Aggressiveness and Reproduction of Four Meloidogyne arenaria Populations on Soybean

Aggressiveness and reproduction differed among four geographical populations of M. arenaria on six soybean cultivars in field microplots. These differences were consistent over 3 years. The populations did not differ in virulence; i.e., population by cultivar interactions were not significant. Perineal pattern morphology, the North Carolina differential host test, chromosome counts of immature oocytes, and esterase phenotypes confirmed that the four populations were M. arenaria. Three populations were host race 2 and one population was host race 1.     

Genome-Wide Association Study of Partial Resistance to P. sojae in Wild Soybeans from Heilongjiang Province,China

Phytophthora root rot (PRR) is a destructive disease of soybeans (Glycine max (L.) Merr) caused by Phytophthora sojae (P. sojae). The most effective way to prevent the disease is growing resistant or tolerant varieties. Partial resistance provides a more durable resistance against the pathogen compared to complete resistance. Wild soybean (Glycine soja Sieb. & Zucc.) seems to be an extraordinarily important gene pool for soybean improvement due to its high level of genetic variation. In this study, 242 wild soybean germplasms originating from different regions of Heilongjiang province were used to identify resistance genes to P. sojae race 1 using a genome-wide association study (GWAS). A total of nine significant SNPs were detected, repeatedly associated with P. sojae resistance and located on chromosomes 1, 10, 12, 15, 17, 19 and 20. Among them, seven favorable allelic variations associated with P. sojae resistance were evaluated by a t-test. Eight candidate genes were predicted to explore the mechanistic hypotheses of partial resistance, including Glysoja.19G051583, which encodes an LRR receptor-like serine/threonine protein kinase protein, Glysoja.19G051581, which encodes a receptor-like cytosolic serine/threonine protein kinase protein. These findings will provide additional insights into the genetic architecture of P. sojae resistance in a large sample of wild soybeans and P. sojae-resistant breeding through marker-assisted selection.     

Isolation of ethylene-insensitive soybean mutants that are altered in pathogen susceptibility and gene-for-gene disease resistance

Plants commonly respond to pathogen infection by increasing ethylene production, but it is not clear if this ethylene does more to promote disease susceptibility or disease resistance. Ethylene production and/or responsiveness can be altered by genetic manipulation. The present study used mutagenesis to identify soybean (Glycine max L. Merr.) lines with reduced sensitivity to ethylene. Two new genetic loci were identified, Etr1 and Etr2. Mutants were compared with isogenic wild-type parents for their response to different soybean pathogens. Plant lines with reduced ethylene sensitivity developed similar or less-severe disease symptoms in response to virulent Pseudomonas syringae pv glycinea and Phytophthora sojae, but some of the mutants developed similar or more-severe symptoms in response to Septoria glycines and Rhizoctonia solani. Gene-for-gene resistance against P. syringae expressing avrRpt2 remained effective, but Rps1-k-mediated resistance against P. sojae races 4 and 7 was disrupted in the strong ethylene-insensitive etr1-1 mutant. Rps1-k-mediated resistance against P. sojae race 1 remained effective, suggesting that the Rps1-k locus may encode more than one gene for disease resistance. Overall, our results suggest that reduced ethylene sensitivity can be beneficial against some pathogens but deleterious to resistance against other pathogens.