BACKGROUND: Phytophthora spp. represent a pivotal genus of plant pathogens with a global distribution, exerting significant deleterious effects on food safety and forestry ecosystems. Numerous pathogenic and invasive Phytophthora species, introduced through imported fruits, have been frequently detected at Chinese ports. With the rise in global trade activities, the plant quarantine of imported fruits is becoming increasingly important but challenging. Fast, simple, and labor-saving techniques are necessary and anticipated.
RESULTS: A polymerase chain reaction restriction fragment length polymorphism capillary electrophoresis (PCR-RFLP-CE) technology-based quarantine approach was developed for 16 Phytophthora species associated with the imported fruits in China. The Ypt1 gene, exhibiting abundant interspecific variations, was selected as the marker gene for PCR. The restriction endonuclease AluI was proven to be capable and compatible in simultaneously separating different Phytophthora species during CE. By combining with a fast and efficient DNA extraction kit, the developed PCR-RFLP-CE technique was successfully applied to identify Phytophthora species in artificially infested fruits.
CONCLUSIONS: We provide a quick, practical, and high-throughput detection approach for hazardous and invasive Phytophthora species associated with imported fruits in China. This strategy can give good convenience and technological support for carrying out massive quarantine activities at Chinese ports. © 2024 Society of Chemical Industry.

Oomycete pathogens deliver many effectors to enhance virulence or suppress plant immunity. Plant immune networks are interconnected, in which a few effectors can trigger a strong defense response when recognized by immunity-related proteins. How effectors activate plant defense response remains poorly understood. Here we report Phytophthora capsici effector RxLR23KM can induce plant cell death and plant immunity. RxLR23KM specifically binds to ERD15La, a regulator of abscisic acid and salicylic acid pathway, and the binding intensity depends on the amino acid residues (K93 and M320). NbNAC68, a downstream protein of ERD15La, can stimulate plant immunity that is compromised after binding with ERD15La. Silencing of NbNAC68 substantially prevents the activation of plant defense response. RxLR23KM binds to ERD15La, releasing NbNAC68 to activate plant immunity. These findings highlight a strategy of plant defense response that ERD15La as a central regulator coordinates RxLR23KM to regulate NbNAC68-triggered plant immunity.

The discovery of readily available and easily modifiable new models is a crucial and practical solution for agrochemical innovation. Antifungal function-oriented fusion of triazole with the prevalidated lead (R)-LE001 affords a novel framework with a broad and enhanced antifungal spectrum. Characterized by the easy accessibility and adjustability of [1,2,4]triazolo[4,3-a]pyridine, modular fine-tuning provided a set of unprecedented leads (e.g., Z23, Z25, Z26, etc.) with superior antifungal potentials than the positive control boscalid. Candidate Z23 exhibited a more promising antifungal activity against Sclerotinia sclerotiorum, Botrytis cinerea, and Phytophthora capsici with EC50 values of 0.7, 0.6, and 0.5 μM, respectively. This candidate could effectively control boscalid-resistant B. cinerea strains and also exhibit good vivo efficacy in controlling gray mold. Noteworthily, both the SDH-inhibition and the efficiency against Oomycete P. capsici are quite distinct from that of the positive control boscalid. A molecular docking simulation also differentiates Z23 from boscalid. These findings highlight the potential of [1,2,4]triazolo[4,3-a]pyridine amide as a novel antifungal model.

Small secreted peptides (SSPs), serving as signaling molecules for intercellular communication, play significant regulatory roles in plant growth, development, pathogen immunity, and responses to abiotic stress. Despite several SSPs, such as PIP, PSK, and PSY having been identified to participate in plant immunity, the majority of SSPs remain understudied, necessitating the exploration and identification of SSPs regulating plant immunity from vast genomic resources. Here we systematically characterized 756 putative SSPs across the genome of Nicotiana tabacum. 173 SSPs were further annotated as established SSPs, such as nsLTP, CAPE, and CEP. Furthermore, we detected the expression of 484 putative SSP genes in five tissues, with 83 SSPs displaying tissue-specific expression. Transcriptomic analysis of tobacco roots under plant defense hormones revealed that 46 SSPs exhibited specific responsiveness to salicylic acid (SA), and such response was antagonistically regulated by methyl jasmonate. It\'s worth noting that among these 46 SSPs, 16 members belong to nsLTP family, and one of them, NtLTP25, was discovered to enhance tobacco\'s resistance against Phytophthora nicotianae. Overexpression of NtLTP25 in tobacco enhanced the expression of ICS1, subsequently stimulating the biosynthesis of SA and the expression of NPR1 and pathogenesis-related genes. Concurrently, NtLTP25 overexpression activated genes associated with ROS scavenging, consequently mitigating the accumulation of ROS during the subsequent phases of pathogenesis. These discoveries indicate that these 46 SSPs, especially the 16 nsLTPs, might have a vital role in governing plant immunity that relies on SA signaling. This offers a valuable source for pinpointing SSPs involved in regulating plant immunity.

Synergistic effect of dimethomorph (DIM) and pyrimethanil (PYM) was evaluated using the Wadley method and the molecular mechanism of the antifungal effects of the combined treatment was systematically investigated. DIM+PYM had a synergistic effect on Phytophthora capsici, with the synergistic effect being observed at 5:1, at which the synergy coefficient was 1.8536. The mycelia of the pathogen treated with DIM+PYM were branched, uneven in thickness, and swollen. Moreover, scanning electron microscopy (SEM) revealed that DIM+PYM caused mycelium breaks, swelling, and apex enlargement, while transmission electron microscopy (TEM) revealed structural damage, cavities, and cell membrane morphological abnormalities. DIM+PYM inhibited the growth of mycelia, destroyed the cell membrane, interfered with energy metabolism, reduced protein and sugar content. Additionally, the transcriptome and metabolome of fungi treated with DIM+PYM changed significantly; specifically, there were 1571 differentially expressed genes and 802 differential metabolites. DIM+PYM may mainly damage the cell membrane, energy, protein, soluble sugar pathways.

The root endophytic fungus Serendipita indica establishes beneficial symbioses with a broad spectrum of plants and enhances host resilience against biotic and abiotic stresses. However, little is known about the mechanisms underlying S. indica-mediated plant protection. Here, we report S. indica effector (SIE) 141 and its host target CDSP32, a conserved thioredoxin-like protein, and underlying mechanisms for enhancing pathogen resistance and abiotic salt tolerance in Arabidopsis thaliana. SIE141 binding interfered with canonical targeting of CDSP32 to chloroplasts, leading to its re-location into the plant nucleus. This nuclear translocation is essential for both their interaction and resistance function. Furthermore, SIE141 enhanced oxidoreductase activity of CDSP32, leading to CDSP32-mediated monomerization and activation of NON-EXPRESSOR OF PATHOGENESIS-RELATED 1 (NPR1), a key regulator of systemic resistance. Our findings provide functional insights on how S. indica transfers well-known beneficial effects to host plants and indicate CDSP32 as a genetic resource to improve plant resilience to abiotic and biotic stresses.

Pepper southern blight, caused by Sclerotium rolfsii, is a devastating soil-borne disease resulting in significant loss to pepper, Capsicum annuum L. production. Here, we isolated an antagonistic bacterial strain XQ-29 with antifungal activity against S. rolfsii from rhizospheric soil of pepper. Combining the morphological and biochemical characteristics with the 16S rDNA sequencing, XQ-29 was identified as Streptomyces griseoaurantiacus. It exhibited an inhibition of 96.83% against S. rolfsii and displayed significant inhibitory effects on Botrytis cinerea, Phytophthora capsica and Rhizoctonia solani. Furthermore, XQ-29 significantly reduced the pepper southern blight by 100% and 70.42% during seedling and growth stages, respectively. The antifungal mechanism involved altering the mycelial morphology, disrupting cell wall and membrane integrity, accompanied by accumulation of reactive oxygen species and lipid peroxidation in S. rolfsii mycelia. Furthermore, XQ-29 promoted growth and stimulated resistance of pepper plants by increasing defense-related enzyme activities and upregulating defense-related genes. Correspondingly, XQ-29 harbors numerous functional biosynthesis gene clusters in its genome, including those for siderophores and melanin production. The metabolic constituents present in the ethyl acetate extracts, which exhibited an EC50 value of 85.48 ± 1.62 μg/mL, were identified using LC-MS. Overall, XQ-29 demonstrates significant potential as a biocontrol agent against southern blight disease.

Quinone outside inhibitor (QoI) has been applied to manage taro leaf blight caused by Phytophthora colocasiae in southeastern of China for many years. The risk of P. colocasiae to QoI and the potential resistant mechanism remain unknown. In this study, the 74 P. colocasiae strains were sampled from southeastern of China. Sequence analysis of the QoI target Cytb showed one nucleotide variant in the fragment of this gene in this population, producing two haplotypes. The nucleotide variant leads to codon change at 142 (GGT to GCT) producing A142 (alanine) and G142 (glycine) in Hap_1 and Hap_2 strains, respectively. The sensitivity differentiation to azoxystrobin of two haplotypes were observed in vitro. The Hap_1 and Hap_2 strains were confirmed resistant and sensitive by control efficacy of label rate fungicide application, which was 3.0% and 88.8% treated with 500 μg/mL azoxystrobin, respectively. In addition, 10.0 μg/mL azoxystrobin plus 50 μg/mL salicylhydroxamic acid (SHAM) supplemented in PDA medium was identified as a discriminatory dose for differentiation of these two phenotype strains. The azoxystrobin resistant frequency reached 86.5%, indicating prevalence of QoI resistance in the field. Further fitness related features showed that no significant difference in temperature sensitivity, mycelial growth rate, sporangia production, zoospore release and aggressiveness between azoxystrobin-resistant and sensitive strains indicating no potential fitness cost for azoxystrobin resistance. Taken together, azoxystrobin resistance need to be taken into consideration to manage taro leaf blight in southeastern of China.

The phytopathogenic oomycete Phytophthora litchii is the culprit behind the devastating disease known as \"litchi downy blight\", which causes large losses in litchi production. Although fluopimomide exhibits strong inhibitory efficacy against P. litchii, the exact mechanism of resistance is still unknown. The sensitivity of 137 P. litchii isolates to fluopimomide was assessed, and it was discovered that the median effective concentration (EC50) of the fungicide had a unimodal frequency distribution with a mean value of 0.763 ± 0.922 μg/mL. Comparing the resistant mutants to the equivalent parental isolates, the resistance mutants\' survival fitness was much lower. While there was no cross-resistance between fluopimomide and other oomycete inhibitors, there is a notable positive cross-resistance between fluopimomide and fluopicolide. According to the thorough investigation, P. litchii had a moderate chance of developing fluopimomide resistance. The point mutations N771S and K847N in the VHA-a of P. litchii (PlVHA-a) were present in the fluopimomide-resistant mutants, and the two point mutations in PlVHA-a conferring fluopimomide resistance were verified by site-directed mutagenesis in the sensitive P. capsici isolate BYA5 and molecular docking.

Phytophthora parasitica causes diseases on a broad range of host plants. It secretes numerous effectors to suppress plant immunity. However, only a few virulence effectors in P. parasitica have been characterized. Here, we highlight that PpE18, a conserved RXLR effector in P. parasitica, was a virulence factor and suppresses Nicotiana benthamiana immunity. Utilizing luciferase complementation, co-immunoprecipitation, and GST pull-down assays, we determined that PpE18 targeted NbAPX3-1, a peroxisome membrane-associated ascorbate peroxidase with reactive oxygen species (ROS)-scavenging activity and positively regulates plant immunity in N. benthamiana. We show that the ROS-scavenging activity of NbAPX3-1 was critical for its immune function and was hindered by the binding of PpE18. The interaction between PpE18 and NbAPX3-1 resulted in an elevation of ROS levels in the peroxisome. Moreover, we discovered that the ankyrin repeat-containing protein NbANKr2 acted as a positive immune regulator, interacting with both NbAPX3-1 and PpE18. NbANKr2 was required for NbAPX3-1-mediated disease resistance. PpE18 competitively interfered with the interaction between NbAPX3-1 and NbANKr2, thereby weakening plant resistance. Our results reveal an effective counter-defense mechanism by which P. parasitica employed effector PpE18 to suppress host cellular defense, by suppressing biochemical activity and disturbing immune function of NbAPX3-1 during infection.