The fungal plant pathogen Sphaerulina musiva (Ascomycota) causes Septoria stem canker, the most economically damaging disease of Populus plantations in North America, yet the genetic determinants of host resistance remain uncharacterized in hybrid poplar. Using an inoculation experiment with the 52-124 pseudo-backcross family of Populus trichocarpa × Populus deltoides (TD × D) hybrid poplar, a single significant QTL was identified on Chromosome 16 (LOD = 4.93) associated with both stem canker count and disease severity score. Transcriptomic analysis of two resistant and two susceptible genotypes across a 72-hour infection time course identified a single differentially expressed gene within the QTL candidate gene window: Podel.16G125900, a putative leucine-rich repeat receptor-like protein (LRR-RLP) with homology to receptor-like protein 33 in Arabidopsis thaliana. Podel.16G125900 is located 3001 bp (0.019 cM) upstream of the QTL peak and showed a strong infection-induced upregulation in susceptible genotype 852 (log2 fold-change = 20.47) and higher baseline expression in resistant genotypes relative to susceptible genotypes across all infection time points, consistent with a resistance mechanism in which expression level contributes to the degree of resistance conferred. Two P. trichocarpa homologs were not differentially expressed and differ substantially in sequence content, suggesting the resistance function is specific to the resistant P. deltoides lineage. These findings identify Podel.16G125900 as a strong candidate gene underlying quantitative resistance mechanisms modulating Septoria stem canker resistance in the 52-124 family of TD × D hybrid poplar and provide a target for future functional validation and marker-assisted resistance breeding.
Over 30 years, the National Cotton Council's National Cottonseed Treatment program has conducted coordinated seed treatment trials across the U.S., resulting in a comprehensive dataset of over 500 field trials. After data curation compiled from annual reports published in the Cotton Beltwide Proceedings, we used data from 409 field trials to develop beta regression models for upland cotton (Gossypium hirsutum L.) seedling emergence that integrates environmental and pathogen variables and to evaluate the efficacy of seed treatments. The minimum air temperature nine days post-planting and the cumulative precipitation three days post-planting were identified as key environmental predictors of emergence. The successful isolation of Pythium spp. from cotton roots was significantly associated with reduced emergence. Seed treatments containing at least three active ingredients targeting both true fungi and oomycetes improved emergence by an average of 10.2% and significantly reduced the risk of falling below the critical threshold of 35,000 emerged plants per hectare, often cited as the population to maintain yield. The resulting model introduces a benchmark tool with an associated error rate of approximately 16 to 20%, enabling future refinement. These findings highlight the long-term value of multi-state field trials and support the development of data-driven tools to guide planting or scouting decisions and optimize seed treatment strategies.
North Dakota, the largest dry bean (Phaseolus vulgaris L.) producing state in the U.S., faces an emerging production threat caused by the soybean cyst nematode (SCN; Heterodera glycines Ichinohe, 1952). Host resistance is an effective management strategy, yet resistance to the virulent SCN population HG type 1.2.5.7 has not been genetically characterized in dry beans. In this study, 170 dry bean genotypes (113 breeding lines/cultivars and 57 germplasm accessions) were evaluated for response to HG type 1.2.5.7 under controlled conditions using female index (FI) as the resistance phenotype. FI values ranged from 4.1% to 78.1%, with one genotype (PI 313733) classified as resistant, 35 moderately resistant, 104 moderately susceptible, and 30 susceptible. Genome-wide association analysis using 2,044 single-nucleotide polymorphism (SNP) markers from the 3.8K Bean Panel chip and the BLINK model identified four significant marker-trait associations on chromosomes Pv02, Pv05, Pv07, and Pv11. Linkage disequilibrium-defined candidate intervals spanned 108 kb (Pv02), 1.50 Mb (Pv05), 798 kb (Pv07), and 1.45 Mb (Pv11), collectively containing 126 annotated genes: 20 on Pv02, 39 on Pv05, 35 on Pv07, and 32 on Pv11. The intervals contained putative genes annotated for signaling and transcriptional regulation, cell wall and carbohydrate metabolism, transport, and secondary metabolism. Together, these findings indicate that the response to HG type 1.2.5.7 in dry bean is quantitative and associated with multiple genomic regions. The identified intervals provide candidate targets for independent validation, fine mapping, functional analysis, and future marker development to support breeding for SCN resistance.
The AP-2 complex is a heterotetrameric complex that mediates polar growth and morphological development and governs development, reproduction, survival and host colonization in phytopathogenic fungi. We previously determined that the AP-2 complex α subunit was essential for growth, metabolism, and pathogenicity in Verticillium dahliae. Building on this, we systematically investigated the functions of its β, μ, and σ subunits. The deletion of these subunits led to radial growth retardation, decreased sporulation and pathogenicity, and promoted melanin accumulation in V. dahliae. Disrupted hyphal polarity resulted in aberrant chitin deposition and cell surface hydrophobicity defects, mechanistically linked to impaired membrane integrity due to compromised ergosterol biosynthesis. Protein-protein interaction assays and transcriptomic profiling confirmed functional cooperativity among these VdAP-2 subunits. These subunits regulate fungal pathogenicity through control of hyphal polarity and ergosterol biosynthesis. Our study not only elucidates the biological functions of the AP-2 complex in V. dahliae but also establishes a molecular foundation for developing novel antifungal therapeutics targeting membrane homeostasis regulation.
The soybean cyst nematode (SCN; Heterodera glycines) poses a major challenge to soybean production, intensified by the declining effectiveness of natural resistance against this pathogen. Although the use of resistant soybean varieties can be effective, their widespread and repeated use ultimately results in the emergence of virulent nematode populations that can successfully attack these resistant hosts. To assess for potential trade-offs between virulence and fitness, we investigated the hatch response, penetration rate, and reproductive potential of SCN adapted to overcome the broad-spectrum resistance source PI 437654. The hatching process is a critical phase in the life cycle of the SCN, influencing its ability to infect hosts and complete its life cycle. Our results indicated that SCN populations exhibit preferential and heightened hatch responses to their adapted host compared to alternative hosts, regardless of their virulence profile. Additionally, we found that SCN populations adapted to overcome broad-spectrum resistance showed reduced reproductive success on susceptible hosts compared to unadapted populations. This reduction in reproductive success was not attributed to differences in hatch response or penetration rates. The results from our study highlight the potential trade-offs associated with SCN virulence adaptation and emphasize the importance of considering these evolutionary dynamics in developing sustainable management strategies.
