Characterization of Phytopythium Species Involved in the Establishment and Development of Kiwifruit Vine Decline Syndrome

Pathogenic diversity and fungicide sensitivity of soybean root rot oomycetes in Heilongjiang Province, China

BACKGROUND

Soybean root rot is a global threat to soybean yield and quality caused by several pathogens, which vary in fungicide sensitivity. Management is challenging due to fungicide resistance and limited synergistic strategies. To understand the pathogenic diversity, the pathogens causing soybean root rot in Heilongjiang Province were identified. The inhibitory activity of different fungicides and synergistic fungicide combinations was further investigated to further develop integrated management strategies for soybean root rot.

RESULTS

This study analyzed soybean root rot samples from 14 locations in Heilongjiang Province, China, identifying four oomycete species in three genera: Phytophthora sojae, Pythium periplocum, Pythium acanthicum, and Phytopythium chamaehyphon, the latter reported for the first time in China as a root rot pathogen. Sensitivity tests on six fungicides showed fluopicolide, azoxystrobin, and dimethomorph were effective against P. sojae but not Pythium periplocum, Py. acanthicum or Ph. chamaehyphon. Oxathiapiprolin is effective against P. sojae and Ph. chamaehyphon. Molecular docking revealed pathogen-specific binding affinities, confirming their selective efficacy. Metalaxyl-M and zoxamide displayed broad-spectrum activity against all three genera. A synergistic 5:1 combination of these fungicides significantly reduced median effective concentration (EC50) values across pathogens, offering an effective integrated management approach.

CONCLUSION

The results enhance our understanding of soybean root rot pathogens, fungicide sensitivities, and optimal combinations. The identification of Ph. chamaehyphon and the discovery of an effective metalaxyl-M and zoxamide combination provide foundations for sustainable control strategies to mitigate this devastating disease. © 2025 Society of Chemical Industry.

Orchard Microclimate Control as a Way to Prevent Kiwifruit Decline Syndrome Onset

A syndrome called "Kiwifruit Decline Syndrome" (KiDS) affects kiwifruit in several Mediterranean areas, causing growth arrest and wilt that rapidly progress to desiccation, scarce root growth, absence of fibrous roots, brown soft-rotting areas, and cortical detachment from the central cylinder. The origin is considered multifactorial, and a correlation with hydraulic conductance impairment caused by a high vapor pressure deficit (VPD) and temperature was detected. In this work, over-tree micro-sprinkler irrigation and shading nets were tested to protect leaves from overheating and locally decrease VPD. Leaf gas exchanges, leaf temperature, stem water potential, stem growth, root starch content, root xylem vessel diameter, density, and vulnerability to cavitation were assessed. A positive effect of over-tree irrigation associated with shading was observed: lower leaf temperature, higher stem water potential, stomatal conductance, and photosynthesis were detected; moreover, root starch content was higher in the summer. Narrow xylem vessel diameters were observed, indicating a long-term adaptation to rising VPD for lower vulnerability to cavitation, in all plants, but higher diameter, lower density, and higher vulnerability index indicated lower plant water stress under over-tree irrigation associated with shading. These results indicate that microclimate control by proper agronomic management can protect kiwifruit from climate stress, decreasing the risk of KiDS onset.

Seasonal dynamics of kiwifruit microbiome: A case study in a KVDS-affected orchard

Over the past decade, Italian kiwifruit orchards and overall production have faced a significant threat from Kiwifruit Vine Decline Syndrome (KVDS). Despite the insights gained from metagenomics studies into the microbial communities associated with the disease, unanswered questions still remain. In this study, the evolution of bacterial, fungal, and oomycetes communities in soil and root endosphere at three different time points during the vegetative season was investigated for the first time in a KVDS-affected orchard in the Lazio Region. The fungal and oomycetes genera previously associated with the syndrome, including Fusarium, Ilyonectria, Thelonectria, Phytophthora, Pythium and Globisporangium, were identified in both groups. In contrast, the characterization of bacterial communities revealed the first instance of the presence of the genus Ralstonia in soil and root samples. The microbiome composition shifts between KVDS-affected and asymptomatic plants were significant as evidenced by the results, particularly after a temperature increase. This temperature change coincided with the onset of severe disease symptoms and may indicate a key role in the progression of KVDS.

Rapid detection of the phytopathogenic oomycete Phytopythium helicoides with a visualized loop-mediated isothermal amplification assay

The phytopathogenic oomycete Phytopythium helicoides, previously known as Pythium helicoides, has emerged as a new threat to the Shatangju citrus cultivar (Citrus reticulata cv. Shatangju; '' in Chinese) in southern China. To enable rapid diagnosis and control of the leaf blight and stem rot caused by P. helicoides, we developed a visualized loop-mediated isothermal amplification (LAMP) assay targeting the β-tubulin gene of the pathogen. Using a carefully selected set of primers and optimized reaction conditions at 60 °C for 60 min, the LAMP assay can specifically detect the pathogen among various citrus-associated phytopathogens. The assay demonstrated high sensitivity, detecting as little as 30 pg of the pathogen DNA, comparable to the sensitivity of quantitative polymerase chain reaction (qPCR). We validated the practical application of this LAMP assay for diagnosing infections in citrus leaves and strawberry crowns. This newly developed LAMP assay offers a specific, sensitive, and rapid detection tool for P. helicoides, aiding in the control of Shatangju citrus leaf blight and stem rot, as well as other related crop diseases like strawberry crown rot.

Physiological and image-based phenotyping assessment of waterlogging responses of three kiwifruit rootstocks and grafting combinations

Introduction

Kiwifruit species have a relatively high rate of root oxygen consumption, making them very vulnerable to low root zone oxygen concentrations resulting from soil waterlogging. Recently, kiwifruit rootstocks have been increasingly used to improve biotic and abiotic stress tolerance and crop performance under adverse conditions. The aim of the present study was to evaluate morpho-physiological changes in kiwifruit rootstocks and grafting combinations under short-term waterlogging stress.

Methods

A pot trial was conducted at the ALSIA PhenoLab, part of the Phen-Italy infrastructures, using non-destructive RGB and NIR image-based analysis and physiological measurements to identify waterlogging stress indicators and more tolerant genotypes. Three pot-grown kiwifruit rootstocks ('Bounty 71,' Actinidia macrosperma-B; 'D1,' Actinidia chinensis var. deliciosa-D; and 'Hayward,' A. chinensis var. deliciosa-H) and grafting combinations, with a yellow-fleshed kiwifruit cultivar ('Zesy 002,' A. chinensis var. chinensis) grafted on each rootstock (Z/B, Z/D, Z/H), were subjected to a control irrigation treatment (WW), restoring their daily water consumption, and to a 9-day waterlogging stress (WL), based on substrate saturation. Leaf gas exchange, photosynthetic activity, leaf temperature, RGB, and NIR data were collected during waterlogging stress.

Results

Stomatal conductance and transpiration reached very low values (less than 0.05 mol m-2 s-1 and 1 mmol m-2 s-1, respectively) in both waterlogged D and H rootstocks and their grafting combinations. In turn, leaf temperature was significantly increased and photosynthesis was reduced (1-6 μmol m-2 s-1) from the first days of waterlogging stress compared to B rootstock and combination.

Discussion

The B rootstock showed prolonged leaf gas exchange and photosynthetic activity, indicating that it can cope with short-term and temporary waterlogging and improve the tolerance of grafted kiwi vines, which showed a decrease in stomatal conductance 5 days after the onset of stress. Morphometric and colorimetric parameters from the image-based analysis confirmed the greater susceptibility of D and H rootstocks and their grafting combinations to waterlogging stress compared to B. The results presented confirm the role of physiological measurements and enhance that of RGB and NIR images in detecting the occurrence of water stress and identifying more tolerant genotypes in kiwifruit.

Kiwifruit Vine Decline Syndrome (KVDS) Alters Soil Enzyme Activity and Microbial Community

Kiwifruit Vine Decline Syndrome (KVDS) has become a major concern in Italy, impacting both plant health and production. This study aims to investigate how KVDS affects soil health indicators and the composition of soil microbial communities by comparing symptomatic and asymptomatic areas in two kiwifruit orchards located in Latium, Italy. Soil samples were collected during both spring and autumn to assess seasonal variations in soil physicochemical properties, enzyme activities, and microbial biomass. The results reveal that KVDS influences several soil properties, including pH, electrical conductivity, and the contents of water-soluble carbon and nitrogen. However, these effects varied between orchards and across different seasons. Additionally, KVDS significantly impacts soil enzyme activities and microbial biomass, as assessed through the phospholipid fatty acid (PLFA) analysis, particularly showing an increase in fungal biomass in symptomatic areas. Metabarcoding further demonstrates that microbial communities differ between symptomatic and asymptomatic soils, exhibiting notable shifts in both diversity and relative abundance. Our findings emphasise the complex interactions between plants, soil, and microbial communities in relation to KVDS. This suggests that the syndrome is multifactorial and likely linked to an imbalance in soil microbial communities at the rhizosphere level, which can negatively affect soil health.

Soil, rhizosphere, and root microbiome in kiwifruit vine decline, an emerging multifactorial disease

Kiwifruit vine decline syndrome (KVDS) is characterized by severe root system impairment, which leads to irreversible wilting of the canopy. Plants usually collapse rapidly from the appearance of the first aboveground symptoms, without recovery even in the following seasons. The syndrome has been negatively impacting kiwifruit yield in different areas of Italy, the main producing European country, since its first outbreak in 2012. To date, a unique, common causal factor has yet to be found, and the syndrome is referred to as multifactorial. In this article, we investigated the whole biotic community (fungi, bacteria, and oomycetes) associated with the development of KVDS in three different belowground matrices/compartments (soil, rhizosphere, and root). Sampling was performed at both healthy and affected sites located in the main kiwifruit-producing area of Northwestern Italy. To address the multifactorial nature of the syndrome and to investigate the potential roles of abiotic factors in shaping these communities, a physicochemical analysis of soils was also performed. This study investigates the associations among taxonomic groups composing the microbiome and also between biotic and abiotic factors. Dysbiosis was considered as a driving event in shaping KVDS microbial communities. The results obtained from this study highlight the role of the oomycete genus Phytopythium, which resulted predominantly in the oomycete community composition of diseased matrices, though it was also present in healthy ones. Both bacterial and fungal communities resulted in a high richness of genera and were highly correlated to the sampling site and matrix, underlining the importance of multiple location sampling both geographically and spatially. The rhizosphere community associated with KVDS was driven by a dysbiotic process. In addition, analysis of the association network in the diseased rhizosphere revealed the presence of potential cross-kingdom competition for plant-derived carbon between saprobes, oomycetes, and bacteria.

Composition and Dynamics of Plant- and Soil-Associated Microbial Communities in Forest and Agricultural Ecosystems

Peter Kropotkin (1842-1921) is well known as an anarchist intellectual, an amiable mass of contradictions who loved humanity and was highly regarded in academic and intellectual circles, yet also penned "fiery peans to violence" in Le Révolté, the anarchist journal he established with Elisée Reclus in the 1870s [...].