Cactorum Infection Research Articles

Overexpression of the Panax ginseng CyP gene enhances abiotic and biotic stress tolerance in transgenic Arabidopsis

To explore the response of the cyclophilin (CyP) gene to abiotic and biotic stress, transgenic Arabidopsis was exposed to salt stress and inoculated with Phytophthora cactorum. The CyP gene enhanced salt tolerance by increasing proline content and slowing chlorophyll decline compared to wild-type plants. Under P. cactorum infection, the CyP protein interacted with spores and restricted spore germination to enhance resistance to P. cactorum. Thus, the CyP protein positively regulates gene expression in the abiotic and biotic stress tolerance networks. The CyP gene may be valuable for ginseng breeding programs aiming to develop new cultivars with enhanced stress tolerance.

Non-invasive assessment and visualization of Phytophthora cactorum infection in strawberry crowns using quantitative magnetic resonance imaging

Phytophthora cactorum is an oomycete species that causes enormous losses on horticultural crops, including strawberries. The purpose of this work was to investigate the alterations caused by P. cactorum inoculation in hydroponically grown strawberry plantlets (Fragaria × ananassa Duch.) using quantitative magnetic resonance imaging (qMRI). It was observed that with MRI, spatial and temporal progression of the infection could be observed in the crown using quantitative MR parameters, namely relaxation time maps. Relaxation times are numeric subject-specific properties that describe the MR signal behavior in an examined anatomical region. Elevated T2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{2}$$\\end{document} relaxation time values were observed inside the infected plant crowns with respect to the healthy references. The T2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{2}$$\\end{document} and T2∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{2}^{*}$$\\end{document} values of healthy plants were small in the crown region and further diminished during the development of the plant. Furthermore, elevated T1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{1}$$\\end{document} relaxation time values were seen in regions where P. cactorum progression was observed in corresponding plant dissection photographs. Quantitative susceptibility maps (QSM) were calculated to estimate the local magnetic field inhomogeneities. The QSM suggests magnetic susceptibility differences near the center of the pith. This study provides novel non-invasive information on the structure and development of strawberry plants and the effects caused by the P. cactorum infection.

Integrated Metabolome and Transcriptome Analysis Unveils the Underlying Molecular Response of Panax ginseng Plants to the Phytophthora cactorum Infection

Due to at least 3 years of cultivation, Panax ginseng (ginseng) is susceptible to being attacked by pathogens which severely affect its quality and yield. Compared with other diseases of ginseng, Phytophthora blight caused by Phytophthora cactorum (P. cactorum) can spread rapidly and destroy almost the entire plant of ginseng, such as leaves, stems, and roots. However, little research was focused on this area, and how P. cactorum affected the metabolic profile of ginseng is still obscure. In the current study, we conducted a comprehensive analysis of metabolomics and transcriptomics to compare the differences in health and P. cactorum-affected ginseng leaves and stems. Metabolome analysis revealed that 110 and 113 significant differential metabolites were observably disturbed separately in ginseng leaves and stems. Transcriptome analysis demonstrated that 6424 and 9508 genes had remarkable variation in ginseng leaves and stems. Using conjoint analysis, we also revealed the changes in pathways “Alanine, aspartate and glutamate metabolism”, “Glycine, serine and threonine metabolism”, and “Biosynthesis of unsaturated fatty acids” and “Plant hormone signal transduction” in ginseng response to the P. cactorum. The current work provides an overview of the alteration of metabolic profile and gene expression profiles in ginseng leaves and stems in response to P. cactorum affection, which may help to further screen out the mechanism of plant-pathogen interaction at the molecular level.

Screening of Alfalfa Varieties Resistant to Phytophthora cactorum and Related Resistance Mechanism

Alfalfa is one of the most important legume forages in the world. Root rot caused by soil-borne pathogens severely restricts the production of alfalfa. The knowledge of the interaction between alfalfa and root rot-pathogens is still lacking in China. Phytophthora cactorum was isolated from symptomatic seedlings of an alfalfa field in Nanjing with high levels of damping-off. We observed the different infection stages of P. cactorum on alfalfa, and found that the purified P. cactorum strain was aggressive in causing alfalfa seed and root rot. The infecting hyphae penetrated the epidermal cells and wrapped around the alfalfa roots within 48 h. By evaluating the resistance of 37 alfalfa cultivars from different countries to P. cactorum, we found Weston is a resistant variety, while Longdong is a susceptible variety. We further compared the activities of various enzymes in the plant antioxidant enzyme system between Weston and Longdong during P. cactorum infection, as well as gene expression associated with plant hormone biosynthesis and response pathways. The results showed that the disease-resistant variety Weston has stronger antioxidant enzyme activity and high levels of SA-responsive PR genes, when compared to the susceptible variety Longdong. These findings highlighted the process of interaction between P. cactorum and alfalfa, as well as the mechanism of alfalfa resistance to P. cactorum, which provides an important foundation for breeding resistant alfalfa varieties, as well as managing Phytophthora-caused alfalfa root rot.

Response of two riparian woody plants to Phytophthora species and drought

Disease combined with drought poses an important threat to plant survival, often compromising success in the restoration of riparian forests. Thus, understanding how biotic and abiotic stressors may affect plant survival and growth performance can greatly increase the success of ecosystem management strategies. The purpose of this study was to understand how two plant species, often used together in restoration of riparian ecosystems but with different ecological preferences, would respond to infection by each of two Phytophthora species in Mediterranean-climate regions, in the absence or presence of a simulated drought. Saplings of the drought resistant species Frangula californica, and of the riparian species Alnus rhombifolia were each inoculated in a greenhouse experiment with one of two Phytophthora species and exposed to two watering regimes. Saplings were allocated to six treatments, combining three levels of pathogen inoculation (no inoculation, inoculation with Phytophthora cactorum and inoculation with Phytophthora crassamura), and two watering regimes (well-watered and drought). The response of A. rhombifolia and F. californica saplings was assessed through the observation of health metrics and morphological parameters. Results showed that both P. cactorum and P. crassamura are important pathogens of A. rhombifolia and F. californica. As expected, drought conditions were the main cause of decline and mortality in A. rhombifolia saplings, while water availability was a facilitator of P. cactorum infection in F. californica saplings. We observed two seemingly contrasting results in A. rhombifolia saplings: infection by Phytophthora spp. decreased survival in well-watered plants, while the opposite was recorded for saplings under drought conditions whose survival increased in Phytophthora-inoculated treatments. Saplings of F. californica were able to cope with drought conditions, even when infected by Phytophthora species and water availability increased root infection and decreased sapling survival. We conclude that the continued use of F. californica and A. rhombifolia in sites infested by Phytophthora species can be beneficial in restoration, if appropriate management actions are adopted. Such actions include avoiding the planting of F. californica saplings in areas subjected to water accumulation, and ensuring that A. rhombifolia is planted in areas where drought stress is minimal and where Phytophthora species are possibly absent. We also emphasize the importance of ensuring that plant stock used in revegetation projects is not infected by Phytophthora species, and that biotic and abiotic risks are assessed prior to restoration actions.

The Sesquiterpene Synthase PtTPS5 Produces (1S,5S,7R,10R)-Guaia-4(15)-en-11-ol and (1S,7R,10R)-Guaia-4-en-11-ol in Oomycete-Infected Poplar Roots.

Pathogen infection often leads to the enhanced formation of specialized plant metabolites that act as defensive barriers against microbial attackers. In this study, we investigated the formation of potential defense compounds in roots of the Western balsam poplar (Populus trichocarpa) upon infection with the generalist root pathogen Phytophthora cactorum (Oomycetes). P. cactorum infection led to an induced accumulation of terpenes, aromatic compounds, and fatty acids in poplar roots. Transcriptome analysis of uninfected and P. cactorum-infected roots revealed a terpene synthase gene PtTPS5 that was significantly induced upon pathogen infection. PtTPS5 had been previously reported as a sesquiterpene synthase producing two unidentified sesquiterpene alcohols as major products and hedycaryol as a minor product. Using heterologous expression in Escherichia coli, enzyme assays with deuterium-labeled substrates, and NMR analysis of reaction products, we could identify the major PtTPS5 products as (1S,5S,7R,10R)-guaia-4(15)-en-11-ol and (1S,7R,10R)-guaia-4-en-11-ol, with the former being a novel compound. The transcript accumulation of PtTPS5 in uninfected and P. cactorum-infected poplar roots matched the accumulation of (1S,5S,7R,10R)-guaia-4(15)-en-11-ol, (1S,7R,10R)-guaia-4-en-11-ol, and hedycaryol in this tissue, suggesting that PtTPS5 likely contributes to the pathogen-induced formation of these compounds in planta.

Expression of resistance gene analogs in woodland strawberry (Fragaria vesca) during infection with Phytophthora cactorum.

Important losses in strawberry production are often caused by the oomycete Phytophthora cactorum, the causal agent of crown rot. However, very limited studies at molecular levels exist of the mechanisms related to strawberry resistance against this pathogen. To begin to rectify this situation, a PCR-based approach (NBS profiling) was used to isolate strawberry resistance gene analogs (RGAs) with altered expression in response to P. cactorum during a time course (2, 4, 6, 24, 48, 96 and 192 h post-infection). Twenty-three distinct RGA fragments of the NB-LRR type were identified from a resistance genotype (Bukammen) of the wild species Fragaria vesca. The gene transcriptional profiles after infection showed that the response of most RGAs was quicker and stronger in the resistance genotype (Bukammen) than in the susceptible one (FDP821) during the early infection stage. The transcriptional patterns of one RGA (RGA109) were further monitored and compared during the P. cactorum infection of two pairs of resistant and susceptible genotype combinations (Bukammen/FDP821 and FDR1218/1603). The 5′ end sequence was cloned, and its putative protein was characteristic of NBS-LRR R protein. Our results yielded a first insight into the strawberry RGAs responding to P. cactorum infection at molecular level.

The effects of calcium on stem lesions of silver birch seedlings

SummaryIn this study, we tested the hypothesis that decreased liming of growth medium has a role in the increase of stem lesions and top dying caused by Phytophthora cactorum in containerized silver birch seedlings (Betula pendula) in Finnish forest nurseries. The effect of limestone dose rates on growth and the nutrient status was also monitored. An index based on severity of symptom expression was used to compare the effect of different liming treatments on P. cactorum infection. Limestone amended into the sphagnum peat growth medium increased the amount of calcium in the seedling stems. Liming did not significantly decrease the disease severity although index values in most cases decreased with the increased limestone dose rates. In general, the lesions were restricted after out‐planting and the mortality of seedlings was low. Only inoculated seedlings on which the lesions had spread around the stem in the nursery died. Phytophthora cactorum appears to be a nursery pathogen, as it did not survive under conditions present in the field. Four years after out‐planting, the tallest birches were those grown in sphagnum peat amended with the highest limestone dose of 8 kg m−3.

Effect of season and aggressiveness of isolates on the response of two apple rootstocks toPhytophthora cactoruminfection

Two inoculation techniques were applied to investigate the effects of season and isolate variability on apple rootstocks in response to Phytophthora cactorum infection. Shoots of rootstocks MM106 and MM109 were inoculated in vitro with a single P. cactorum isolate once a month for 26 months. Rootstock susceptibility measured as lesion lengths generally cycled to a low level during dormancy in winter and to a high level during active growth in summer. Direct inoculation on excised stems was used to assess the relative aggressiveness of P. cactorum isolates. Bark was removed and stems were inoculated with mycelial discs of various P. cactorum isolates. Rootstock×isolate interactions complicated this evaluation, causing variable results. However, differences in relative aggressiveness of isolates were apparent during the dormant stage of apple stems. It was shown that the season during which evaluation was performed and variation of isolate aggressiveness affected the host reaction to P. cactorum infection.

Relative resistance of newly released apple rootstocks to Phytophthora cactorum

New rootstocks from series SJM (St-Jean-Morden) and SJP84 (ST-Jean-1984) have been evaluated for agronomic qualities since 1970 and 1975, respectively. As a result of the evaluation, seven and nine rootstocks from the SJM and SJP84 series, respectively, were selected. However, these were not evaluated for crown rot resistance. Excised shoot assay was used to evaluate resistance of 22 apple rootstocks to crown rot caused by Phytophthora cactorum (Leb. and Cohn.) Schroet. The pathogenicity of four isolates of P. cactorum to apple rootstocks was confirmed using the same excised twig assay. For both tests, relative lesion length was used as a measure of susceptibility. The analysis of variance showed that there was a significant effect of rootstocks, isolate and the interaction between rootstock and isolate. In general, apple rootstocks were more susceptible to isolate PC04-02 followed by isolates PC04-03 and PC04-01 and less susceptible to isolate PC04-04. The selection SJM189 was the least susceptible to P. cactorum and SJP84-5162 and SJM15 were the most susceptible suggesting that these rootstocks may not be suitable in orchards with favourable conditions to P. cactorum infection. Excised twigs of the SJP84-5180, SJP84-5189, SJP845174, O.3, SJP84-5230, O.3A, SJP84-5198, SJM167 and M.44 showed low to moderate susceptibility, whereas, rootstocks SJP845231, SJM150 and M.26 showed moderate susceptibility to P. cactorum. Rootstocks SJM188, SJP84-5217, MM.111, SJM127, SJP84-5218 and MM.106 showed high susceptibility to P. cactorum. The present results confirmed that none of the released or commercial rootstocks are completely resistant to P. cactorum and an integrated approach including resistance, chemical control and cultural practices is recommended to manage P. cactorum in apple orchards. Key words: Apple breeding, crown rot, Malus domestica Borkh., root rot

THE USE OF NESTED PRIMERS IN THE POLYMERASE CHAIN REACTION FOR THE DETECTION OF PHYTOPHTHORA FRAGARIAE AND P. CACTORUM IN STRAWBERRY

Phytophthora fragariae var. fragariae Hickman, which causes red core disease of strawberry, is a quarantine organism on which a nil tolerance is placed. Detection of the fungus is by a root tip bait test which is highly specific and sensitive but time-consuming (5–6 weeks), has to be done at 12°C and can require some taxonomic experience. Even with the test, detecting red core can still be difficult, especially with early primary infection of propagation beds or infected symptomless resistant cultivars. Moreover, P. cactorum, a closely related fungus, causes crown rot of strawberry. It is not a quarantine organism, typical tolerances of 1␒nfection are allowed, and can confuse diagnosis. Techniques based to the Polymerase Chain Reaction (PCR) are promising alternatives. Various parts of the ribosomal RNA gene repeat (rDNA) have been used to design primers with different specificities: specific PCR primers that can differentiate between P. fragariae and P. cactorum and others designed to detect a wider range of Peronosporales, to which Phytophthora belongs. In nested PCR, combinations of these primers can detect both pathogens with high specificity and sensitivity. Competitive PCR has also been developed to allow quantification of P. cactorum infection in strawberry crowns. With these techniques, P. fragariae was detected in strawberry plants one day after inoculation whereas the symptoms were only visible after one week. Moreover, very low numbers of zoospores could be detected in water samples. The test has been evaluated on samples provided by the inspection services of Scotland and The Netherlands.

Biocontrol of Phytophthora cactorum in vitro with Enterobacter aerogenes

Phytophthora cactorum causes significant mortality of mature trees in New Zealand pipfruit orchards. Replants of infected sites often succumb to this pathogen within 3 years. Enterobacter aerogenes, strain B8 was reported to control P. cactorum infection of apples in nursery soils in British Columbia. This strain was imported to New Zealand in 1991 and compared with indigenous isolates of E. aerogenes. The Canadian isolate differed from New Zealand isolates in utilisation of tartrate, tolerance of NaCl (5 cf. 7%), and inhibition of P. cactorum in vitro. Strain B8 was fungicidal whereas New Zealand isolates were fungistatic. Electron microscopy of mycelium exposed to strain B8 on agar revealed extensive disruption of cell membranes, intermixing and aggregation of organelles, necrosis, vacuolation, breakdown of the cell wall, and hyphal death. Hyphae exposed to New Zealand isolates of E. aerogenes exhibited vacuolation of the outer cytoplasm and degradation of the cell wall and plasmalemma but not cell degradation and death.

Effect of nitrogen form and application method on incidence and severity ofPhytophthora crown and root rot of apple trees

The effect of ammonium nitrate broadcast as a soil or through irrigation, urea applied as a foliar spray, and monoammonium phosphate applied as a planting hole treatment on the incidence ofPhytophthora crown and root rot of apple trees was determined under orchard conditions in the Okanagan Valley of British Columbia, Canada. Results from the eight year study showed that ammonium nitrate applied as a single dose in spring at 240 g tree−1 year−1, as a split dose at 120 g tree−1 each in spring and early autumn, and in irrigation water (fertigation) at 7.5 g tree−1 wk−1 for 10 wk year−1 significantly increasedPhytophthora crown and root rot of Macspur on MM106 rootstock. There was no significant difference inP. cactorum infection between the unfertilized control and treatments with urea applied as a foliar spray at 1.0 kg 100 l−1 of water in spring and early autumn, and monoammonium phosphate applied as a planting hole treatment at 1 g l−1 of soil at planting time.

Splash dispersal of Colletotrichum acutatum and Phytophthora cactorum by short‐duration simulated rains

The effect of short rain durations (≤ 16 min) on splash dispersal of Colletotrichum acutatum, the cause of strawberry anthracnose, and Phytophthora cactorum, the cause of strawberry leather rot. was investigated using a rain simulator. Potted strawberry plants were held in two concentric circles, of radius 30 and 60 cm, respectively, surrounded by soil in an area that was uniformly exposed to simulated rain falling at 15 mm/h. Infected fruit with sporulating lesions (source fruit) were placed in the centre and healthy (target) fruit were placed in front of each circle of plants. Dispersal was measured as the proportion of fruit infected (disease incidence). Disease incidence increased with increasing rain duration. The incidence of anthracnose 30 cm from the inoculum source increased from c. 25% after 30s of rain to 99% after 16 min. The incidence of leather rot increased from 1% after 2 min to 26% after 16 min. In other experiments, source fruit and the entire target area were first exposed to 4 or 8 min of rain (pre‐rain treatments), source fruit were then removed, and target fruit were placed on the soil and exposed to 4 or 16 min of rain. Splash dispersal still occurred, although there was a significant effect on disease incidence of a pre‐rain on the source fruit. The incidence of C. acutatum infection was 68 and 98% for the 4‐ and 8‐min pre‐rain treatments, respectively, after 16 min of rain at 30 cm from the source. The incidence of P. cactorum infection was 15 and 36% for the 4‐ and 8‐min pre‐rain treatments, respectively, after 16 min of rain at 30 cm from the source. High disease incidence with pre‐rain treatments was probably due to the rapid removal of spores by rain. Between 44 and 50% of spores of both pathogens were removed from the source fruit after 4 min of rain. When plants and fruit were arranged on a slope of 7° inclination, there was greater dispersal of C. acutatum downhill than uphill. These results indicate that very short rains can result in high levels of disease if subsequent conditions are favourable for infection.