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The efficacy of hydrogen peroxide (H O ) was evaluated for the inhibition of mycelial growth of Phytophthora cinnamomi 2 2 in vitro. Phytophthora cinnamomi infects many crops globally causing root, collar and crown rot, resulting in significant economic losses for producers. Two 30% (w/v) H O products, each stabilised with a different concentration of 1-hydroxy - 2 2 ethylidene-1, 1-diphosphonic acid (HEDP) (3% versus 0.003% w/v) were compared to determine the most efficacious H O concentration as well as potential interactive effects of the stabilising compound. Inhibition of P. cinnamomi growth 2 2 was evaluated by amending potato dextrose agar media (PDA) with a range of concentrations of the test solutions. The biocidal activity of H O was enhanced by a higher concentration of HEDP. Concentrations from 6.25 mL/L of the H O 2 2 2 2 product with 3% HEDP provided 100% inhibition of mycelial growth in vitro. Neither the product with 0.003% HEDP, nor HEDP stabiliser without H O achieved comparable inhibition. Our results highlight an opportunity to expand the 2 2, use of stabilised H O products developed for cleaning of drip irrigation emitters to include the control of Phytophthora 2 2 spp. and potentially other waterborne plant pathogens. Keywords Amended media · Irrigation emitter cleaning · Mycelial inhibition · Root rot Introduction Soil moisture is essential for the production of sporangia and the release and spread of P. cinnamomi zoospores, which Phytophthora cinnamomi Rands is a soil borne oomycete means high rainfall and waterlogged conditions greatly exac- plant pathogen of great economic significance to plant indus- erbates the disease (Hardham 2005). Conditions favourable tries worldwide. It can cause root, crown or collar rot in to P. cinnamomi reproduction and spread are often found in almost 5000 plant species, resulting in enormous losses in irrigated cropping and nursery propagation environments. horticulture, forestry, agriculture, and in natural ecosystems The regular supply of soil moisture through irrigation or across the world (Hardham 2005, Jung et al. 2013). Phy- movement of contaminated water can encourage pathogen tophthora cinnamomi is likely to have originated in Papua proliferation and spread and result in devastating losses for New Guinea (Dobrowolski et al. 2003). It was first isolated producers (Hong and Moorman 2005). Hong and Moorman from cinnamon trees in Sumatra in 1922 and is now found (2005) suggest that contaminated water is the primary source worldwide due to movement of contaminated plant materials of Phytophthora inoculum in fruit, vegetable and nursery (Hardham 2005). In Australia, P. cinnamomi infects many production systems. Hydrogen peroxide ( H O ) has been 2 2 economically important crops including avocado, pineapple, adopted as a disinfectant in irrigation systems, and can aid macadamia, chestnut and many stone fruit species, including the control of water borne pathogens (Bosmans et al. 2016; peach (Hardham 2005). Hong and Moorman 2005; Raudales et al. 2014). H O is a naturally occurring molecule produced in the 2 2 environment (Newman 2004) and plant and animal cells. It is also synthesised for a wide range of commercial uses * Laura Mannion (Linley et al. 2012). Whilst H O is a powerful oxidising 2 2 email@example.com agent, it is considered to be environmentally friendly, as it Institute for Future Farming Systems, School of Health readily breaks down into water and oxygen leaving no toxic Medical and Applied Science, Central Queensland residues (Linley et al. 2012). In horticultural applications it University, Rockhampton, QLD 4701, Australia Vol.:(0123456789) 1 3 L. Mannion et al. has potential for implementation into foliar disease control concentrations of the stabiliser HEDP with a stated upper programs, as it has no withholding or re-entry periods fol- limit concentration of 0.003% and 3% (w/v) respectively. lowing application, and unlike most fungicides, has little For rate calculations and comparisons, these upper limit TM toxicity to humans (Copes 2009). One disadvantage, com- concentrations of HEDP were assumed. R edox Phos- pared to fungicides, is that H O is readily broken down phonate HEDP (58 – 62% w/v HEDP), without H O was 2 2 2 2, when it reacts with organic matter or catalysts and therefore used to evaluate any effect of the stabiliser alone. For cal- TM leaves no residual protection against subsequent pathogen culations and comparisons, it was assumed the R edox exposure (Copes 2009). However, if H O is stabilised with Phosphonate HEDP concentration was 60% (w/v). This was 2 2 a chemical such as 1-hydroxyethylidene-1, 1-diphosphonic diluted to 3% prior to addition to agar media, allowing acid (HEDP), pathogen exposure time to H O would be direct comparison with HP (Table 1). 2 2 High. increased. This could potentially provide continuous pro- tection against waterborne, root disease causing pathogens Design and procedures present in irrigation water if applied at a rate which inhibits pathogen survival, growth and spread without being phyto- Four laboratory trials using a range of concentrations of the toxic (Copes 2009). products were conducted. A completely randomised design HEDP, also known as etidronic acid, has the molecular (CRD) with six independently cultured biological replicates formula C H O P . Phosphonate compounds, such as HEDP, was used in each trial. Culture maintenance and storage pro- 2 8 7 2 are commonly utilised in water treatment systems as corro- cedures were adapted from Drenth and Sendall (2001) and sion and scale inhibitors due to their ability to sequester metal Lawrence et al. (2017). The agar growing medium amend- ions and mineral salts from solution (FAO 2016; Garcia et al. ment procedure was adapted from Bekker et al. (2013). 2001). Addition of HEDP to antimicrobial solutions contain- ing unstable peroxyacids, such as H O , prevents degradation Culture maintenance 2 2 of H O by contaminants and prolongs storage life (EFSA 2 2 2014). HEDP is added to antimicrobial solutions as a stabi- Phytophthora cinnamomi cultures were provided by the liser rather than as an antimicrobial agent (FAO 2004). How- Queensland Plant Pathology Herbarium, Department of ever, the use of HEDP to stabilise H O in drip irrigation Agriculture and Fisheries, Dutton Park, Queensland 4102 2 2 systems to reduce emitter clogging may have implications in Australia. One isolate (number 66973) was used for all the control of crop pathogens. experiments. Cultures were stored as approximately 10 x 5 The aims of this research are to establish a minimum mm PDA plugs in glass bottles in sterile, reverse osmosis TM inhibitory concentration (MIC) of HEDP stabilised H O for (RO) Millipore filtered water in darkness at approximately 2 2 control of P. cinnamomi mycelia in vitro, and to evaluate the 22 °C and cultured onto BD Difco™ PDA (39 g/L) when potential interactive effects of HEDP and H O .The outcome required for trials. All P. cinnamomi cultures were main- 2 2 of this research will provide a basis for further investigation tained on PDA and incubated at 25 °C in darkness. Indepen- into optimising the use of H O for irrigation emitter clean- dently grown biological replicates were sub - cultured from 2 2 ing, as well as suppression of Phytophthora spp. and other a single PDA culture onto V8 agar (V8A) containing 20% waterborne pathogens, in order to reduce losses associated (v/v) Campbell’s V8™ juice, 1% CaC O (w/v) and 1.5% with diseases caused by these pathogens. (w/v) technical agar, seven days prior to the start date of each experiment. Materials and methods Preparation of amended media Products Schott bottles each containing 100 mL of PDA (39 g/L) were autoclaved for 15 minutes at 121 °C and allowed to A series of laboratory trials were carried out to evaluate the inhibition of mycelial growth of Phytophthora cinnamomi Table 1 Hydrogen peroxide (H O ) and 1-hydroxyethylidene-1, 1-diphos- 2 2 in vitro in treatments containing hydrogen peroxide (H O ) phonic acid (HEDP) concentration in the products HP , HP and 3% 2 2 Low High, TM Redox HEDP solution stabilised with 1-hydroxyethylidene-1, 1-diphosphonic acid (HEDP), or HEDP alone. Potato dextrose agar (PDA) Treatment HEDP HEDP H 0 H 0 2 2 2 2 growing medium was amended with a range of concentra- Products (M) (% w/v) (M) (% w/v) tions of two HEDP stabilised H O products (referred to 2 2 HP 0.000211 0.003 9.79 30 Low as HP and HP ) (Evonik Industries AG, Essen Ger- Low High HP 0.211 3 9.79 30 High many). While both HP and HP contain the same Low High HEDP 0.211 3 0 0 concentration of H O (30% w/v) they contain different 2 2 1 3 Inhibition of Phytophthora cinnamomi mycelial growth with stabilised hydrogen peroxide cool to 50 °C in a water bath. Under sterile conditions in Petri dishes were then wrapped in aluminium foil to prevent a biohazard hood, PDA solution equivalent to the required exposure to light and drying of the media, and incubated for volume of treatment product to be added was first extracted 5 - 7 days in darkness at 25 °C. from the 100 mL of PDA and discarded. The required prod- uct to achieve desired final concentration in media was then Data collection and analysis pipetted into each bottle (Table 2). This method ensured a final solution volume of 100 mL for each treatment. The Following incubation, two perpendicular measurements of solution was then gently swirled and inverted to mix for the mycelial mat diameter on each petri dish were taken a minimum of 30 seconds before pouring evenly into six, using digital calipers. These were averaged to obtain a radial 90 mm polystyrene sterile Petri dishes. Control media was growth measurement. All diameter measurements include poured directly into the six plates without any removal of the V8A culture plug at the centre of growth when visible solution or the addition of any treatment product. Petri growth into the surrounding media was present. The inhibi- dishes containing media were then left to cool in the bio- tion of growth was calculated using the formula from Bekker hazard hood for a minimum of 15 minutes prior to inocula- et al. (2013): tion with P. cinnamomi. % Inhibition = (C − T) ∗ 100∕C where C is the average diameter of the control fungal colony Culture and incubation and T is the average diameter of the treatment fungal col- ony. Statistical analysis was carried out by ANOVA using An approximately 5 mm agar plug was taken from the ® th Genstat, 19 Ed (VSN International). Pearson correlation actively growing edge of the mycelial mat of the randomly analysis and linear and exponential rise to maximum regres- assigned biological replicate growing on V8A and placed sion of data were performed using SigmaPlo t 14.0 (Systat onto the centre of the PDA media in each Petri dish. All Software Inc. California). Table 2 Summary of hydrogen peroxide (H O ) and 1-hydroxyethyl- 2 2 Measurement of pH and detection of H O 2 2 idene-1, 1-diphosphonic acid (HEDP) concentrations in treatment product dilutions The second and third trials conducted involved measure- Treatment Dilution V in 100 H O HEDP (mM) 2 2 ment of the initial and final pH and detection of H O in 2 2 product (mL/L) mL media (mM) the amended media. In these trials, 120 mL of PDA media (µL) was prepared as described previously. Following addition Control 0 0 0 0 of treatment products, 20 mL of media was poured into two HP 1 100 9.79 0.0002 Low sterile 50 mL centrifuge tubes (10 mL in each) and allowed HP 5 500 48.95 0.0011 Low to cool for a minimum of 15 minutes before capping and HP 10 1000 97.90 0.0021 Low setting aside for initial pH measurement. The remaining 100 HP 50 5000 489.50 0.0106 Low mL of media was poured evenly into the six Petri dishes. HP 100 10000 979.00 0.0211 Low Control treatments were handled in the same way without HP 0.001 0.1 0.01 0.0002 High the addition of any treatment product. Initial pH measure- HP 0.005 0.5 0.05 0.0011 High ments were taken within 48 h of media production. For HP 0.01 1 0.10 0.0021 High measurement of final pH, media in each Petri dish (includ- HP 0.05 5 0.49 0.0106 High ing mycelial culture, if present) was cut with a scalpel into HP 0.1 10 0.98 0.0211 High small sections, transferred into 50 mL centrifuge tubes and HP 1 100 9.79 0.2110 High thoroughly cut and mixed with a scalpel to homogenize. This HP 5 500 48.95 1.0550 High provided two replicates of initial measurements per treat- HP 10 1000 97.90 2.1100 High ment and six replicates for final measurements. HEDP 0.001 0.1 0 0.0002 The pH of the media was measured using a calibrated HEDP 0.005 0.5 0 0.0011 TM Testo 205 hand - held T bar pH meter. The probe was HEDP 0.01 1 0 0.0021 inserted directly into the media at the bottom of the centri- HEDP 0.05 5 0 0.0106 fuge tube and washed and dried between each sample. H O 2 2 HEDP 0.1 10 0 0.0211 was detected by transferring the media from the centrifuge HEDP 0.5 50 0 0.1055 tubes and Petri dishes into 20 mL plastic syringes and forcing HEDP 1 100 0 0.2110 TM it through Millipor e 0.45 µm nylon mesh syringe filters. HEDP 10 1000 0 2.1100 Liquid extracted from the media was collected for testing. 1 3 L. Mannion et al. TM Quantofix peroxide colorimetric test strips were used in a – 2.11 mM HEDP. HEDP without H O up to 2.11 mM did 2 2 Macherey–Nagel Quantofix Relax reflectance photometer to not significantly inhibit P. cinnamomi growth. Only at very detect H O with a lower detection limit of 0.5 mg/L. high concentrations, from ca. 5.3 mM, did HEDP inhibit 2 2 growth. All lower rates either stimulated pathogen growth or had no effect (Fig. 3). Even the highest tested concentrations Results of HEDP did not result in 100% inhibition (data not shown due to the lack of efficacy of HEDP in isolation). Mycelial inhibition data from all four trials were collated and presented as Fig. 1. In summary, HP was signifi- High Amended Media pH cantly inhibitory compared to the control from rates of 4.89 mM H O and 0.11 mM HEDP (0.5 mL/L of product). 2 2 The initial and final pH of the amended media from the sec- HP was significantly inhibitory compared to the control Low ond and third trials were measured to determine whether from rates of 48.95 mM H O and 0.001 mM HEDP (5 mL/L 2 2 pH was significantly correlated to P. cinnamomi growth in of product). HP at the highest rate included of 979 mM Low vitro. The correlation between mycelial diameter and initial H O and 0.021 mM HEDP (100 mL/L of product) provided 2 2 pH was not significant for either trial (r = 0.79, P = 0.0044 90.7 % mycelial inhibition. HP provided 100% mycelial High and r = -0.55, P = 0.5407 for Trial 2 and 3 respectively). The inhibition from 61.19 mM H O and 1.32 mM HEDP (6.25 2 2 correlation between mycelial diameter and final pH was not mL/L of product). significant for Trial 2 (r = 0.17, P = 0.0862) but was signifi- Collated HP data were modelled to develop a response High cant for Trial 3 (r = 0.98, P = 0.2607) (Fig. 4). All final pH curve to interpolate the effect and estimate the minimum values were lower than the corresponding initial pH values inhibitory concentration (MIC) of HP . MIC was defined as High except for the Trial 3 HEDP treatments (ca. 1.8 – 2.1 mM the minimum concentration which results in 100% inhibition HEDP), which all showed a similar increase in pH alongside of pathogen growth. The model which best fits HP data is High the same level of stimulation of mycelial diameter. the 2-parameter exponential rise to maximum equation: ∗ ∗ Detection of H O in media f = a (1 − exp(−b x)) 2 2 where a = 102.7952 and b = 0.0472 All initial measurements in the second and third trials This model predicted a MIC of ca.76.5 mM H O Based detected H O except for HP treatments at 0.001 mL/L 2 2. 2 2 High on this, HP at 8 mL/L (78.32 mM H O and 1.6880 mM (0.00979 mM H O and 0.0002 mM HEDP) and 0.005 mL/L High 2 2 2 2 HEDP) is likely to achieve 100% mycelial inhibition (Fig. 2). (0.04895 mM H O and 0.0011 mM HEDP) of product. 2 2 The concentration range of HEDP stabiliser in HP and After seven days of incubation, H O was only detected in High 2 2 HP treatments included in Trials 1 - 4 was 0.0002 mM HP at concentrations of 50 mL/L of product (489.5 mM Low Low Fig. 1 Phytophthora cinnamomi mycelial inhibition (%) for HP and HP treatments High Low 1 3 Inhibition of Phytophthora cinnamomi mycelial growth with stabilised hydrogen peroxide Fig. 2 Phytophthora cinnamomi mycelial growth on PDA media (a) Control (b) – (f) HP treatments at 0.5, 1, 2, 4 and 8 mL/L respectively High H O and 0.0106 mM HEDP) or higher but was detected in Although the exact mechanism by which HEDP increased 2 2 HP at concentrations as low as 4 mL/L of product (39.16 the biocidal effect of H O in this study is not yet fully under- High 2 2 mM H O and 0.844 mM HEDP) (Table 3). stood, there have been many studies performed investigating 2 2 the additive and synergistic effects of chemicals working in combination with H O Steinberg et al. (1999) reported 2 2. antibacterial synergism between H O and chlorhexidine 2 2 Discussion against Streptococcus spp. The authors suggested that the chlorhexidine interacted with the bacterial cell surface and The results of these trials demonstrate that HEDP stabilised allowed H O to enter the cell, thereby increasing the anti- 2 2 H O significantly inhibits the growth of P. cinnamomi bacterial effect. Zubko and Zubko ( 2013) demonstrated both 2 2 mycelia in vitro. The results suggest HEDP enhanced the additive and synergistic effects of H O and iodine against 2 2 biocidal activity of H O as HP which contains a higher bacteria and yeast. Many studies on the enhanced antibac- 2 2, High, concentration of HEDP, was significantly more efficacious terial activity of combining silver and H O exist (Davoudi 2 2 than HP as a biocide against P. cinnamomi. HEDP alone et al. 2012; Martin et al. 2015; Pedahzur et al. 1997). Martin Low did not inhibit growth at concentrations equivalent to those et al. (2015) demonstrated the biocidal activity of H O was 2 2 in the product HP , and the higher concentrations of H O enhanced by the biocidal activity of silver itself, but also by High 2 2 did not provide comparable levels of inhibition when the the interaction of silver with the cell membrane of the target concentration of HEDP was reduced. Complete suppression organism, making it easier for H O to enter the cell. The 2 2 was not achieved with either HP or HEDP treatments authors also suggested that silver increases the stability of Low alone at the concentrations trialled. These results indicate H O ensuring it is not degraded as easily, thereby enhanc- 2 2, that HP is a promising product for incorporation into ing its effect. High irrigation to supress P. cinnamomi growth and potentially In our study, HEDP is added to stabilise H O in the prod- 2 2 control plant disease. ucts tested and may have protected H O from breakdown 2 2 1 3 L. Mannion et al. Fig. 3 Phytophthora cinnamomi mycelial growth on PDA media (a) Control (b) - (f) HEDP treatments at concentrations equivalent to those of HP at 0.5, 1, 2, 4 and 8 mL/L respectively High in the media, resulting in prolonged H O contact with the H O is also often formulated with peracetic (peroxy- 2 2 2 2 mycelial cultures and increased biocidal activity. This is sup- acetic) acid for use as an oxidising agent against bacteria ported by the initial and final H O measurements which and fungi (Brinez et al. 2006). Raudales et al. (2014) pro- 2 2 detected H O in the product with a higher concentration of vided a comprehensive review of water treatment options 2 2 HEDP, but not in the product with a lower HEDP concen- that are potentially able to control pathogens. The authors tration, despite treatments containing the same initial H O referenced two in vitro industry studies which reported 2 2 concentration. However, this observation may also be the H O concentration as low as 12.3 mg/L combined with 8 2 2 result of further breakdown of H O by increased mycelial mg/L peroxyacetic acid, and as high as 185 mg/L combined 2 2 growth in HP treatments due to lower biocidal activity. A with 120 mg/L peroxyacetic acid achieved 100% mortal- Low more detailed analysis of the residual H O in media in the ity of Phytophthora spp. (Choppakatla 2009; Steddom and 2 2 presence and absence of mycelial growth could determine Pruett 2012 in Raudales et al. 2014). These contrasting whether these results are specifically due to stabilisation of concentrations indicate a need for more detailed MIC stud- H O in media by HEDP, or due to more complex interac- ies for stabilised H O products and their ability to control 2 2 2 2 tions between media, mycelium, H O and HEDP. Increased specific pathogens. 2 2 stability of H O is important in applications where contact The amendment of media with potential biocides is 2 2 with organic matter and metal ions will degrade or cata- likely to alter the pH of the media, and possibly influence lyse the H O impacting the longevity of effect. If HEDP pathogen growth, as shown by the addition of potassium 2 2, is increasing the biocidal effect of H O in this way, it is silicate to PDA media (Bekker et al. 2013). In that study, 2 2 a promising formulation for use in irrigation systems as a the authors included treatments of pH adjusted PDA in cleaning product with the added benefit of controlling dis- the absence of potassium silicate to investigate the iso- eases caused by P. cinnamomi. lated effect of the pH change of each of the potassium 1 3 Inhibition of Phytophthora cinnamomi mycelial growth with stabilised hydrogen peroxide Fig. 4 Correlation between pH and Phytophthora cinnamomi mycelial diameter on amended PDA (a) Trial 2 initial pH (b) Trial 2 final pH (c) Trial 3 initial pH (d) Trial 3 final pH silicate concentrations on pathogen inhibition. In our cur- Even where HEDP treatments did not affect mycelium rent study, the initial and final pH of the amended media diameter, the density of the mycelia was visually increas- was measured to identify any significant change in pH, and ingly sparser with increasing concentrations of HEDP to assess the potential relationships with mycelial growth. (Fig. 1). This suggests HEDP in isolation had some effect The only significant correlation found was between myce- on the mycelial growth, although not necessarily an inhibi- lial diameter and pH for the final pH results in one trial, tory one. The biocidal action of H O was required to reduce 2 2 where it was due to an increase in final pH and stimulation colony diameter significantly at those same HEDP concen- of mycelial growth by 3% HEDP treatments. The authors trations. For greater understanding of the effects of HEDP speculate that the pathogen breaks down and removes and H O on mycelial growth in vitro, more functional 2 2 HEDP and therefore reduces the acidity of the media, as parameters other than colony diameter, such as reproductive these 3% HEDP treatments had the largest mycelial diam- health, and colony density or mass, are suggested. eters. There was no such significant increase in growth for The current study focussed on mycelial inhibition in the lower rates of HEDP, potentially explaining the lack of vitro. Many publications reported the amendment of growth pH reduction for those treatments. Also, there was no sig- media with fungicides to inhibit mycelial growth in vitro nificant correlation between mycelial diameter and initial as a method to investigate the potential for products to be pH for the same trial, suggesting pH did not affect growth, used to control oomycetes in general, and Phytophthora spp. but instead, growth affected pH. This indicates pH had no specifically (Bekker et al. 2013; Bittner and Mila 2016; Hu significant effect on the growth of P. cinnamomi and the et al. 2007; Hu et al. 2008; Liu et al. 2014; Miao et al. 2016). products tested had a direct biocidal effect. However, the main method of P. cinnamomi dissemination 1 3 L. Mannion et al. Table 3 Trials 2 and 3 combined results for initial and final detection control of the pathogen in vitro. This concentration of H O 2 2 of hydrogen peroxide (H O ) in PDA media of the control and treat- 2 2 is likely to be phytotoxic to many plant species. However, ment products (+/- indicates presence or absence of H O in media 2 2 as the concentration of stabilised H O required to inhibit 2 2 respectively) zoospore survival in irrigation water is likely to be lower Treatment H O (mM) HEDP (mM) Initial H O Final 2 2 2 2 than that for mycelial inhibition, the application of HEDP (mL/L) H O 2 2 stabilised H O could be kept below phytotoxic thresholds 2 2 Control 0 0 - - and still efficiently inhibit the pathogen. Disease progression HP 1 9.79 0.000211 + - and pathogen mortality need to be investigated in more detail. Low HP 5 48.95 0.001055 + - Results suggest the higher concentration of HEDP in Low HP 10 97.9 0.00211 + - HP enhanced the biocidal activity of H O . However, this Low High 2 2 HP 50 489.5 0.01055 + + was not due to biocidal activity of HEDP. It is likely that the Low HP 100 979 0.0211 + + higher concentrations of HEDP stabilised the H O in the Low 2 2 HP 0.001 0.00979 0.000211 - - PDA media more effectively and slowed the breakdown of High HP 0.005 0.04895 0.001055 - - H O thereby enhancing the biocidal activity of H O . This High 2 2, 2 2 HP 0.01 0.0979 0.00211 + - work provides the basis for further investigation into the High HP 0.05 0.4895 0.01055 + - use of H O irrigation products for the control of Phytoph- High 2 2 HP 0.1 0.979 0.0211 + - thora spp. The adoption of HP as an irrigation cleaning High High HP 1 9.79 0.211 + - product could have the added benefit of reducing diseases High HP 4 39.16 0.844 + + caused by water and soil borne plant pathogens including P. High HP 4.5 44.055 0.9495 + + cinnamomi, as used in this research. High HP 5 48.95 1.055 + + High Acknowledgements The authors gratefully acknowledge the technical HP 5.5 53.845 1.1605 + + High support provided by Giselle Weegenaar, Charmain Elder, and Andrew HP 6.5 63.635 1.3715 + + High Bryant, draft revision by Professor Michael Tausz, and the provision of HP 7 68.53 1.477 + + O products by Evonik Industries AG, Rellinghauser Straße 1—11, High 2 2 45128 Essen Germany. HP 7.5 73.425 1.5825 + + High HP 8 78.32 1.688 + + High Funding Open Access funding enabled and organized by CAUL and HP 10 97.9 2.11 + + High its Member Institutions. Declarations is via zoospores in moist environments (Hardham 2005). Conflict of interests The authors of this manuscript have no conflict of As the products tested in these trials are intended for use in interest to disclose. irrigation systems, the next step would be to investigate the Open Access This article is licensed under a Creative Commons Attri- concentration of HP required to inhibit spore survival in High bution 4.0 International License, which permits use, sharing, adapta- irrigation water. Fungal reproductive structures can be more tion, distribution and reproduction in any medium or format, as long sensitive to biocides than mycelia (Cayanan et al. 2009). as you give appropriate credit to the original author(s) and the source, However, longer lasting reproductive propagules (e.g., chla- provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are mydospores and oospores) and mycelial fragments within included in the article's Creative Commons licence, unless indicated organic matter could potentially survive rates required for otherwise in a credit line to the material. If material is not included in the control of zoospores. Oospores can be produced in the article's Creative Commons licence and your intended use is not response to an environmental stress (Jung et al. 2013). It is permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a possible that exposure to a biocide could stimulate a stress copy of this licence, visit http://cr eativ ecommons. or g/licen ses/ b y/4.0/ . response in the pathogen and encourage longevity and prolif- eration. It will be very important to consider how significant these reproductive propagules are in pathogen spread and disease development. 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Australasian Plant Pathology – Springer Journals
Published: May 1, 2023
Keywords: Amended media; Irrigation emitter cleaning; Mycelial inhibition; Root rot
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