Biological control of sclerotinia stem rot of canola using antagonistic bacteria

Stem rot caused by Sclerotinia sclerotiorum is a major fungal disease of canola worldwide. In Australia the management of stem rot relies primarily on strategic application of synthetic fungicides. In an attempt to find alternative strategies for the management of the disease, 514 naturally occurring bacterial isolates were screened for antagonism to S. sclerotiorum. Antifungal activity against mycelial growth of the fungus was exhibited by three isolates of bacteria. The bacteria were identified as Bacillus cereus (SC‐1 and P‐1) and Bacillus subtilis (W‐67) via 16S rRNA sequencing. In vitro antagonism assays using these isolates resulted in significant inhibition of mycelial elongation and complete inhibition of sclerotial germination by both non‐volatile and volatile metabolites. The antagonistic strains caused a significant reduction in the viability of sclerotia when tested in a greenhouse pot trial with soil collected from the field. Spray treatments of bacterial strains reduced disease incidence and yielded higher control efficacy both on inoculated cotyledons and stems. Application of SC‐1 and W‐67 in the field at 10% flowering stage (growth stage 4·00) of canola demonstrated that control efficacy of SC‐1 was significantly higher in all three trials (over 2 years) when sprayed twice at 7‐day intervals. The greatest control of disease was observed with the fungicide Prosaro^® 420SC or with two applications of SC‐1. The results demonstrated that, in the light of environmental concerns and increasing cost of fungicides, B. cereus SC‐1 may have potential as a biological control agent of sclerotinia stem rot of canola in Australia.     

Inhibition of Botrytis cinerea growth and suppression of botrytis bunch rot in grapes using chitosan

Chitosan inhibited growth of Botrytis cinerea in liquid culture and suppressed grey mould on detached grapevine leaves and bunch rot in commercial winegrapes. Germination of B. cinerea was completely inhibited in malt extract broth containing chitosan at concentrations greater than 0·125 g L^?1. However, treated conidia were able to infect detached Chardonnay leaves and pathogenicity was not affected, even after incubation for 24 h in chitosan at 10 g L^?1. When added after conidial germination, chitosan inhibited B. cinerea growth and induced morphological changes suggestive of possible curative activity. The effective concentration of chitosan that reduced mycelial growth by 50% (EC₅₀) was 0·06 g L^?1. As a foliar treatment, chitosan protected detached Chardonnay leaves against B. cinerea and reduced lesion diameter by up to 85% compared with untreated controls. Peroxidase and phenylalanine ammonia‐lyase activities were also induced in treated leaves. In vineyard studies, Chardonnay winegrapes exhibited 7·4% botrytis bunch rot severity at harvest in 2007 after treatment with an integrated programme that included chitosan sprays from bunch closure until 2 weeks preharvest, compared with 15·5% in untreated controls and 5·9% with fungicide treatment. In the following season, botrytis bunch rot severity was 44% in untreated Chardonnay at harvest and the integrated programme (21%) was less effective than fungicides (13·8%). However, in Sauvignon blanc winegrapes, the integrated and the fungicide programme each reduced botrytis bunch rot severity to 4% and were significantly different from the untreated control (11·5%). This study provides evidence that suppression of botrytis in winegrapes by chitosan involves direct and indirect modes of action.     

Phylogenetic relationships,pathogenicity and fungicide sensitivity of Greeneria uvicola isolates from Vitis vinifera and Muscadinia rotundifolia grapevines

Greeneria uvicola causes bitter rot on Vitis vinifera (bunch grapes) and Muscadinia rotundifolia (muscadine grapes) in warm moist temperate and subtropical regions. This study investigated the phylogenetic relationship of G. uvicola representatives from Australia (67 isolates), the USA (31 isolates), India (1 isolate) and Costa Rica (1 isolate) and compared their pathogenicity and fungicide sensitivity. Differences in cultural and conidial morphology were observed between the isolates from Australia and the USA. Phylogenetic relationships were determined based on three gene regions: the ribosomal DNA (rDNA) internal transcribed spacer 1 (ITS1–5?8S–ITS2), 28S large subunit (LSU) nuclear rDNA and β‐tubulin‐2. Greeneria uvicola isolates were clearly differentiated into four groups: isolates from Australia and India; USA isolates from V. vinifera; USA isolates from M. rotundifolia; and the isolate from Costa Rica. All isolates were pathogenic on V. vinifera (cv. Chardonnay) berries although those originating from M. rotundifolia were not as aggressive as isolates from V. vinifera, irrespective of geographical origin. Sensitivity to pyraclostrobin and salicylhydroxamic acid (SHAM) was studied. Despite differences in fungicide applications, hyphal growth inhibition was not significantly different for geographical location, cultivar, tissue, year of collection or different spray regimes. For the Australian and USA isolates, fungal growth inhibition was significantly greater for pyraclostrobin than for SHAM, and was significantly greater for the combined treatment than for each of the fungicides applied singly. The aetiological and epidemiological knowledge of bitter rot collected through this study will aid better prediction and management strategies of this pathogen.     

Effect of hot water treatment on peach volatile emission and Monilinia fructicola development

The effect of hot water treatment (HWT) to control peach brown rot was investigated. Peaches were dipped in water at 60°C for 60 s and artificially inoculated with Monilinia fructicola conidia. HWT failed to control brown rot if applied before inoculation and microscopic observations revealed a stimulatory effect on germ tube elongation of M. fructicola conidia placed immediately after HWT on the fruit surface, compared to the control. The influence of fruit volatile emission due to HWT was performed on the pathogen conidia exposed to the headspace surrounding peaches. The results showed an increase of M. fructicola conidial germination ranging from 33 to 64% for cultivars Lucie Tardibelle and Red Haven heat‐treated peaches, respectively, compared to the control. The volatile blend emitted from heat‐treated fruit was analysed by solid‐phase microextraction/gas chromatography‐mass spectrometry (SPME/GC‐MS) and proton transfer reaction‐time of flight‐mass spectrometry (PTR‐ToF‐MS). Fifty compounds were detected by SPME/GC‐MS in volatile blends of cv. Lucie Tardibelle peaches and significant differences in volatile emission were observed among heated and control fruit. Using PTR‐ToF‐MS analysis, acetaldehyde and ethanol were detected at levels 15‐ and 28‐fold higher in heated fruit compared to unheated ones, respectively. In vitro assays confirmed the stimulatory effect (60 and 15%) of acetaldehyde (0·6 μL L^?1) and ethanol (0·2 μL L^?1) on M. fructicola conidial germination and mycelial growth, respectively. The results showed that volatile organic compounds (VOCs) emitted from heat‐treated peaches could stimulate M. fructicola conidial germination, increasing brown rot incidence in treated peaches when the inoculation occurs immediately after HWT.     

The influence of formulation on Trichoderma biological activity and frosty pod rot management in Theobroma cacao

Frosty pod rot (FPR), caused by Moniliophthora roreri, is responsible for significant losses in Theobroma cacao. Due to limited options for FPR management, biological control methods using Trichoderma are being studied. Combinations of three formulations and two Trichoderma isolates were studied between May 2009 and April 2011. The formulations were 0·3 mL L^?1 of the surfactant BreakThru 100SL (BT), a mixture of 1% w/v Sure‐Jell (source of pectin) and 1% w/v potato dextrose broth (PDB) (PP), and an invert oil emulsion of 50% v/v corn oil/2·5% w/v lecithin/0·5% w/v PDB (COP). Water and fungicide, copper oxychloride, were included as controls. Humidity chamber studies indicated that Trichoderma conidia germinated in all formulations if free water was maintained, while only the COP formulation supported germination under drying conditions. In the field, Trichoderma ovalisporum DIS‐70a and Trichoderma harzianum DIS‐219f were applied monthly in each of the three formulations at a rate of 180 mL per tree, 2·46 × 10⁷ conidia per mL. The COP/DIS‐70a formulation provided the largest yield increase compared to all other treatments, including the fungicide control. Averaged over the 2 years, the COP formulation increased yield to 30·7% healthy pods compared to 9·7% healthy pods in the water control. Although the formulation/isolate combinations did not consistently increase endophytic colonization, the PP/DIS‐219f, COP/DIS‐219f and COP/DIS‐70a combinations increased total endophytic/epiphytic colonization by Trichoderma. The invert corn oil formulation of DIS‐70a significantly enhanced yield of healthy cacao pods over 2 years providing a promising model for optimizing Trichoderma‐based biocontrol strategies.     

Suppression of clubroot by Clonostachys rosea via antibiosis and induced host resistance

The mechanism of the biofungicide Prestop^® (Clonostachys rosea) was investigated for control of clubroot (Plasmodiophora brassicae) on canola. The key product components were partitioned and assessed for their effect on pathogen resting spores, root hair infection (RHI) and disease development using light microscopy, quantitative PCR and different application treatments during infection. The whole product of Prestop was consistently more effective than the C. rosea conidial suspension or product filtrate alone in reducing RHI and clubroot development. This biofungicide showed little effect on germination or viability of resting spores. Two‐application treatments at seeding and 7–14 days after seeding achieved greater clubroot control than a single application of the biofungicide at either seeding or post‐seeding stage. This may indicate the need to maintain a high biofungicide dose in the soil during primary and secondary infection. This biocontrol fungus colonized the rhizosphere and interior of canola roots extensively, and possibly induced plant resistance based on up‐regulation of the genes that are involved in jasmonic acid (BnOPR2), ethylene (BnACO) and phenylpropanoid (BnOPCL, BnCCR) biosynthetic pathways. It is concluded that the biofungicide Prestop suppressed clubroot on canola at least via root colonization and induced systemic resistance (ISR), and the latter may be through the modulation of phenylpropanoid and jasmonic acid/ethylene metabolic pathways elicited by the fungus.     

Efficacy of UV‐C radiation to reduce seedborne anthracnose (Colletotrichum acutatum) from Andean lupin (Lupinus mutabilis)

The potential of UV‐C radiation of Andean lupin (Lupinus mutabilis) seeds to eradicate seedborne infections of anthracnose caused by Colletotrichum acutatum was investigated. UV‐C doses from 0 to 691.2 kJ m^?2 (resulting from 0 to 96 h of exposure time) on disease incidence reduction and germination on artificially and naturally infected seed were evaluated. The degree of incidence reduction and seed germination was dependent on the dose of UV‐C. The UV‐C doses of 86.4 kJ m^?2 and higher reduced incidence from 6% to 7% to undetectable levels, but these UV‐C doses also reduced seed germination. UV‐C can deleteriously affect physiological processes and overall growth. To assess its impact, L. mutabilis seeds irradiated with UV‐C doses of 57.6 and 86.4 kJ m^?2 were grown. Seedlings grown from noninfected seed and UV‐C treated seed showed an increased concentration of chlorophyll and protein contents, as well as an increase in the activation of defence enzymes peroxidase and catalase, in comparison with plants grown from infected seed. UV‐C doses resulted in seed emergence and seedling dry weight rates that were similar to the noninfected control or better than the fungicide control. Moreover, 57.6 kJ m^?2 reduced transmission of the pathogen from seed to the plantlets by 80%, while 86.4 kJ m^?2 apparently eradicated the pathogen, under greenhouse conditions. The use of UV‐C, first reported here, is advantageous for controlling anthracnose in lupin.     

The effect of environmental factors on infection of blueberry fruit by Colletotrichum acutatum

Anthracnose fruit rot of blueberries caused by Colletotrichum acutatum is a serious problem in humid blueberry‐growing regions of North America. In order to develop a disease prediction model, environmental factors that affect mycelial growth, conidial germination, appressorium formation and fruit infection by C. acutatum were investigated. Variables included temperature, wetness duration, wetness interruption and relative humidity. The optimal temperature for mycelial growth was 26°C, and little or no growth was observed at 5 and 35°C. The development of melanized appressoria was studied on Parafilm‐covered glass slides and infection was evaluated in immature and mature blueberry fruits. In all three assays, the optimal temperature for infection was identified as 25°C, and infections increased up to a wetness duration of 48 h. Three‐dimensional Gaussian equations were used to assess the effect of temperature and wetness duration on the development of melanized appressoria (R² = 0·89) on Parafilm‐covered glass slides and on infection incidence in immature (R² = 0·86) and mature (R² = 0·90) blueberry fruits. Interrupted wetness periods of different durations were investigated and models were fitted to the response of melanized appressoria (R² = 0·95) and infection incidence in immature (R² = 0·90) and mature (R² = 0·78) blueberry fruits. Additionally, the development of melanized appressoria and fruit infection incidence were modelled in relation to relative humidity (R² = 0·99 and 0·97, respectively). Three comprehensive equations were then developed that incorporate the aforementioned variables. The results lay the groundwork for a disease prediction model for anthracnose fruit rot in blueberries.     

Temporal development and relationship amongst brown rot blossom blight,fruit blight and fruit rot in integrated and organic sour cherry orchards

The aim of this 4‐year study was to characterize temporal development of brown rot blossom blight and fruit blight (caused by Monilinia spp.) and their sporulating areas in sour cherry orchards; and to determine the relationships amongst incidence and sporulating area of blossom blight, fruit blight and fruit rot. The study was performed in integrated and organic orchard blocks on two cultivars (Újfehértói fürtös and Érdi b?term?). On both cultivars, disease progress on flowers and fruits was 2–10 times slower in the integrated than in the organic management system. The peak incidence values were 9 and 31 days after petal fall for blossom blight and fruit blight, respectively. After these dates, no new blight symptoms on flowers and/or fruits appeared and the disease was levelling off. Final blossom blight incidence ranged from 1 to 5% and from 12 to 34%, and fruit rot incidence from 2 to 6% and from 11 to 26% in the integrated and the organic orchards, respectively. The sum of fruit blight incidence ranged from 9 to 22% for the organic system, but was below 5% for the integrated system, while the final sporulating area was 5–16 mm² and <3 mm², respectively. Among the five highest Pearson's correlation coefficients, relationships between blossom blight and early fruit blight stage (r = 0·845, P = 0·0087 integrated; r = 0·901, P = 0·0015 organic), and between sporulating area and fruit rot (r = 0791, P = 0·0199 integrated; r = 0·874, P = 0·0039 organic) were the most significant relationships from an epidemic standpoint as they indicated a connection between different brown rot symptom types.     

Use of nitrate non‐utilizing (nit) mutants to determine phenological stages at which Botrytis cinerea infects wine grapes causing botrytis bunch rot

Botrytis bunch rot (BBR), caused by Botrytis cinerea, degrades wine grapes during ripening, even though infection can occur as early as flowering. Effective BBR management requires knowledge of whether some stages of fruit development are more important than others in relation to infection and BBR severity at harvest. Bunches of Vitis vinifera ‘Sauvignon blanc’ and/or ‘Pinot noir’ were inoculated in two vineyard trials and one glasshouse trial with nitrate non‐utilizing (nit) mutant strains at three phenological stages: early flowering, pre‐bunch closure (PBC) and veraison. Isolates recovered from symptomless berries at veraison and from bunches with symptoms at harvest were screened to measure the incidence of the nit strains used in the inoculations. It was found that latent infections, which resulted in BBR at harvest, could become established at all three phenological stages and no single stage was associated with greater latent incidence or harvest severity than any other stage. It was concluded that a proportion of BBR at harvest resulted from the expression of latent infections that had accumulated throughout the season. However, the time between infection and BBR symptom expression in near‐ripe grape berries was sufficiently short for polycyclic secondary infection to also contribute to epidemic development.     

Spatiotemporal analyses of rhizopus rot progress in peach fruit inoculated with Rhizopus stolonifer

Rhizopus rot, caused by Rhizopus stolonifer, is one of the main postharvest diseases in stone fruits, but there is little known about the processes of disease development during transport and postharvest storage. The objective of this study was to characterize temporal progress and spatial distribution of the disease in peach fruit. Rhizopus rot development was evaluated using two different fruit arrangements. Only one fruit of each arrangement was inoculated with a R. stolonifer spore suspension. Disease incidence and severity were assessed daily for all the fruit. Nonlinear models were fitted to the quantity of fruit and to the area of fruit that became infected over time and distance in relation to the source of inoculum. Disease‐free fruit placed next to the artificially inoculated peaches showed disease symptoms due to pathogen dissemination by mycelial stolons. The disease incidence and severity progress rates varied from 0.33 to 0.53 day^?1 and from 0.30 to 0.49 day^?1, respectively. The spatial spread of the disease followed a dispersive wave pattern with increasing speed over time, but decreasing speed with disease severity. For disease severity y = 0.5, the velocity at day 3 varied from 0.14 to 0.32 fruit diameter day^?1, while it ranged from 0.38 to 1.46 fruit diameter day^?1 at day 12.     

A quantitative real‐time PCR assay for detection of Colletotrichum lindemuthianum in navy bean seeds

Bean anthracnose is a seedborne disease of common bean (Phaseolus vulgaris) caused by the fungal pathogen Colletotrichum lindemuthianum. Using seed that did not test positive for the pathogen has been proven to be an effective strategy for bean anthracnose control. To quantify the extent of anthracnose seed infection, a real‐time PCR‐based diagnostic assay was developed for detecting C. lindemuthianum in seeds of the commercial bean class navy bean. The ribosomal DNA (rDNA) region consisting of part of the18S rDNA, 5^.8S rDNA, internal transcribed spacers (ITS) 1, 2 and part of the 28S rDNA of seven races of C. lindemuthianum, 21 isolates of Colletotrichum species and nine other bean pathogens were sequenced with the universal primer set ITS5/ITS4. Based on the aligned sequence matrix, one primer set and a probe were designed for a SYBR Green dye assay and a TaqMan MGB (minor groove binder) assay. The primer set was demonstrated to be specific for C. lindemuthianum and showed a high sensitivity for the target pathogen. The detection limit of both assays was 5 fg of C. lindemuthianum genomic DNA. To explore the correlation between the lesion area and the DNA amount of C. lindemuthianum in bean seed, seeds of the navy bean cultivar Navigator with lesions of different sizes, as well as symptomless seeds, were used in both real‐time PCR assays.     

Virulence of Pectobacterium carotovorum subsp. brasiliense on potato compared with that of other Pectobacterium and Dickeya species under climatic conditions prevailing in the Netherlands

In western Europe, Pectobacterium carotovorum subsp. brasiliense is emerging as a causal agent of blackleg disease. In field experiments in the Netherlands, the virulence of this pathogen was compared with strains of other Dickeya and Pectobacterium species. In 2013 and 2014, seed potato tubers were vacuum infiltrated with high densities of bacteria (10⁶ CFU mL^?1) and planted in clay soil. Inoculation with P. carotovorum subsp. brasiliense and P. atrosepticum resulted in high disease incidences (75–95%), inoculation with D. solani and P. wasabiae led to incidences between 5% and 25%, but no significant disease development was observed in treatments with P. carotovorum subsp. carotovorum, D. dianthicola or the water control. Co‐inoculations of seed potatoes with P. carotovorum subsp. brasiliense and D. solani gave a similar disease incidence to inoculation with only P. carotovorum subsp. brasiliense. However, co‐inoculation of P. carotovorum subsp. brasiliense with P. wasabiae resulted in a decrease in disease incidence compared to inoculation with only P. carotovorum subsp. brasiliense. In 2015, seed potatoes were inoculated with increasing densities of P. carotovorum subsp. brasiliense, D. solani or P. atrosepticum (10³–10⁶ CFU mL^?1). After vacuum infiltration, even a low inoculum density resulted in high disease incidence. However, immersion without vacuum caused disease only at high bacterial densities. Specific TaqMan assays were evaluated and developed for detection of P. carotovorum subsp. brasiliense, P. wasabiae and P. atrosepticum and confirmed the presence of these pathogens in progeny tubers of plants derived from vacuum‐infiltrated seed tubers.     

Combination of hot water, <Emphasis Type="Italic">Bacillus subtilis</Emphasis> CPA-8 and sodium bicarbonate treatments to control postharvest brown rot on peaches and nectarines

The aim of this study was to evaluate the effect of hot water (HW), antagonists and sodium bicarbonate (SBC) treatments applied separately or in combination to control Monilinia spp. during the postharvest storage of stone fruit. Firstly, we investigated the effect of HW temperatures (55–70°C) and exposure times (20–60 s), seven antagonists at two concentrations (10⁷ or 10⁸ cfu ml⁻¹) and four SBC concentrations (1–4%). The selected treatments for brown rot control without affecting fruit quality were HW at 60°C for 40 s, SBC at 2% for 40 s and the antagonist CPA-8 (Bacillus subtilis species complex) at 10⁷ cfu ml⁻¹. The combinations of these treatments were evaluated in three varieties of peaches and nectarines artificially inoculated with M. laxa. When fruit were incubated for 5 d at 20°C, a significant additional effect to control M. laxa was detected with the combination of HW followed by antagonist CPA-8. Only 8% of the fruit treated with this combination were infected, compared to 84%, 52% or 24% among the control, CPA-8, and HW treatments, respectively. However, the other combinations tested did not show a significant improvement in effectiveness to control brown rot in comparison with applying the treatments separately. When fruit were incubated for 21 d at 0°C plus 5 d at 20°C, the significant differences between separated or combined treatments were reduced and generally the incidence of brown rot was higher than when fruit were incubated for 5 d at 20°C. Similar results were observed testing fruit with natural inoculum.     

Non‐pathogenic rhizosphere bacteria belonging to the genera Rhizorhapis and Sphingobium provide specific control of lettuce corky root disease caused by species of the same bacterial genera

Lettuce corky root (CR) is caused by bacteria in the genera Rhizorhapis, Sphingobium, Sphingopyxis and Rhizorhabdus of the family Sphingomonadaceae. Members of this family are common rhizosphere bacteria, some pathogenic to lettuce. Sixty‐eight non‐pathogenic isolates of bacteria obtained from lettuce roots were tested for control of CR caused by Rhizorhapis suberifaciens CA1^T and FL1, and Sphingobium mellinum WI4^T. In two initial screenings, 10 isolates significantly reduced CR induced by one or more pathogenic strains on lettuce seedlings in vermiculite, while seven non‐pathogenic isolates provided significant CR control in natural or sterilized field soil. Rhizorhapis suberifaciens FL11 was effective at controlling all pathogenic strains, but most effective against R. suberifaciens CA1^T. The other selected isolates controlled only pathogenic strains belonging to their own genus. In a greenhouse experiment, a soil drench with selected biocontrol agents (R. suberifaciens FL11, Sphingomonas sp. NY3 and S. mellinum CA16) controlled CR better than seed treatments or application of alginate pellets. In microplots infested with R. suberifaciens CA1^T, seed treatment with R. suberifaciens FL11 provided complete control and a soil drench with FL11 significantly reduced the disease. Pathogenicity tests with FL11 on 23 plant species in 10 families resulted in slight yellowing on roots of lettuce and close relatives; similar yellowing appeared on some roots of non‐inoculated lettuce plants. This research showed that biocontrol agents can be genus‐specific. Only one isolate, FL11, provided more general control of various pathogenic strains causing CR even in field soil in pots and microplots.     

Identification of Neofabraea species causing bull's eye rot of apple in Poland and their direct detection in apple fruit using multiplex PCR

Based on partial sequence analysis of the β‐tubulin gene, 19 isolates of fungi causing bull's eye rot on apple in Poland were classified into species: Neofabraea alba, N. perennans and N. kienholzii. To the authors’ knowledge, the detection of N. kienholzii is the second in Europe and the first in Poland. Species affiliation of these fungi was confirmed by a new species‐specific multiplex PCR assay developed on the basis of previously published methods. The new protocol allowed for the specific identification of bull's eye rot‐causing species, both from pure cultures and directly from the skin of diseased or apparently healthy apples. In 550 samples of diseased fruits collected from nine cold storage rooms located in three regions of Poland, in 2011 and 2012, N. alba was detected as the predominant species causing bull's eye rot, occurring on average in 94% of the tested samples. Neofabraea perennans was found in a minority of apple samples, N. kienholzii was found only in two apple samples, while N. malicorticis was not detected in any sample tested. In tests on 120 apparently healthy fruits, only N. perennans was detected in a single sample. The results of genetic diversity analyses of bull's eye rot‐causing fungi based on the β‐tubulin gene sequence and an ISSR (inter‐simple sequence repeat) PCR assay with two primers were consistent, showing the expected segregation of tested isolates with respect to their species boundaries. However, the genetic distance between N. perennans and N. malicorticis was very low, as reported previously.     

Meta‐analytic modelling of the incidence–yield and incidence–sclerotial production relationships in soybean white mould epidemics

White mould (Sclerotinia sclerotiorum) is a destructive disease of soybean worldwide. However, little is known of its impact on soybean production in Brazil. A meta‐analytic approach was used to assess the relationship between disease incidence and soybean yield (35 trials) and between incidence and sclerotia production (29 trials) in experiments conducted in 14 locations across four seasons. Region, site elevation and season included as moderators in random‐effects and random‐coefficients models did not significantly explain the variability in the slopes of the incidence–yield relationship. The Pearson's r, obtained from back‐transforming the Fisher's Z estimated by an overall random‐effects model, showed that incidence of white mould was moderately and negatively correlated with yield (r = ?0.76, P < 0.0001). A random‐coefficients model estimated a slope of ?17.2 kg ha^?1%^?1, for a mean attainable yield of 3455 kg ha^?1, indicating that a 10% increase in white mould incidence would result in a mean yield reduction of 172 kg ha^?1. White mould incidence and production of sclerotia were strongly and positively correlated (r = 0.85, P < 0.0001). For every 10% increase in white mould incidence, 1 kg ha^?1 of sclerotia was produced. The relationship between disease incidence and production of sclerotia was stronger in southern regions and at higher elevation. In the absence of management, economic losses associated with white mould epidemics, assuming 43% incidence in 22% of the soybean area, were estimated at approximately US $1.47 billion annually within Brazil.     

Silencing of Erwinia amylovora sy69 AHL‐quorum sensing by a Bacillus simplex AHL‐inducible aiiA gene encoding a zinc‐dependent N‐acyl‐homoserine lactonase

Quorum sensing in Gram‐negative bacteria is regulated by diffusible signal molecules called N‐acyl‐l ‐homoserine lactones (AHLs). These molecules are degraded by lactonases. In this study, six Bacillus simplex isolates were characterized and identified as a new quorum‐quenching species of Bacillus. An aiiA gene encoding an AHL‐lactonase was identified based on evidence that: (i) it showed high homology with other aiiA genes of Bacillus sp.; (ii) the deduced amino acid sequence contained two conserved regions, ¹⁰⁴SHLHFDH¹¹¹ and ¹⁶⁵TPGHTPGH¹⁷³, characteristic of the metallo‐β‐lactamase superfamily; and (iii) the protein had zinc‐dependent AHL‐degrading activity. Additionally, the expression of the aiiA gene was significantly up‐regulated by 3‐oxo‐AHL. The AHL‐lactonase inhibited multiplication of the 3‐oxo‐C6‐AHL‐producing plant pathogen Erwinia amylovora sy69 both in vitro and in planta. The results provide support for the use of the quorum‐quenching functionality of B. simplex in the integrated control of the devastating fire blight pathogen.     

Temperature adaptation in isolates of Sclerotinia sclerotiorum affects their ability to infect Brassica carinata

Sclerotinia stem rot (Sclerotinia sclerotiorum) is a serious disease in oilseed Brassica crops worldwide. In this study, temperature adaptation in isolates of S. sclerotiorum collected from differing climatic zones is reported for the first time on any crop. Sclerotinia sclerotiorum isolates from oilseed rape (Brassica napus) crops in warmer northern agricultural regions of Western Australia (WW3, UWA 7S3) differed in their reaction to temperature from those from cooler southern regions (MBRS‐1, UWA 10S2) in virulence on Brassica carinata, growth on agar, and oxalic acid production. Increasing temperature from 22/18°C (day/night) to 28/24°C increased lesion diameter on cotyledons of B. carinataBC054113 more than tenfold for warmer region isolates, but did not affect lesion size for cooler region isolates. Mean lesion length averaged across two B. carinata genotypes (resistant and susceptible) fell from 4·6 to 2·4 mm for MBRS‐1 when temperature increased from 25/21°C to 28/24°C but rose for WW3 (2·35 and 3·21 mm, respectively). WW3, usually designated as low in virulence, caused as much disease on stems at 28/24°C as MBRS‐1, historically designated as highly virulent. Isolates collected from cooler areas grew better at low temperatures on agar. While all grew on potato dextrose agar between 5 and 30°C, with maximum growth at 20–25°C, growth was severely restricted above 32°C, and only UWA 7S3 grew at 35°C. Oxalate production increased as temperature increased from 10 to 25°C for isolates MBRS‐1, WW3 and UWA 7S3, but declined from a maximum level of 101 mg g^?1 mycelium at 20°C to 24 mg g^?1 mycelium at 25°C for UWA 10S2.