Effects of temperature and leaf age on conidial germination and disease development of powdery mildew on rubber tree

Powdery mildew is an important disease of rubber trees worldwide. To assess the effects of temperature and leaf age on conidial germination and disease development, conidia were inoculated onto rubber tree seedlings with leaves at three phenological stages (copper bronze, colour-changing, and light green) and then incubated at six constant temperatures (10, 15, 20, 25, 30, and 35°C). Leaf age did not affect conidial germination (p = .296) whilst temperature did (p < .0001), although conidia were able to germinate at all tested temperatures. The estimated optimal temperature for conidial germination was 23.2°C. Leaf age, temperature, and their interactions had significant effects on conidial infection and hypha number (p < .0001). At 10 and 35°C, more than 2 and 4 days were needed for infection to complete, respectively, compared to <2, 1, 0.5, and 0.5 days for 15, 20, 25, and 35°C, respectively. Sporulation and mildew symptoms were only observed on those inoculated leaves of all stages at 20 and 25°C, and at the copper bronze stage only at 15°C. The latent period on the copper bronze leaves at 15°C was longer (9 days) than at 20 and 25°C (4 days). The latent period at 20 and 25°C increased from 4 to 7 days as the leaf development stage increased from copper bronze to light green. Therefore, temperature affected germination and postgermination growth of rubber tree powdery mildew, whereas leaf age primarily affected postgermination growth of the pathogen.     

Influence of environmental factors on conidial germination and survival of Sphaeropsis pyriputrescens

Sphaeropsis pyriputrescens is the cause of Sphaeropsis rot in apples and pears. In this study, effects of temperature, wetness duration, relative humidity (RH), dryness, and interrupted wetness duration on conidial germination of the fungus were evaluated. Conidial germination and germ tube elongation occurred at temperatures from 0°C to 30°C. The optimum temperature for germination and germ tube elongation appeared to be 20°C, at which a minimum wetness period of 5 h was required. Conidia germinated at RH as low as 92% after 36 h at 20°C, but not at 88.5% RH. The effect of dry periods on germination depended on RH. Conidial germination at 85% RH was higher than that at 25% RH within a 4-h dry period, after which time no difference was observed. Less than 10% conidia germinated after a 10-day dry period at both 20°C and 28°C. Conidial germination decreased as the wetness duration prior to dryness increased. Conidia wetted for 6 h prior to dryness died within a 1-h dry period. After a 12-h dry period, no or few conidia germinated at 25% RH, whereas 3% to 10% of the conidia germinated at 85% RH and no further decrease was observed as the dry period increased. The results contribute to our understanding of conditions required for conidial germination of S. pyriputrescens and infection of fruit leading to Sphaeropsis rot.     

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.     

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.     

Conidial production and viability of Calonectria pseudonaviculata on infected boxwood leaves as affected by temperature,wetness, and dryness periods

Calonectria pseudonaviculata causes lesions on boxwood leaves and twigs. Controlled-environment experiments were conducted to determine the effects of temperature and leaf wetness period on C. pseudonaviculata sporulation on diseased (cv. Suffruticosa) leaves and of dryness periods and high temperature on conidial survival. Infected leaves were incubated in moist chambers and subjected to six temperatures (9, 13, 17, 21, 25, and 29°C) and six leaf wetness periods (0, 12, 24, 40, 48, and 72 h). Spore production was influenced significantly by wetness period, temperature, and their interaction. Increasing duration of leaf wetness and increasing temperature generally increased sporulation, with no sporulation occurring at 29°C or 9 and 13°C, except at 72 h of wetness exposure, while it was optimal at 21°C. Detached leaves with profuse conidia were subjected to a range of drying (relative humidity at 65%) times (0, 2, 4, 6, and 8 h) at two temperatures of 21 and 29°C. Conidia were then harvested and plated on water agar. Germinating conidia were counted to measure the spore viability. Spore mortality increased with increasing dryness duration at both temperatures but occurred more quickly and severely at 29 than 21°C. Overall, this study extended biological knowledge of conditions required for crucial stages of the C. pseudonaviculata disease cycle and the obtained results will be vital for developing boxwood blight forecasting and management tools.     

<Emphasis Type="Italic">Phoma glomerata</Emphasis> (Corda) Wollenw. &; Hochapfel a new threat causing cankers on shoots of peach trees in Greece

Shoot blights are common diseases of peach trees in Greece. This study is the first report of a shoot blight and canker disease of peach in Greece caused by the fungus Phoma glomerata (Corda) Wollenw. & Hochapfel. The pathogen caused distinct cankers with abundant gumming on shoots of peach trees. The rate of development of P. glomerata in vitro was reduced as temperatures increased from 25°C to 30°C, decreased from 25°C to 15°C, and was totally inhibited at 35 and 10°C. The rate of conidial germination and the germ tube elongation in vitro was reduced as temperatures increased from 25°C to 35°C, decreased from 25°C to 10°C, and was totally inhibited at 2–4°C. Pathogenicity tests showed that 24 peach and nectarine cultivars grown in Imathia Perfecture, Greece, were equally susceptible to P. glomerata. The fungicides thiophanate methyl, carbendazim, and tebuconazole were evaluated against the development of P. glomerata and disease symptoms. All fungicides inhibited the growth and conidial germination of P. glomereta and disease symptoms, and all 30 isolates tested were sensitive to the above fungicides. The disease caused by P. glomerata could be a threat to peach cultivation in Greece and its management should be investigated in the field.     

Heat treatment effect on Cadophora luteo-olivacea of kiwifruit

Heat treatment represents an alternative method to fungicides to control latent fruit pathogens, such as Cadophora luteo-olivacea of kiwifruit. This study reports the efficacy of different hot water (HW) and hot air (HA) treatments (45, 50, 55, 65, and 70°C with durations of 10, 15 or 20, 5 or 10, 5, and 3 min, respectively) on the conidial and mycelial growth of fungal isolates by in vitro assays. Both treatments at 70°C were the most effective in inhibiting conidial and mycelial growth of C. luteo-olivacea isolates. Treatment efficacy for HW and HA was on average 88% and 71%, respectively, on mycelial growth, and 100% and 91.3%, respectively, on conidial growth. A significant reduction of xylanase and pectinase enzyme activities of the isolates was detected after HW and HA treatment (70°C × 3 min). In most cases, both treatments showed a total reduction, sometimes varying with the target isolate. HA treatment was the most efficient treatment for reducing the skin pitting incidence in in vivo experiments, showing an average efficacy of 46.6%. Results show that heat treatments are effective against C. luteo-olivacea, but the main challenge will be to develop the optimal time × temperature combinations.     

Effect of environmental conditions on spore production by Fusarium verticillioides, the causal agent of maize ear rot

Silk infection by Fusarium verticillioides is caused by conidia produced on maize crop residues and results in kernel infection and consequent accumulation of fumonisins. Studies were carried out in both controlled and field conditions to understand the dynamics of sporulation on maize residues. The effect of temperature (5°C to 45°C) and incubation time (3 to 41 days) on spore production on maize meal agar was described by a logistic model that accounted for 85% of variability. The rate parameter depended on the length of incubation and the asymptote on temperature. Maximum sporulation occurred at 27°C, with a progressive increase between 5°C and 27°C and then a rapid decline, with no sporulation at 45°C. Fusarium verticillioides strains from different geographic origins showed different sporulation capabilities, with similar optimum temperatures. Pieces of stalk residues inoculated with F. verticillioides and placed above the soil between rows of maize crops, in 2003 to 2005, produced conidia continuously and abundantly for some weeks, particularly during the period after silk emergence, with an average of 1.59 × 10⁷ conidia g⁻¹ of stalk, over a wide range of environmental conditions. Sixty-seven percent of variability of the spore numbers found on stalks was accounted for by a multiple regression model. Precipitation (rain or overhead irrigation) in the 14 days before stalk sampling decreased the number of spores, whilst the number of days with conducive conditions of moisture (i.e. days with rainfall, average relative humidity >85% or vapour pressure deficit <4 hPa) and greater degree-days (base 0°C) in the 14 and 3 days before sampling, respectively, increased sporulation.     

Mating type and fungicide resistance in populations of Podosphaera xanthii in south Italy

Powdery mildew is one of the most common and severe diseases of cucurbits, causing heavy yield losses in all growing areas when not successfully controlled. Two different fungal species, Podosphaera xanthii and Golovinomyces orontii, are generally recognized as causal agents. The results of monitoring carried out in 2016 and 2018 confirmed that P. xanthii is the exclusive pathogen causing cucurbit powdery mildew (CPM) in southern Italy. P. xanthii is a bipolar heterothallic fungus; a PCR-based method for distinguishing MAT1-1 and MAT1-2 idiomorphs was applied for assessing mating type distribution in fungal populations present on cucurbits in different sites. The idiomorph MAT1-2 was prevalent over the MAT1-1 in 2016, whereas they were approximately in a 1:1 ratio in 2018; this finding corroborated the hypothesis that the MAT1-1 idiomorph was more recently introduced in the area. Cyflufenamid-resistant isolates were widespread in commercial greenhouses and field plantings even though use of this fungicide had been drastically reduced by the farmers 1 year before the monitoring due to the effectiveness losses observed in CPM control. Occurrence of cyflufenamid resistance and its impact on efficacy were evaluated in a field trial comparing different fungicide spray schedules. Cyflufenamid-resistant isolates were detected even at the first appearance of symptoms on leaves, increasing over time. Isolates resistant to cyflufenamid showed a resistance factor as high as 900. Generally, P. xanthii was better controlled when cyflufenamid was used in integrated strategies rather than in spray schedules based on the exclusive use of the fungicide.     

疏水表面诱导橡胶树炭疽菌侵染结构的发育分化过程

为了解橡胶树2种炭疽病菌的侵染结构发育分化过程,采用平板菌落生长速率法测定了3株胶孢炭疽菌Colletotrichum gloeosporioides和3株尖孢炭疽菌C.acutatum的菌丝生长速率,测量其分生孢子大小,显微观察2种炭疽菌在疏水表面诱导下侵染结构的发育分化过程。结果表明,胶孢炭疽菌菌丝生长速率为0.96~1.36 cm/d,显著高于尖孢炭疽菌的菌丝生长速率0.72~0.89 cm/d,但二者分生孢子大小无显著差异。在疏水表面诱导下,2种炭疽菌分生孢子在接种2~6 h后开始萌发,12 h孢子萌发率为71.70%~88.05%,13~16 h开始分化附着胞,24 h附着胞形成率为48.99%~70.74%,36 h菌丝诱发形成大量附着枝,48 h后分生孢子产生的次生菌丝也可诱发形成附着枝,附着枝呈圆形、姜瓣形、梨形或不规则形。分生孢子极易产生,可在菌丝顶端成簇或菌丝侧面排列产生,也可由分生孢子形成的芽管产生,或在芽管分化附着胞过程分枝形成分生孢子;附着胞多着生于芽管顶端,少数附着胞顶端可继续萌发类似短芽管结构,再次分化形成可黑色化的次级附着胞。表明橡胶树2种炭疽菌不同菌株间分生孢子萌发时间、孢子萌发率、附着胞形成时间和形成率有一定差异,但种间无明显差异;橡胶树炭疽菌分生孢子极易形成,在疏水表面容易分化形成附着胞和附着枝,说明具有极强的适生性。     

Effects of some fungicides on <Emphasis Type="Italic">Isaria farinosa</Emphasis>, and <Emphasis Type="Italic">in vitro</Emphasis> growth and infection rate on <Emphasis Type="Italic">Planococcus citri</Emphasis>

The effects of some fungicides used against citrus diseases, on mycelial growth and conidial germination of Isaria farinosa (Holmsk.) Fries [Sordariomycetes: Hypocreales] and also on the pathogenicity of the fungus on citrus mealybug, Planococcus citri (Risso), were determined. Systemic fungicides such as tebuconazole, penconazole and nuarimol were the most effective as regards both conidial germination and mycelial growth. Protective fungicides such as captan, chlorothalonil, mancozeb and propineb inhibited conidial germination at between 1 and 5 μg ml⁻¹ concentration, but captan, chlorothalonil and propineb did not inhibit the mycelial growth at 5,000 μg ml⁻¹. Mancozeb inhibited mycelial growth between 2,500 and 5,000 μg ml⁻¹. Sulphur and copper oxychloride did not inhibit the fungus even at very high concentrations. Sulphur, copper oxychloride, fosetyl-al, chlorothalonil and carbendazim did not decrease the mortality percentage caused by I. farinosa. Tebuconazole, penconazole and mancozeb were the most effective and respectively reduced the mortality from 83% to 33%, 28% and 30% in the ovisacs, from 81% to 29%, 27% and 29% in the 1st instar larvae, and from 84% to 34% in the adult females.     

Factors influencing biological traits and aggressiveness of Colletotrichum species associated with cashew anthracnose in Brazil

Anthracnose is the main fungal disease on cashew orchards in Brazil, occurring on both vegetative and reproductive organs of cultivated and noncultivated host plants. Understanding the effect of physical and chemical exogenous factors on the biological traits of Colletotrichum spp. and determining their host range are key to developing appropriate anthracnose control measures. The present study aimed to estimate the optimum temperatures for mycelial growth, sporulation, and conidial germination of seven Colletotrichum species (C. chrysophilum, C. fragariae, C. fructicola, C. gloeosporioides, C. queenslandicum, C. siamense, and C. tropicale) associated with cashew anthracnose in Brazil. Their aggressiveness on cashew leaves and six alternative host fruits, and their sensitivity to three fungicides were also investigated. The optimum temperatures for mycelial growth, sporulation, and conidial germination ranged from about 25 to about 33°C. All Colletotrichum species induced anthracnose symptoms on wounded cashew leaves, but none of them caused lesions on intact leaf surfaces. The Colletotrichum species, except for C. fragariae and C. fructicola, were pathogenic to wounded fruits of avocado, banana, guava, mango, and papaya, and some isolates also produced lesions on nonwounded fruit tissues. No symptoms were observed on passion fruits, regardless of the inoculation method. Mycelial growth, sporulation, conidial germination, and/or appressorial formation of the seven Colletotrichum species were inhibited by azoxystrobin, difenoconazole, and thiophanate-methyl to varying degrees. The present study will contribute to the development of forecasting models based on prevailing weather of cashew cropping zones and improve cashew anthracnose management in Brazil.     

Pseudocercospora griseola,the causal agent of common bean angular leaf spot: Strain characterization and sensitivity to fungicides

Angular leaf spot (ALS), an important disease of common bean (Phaseolus vulgaris), is caused by the fungus Pseudocercospora griseola. This pathogen has a wide genetic variability and, therefore, poses a challenge to integrated disease management. The use of resistant cultivars is difficult; hence, the application of fungicides has been a common practice in common bean cultivation. P. griseola strains were morphophysiologically characterized and their sensitivity to common fungicides used to control ALS was studied. The strains were evaluated for sporulation capacity and a representative sample of 34 strains was bioassayed to determine their sensitivity to commercial concentrations of five fungicides, namely pyraclostrobin, mancozeb, pyraclostrobin + metconazole, chlorothalonil and tebuconazole. Another sample of 29 strains was studied for conidial germination and dimensions. Sporulation capacity ranged from 0.88 to 27.67 × 10⁴ conidia/ml and germination percentage ranged from 39% to 72%. The large differences among strains suggest a wide genetic variability among the strains. A wide variability in aggressiveness of P. griseola was observed, which has consequences for breeding programmes aimed at resistance. The behaviour of pathogen strains differed in every fungicide evaluated, even in a population that has not been under selection pressure in the field. These results confirm the need for further studies and may guide future research with this pathogen.     

Solar UV-B radiation limits seedborne anthracnose infection and induces physiological and biochemical responses in Lupinus mutabilis

The aim of this study was to test whether solar UV-B radiation and temperature have an effect on infection of lupin seeds by Colletotrichum acutatum. Samples of infected seed were placed in a solar oven and exposed on sunny days for 15, 30, 45, 60, 75, 90 and 120 min. The degree of reduction in disease incidence and seed germination was dependent on the exposure time. Exposure times of 75 min (UV-B 4.41 kJ m⁻², ≈76 °C) and higher reduced incidence from 5% to undetectable levels, but also reduced seed germination by around 10% compared with untreated seed. Therefore, in a second experiment, infected seeds were exposed for 45 or 60 min in the solar oven (UV-B 2.83 or 3.75 kJ m⁻², respectively, ≈76 °C), for 60 min at ambient temperature (UV-B 3.75 kJ m⁻², ≈21 °C) or to dry heat for 60 min at 75 °C. Exposure for 60 min in the solar oven reduced seed infection by 99%, while UV-B-radiated seed at ambient temperature or dry-heat reduced infection by 60% or 32%, respectively. To evaluate the effect of UV-B plus high temperature on seedlings, lupin seed exposed for 45 or 60 min (UV-B 2.83 or 3.75 kJ m⁻², respectively, at ≈76 °C) were grown and physiological and biochemical responses of the seedlings were assessed. Seedlings from exposed seed had higher total concentrations of chlorophyll, protein and peroxidase activity than those grown from unexposed infected seed.     

Effect of apple cultivars and storage periods on the virulence of Neofabraea spp.

Bull’s eye rot is a typical quiescent postharvest apple disease in major fruit-growing areas. The susceptibility of different apple cultivars to Neofabraea spp. (N. vagabunda and N. malicorticis) was assessed, with Granny Smith showing the most resistance and Cripps Pink the most susceptibility. To assess the factors involved in conidial germination, Neofabraea spp. were grown on crude protein extracts (CPEs) collected from apple fruits at different storage periods. Fungal germ tube growth rate and pathogenic enzyme (cellulase and xylanase) activity were assessed. Results showed that CPEs collected after 2 and 4 months of storage progressively stimulated conidial germination and germ tube elongation, while a lesser effect was observed from CPEs after 1 month of storage. Xylanase proved to be the main degrading enzyme secreted by all the isolates, while cellulase was produced only by N. vagabunda isolates. Overall, the isolate ID02 was the most virulent, based on more rapid germ tube elongation and greater activity of the lytic enzymes.     

不同杀菌剂对黄瓜靶斑病菌的毒力作用特性比较

为筛选防治黄瓜靶斑病的有效药剂,采用菌丝生长速率法、孢子萌发法和芽管伸长法测定了19种杀菌剂对黄瓜靶斑病菌的毒力,探究了4种毒力较高杀菌剂对病原菌菌丝形态的影响。结果表明:氟啶胺、吡唑萘菌胺、咯菌腈和四霉素对黄瓜靶斑病菌菌丝生长、孢子萌发和芽管伸长各生长发育阶段均有较强的抑制活性,其中,4种药剂抑制菌丝生长的平均EC₅₀值分别为0.516 3、1.538、1.605和0.648 2 mg/L,抑制孢子萌发的平均EC₅₀值分别为0.164 4、1.359、1.127和0.002 5 mg/L,抑制芽管伸长的平均EC₅₀值分别为0.189 6、0.144 7、0.060 4和0.001 5 mg/L;啶酰菌胺、百菌清和肟菌酯3种不同作用机制杀菌剂对黄瓜靶斑病菌孢子萌发和芽管伸长的抑制活性较强,3种药剂抑制孢子萌发的平均EC₅₀值分别为1.564、0.373 0和0.021 3 mg/L,抑制芽管伸长的平均EC₅₀值分别为0.629 5、0.233 4和0.405 0 mg/L,但对菌丝生长的抑制作用较弱,平均EC₅₀大于16 mg/L;氟啶胺、吡唑萘菌胺、咯菌腈和四霉素可引起黄瓜靶斑病菌菌丝不同程度的异常生长,主要表现为菌丝隔膜间距变小、菌丝节间肿大、主菌丝上二次分枝发生频繁、菌丝变形黏连、菌丝新分枝处生长受抑制或分生孢子生长变形。研究表明,氟啶胺、吡唑萘菌胺、咯菌腈和四霉素对黄瓜靶斑病菌具有较高的毒力,在黄瓜靶斑病的田间防治中具有较好的开发应用潜力。     

Dormancy,germination and emergence of Urochloa panicoides regulated by temperature

Urochloa panicoides is an annual weed of summer crops. In Argentina, in subhumid areas with monsoon rainfall, it germinates and establishes in a single flush. To (i) identify the environmental factors that modify its seed dormancy level and germination and (ii) quantify the parameters describing the thermal behaviour of the germination and emergence dynamics of this weed under non‐limiting water conditions, we established a set of germination experiments performed (i) under controlled conditions using seeds after ripened for 3 or 6 months in different thermal and hydric conditions and (ii) under field conditions, where the soil temperature was modified by applying different shading levels. Seed dormancy level remained high with 3 months after ripening in all treatments. After 6 months, seeds stored at 4°C in dry conditions did not germinate at any temperature, while seeds stored at 25°C in dry conditions and in situ germinated c. 20% and 60% respectively. Germination percentage was higher in seeds harvested before their natural dispersal. The base, optimum and maximum temperatures for seed germination were 6, 35 and 45°C respectively. Shading reduced the number of emerged seedlings, possibly by reducing the soil thermal amplitude. The results explained the dormancy‐breaking mechanism of U. panicoides that allows a high germination rate in the field when rainfall occurs.     

Effect of initial darkness duration on the pathogenicity of Calonectria pseudonaviculata on boxwood

Light is an important environmental stimulus that regulates many physiological activities within plants and pathogenic fungi. Boxwood blight (causal agent: Calonectria pseudonaviculata) is a newly emergent disease in the United States and a significant threat to the boxwood industry. A disease‐forecasting model has been developed to aid boxwood growers in their management decisions, but light is not included as a variable within the programme. Growth chamber experiments were conducted to evaluate the effect of an initial dark period on disease severity, mycelial growth and conidial germination of C. pseudonaviculata. Treatments varied by darkness duration (0, 6, 12 or 24 h dark), and were followed by a 14 h day length at a 25/21 °C day/night temperature. Neither boxwood blight severity nor fungal colony development was enhanced by an initial dark period. However, darkness duration was associated with a significant increase in conidial germination in vitro. This study suggests the predictive performance of the current boxwood blight disease‐forecasting model would not be improved by inclusion of photoperiod.     

Inhibitory potential of metabolites produced by Cercospora sp. strain ME202 isolated from Trifolium incarnatum against anthracnose caused by Colletotrichum orbicular

Chemical fungicides are mainly used to control Colletotrichum orbiculare, but this fungal pathogen usually develops resistance to the pesticides. Natural compounds are therefore desirable for controlling C. orbiculare. Here, a culture filtrate (CF) from ME202, a fungal strain isolated from Trifolium incarnatum in Shimane Prefecture in 2020, was tested in vitro and found to inhibit conidial germination of C. orbiculare. The inhibitory compound in ME202-CF was soluble in ethyl acetate. The ethyl acetate extract of ME202-CF (ME202-ECF) significantly inhibited in vitro conidial germination of C. orbiculare in a dose-dependent manner and lesion formation on cucumber leaves. The inhibitory compounds were heat stable at 40–121 °C and molecular mass?≥?500 and ≥?1000 Da. Thin layer chromatography–bioautography of ME202-ECF showed that the compounds inhibiting C. orbiculare growth had an Rf of 0.81 and 0.91. Furthermore, ME202 was found to be a member of the genus Cercospora through sequence analysis of the internal transcribed spacer and 5.8 S rDNA. These results suggest that secondary metabolites of Cercospora spp., such as ME202, can be used to develop new fungicides against anthracnose.

     

Characterization of Neofabraea vagabunda isolates causing apple bull's eye rot in Italy (Emilia‐Romagna region)

Neofabraea vagabunda is the prevalent cause of bull's eye rot, one of the main postharvest diseases of apple, in many producing areas, but its biology has not been studied in detail. The molecular identification, by DNA sequencing of the β‐tubulin region, of 41 isolates collected from apples showing bull's eye rot in the Emilia‐Romagna region confirmed N. vagabunda as the main species in Italy. A biological and morphological characterization of N. vagabunda isolates was performed in vitro. Assays at temperatures ranging from 0 to 30 °C carried out on 10 isolates demonstrated: (i) a marked influence of temperature on colony morphology, conidial production, conidial size and mycelial growth, showing the cold‐tolerant character of N. vagabunda; and (ii) that culture at 15 °C on tomato agar (TA) for 14 days is a rapid and reliable method to favour pathogen conidial production. Trials performed on 38 isolates using these incubation conditions recorded the presence of two N. vagabunda morphotypes, differing for colony morphology, conidial size, conidiomata formation and temperature requirement. The alkalizing ability of the pathogen during growth on TA was also demonstrated for the first time. The pathogenicity of 25 N. vagabunda isolates was proved in vivo on artificially infected Cripps Pink apples. A pH increase was also recorded in apple tissue infected by N. vagabunda isolates (on average 0.2 and 0.3 units of pH after 60 and 120 days of incubation, respectively), suggesting that the N. vagabunda transition from quiescence to necrotrophic colonization in apples could involve the secretion of alkalizing compounds.