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。     

Characterization and epidemiology of Colletotrichum acutatum sensu lato (C. chrysanthemi) causing Carthamus tinctorius anthracnose

In 2012, Colletotrichum isolates were collected from field‐grown safflower (Carthamus tinctorius) crops in central Italy from plants exhibiting typical anthracnose symptoms. Colletotrichum isolates were also collected from seed surfaces and from within seeds. The genetic variability of these isolates was assessed by a multilocus sequencing approach and compared with those from Colletotrichum chrysanthemi and Colletotrichum carthami isolates from different geographic areas and other Colletotrichum acutatum sensu lato‐related isolates. Phylogenetic analysis revealed that all of the strains isolated from C. tinctorius belonged to the species described as C. chrysanthemi, whereas all of the strains belonging to C. carthami had been isolated from Calendula officinalis. Phenotypic characterization of isolates was performed by assessing growth rates at different temperatures, morphology of colonies on potato dextrose agar (PDA) and the size of conidia. All C. chrysanthemi isolates from safflower had similar growth rates at different temperatures, comparable colony morphologies when grown on PDA and conidial sizes consistent with previously described C. chrysanthemi isolates. Pathogenicity tests were performed by artificially inoculating both seeds and plants and confirmed the seedborne nature of this pathogen. When inoculated on plants, C. chrysanthemi caused the typical symptoms of anthracnose on leaves. This is the first record of this pathogen on C. tinctorius in Italy, and it presents an updated characterization of Colletotrichum isolates pathogenic to safflowers in Europe.     

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.     

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.     

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.     

Aetiology of branch dieback,panicle and shoot blight of pistachio associated with fungal trunk pathogens in southern Spain

Pistachio represents an emerging nut crop across the Mediterranean basin. In Spain, pistachio has been traditionally cultivated in marginal-dry areas with unfavourable climatic conditions for plant diseases. Consequently, little attention has been given to research on pistachio diseases until recently. Symptoms of branch dieback and cankers, and shoot and panicle blight have been recently observed in commercial pistachio orchards across southern Spain. In this study, 10 commercial pistachio orchards showing disease symptoms were surveyed between 2017 and 2018. Botryosphaeriaceae fungi were consistently isolated from affected shoots, among other fungal families with minor relevance. Representative isolates of each family were characterized based on colony and conidial morphology, optimum growth temperature, and the comparison of DNA sequence data (ITS, LSU, EF, TUB2, and ACT genomic regions). Detached and attached shoots, and attached panicles of pistachio cv. Kerman were inoculated with mycelial plugs or conidial suspensions to demonstrate the pathogenicity of the selected isolates. Botryosphaeria dothidea, Lasiodiplodia pseudotheobromae, Neofusicoccum mediterraneum, N. parvum, Diaporthe neotheicola, Diaporthe sp., Eutypa lata, Eutypa sp., Cytospora sp., and Phaeoacremonium minimum were identified. P. minimum had the highest optimum growth temperature (29.6 °C) and Cytospora sp. the lowest (21–22 °C). Botryosphaeriaceae isolates showed the largest lesions on inoculated shoots, with L. pseudotheobromae being the most aggressive, followed by Neofusicoccum species. Panicles inoculated with N. mediterraneum showed blight symptoms and canker formation 6 weeks after inoculation, without significant differences in aggressiveness between isolates. This work reports relevant information about this emerging disease in the novel Spanish pistachio-growing areas.     

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.     

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.     

Effect of temperature on infection and development of powdery mildew on cucumber

Podosphaera xanthii and Golovinomyces orontii are the causal agents of cucurbit powdery mildew. The effect of temperature on conidial germination, infection and sporulation was studied under controlled conditions. Conidia were inoculated on cucumber leaf discs, and incubated at six constant temperatures (from 10 to 35 °C in 5 °C steps) for 3 to 72 h to evaluate conidial germination and infection, and for 6–15 days to evaluate sporulation intensity. Germination took place at all tested temperatures, but was close to zero at 35 °C. The longest germ tubes measured in this experiment were 141.74 μm for the secondary germ tube of P. xanthii at 20 °C after 48 h of incubation, and 67.92 μm for G. orontii for the primary germ tube at 20 °C after 48 h of incubation. The optimal temperatures for conidial germination, infection and sporulation were 24.4, 25.7 and 22.3 °C, respectively, for P. xanthii, and 17.9, 17.3 and 14.9 °C, respectively, for G. orontii. Equations were developed to describe conidial germination with a coefficient of determination (R²) of 0.85 and 0.90 for P. xanthii and G. orontii, respectively. Infection equations resulted in R² of 0.94 and 0.93 for P. xanthii and G. orontii, respectively; and for sporulation, R² of 0.75 and 0.76 for P. xanthii and G. orontii respectively, as a function of temperature. These results can be used to develop models for the risk of cucurbit powdery mildew under field conditions.     

Phenotypic and genetic characterization of Colletotrichum isolates from Belgian strawberry fields

Colletotrichum isolates (457) were collected from strawberry plant tissues with and without typical anthracnose symptoms and from symptomless weeds in 19 Belgian strawberry fields. The isolates were characterized based on genetic, morphological and pathological features. Isolates were classified according to rDNA‐ITS sequencing: 97% of 211 representative isolates were C. acutatum, 2%C. gloeosporioides and 1%C. coccodes. The C. acutatum isolates belonged to the intraspecific groups A2 (33%), A3 (5%), A4 (50%), A5 (3%) and A7 (6%). Differences in spore morphology, growth rate and colony colour of a selection of 146 isolates confirmed the genetic grouping. Multiple Colletotrichum genotypes were detected in the same field. There was no association between the most common genotypes and geographic origin, presence or absence of symptoms, nor plant species or plant part. Representative Belgian Colletotrichum isolates were used in pathogenicity tests, together with European and American reference isolates. The C. acutatum A2 and the Belgian C. gloeosporioides isolates were the most aggressive on fruits, followed by C. acutatum A3, A4, A5, A7 and C. coccodes isolates. When inoculated into crowns, C. acutatum A2, A5 and American C. gloeosporioides isolates were the most aggressive, followed by C. acutatum A3 isolates. The A4 and A7 isolates and all European C. gloeosporioides isolates were non‐pathogenic on crowns. These data indicate that an unusually diverse Colletotrichum population is present in Belgium. The traditional differentiation between C. acutatum and C. gloeosporioides as causal agents of fruit and crown rot, respectively, proved not to be valid in Belgian strawberry fields.     

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.     

Effects of low temperature on mycelial growth and spore germination of Botrytis allii in culture and on its pathogenicity to stored garlic bulbs

Botrytis allii was incubated at 20, 10,4, 2,0, – 2 and –4° to investigate effects of temperature on growth, sporulation and germination on potato dextrose agar (PDA), and to estimate incidence and severity of disease on garlic bulbs inoculated with the pathogen during storage. B. allii-was capable of growing to a colony diameter of 17 mm after 20 weeks, sporulating and germinating on PDA at temperature as low as – 4°C. After 12 weeks at –4 and -2°C the mycelial growth was observed only on 45–54% of bulbs wound-inoculated with conidial suspension, and infection was limited to 5 mm in diameter on the surface of inoculation sites without producing any symptoms of the disease. Temperature responses were similar for mycelial growth, conidial germination and infection, but mycelial growth and sporulation was slower and later on garlic bulbs than in culture. Wounds were readily colonized by B. allii. No disease was found on unwounded bulbs that were inoculated with conidial suspensions and with mycelial plugs at various temperatures. Only 16–95% of cloves became infected by contact with other cloves within the same bulb after 12 weeks of storage at temperatures of 4–20 C.     

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.     

Antifungal activities of hyoscyamine and scopolamine against two major rice pathogens: <Emphasis Type="Italic">Magnaporthe oryzae</Emphasis> and <Emphasis Type="Italic">Rhizoctonia solani</Emphasis>

The antifungal activities of hyoscyamine and scopolamine, major alkaloids extracted from the desert plant Hyoscyamus muticus, against two rice pathogens, Magnaporthe oryzae and Rhizoctonia solani, were studied. The minimum inhibitory concentration of hyoscyamine that resulted in distinctive inhibition (MIC₅₀) was 1 μg/ml for both fungi. Exposure to hyoscyamine caused the leakage of electrolytes from the mycelia of both fungi. Hyoscyamine (>1 μg/ml) irreversibly delayed or inhibited conidial germination and appressorium formation in M. oryzae grown on polystyrene plates. Hyoscyamine effectively inhibited the attachment of conidia to the surface of rice (Oryza sativa) leaves and inhibited appressorium formation on the leaves. A high concentration of scopolamine (1000 μg/ml) also delayed or inhibited conidial germination in M. oryzae, but conidial germination was restored after washing the conidia with water. Antifungal activity of hyoscyamine was reduced by scopolamine. Magnaporthe oryzae infection was significantly suppressed (by >95%) in leaves of intact rice plants treated with hyoscyamine (10 μg/ml). Moreover, 10 μg hyoscyamine/ml significantly reduced the disease severity index for sheath blight to ≤0.2, when compared with the disease index of control plants (>7.0). Hyoscyamine (>20 μg/ml) completely inhibited sclerotial germination and development of R. solani by delaying the initiation, maturation, and melanization of the sclerotia. These results suggest that tropane alkaloids may be useful for controlling blast and sheath blight diseases of rice and for studying the mechanisms that regulate conidial germination in M. oryzae and sclerotial germination and development in R. solani.     

Intraspecific variation in susceptibility to dothistroma needle blight within native Scottish Pinus sylvestris

Dothistroma needle blight (DNB), caused by Dothistroma septosporum, is the most important disease currently affecting pine plantations in Britain. Intraspecific variation in susceptibility to DNB has been observed in several pine species, but it is not clear if similar variation occurs in Pinus sylvestris (Scots pine), Britain's only native pine. In three separate experiments 2‐ and 3‐year‐old Scots pine saplings from six native Scottish populations were artificially inoculated with D. septosporum conidial suspensions and incubated under conditions optimal for disease development. Conidial suspensions were produced using a single isolate from northeast Scotland. In one experiment, plants were also treated with various spore suspension concentrations to assess the impact of inoculum load on disease severity. There were no significant interactions between host population, plant height, and experiment/inoculum load (anova , P > 0·05), but population, height and inoculum load all significantly affected disease severity (anova , P < 0·05). Among the 2‐year‐old trees, those from Amat were less susceptible than those from Glen Loyne and Glen Cannich (anova , P < 0·05). Among the 3‐year‐old trees, those from Beinn Eighe were less susceptible than those from Abernethy. Plant height and DNB susceptibility had a slightly negative relationship. The use of a spore suspension with a concentration of 1·6 × 10⁶ spores mL^?1 was optimum for disease development. In an in vitro experiment, production of conidia was greater when cultures were incubated in darkness. This paper is the first to report intraspecific variation in DNB susceptibility within Scots pine.     

Ultrastructural changes observed in Colletotrichum alienum conidia following treatment with cold plasma or plasma-activated water

Previous studies demonstrated that a reduction in germination of Colletotrichum alienum conidia could be achieved following treatment with cold plasma (CP) or incubation with plasma-activated water (PAW). In this study, the mode of action of CP and PAW on C. alienum conidia was explored using transmission electron microscopy. Following treatment of the conidia, noticeable ultrastructural changes were observed, including cell wall maceration, disorganization of the cytoplasm and vacuole, and changes to the nuclei and mitochondria. Disorganization of the cytoplasm was exhibited by 85% of conidia after CP or PAW treatment. Also, 85% of conidia were observed with disorganized vacuoles after 6 min of CP treatment and 65% after 3 hr incubation in PAW. Further, 45% or more conidia had modified cell walls after PAW incubation or CP treatment. Deformation of conidia was observed in 23% of conidia after PAW incubation. These ultrastructural changes are a likely reason for the reduced germination of C. alienum conidia following CP or PAW treatment.     

Plasma-activated water inhibits in vitro conidial germination of Colletotrichum alienum,a postharvest pathogen of avocado

Cold plasma, an ionized gas produced by applying an electrical current to air, can be used to produce plasma-activated water (PAW), which has excellent antimicrobial properties. In this study PAW was applied to conidia of Colletotrichum alienum to investigate its impact on conidial germination in vitro. PAW was produced by treating tap, deionized, or distilled water with cold plasma for 30 or 60 min to produce PAW30 or PAW60, each of which was then incubated for up to 24 hr with a conidial suspension of C. alienum in a ratio of 1:1, 1:2, or 1:3 (conidial suspension:PAW), and the percentage germination measured. The greatest reduction in germination occurred when conidia were incubated with PAW60 produced from deionized water or distilled water, for all ratios. For PAW30, deionized water was the most effective for all three ratios, and on this basis, deionized water was selected for all further experiments. PAW produced from smaller volumes of water and at shorter distances from the cold plasma source was more effective at reducing germination. Treatment of conidia with acidified water was not as effective as PAW at inhibiting germination. Nitrates and nitrites were present in the PAW in varying concentrations and may have contributed to the inhibition of germination. PAW retained activity and reduced germination even after storage for 15 days. These findings demonstrate the potential of PAW as a novel treatment for postharvest fungal pathogens.     

Effects of temperature on germination of sporangia,infection and protein secretion by Phytophthora kernoviae

Phytophthora kernoviae is a pathogen on a wide range of plants, but little is known of optimal infection conditions. Rhododendron ponticum leaves were inoculated with six different isolates of P. kernoviae sporangia and incubated at different temperatures from 10 to 28 °C. After 1 week, lesion development and pathogen recovery were only observed from all isolates at 15 and 20 °C and a few isolates at 10 °C. In an experiment with temperatures ranging from 20 to 25 °C, lesion development and pathogen recovery on R. ponticum, Magnolia stellata and Viburnum tinus occurred consistently at 20 and 21 °C, was limited at 22 °C, and did not occur at 23 °C and above. There was no difference in sporangia and zoospore germination at 20–25 °C. In a temperature fluctuation experiment, the necrotic area of inoculated R. ponticum leaves increased with longer incubation at 20 °C and decreased with longer incubation at 24 °C. Crude extracts of secreted proteins from P. kernoviae cultures grown at 20 and 24 °C were compared to determine any effects of temperature on pathogenicity. When spot tested on R. ponticum leaves, crude protein suspensions from cultures grown at 20 °C induced necrosis, while proteins from cultures grown at 24 °C did not. Proteomic analysis confirmed that a 10 kDa protein secreted at both 20 and 24 °C shared sequence homology to the conserved domains of known elicitins of other Phytophthora spp. The protein secreted at 20 °C that was responsible for necrosis has not been identified.     

云南葡萄产区葡萄炭疽病病原鉴定及致病力分析

为了明确引起云南葡萄产区炭疽病的病原种类,利用形态鉴定和特异性引物分子检测相结合的方法对从云南省主要葡萄产区采集的60株炭疽病菌菌株进行了鉴定。葡萄炭疽病菌菌株的菌落形态和生长速率与对照菌株尖孢炭疽菌Colletotrichum acutatum差异不明显,但其分生孢子大小显著小于尖孢炭疽菌,附着胞深褐色,球形或不规则形。胶孢炭疽菌Colletotrichum gloeosporioides特异性引物CgInt/ITS4从供试葡萄炭疽病菌菌株基因组DNA中扩增出1条约500 bp的特异性条带,而尖孢炭疽菌特异性引物CaInt2/ITS4对葡萄炭疽病菌无扩增条带。研究表明,引起云南葡萄主产区炭疽病的病原为胶孢炭疽菌;供试胶孢炭疽菌对红提葡萄均有致病力,但菌株致病力差异较大,对番茄和草莓存在交叉侵染的能力,且对多菌灵的敏感性较尖孢炭疽菌高。     

Phylogenetic and morphological identification of Colletotrichum boninense: a novel causal agent of anthracnose in avocado

In recent years, anthracnose has become a significant disease affecting avocado fruit in the state of Michoacan, Mexico, where it significantly reduces fruit quality and commercial yield. Anthracnose has been assumed to involve Colletotrichum gloeosporioides and C. acutatum as causal agents. However, because of the increasing incidence of anthracnose, a more precise identification of the Colletotrichum spp. involved in this disease has become desirable. During the years 2004–2007, avocado fruits of different sizes exhibiting brown‐black and reddish spots on the pericarp and soft rot in the mesocarp, were gathered from orchards in nine counties. Fungal isolates were cultured on potato dextrose agar, and among these, 31 were selected for molecular, morphological and pathogenicity analyses. The molecular approaches used sequence typing of the internal transcribed spacer region and the partial nuclear large ribosomal subunit, allowing the unequivocal identification of C. gloeosporioides (71%), C. acutatum (16%) and C. boninense (13%). This last species has not been previously reported as being associated with anthracnose symptoms in avocado fruits anywhere in the world. Various morphological characteristics such as the size and shape of conidia were determined, as well as the conidial mass colour. Pathogenicity tests performed with all three species were conducted by inoculating healthy fruits. In each case, identical symptoms developed within 3 days of inoculation. Knowledge of the Colletotrichum populations in the Michoacan state, including the newly encountered avocado pathogen C. boninense, will facilitate further studies addressing the relationships between these Colletotrichum spp. and their avocado host.