Influence of host resistance and phenology on South American leaf blight of the rubber tree with special consideration of temporal dynamics

South American leaf blight (SALB), the most dangerous disease of the rubber tree, is responsible for the lack of significant natural rubber production in South America and is a major threat to rubber tree plantations in Asia and Africa. Although the selection of resistant clones is the preferred disease control method, greater knowledge is required of the relationship between host and pathogen, in order to construct more durable resistance. Based on small-scale trials, this study set out to compare the dynamics of SALB on two highly susceptible and one moderately susceptible clone and to analyse the effect of host phenology on disease severity, at leaflet and flush scales. Clonal resistance was found to have a noticeable effect on disease severity, asexual sporulation and stromatal density at both leaflet and flush levels, and on disease dynamics at a leaflet level; time for symptom and sporulation appearance were longer on the moderately susceptible clone than on the susceptible clones. On the moderately susceptible clone, the stromatal density was largely dependent on disease severity. The phenology did not differ among the three clones and could not be considered as a factor in genetic resistance to SALB. However, for the three clones, the position of the leaflet in the flush affected the duration of the immature stages and the disease: the shorter the duration of leaflet development, the lower the disease severity, the sporulation intensity and the stromatal density.     

Photosynthetic performance of Hevea brasiliensis affected by South American Leaf Blight under field conditions

South American Leaf Blight (SALB), caused by the fungus Pseudocercospora ulei, is the principal rubber crop disease in Latin America. Several studies have focused on the genetics of resistance and the epidemiology of this disease, but few have analyzed the physiological alterations caused by SALB in Hevea brasiliensis. In addition, changes under field conditions are poorly understood. The present study aimed to analyze changes in gas exchange and chlorophyll a fluorescence traits in leaflets with different leaf stages and SALB severity levels from two H. brasiliensis clones with distinct susceptibility to disease in juvenile plants grown under field conditions (clonal garden). The photosynthetic performance was strongly limited in the high susceptibility clone (FX 3864), mainly in the young leaflets with maximum SALB severity (‘3’ and ‘4’), as compared to the low susceptibility clone (FX 4098). The principal alterations included a reduction in the photosynthetic rate (>?79%), stomatal conductance (>?85%), extrinsic water use efficiency (>?85%), and ability to capture, use and dissipate light energy in photosystem II, as compared to healthy leaflets. The damage was less intense in mature leaflets from both rubber tree clones. The favorable performance observed in clone FX 4098 means it is a potential candidate for commercial scale use under non-SALB escape conditions in the Amazon region.

     

Role of ascospores and conidia in the initiation and spread of South American leaf blight in a rubber tree plantation

Microcyclus ulei, the fungus causing South American leaf blight (SALB) on rubber tree leaves, produces two main types of spores: ascospores and conidia. To assess their respective epidemiological role, a field experiment was conducted in French Guiana over 3 years. Tree phenology, disease severity and climate variables were recorded while airborne spores were trapped and quantified. Ascospores were shown to play an essential role in the perpetuation of the disease outside the host's growth periods, in the resumption of epidemics, and in the spread of the disease to disease‐free zones. Conidia were trapped in visibly infected plots only, during periods of host growth. Disseminated over short distances and present only temporarily on leaves, the conidia enabled the disease to spread stepwise when the climate was conducive. Segmentation analysis revealed that the duration of high relative humidity was the climatic variable most related to ascospore trapping. Ascospore release did not require low temperatures. Considering the essential role of the ascospores in the initiation and spread of disease, artificial defoliation as a means of reducing the inoculum pressure during tree refoliation is proposed to control SALB. To check the validity of this method, a survey over several years of natural defoliation–refoliation in relation to climate and other leaf diseases is needed.     

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.     

Single-chain variable fragments antibody specific to <Emphasis Type="Italic">Corynespora cassiicola</Emphasis> toxin,cassiicolin, reduces necrotic lesion formation in <Emphasis Type="Italic">Hevea brasiliensis</Emphasis>

Corynespora leaf disease poses a serious threat to rubber cultivation because infected leaves develop necrotic lesions and abscise, leaving the tree unproductive. The destructiveness of Corynespora cassiicola has been largely attributed to cassiicolin, a protein toxin secreted by the fungus. Recombinant antibody technology offers hope to curtail the disease whereby single-chain variable fragments (scFv) specific to cassiicolin could bind and deactivate the toxin in genetically modified rubber trees that harbour the antibody gene. A scFv phage library was constructed from heavy and light variable chains of IgG from cassiicolin immunized Balb/C mice spleen. Biopanning of the phage library yielded a scFv clone with high specificity to cassiicolin. The nucleotide sequence and deduced amino acid sequence information of the scFv were obtained. Hemagglutinin (HA)-tagged scFv expressed in Escherichia coli is discerned as a band at ca. 30 kDa on SDS-PAGE, and the corresponding band was detected by anti-HA IgG on a Western immunoblot. Deactivation of cassiicolin by the affinity-purified scFv was demonstrated in a detached-leaf bio-assay on selected susceptible Hevea clones (PB 260, RRIM 2020, RRIM 901 and RRIM 929). The assay was also performed on clones that are relatively more resistant to the fungus (RRIM 600 and GT-1), and the results were as expected. Thus, we have successfully demonstrated that the cassicolin-specific scFv can effectively reduce cassicolin toxicity.     

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.     

巴西橡胶树品系对棒孢霉落叶病的抗病性鉴定

采用巴西橡胶树棒孢霉落叶病病原菌的分生孢子接种和其毒素接种分别测定了国内天然橡胶主产区9个主栽品系的抗病性,结果表明过滤灭菌毒素划伤接种橡胶离体小叶片可以产生与分生孢子接种相似的症状,而不划伤接种则不产生病害症状;121℃、20 min湿热灭菌毒素接种无论划伤与否均不产生病害症状;分生孢子和病原菌毒素两种接种方法所测橡胶品系的抗病性之间有很好的一致性,说明毒素接种可以用来代替病原菌接种测定橡胶品系的抗病性。抗病性测定结果显示,供试9个巴西橡胶树品系中,PB86、热研88-13、南华1、PR107、热研7-33-97对病原菌表现出高抗,而RRIM600、南强1-97、热研44-9则表现高感,GT1则表现中感。     

Selection and orchard testing of antagonists suppressing conidial production by the apple scab pathogen <Emphasis Type="Italic">Venturia inaequalis</Emphasis>

Apple scab caused by Venturia inaequalis is a major disease in apple production. Epidemics in spring are initiated by ascospores produced on overwintering leaves whereas epidemics during summer are driven by conidia produced on apple leaves by biotrophic mycelium. Fungal colonisers of sporulating colonies of V. inaequalis were isolated and their potential to reduce the production of conidia of V. inaequalis was evaluated on apple seedlings under controlled conditions. The four most effective isolates of the 63 screened isolates were tested subsequently under Dutch orchard conditions in 2006. Repeated applications of conidial suspensions of Cladosporium cladosporioides H39 resulted in an average reduction of conidial production by V. inaequalis of approximately 40%. In 2007, applications of conidial suspensions of C. cladosporioides H39 reduced conidial production by V. inaequalis by 69% on August 6 and by 51% on August 16, but no effect was found on August 20. However, viability of available conidia of C. cladosporioides H39 was low at the end of the experiment. Epiphytic and endophytic colonisation by Cladosporium spp. of leaves treated during the experiment with C. cladosporioides H39 was significantly higher than on control leaves sampled 6 weeks after the last application. It is concluded that C. cladosporioides H39 has promising potential as a biological control agent for apple scab control. More information is needed on the effect of C. cladosporioides H39 on apple scab epidemics as well as on mass production, formulation and shelf life of conidia of the antagonist.     

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.     

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.     

橡胶树白粉菌Oidium heveae侵染寄主拟南芥的筛选

为筛选出橡胶树白粉菌Oidium heveae Steimnann新的寄主载体,通过接种野生型拟南芥Col-0、突变体Sr1-4D及eds1,观察了橡胶树白粉菌侵染不同拟南芥突变体的过程,PCR扩增测序法验证相关致病基因,构建橡胶树白粉菌-拟南芥互作体系。结果表明,在Col-0、Sr1-4D叶片上面,橡胶树白粉菌产生部分菌丝后停止生长,不能形成典型的橡胶树白粉病症状;但能成功侵染eds1叶片,在叶片的正、背面有银白色辐射状菌丝,后期在病斑上出现一层粉层,表现橡胶树白粉病的典型症状。组织染色和显微观察结果显示,在突变体eds1叶片上橡胶树白粉菌完成了侵染过程。PCR扩增测序结果表明接种后突变体eds1叶片上及组织中病菌均为橡胶树白粉菌;使用橡胶树白粉菌3个致病相关基因作为靶标,验证了eds1和橡胶树上白粉菌基因组中的3个致病相关基因相似度均达到99%~100%。表明橡胶树白粉菌可侵染拟南芥突变体eds1。     

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.     

橡胶树重要品系对胶孢炭疽菌抗性评价

橡胶树抗性种质的鉴定与利用是控制橡胶树炭疽病的一项重要措施。采用室内离体橡胶叶接种法、田间种质圃人工接种和自然发病条件下定期田间病害调查方法, 2011-2012年在海南省儋州开展46份重要橡胶树种质对胶孢炭疽菌病抗性鉴定和评价。把抗炭疽病程度划分为高度抗病(HR)、抗病(R)、中度感病(MS)、感病(S)和高度感病(HS)共5个级别,根据抗性评价结果分析得出：高度抗病(HR)类型的0份;抗病(R)类型8份, 占17.39%; 中度感病(MS)类型19份,占41.30%;感病(S)类型16份,占34.78%;高度感病(HS)类型3 份,占6.52%。筛选出的抗病品种,是今后可利用的抗性种质资源。本研究结果为炭疽病抗性种质资源的利用、培育及病害管理提供参考数据。     

A New Method for Producing Mycelium-Free Conidial Suspensions from Cultures of Microdochium nivale

A technique to improve the sporulation of Microdochium nivale in culture and to produce mycelium-free conidial suspensions was evaluated using cellophane-covered potato dextrose agar (PDA). Time to sporulation was significantly shorter on the cellophane-covered PDA (P < 0.001), yields of conidia were higher (P < 0.01) and conidial suspensions were produced virtually free of the mycelial fragments present in suspensions from PDA only. The conidial inoculum produced on cellophane had lower pathogenicity to wheat cv. Equinox in a detached leaf assay, showing significantly longer incubation periods (P < 0.05) and latent periods (P < 0.01), than conidia produced on PDA alone. However, the apparent decline in pathogenicity of conidial suspensions produced on cellophane compared to PDA alone was small.     

Diseases of Rubber and their Control

Abstract

Most of the major diseases of Hevea brasiliensis are of worldwide distribution (with the notable exception of South American leaf blight, against which strict quarantine regulations are enforced by rubber-growing countries outside the Americas to prevent the unauthorised import of Hevea) but their local severity and importance vary from one region to another. Root diseases are a serious problem nearly everywhere and regular rounds of inspection and treatment are essential while the trees are still young in order to prevent serious losses. The recently introduced prophylactic collar protectant dressings specific to each of the three main diseases are valuable aids to control.

Diseases of the tapping panel may prevent tapping or hinder bark regeneration; black stripe in particular (Phytophthora palmivora) can be very persistent and is often eradicated only by repeated therapeutic fungicidal treatment of the bark. Stem diseases, chiefly pink disease (Corticium salmonicolor), are important in certain areas in wet weather, and can lead to severe damage and even dieback in the absence of effective treatment.

Four major leaf diseases can have a debilitating effect on the tree. Abnormal leaf fall (Phytophthora spp.) is severe in India, causing the abscission of mature leaves during the monsoon rains; treatment necessitates the application of a pre-monsoon prophylactic copper spray. Secondary leaf fall, caused both by Oidium heveae and Colletotrichum gloeosporioides which infect the flushes of new leaves produced after the annual leaf change (wintering), varies greatly in severity according to local weather and cultivar. It can be controlled by repeated rounds of an appropriate prophylactic fungicide or, under certain conditions, by artificially hastening the onset of wintering (and thus of refoliation) by removing the old leaves with a contact herbicide. By far the most important leaf disease is South American leaf blight (Microcyclus ulei); it is largely responsible for the lack of a vigorous rubber industry in South America, the home of the rubber tree. It can only be effectively countered by the use of resistant cultivars.

The economic importance of the above diseases is discussed and current control measures described.     

Sporulation of Pyrenopeziza brassicae (light leaf spot) on oilseed rape (Brassica napus) leaves inoculated with ascospores or conidia at different temperatures and wetness durations

In controlled environment experiments, sporulation of Pyrenopeziza brassicae was observed on leaves of oilseed rape inoculated with ascospores or conidia at temperatures from 8 to 20°C at all leaf wetness durations from 6 to 72 h, except after 6 h leaf wetness duration at 8°C. The shortest times from inoculation to first observed sporulation ( l ₀), for both ascospore and conidial inoculum, were 11–12 days at 16°C after 48 h wetness duration. For both ascospore and conidial inoculum (48 h wetness duration), the number of conidia produced per cm² leaf area with sporulation was seven to eight times less at 20°C than at 8, 12 or 16°C. Values of Gompertz parameters c (maximum percentage leaf area with sporulation), r (maximum rate of increase in percentage leaf area with sporulation) and l ₃₇ (days from inoculation to 37% of maximum sporulation), estimated by fitting the equation to the observed data, were linearly related to values predicted by inserting temperature and wetness duration treatment values into existing equations. The observed data were fitted better by logistic equations than by Gompertz equations (which overestimated at low temperatures). For both ascospore and conidial inoculum, the latent period derived from the logistic equation (days from inoculation to 50% of maximum sporulation, l ₅₀) of P. brassicae was generally shortest at 16°C, and increased as temperature increased to 20°C or decreased to 8°C. Minimum numbers of spores needed to produce sporulation on leaves were ≈25 ascospores per leaf and ≈700 conidia per leaf, at 16°C after 48 h leaf wetness duration.     

布朗李叶枯病菌生物学特性研究

对布朗李叶枯病菌(Macrophoma kawatsukai Hara)生物学特性研究表明,该菌最适生长和产孢的培养基为布朗李果汁。菌丝生长和产孢的最佳碳源分别为蔗糖、麦芽糖和果糖;氮源分别为酪氨酸、谷氨酰胺、天门冬酰胺和半胱氨酸。菌丝生长最适温度25℃,最适pH5～7;分生孢子形成最适温度25～30℃,最适pH8,饱和湿度有利于产孢,阳光照射形成分生孢子器最多,紫外光照射对分生孢子器形成有一定的抑制作用。孢子萌发最适温度为20～30℃,最适pH6～9,相对湿度为90%～100%,以在水滴中萌发最好。布朗李杆煎汁和布朗李果汁对孢子萌发有促进作用。     

Infection by Neopestalotiopsis spp. occurs on unwounded eucalyptus leaves and is favoured by long periods of leaf wetness

Brazil is the leader in the global ranking of forest productivity; however, one of the major challenges to eucalyptus production is the existence of fungal diseases. A severe epidemic caused by pestalotiopsis-like fungi was observed in a forest nursery in Brazil, causing a huge impact on the eucalyptus micropropagation stages. The aims of the present study were to identify the causal agents associated with pestalotiopsis leaf spot and dieback in eucalyptus, assess their pathogenicity to different commercial clones, and evaluate which conditions favour conidial germination and infection by the pathogens. Multilocus phylogenetic analyses using ITS, TEF and TUB identified the isolates as members of Neopestalotiopsis and segregated them into three species. Isolates from all Neopestalotiopsis spp. caused symptoms on unwounded eucalyptus leaves and disease development was strongly dependent on long leaf wetness periods (≥72 h). All four commercial clones tested were susceptible to the pathogen. These results clearly dispute the commonly held assumption that pestalotioid fungi are weak and opportunistic pathogens. This is the first report of different phylogenetic species of Neopestalotiopsis causing dieback, leaf and stem lesions in eucalyptus cuttings and provides a basis for developing novel disease management strategies in forest nurseries.     

Resistance assessment of grapevine leaves to downy mildew with sporulation area scoring

The use of resistant individuals obtained through a breeding program, aimed at decreasing chemical treatments, is one of the most promising strategies for control of downy mildew caused by Plasmopara viticola in grapevine. In this study, 869 hybrid grape individuals, obtained by crossing the resistant Regent grape cultivar with sensitive Alphonse Lavallée, were tested after artificial inoculation of detached leaves by drops of the pathogen inoculum. Sporulation severity, as visual evaluation of sporulation density including necrosis, and sporulation incidence were scored to assess resistance level, then the sporulation area (mm²) was measured for each individual. The criterium of sporulation incidence could not describe all resistance levels. Sporulation area made it possible to measure the entire area in detail for how the pathogen spread at the inoculation site. Sporulation area was not fully consistent with sporulation severity. In this context, a new scale for sporulation area was developed to determine resistance level to the pathogen by taking into account the distribution of sporulation area values within those obtained from sporulation severity scales. Six categories ranging from 0 to 0.05 mm² (extremely resistant-ER) to ≥15.1 mm² (extremely sensitive-ES) were defined. 43 of the 869 individuals tested through the three evaluation criteria, in which no sporulation was observed, and 18 additional individuals with sporulation area of <0.05 mm² were scored in the ER group. Microscopic analysis confirmed findings for the ER group and other resistance levels. The authors suggest that the scale of sporulation area will be useful for assessment of resistance to downy mildew on grapevine leaves.

     

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。