Nitric oxide functions as a signal in induced systemic resistance

The study was aimed to search out the probable molecule behind the activation of a broad spectrum resistance during Pseudomonas aeruginosa WS-1 mediated induced systemic resistance (ISR) in Capsicum annuum where plants were challenged inoculated with its pathogen Colletotrichum capsici 24 h after induction of ISR. On the fourth day after pathogen inoculation a significant increase of pathogenesis-related (PR) proteins, other defence enzymes and phenolics as well as a two-fold increase of nitric oxide (NO) a potent defence signalling molecule were observed. Treatment of the host with NO donor also induced the same defence molecule in a similar manner. Results suggest the possible signalling role of NO in ISR during crosstalk between ISR inducing agent and pathogen within the host system.     

First report of anthracnose caused by Colletotrichum gloeosporioides on Boehravia diffusa in India

Leaf spot symptoms were observed on the leaves of Boehravia diffusa L. plants from different regions of Bilaspur, Himachal Pradesh, India. The symptoms initially appeared as a small light-pale coloured, circular spots enlarge gradually and ultimately leading to drying of the leaves. The disease was found to be caused by a fungus. The fungus was cultured on potato dextrose agar medium and identified as Colletotrichum gloeosporioides. According to the literature, this is thefirst report of anthracnose disease of B. diffusa caused by C. gloeosporioides in India.     

Microscopic and biochemical aspects of sorghum resistance to anthracnose mediated by silicon

The use of silicon (Si) in agriculture has attracted a great deal of interest from researchers because of the numerous benefits of this element to plants, especially when they are submitted to abiotic and/or biotic types of stress. The host's increased resistance to diseases, promoted by Si, is mainly associated with the deposition of this element in the tissues and the potentiation of defence mechanisms. However, the mechanisms involved in Si‐mediated host resistance need to be further investigated. Thus, this study aimed to microscopically and biochemically elucidate the resistance of sorghum to anthracnose. In the leaves of plants supplied with Si, in addition to a greater deposition of Si at the infection sites, the acervuli were smaller in number compared to the leaves of plants not supplied with Si. Additionally, the activities of the defence enzymes peroxidases and polyphenoloxidases and the concentration of anthocyanins were higher in the leaves of plants supplied with Si. It can be concluded that Si, in addition to participate in the physical barrier that slows or prevents Colletotrichum sublineolum penetration in sorghum leaves, also plays a role in the biochemical aspect of sorghum resistance to anthracnose.     

日本菟丝子的生防研究——寄生真菌的筛选和利用

对日本菟丝子有较强致病力的刺盘孢菌,其在PDA培养基上的特点是,菌落桔红色,产孢量大,气生菌丝稀疏,不形成分生孢子盘和刚毛。 不太可能筛选出一个对所有寄主上的日本菟丝子都有较强致病力的菌株,但完全有可能筛选出对其中少数几个主要寄主上的菟丝子均有较强致病力的菌株。 高温高湿和伤口对菌株的侵染有利;菌株的孢子悬浮液中加入2％蔗糖或少量菟丝子压榨液可促使孢子提早萌发并提高其萌发率。 菟丝子的茎蔓尤其幼嫩部分比花穗更易感病。 固体扩大培养基的成分中,用80％麦麸加20％玉米粉配制较好,菌株的产孢量大。     

Detection and differentiation of Colletotrichum gloeosporioides isolates using PCR

An oligonucleotide primer (CgInt), synthesised from the variable internally transcribed spacer (ITS) 1 region of ribosomal DNA (rDNA) of Collectotrichum gloeosporioides was used for PCR with primer ITS4 (from a conserved sequence of the rDNA) to amplify a 450-bp fragment from the 25 C. gloeosporioides isolates tested. This specific fragment was amplified from as little as 10 fg of fungal DNA. A similar sized fragment was amplified from DNA extracted from C. gloeosporioides-infected tomato tissue. RAPD analysis divided 39 C. gloeosporioides isolates into more than 12 groups linked to host source and geographic origin. Based on the results obtained, the potential of PCR for detection and differentiation of C. gloeosporioides is discussed.     

Pathogenic and genetic variability among Colletotrichum gloeosporioides isolates from different yam hosts in the agroecological zones in Nigeria

Anthracnose, caused by Colletotrichum gloeosporioides Penz., is the most severe foliar disease of water yam (Dioscorea alata) worldwide. Population genetic analyses can yield useful insights into the evolutionary potential of C. gloeosporioides and thus lead to the development of appropriate disease management strategies. The genetic structure of C. gloeosporioides populations from yam and non‐yam hosts in three agroecological zones of Nigeria was investigated. Microsatellite‐primed polymerase chain reaction (MP‐PCR), virulence phenotyping using five putative D. alata differentials, cross‐inoculation tests, and the presence/absence of a Glomerella teleomorph in yam fields were used to infer the evolutionary potential of C. gloeosporioides on yam. We observed high genotypic diversity (GD = 0.99 to 1.00) for populations from all hosts and agroecological zones, with multiple pathogen genotypes in individual anthracnose lesions. Genetic differentiation was low among pathogen populations from different hosts (G_ST = 0.10, θ = 0.034), and agroecological zones (G_ST = 0.04, θ = 0.018), indicating limited host differentiation and significant gene flow. No evidence was found for the existence of C. gloeosporioides f. sp. alatae reported in previous studies. The fungus was recovered from several non‐yam host species commonly found in yam fields but non‐yam isolates caused only mild to moderate symptoms on yam. Eighteen C. gloeosporioides virulence phenotypes were identified among 217 isolates but there was a weak correlation (r = 0.02, P = 0.40) between virulence phenotype and MP‐PCR haplotype. Consistent with the above findings, we observed for the first time the Glomerella teleomorph on anthracnose‐infected yam plants in Nigeria, indicating that sexual recombination might play an important role in anthracnose epidemics on yam. The implications of these findings for C. gloeosporioides evolutionary potential and anthracnose resistance breeding are discussed.     

Two Genetically Distinct Populations of Colletotrichum gloeosporioides Penz. Causing Anthracnose Disease of Yam (Dioscorea spp.)

Variation within Colletotrichum gloeosporioides, the causal agent of yam anthracnose disease, is still poorly defined and this hinders breeding for resistance. Two morphotypes of C. gloeosporioides, designated slow‐growing grey (SGG) and fast‐growing salmon (FGS), are associated with anthracnose disease of yam in Nigeria. The morphotypes are distinguishable based on colony and conidial morphology, growth rate, virulence, as well as vegetative compatibility, but molecular differentiation of SGG and FGS strains is needed to facilitate epidemiological studies. Denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)‐amplified small subunit (18S) rDNA fragments, and microsatellite‐primed PCR (MP‐PCR) genomic fingerprinting were employed to provide a basis for molecular differentiation of the morphotypes. DGGE analysis revealed patterns that clearly differentiated isolates of the aggressive defoliating SGG from the moderately virulent non‐defoliating FGS strains. Genetic analysis based on 52 MP‐PCR markers revealed highly significant differentiation between the SGG and FGS populations on yam (G_ST = 0.22; Nei's genetic identity = 0.85; θ = 0.28, P < 0.001), indicating that the SGG and FGS morphotypes represent genetically differentiated populations. The results of the molecular typing using DGGE and MP‐PCR analyses were consistent with the disease phenotype caused by the two morphotypes. Consequently, these molecular techniques might be used, at least partly, to replace time‐consuming virulence studies on yam.     

Effect of environmental conditions and inoculum density on infection of guava fruits by Colletotrichum glososporioides

The influence of environmental factors (temperature and humidity), inoculum density on infection by Colletotrichum glososporioides and development of anthracnose lesions were determined on uninjured, sand-injured and punctured fruits. The optical temperature for severe infection was 30 °C, whereas the disease incidence was less at 20 and 35 °C. Inoculated guavas that received 1–60 h of continuous free moisture developed lesions, but the disease was minimal (0–7%) after 1–6 h free moisture. Infection rates of uninjured, sand-injured and punctured fruits receiving 60 h of free moisture were 34, 70 and 100%, respectively. Disease incidence increased as inoculum density increased from 101 to 106 conidia/ml. In field conditions, the development of anthracnose lesions was greater on punctured guavas than on uninjured or sand-injured ones, in both rainy and winter seasons. In general, the number of lesions was highest in sand-injured fruits, followed by punctured and uninjured fruits. In rainy season the number of lesions on injured and uninjured fruits was greater than similarly treated guavas in winter. This revised version was published online in June 2006 with corrections to the Cover Date.     

日本菟丝子寄生菌致病力的专化性研究

日本菟丝子(Cuscuta japonica)吸取不同寄主植物的营养,经过营养代谢其机体内的过氧化物酶同工酶的活性或酶带数发生变化,从而改变了它对胶孢炭疽菌菟丝子专化型[Col-letotrichum gloeosporioides(Penz.)Sacc.f.sp.Cuscutael]同一菌株的抗性,以此为依据,采用寄生在不同植物上的日本菟丝子做为鉴定寄主,可以鉴别出胶孢炭疽菌菟丝子专化型中不同菌株的致病力差异。 初步认为:龙眼、桂花、柚子和冬青上的紫色菟丝子及泡桐、桂花和冬青上的黄色菟丝子可以作为鉴定寄主。