The Effect of Spatial Distributions of Mycoparasites on Biocontrol Efficacy: a Modelling Approach

The spatial distribution of propagules in soil is an important factor in determining the ability of mycoparasites to control soilborne plant pathogens. The assumptions of uniform, random and aggregated propagule distribution were used to evaluate the importance of spatial distribution patterns of propagules of a mycoparasite. For the random and uniform cases explicit expressions were obtained for the average distance between propagules. Average distances among propagules are 40-50% smaller for the random compared to the uniform distribution. For the aggregated case no explicit expression is possible and numerical simulations were used to generate spatial distributions. The consequences for host inactivation by the mycoparasite were evaluated using a simple model of omnidirectional and constant growth of the mycoparasite. A random distribution of propagules gave a considerably slower rate of inactivation than the uniform distribution. Numerical simulations were made to generate comparable patterns of host inactivation for aggregated distributions in which propagule clusters were located at random in three-dimensional space and the distances between propagules with centres followed a normal distribution. The number of propagule centres and propagules/centre varied for a given inoculum density. Parameters were estimated from published data for sclerotia of Sclerotium minor inactivation at different densities of macroconidia of Sporidesmium sclerotivorum. Differences in host inactivation between the uniform and random distributions were small but both gave poor predictions of the field data at low and high densities. The aggregated distribution gave an improved fit for the higher propagule densities but no improvement at the lower. In studying the dynamics of mycoparasites it may be more significant epidemiologically to design treatments based on differences in mean distances between propagules rather than population densities. Density-dependent effects on growth rate need more attention in models and studies on mycoparasite ecology.     

Anti-fungal activity of essential oils of Ceylon Eucalyptus species for the control of Fusarium solani and Sclerotium rolfsii

The essential oils were extracted from the leaves of Eucalyptus microcorys, Eucalyptus grandis and Eucalyptus robusta which were grown in Sri Lanka and their major chemical compounds were determined. 1,8-Cineole and α-pinene were identified as major aroma compounds in these oils. In this study, the anti-fungal activity of essential oils of E. microcorys, E. grandis and E. robusta, ethanol extract of E. microcorys and 1,8-cineole were evaluated against Sclerotium rolfsii, a fungi responsible for leaf spot disease of indoor plants and Fusarium solani, a fungi responsible for dry rot diseases of potato by poisoned food technique, and minimum inhibitory concentrations (MICs) were determined. The essential oils from three Eucalyptus species showed significant inhibitory effect against S. rolfsii and F. solani than the ethanol extract of E. microcorys. Of treatments, the essential oil of E. grandis showed the best anti-fungal activity with the MIC values of less than 0.1% for S. rolfsii and 0.5% for F. solani. The MICs of the oils of E. microcorys and E. robusta were between 0.3–0.5% against S. rolfsii and 0.5–0.75% for F. solani. The 1,8-cineole did not exhibit inhibition activity as much of Eucalyptus essential oils and hence, it can be assumed that minor chemical components of the oils contribute to the growth inhibition of the tested fungi. This is the first report of anti-fungal activity of Sri Lankan oils of E. microcorys, E. grandis and E. robusta and ethanol extract of E. microcorys against S. rolfsii and F. solani. These findings would be useful for the designing of natural fungicide for agriculture- and food-based industries.     

Induction of resistance in Camellia sinensis against Sclerotium rolfsii by dual application of Rhizophagus fasciculatus and Bacillus pumilus

Rhizophagus fasciculatus and Bacillus pumilus, isolated from rhizosphere of tea (Camellia sinensis (L.) O.Kuntze) bushes, were selected for the present study. Inoculation of tea bushes with any of the two micro-organisms increased growth of plants but significant increase was obtained in case of dual application. B. pumilus exhibited plant growth promoting rhizobacterial traits and antagonistic activity against Sclerotium rolfsii in vitro. Disease reduction following application of R. fasciculatus and B. pumilus was obtained when applied individually but joint application gave more significant results. A sharp increase was found in polyphenolic accumulation and activities of four defence enzymes which play a key role in disease suppression. Immunodetection of S. rolfsii in soil was done after treatments with bioinoculants using PAb of S. rolfsii and its population was significantly reduced owing to application of B. pumilus and R. fasciculatus.     

Introduction of some new endophytic bacteria from Bacillus and Streptomyces genera as successful biocontrol agents against Sclerotium rolfsii

Endophytic bacteria live inside plant tissues without causing disease and not only promote plant growth but can also protect plants against plant pathogens. During 2010–2011 crop years, some endophytic bacteria were collected and are then biochemically and molecularly identified (16srRNA) from bean farms of East Azarbaijan, Iran. Among these bacteria isolates, four isolates from Bacillus genera and four isolates from Streptomyces genera were selected for evaluation of their ability for biocontrol of Sclerotium rolfsii in laboratory and glasshouse conditions. Except one isolate named Streptomyces parvus, the rest of isolates could significantly inhibit mycelial growth in dual culture on PDA medium. All seven selected isolates showed significant inhibition in disease treatments in glasshouse experiments. Biological traits, such as length, wet and dry weight of roots and stems in endophytic bacterial treatment showed no differences with healthy control.     

Induction of Systemic Acquired Resistance in Arachis hypogaea L. by Sclerotium rolfsii Derived Elicitors

Plants evolve a strategy to survive the attacks of potential pathogens by inducing the microbial signal molecules. In this study, plant defence responses were induced in four different varieties of Arachis hypogaea (J‐11, GG‐20, TG‐26 and TPG41) using the fungal components of Sclerotium rolfsii in the form of fungal culture filtrate (FCF) and mycelial cell wall (MCW), and the levels of defence‐related signal molecule salicylic acid (SA), marker enzymes such as peroxidase (POX), phenylalanine ammonia lyase (PAL), β‐1,3‐glucanase and lignin were determined. There was a substantial fold increase in POX, PAL, SA, β‐1,3‐glucanase and lignin content in FCF‐ and MCW‐treated plants of all varieties of groundnut when compared to that of control plants. The enzyme activities were much higher in FCF‐treated plants than in MCW‐treated plants. The increase in fold activity of enzymes and signal molecule varied between different varieties. These results indicate that the use of fungal components (FCF and MCW) had successfully induced systemic resistance in the four different varieties of groundnut plants against Sclerotium rolfsii.     

Effect of Fusarium oxysporum f. sp. glycines and Sclerotium rolfsii on the pathogenicity of Meloidogyne incognita race 2 to soybean

Screenhouse studies were conducted to investigate the effects of Fusarium oxysporum f. sp. glycines and Sclerotium rolfsii on the pathogenicity of Meloidogyne incognita race 2 on soybean and the influence of the nematode on wilt incidence and growth of soybean. The interaction of each fungus with the nematode resulted in reduced shoot and root growth. Final nematode population was also reduced with concomitant inoculation of nematode and fungus or inoculation of fungus before nematode. While M. incognita suppressed wilt incidence in two nematode-susceptible cultivars of soybean (TGX 1485-2D and TGX 1440-IE), it had limited effect on wilt incidence in the nematode resistant cultivar of soybean (TGX 1448-2E). When F. oxysporumwas inoculated with the nematode, the mean number of nematodes that penetrated soybean roots decreased by 75% in TGX 1448-2E, 68% in TGX 1485-1D and 65% in TGX 1440-1E. Similarly when the soil was treated with S. rolfsii, the number decreased by 78% in TGX 1448-2E, 77% in TGX 1485-1D and 68% in TGX 1440-1E. The nematode did not develop beyond second-stage juvenile in TGX-1448-2E.     

大蒜叶片活性氧及保护酶系对白腐病菌粗毒素胁迫的响应

以大蒜抗病品种‘汉中红皮’和感病品种‘改良蒜’为材料,研究了它们在苗期用白腐病菌毒素处理后的叶片细胞超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性以及超氧阴离子(O2-.)和丙二醛(MDA)含量的动态变化。结果表明,白腐病菌粗毒素处理后,2个品种大蒜叶片的SOD、POD活性均升高,而CAT活性降低;抗病品种的SOD、POD和CAT活性均高于感病品种,且SOD、POD活性峰值出现早,并以POD对毒素胁迫最敏感。2个品种在白腐病菌粗毒素处理后的O2.-含量始终高于同期对照,而感病品种O2.-含量在毒素处理24h后均高于同期抗病品种。MDA含量变化趋势与O2.-的变化基本相似。研究认为,大蒜叶片的活性氧含量和保护酶活性与其抗病性密切相关。     

Effect of different soil and clove treatments in the control of white rot of garlic

Soil solarisation was consistently efficacious in reducing inoculum density to undetectable levels in a field naturally‐infested with Sclerotium cepivorum. This treatment delayed epidemic onset of white rot of garlic 2–3 months as compared with the untreated control or the inoculation of planting furrows with Glomus intraradices. Furthermore, significant reductions of disease incidence and of the standardised AUDPC were also observed in solarised plots, resulting in quantitative and qualitative yield improvement. Similar effects were observed in plots planted with tebuconazole‐treated cloves, confirming previous results, whereas Trichoderma harzianum was ineffective as a biocontrol agent, when applied to planting furrows. The inoculation of plots with G. intraradices before planting, in three consecutive years, was neither effective for disease control nor on the development of garlic, although the root systems of garlic plants from all the experimental treatments were heavily mycorrhizal at harvest, indicating the presence of native arbuscular mycorrhizal propagules in the soil and their survival after soil solarisation.     

Trichoderma sp. as a microbial suppressive agent of Sclerotium rolfsii on vegetables

World Journal of Microbiology and Biotechnology -     

电穿孔法转化齐整小核菌

【目的】建立齐整小核菌(Sclerotium rolfsii)的电穿孔法转化方案,以实现经济、快速地遗传转化。【方法】将齐整小核菌gpd基因启动子控制的basta抗性基因bar与红色荧光蛋白基因DsRed Max组成的融合蛋白表达盒,通过电击转入野生型齐整小核菌细胞中,筛选转化子并进行PCR与荧光观察验证。在此基础上,测试了不同电压、脉冲时间、外源DNA片段与受体细胞比例等条件下的转化效率,以得到优化的电转化参数。最后,采用优化的条件,尝试转化多种抗性基因与荧光蛋白融合表达盒以测试其可用性。【结果】成功得到了bar、sdhR与aphI基因的转化子。【结论】成功建立了优化的齐整小核菌电穿孔转化法。优化的参数条件为电压2kV/cm、脉冲时间1 ms、DNA/匀浆细胞比例3μg/300 mg,电击1次。