The potential for using cyanobacteria (blue-green algae) and algae in the biological control of plant pathogenic bacteria and fungi

Cyanobacteria (blue-green algae) and eukaryote algae occur in freshwater, marine, and terrestrial (soil) habitats. In fact, these microorganisms comprise most of the world's biomass. Although the cyanobacteria are mostly photoautotrophic, some are facultative heterotrophs, capable of growing on certain substrates in darkness. Also, some are non-phototrophic and hence, are obligate heterotrophs. A number of cyanobacteria and eukaryote algae, particularly macroalgae, produce various, biologically active compounds. These include antibiotics which in laboratory tests inhibited bacteria and fungi that incite diseases of humans. In addition, the following fungi which are of interest to plant pathologists, were inhibitedin vitro by substances produced by various cyanobacteria: The saprophytesChaetomium globosum, Cunninghamella blakesleeana, andAspergillus oryzae and the plant pathogensRhizoctonia solani andSclerotinia sclerotiorum. Extracts from seaweeds (macroalgae) sprayed on plants have been reported to reduce the incidence ofBotrytis cinerea (gray mold) on strawberries,Erysiphe polygoni (powdery mildew) on turnips, and damping-off of tomato seedlings. Because many cyanobacteria and algae produce a large number of antibacterial and antifungal materials, are almost never a threat to the environment, and many can be grown in quantity in mass culture, they are suitable candidates for exploitation as biocontrol agents of plant pathogenic bacteria and fungi. Much additional work remains to be done however, to thoroughly evaluate cyanobacteria and algae and their products for this role.     

3种植物次生物质对金银花蚜虫的活性测定及防效评价

为明确反式-2-己烯醛、牛至油和百里香油对金银花蚜虫的生物活性及橙皮精油、有机硅对这3种药剂杀蚜活性的增效作用,本研究以金银花蚜虫的优势种胡萝卜微管蚜为试虫,采用浸虫浸叶法和叶面喷雾法进行生物活性测定及防效评价。室内测定结果显示百里香油毒力最高,LC 50为1.793 mg/L,添加橙皮精油、有机硅对供试药剂杀蚜活性均有提高,其中反式-2-己烯醛、牛至油、百里香油与有机硅组合有明显增效作用,毒力系数为1.80、1.48、1.45。田间试验结果表明常规施药后百里香油校正防效最高,施药7 d后3种药剂防治效果均高于对照组;3种药剂减量20%添加有机硅处理施药1 d后防治效果提高约10%,施药4 d后防治效果均高于对照组,施药14 d后防治效果达98%。综上,百里香油对胡萝卜微管蚜的毒力和防治效果最高,3种药剂结合有机硅使用减量增效作用明显,具有进一步开发的潜力。     

Yucca schidigera extract: a potential biofungicide against seedborne pathogens of sorghum

Treatment of seeds with an aqueous extract of yucca (YE), Yucca schidigera, was evaluated for antifungal activity against seedborne pathogens as well as its effect on seed germination and seedling growth of sorghum (Sorghum bicolor). The antifungal effect of YE was observed against Leptosphaeria sacchari (syn. Phoma sorghina) when the extract was applied at 2·5 and 10% concentrations. At 10% concentration, YE significantly reduced not only the incidence of L. sacchari, but also that of Fusarium spp., Cochliobolus lunatus (syn. Curvularia lunata) and Cladosporium spp. The effect of 10% YE on seedborne fungi was broader than the fungicide fludioxonil, particularly with regard to Fusarium. Furthermore, the number of normal, healthy‐looking seedlings increased in a dose‐responsive manner with YE treatment. Seedling vigour was also stimulated by YE but no correlation was observed with the concentrations tested. Under glasshouse conditions, the treatment of seeds with 10% YE increased the emergence of seedlings and plant height and reduced the number of seedlings with crown rot compared to negative controls and saponin. The positive effect was similar to the effect obtained with fungicide‐treated seeds. Treatment of seeds with synthetic saponin inhibited seedborne fungi less effectively and also negatively affected germination and vigour of the seedlings, compared to the treatment with YE. The results demonstrate an agronomic potential for the use of YE as a biofungicide for seed treatment of sorghum. The difference between the antifungal and the vigour‐stimulating effects of YE warrants further investigation.     

Investigation on the transformation of fluchloralin by soil fungi: Identification of some metabolites

Fluchloralin [N-(2-chloroethyl)-α,α,α,-trifluoro-2,6-dinitro-N-propyl-p-toluidine] was transformed by two common soil fungi, Aspergillus flavus Link and Fusarium solani (Mart.) Sacc. in pure culture. The fungi were isolated from enrichment cultures of an analogous herbicidal compound, pendimethalin [N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine)]. Transformation of fluchloralin by these fungi resulted in the formation of several metabolites, 13 of which were identified. Besides the known mechanisms of microbial transformation of dinitroanilines, methylation of the anilino nitrogen and direct elimination of a nitro group at 2 position from the aromatic ring without any further substitution were also observed.     

Crossover between the control of fungal pathogens in medicine and the wider environment,and the threat of antifungal resistance

Fungal propagules existing in the natural environment can easily be transmitted to the human body, mostly by inhalation of contaminated air or direct contact onto the skin, nails, and mucosa. Fungal infections in humans are, as compared to viral and bacterial infections, rarely serious (life-threatening) unless the immune system is weakened. Because azole fungicides (demethylation inhibitors, DMIs) are among the most important antifungal compounds used broadly in human and animal medicine as well as in agriculture and material protection, fungal propagules may come into contact with azoles almost everywhere, presenting a potential “crossover-use-pattern” and “cross-contamination-risk” for resistant propagules in all areas. A “hot-spot” in terms of the emergence of azole resistance in a fungal species is defined as a habitat in which the species is actively propagating and exposed to a fungicidally effective azole at available concentrations high enough to select for resistant individuals, potentially multiplying and spreading to other habitats. Intrinsic antifungal resistance may exist in less sensitive or insensitive species independent of previous exposure to antifungal compounds, whereas acquired antifungal resistance can evolve if triggered by the exposure of an originally sensitive species (or population) to agricultural or medical antifungal agents, resulting in the selection of resistant individuals. The origin and risks of these developments in medical settings and the wider environment are elucidated for the most relevant life-threatening fungal human pathogens, including several species of Cryptococcus, Candida, Pneumocystis, Aspergillus, Histoplasma, Coccidioides, Rhizopus, Mucor, Fusarium, and Scedosporium.     

Auxin‐mediated relationships between apple plants and root inhabiting fungi: impact on root pathogens and potentialities of growth‐promoting populations

This study aimed to elucidate the relationship between plant hosts and root‐colonizing fungi recovered from apple orchard soils that had been replanted over multiple generations. Functional relationships of three groups of filamentous fungi (Ceratobasidium sp., Cylindrocarpon‐like group and Fusarium acuminatum) with apple rootstocks were evaluated in plant growth bioassays. The Cylindrocarpon‐like group and Ceratobasidium sp. showed a relationship with the host plant varying from pathogenic to commensal through to mutualistic for the latter group, while that of F. acuminatum tended to be mutualistic. Seven fungal isolates of each group, which induced the highest plant growth in bioassays, were evaluated for auxin (IAA) and gibberellin (GA₃ and GA₄) production in culture filtrate. All isolates of F. acuminatum as well as most of those of the Ceratobasidium sp. and Cylindrocarpon‐like groups produced IAA in culture filtrate. IAA production was evaluated for additional isolates of endophytic fungal species from fruit tree orchards and the functionality of IAA was confirmed by growing in vitro micropropagated plantlets of apple rootstock on MS medium supplemented with fungal culture filtrate. Findings from this study may explain the difficulty in defining the precise role of diverse root‐colonizing fungal populations in replant disease aetiology of fruit tree orchards. However, the results demonstrate the presence of a positive and widely available biotic component of the orchard soil biology that may be exploited for the benefit of tree growth and production.     

雷帕霉素对4种植物病原真菌的抑菌活性

采用菌丝生长速率法,测定了雷帕霉素对番茄灰霉病菌、油菜菌核病菌、水稻纹枯病菌和棉花枯萎病菌的抑菌活性,比较了嘧菌酯、丙烷脒及雷帕霉素对番茄灰霉病菌的抑菌效果,并通过电子显微镜观察了雷帕霉素对番茄灰霉病菌菌丝生长的影响。结果表明:雷帕霉素对供试4种植物病原真菌菌丝均表现出了极强的抑制活性,其中对油菜菌核病菌的抑制作用最强,EC50值为2.23×10-4μg/mL,对番茄灰霉病菌、水稻纹枯病菌和棉花枯萎病菌的EC50值分别为1.32×10-3、4.05×10-3及3.82×10-3μg/mL;雷帕霉素对番茄灰霉病菌菌丝的抑制活性显著高于嘧菌酯(EC50值为3.24μg/mL)和丙烷脒(EC50值为3.81μg/mL)。电镜观察发现,经雷帕霉素处理后,番茄灰霉病菌菌丝表现出提前衰老等症状。研究结果可为深入探讨雷帕霉素对植物病原真菌的作用机制奠定基础。     

寄主营养和次生代谢物质对牛角花齿蓟马(缨翅目：蓟马科)产卵选择的影响

为探究牛角花齿蓟马Odontothrips loti的产卵选择及寄主营养和次生代谢物质对其产卵行为的影响,本研究观测了牛角花齿蓟马在苜蓿Medicago sativa、草木樨Melilotus officinalis、红豆草Onobrychis cyri和红三叶Trifolium pratense 4种豆科牧草叶片上的产卵量和卵孵化率,同时测定、分析了牧草主要营养和次生代谢物质含量与蓟马产卵选择的相关性。结果表明,无选择条件下,牛角花齿蓟马在苜蓿上产卵量最高,为59.1粒/复叶,其次是草木樨,15.7粒/复叶,在红豆草和红三叶上的产卵量仅为0.9粒/复叶和1.1粒/复叶。卵孵化率在苜蓿上最高,为85.05%,在草木樨和红豆草上分别为40.09%和39.18%,红三叶上最低,为5.48%。两两选择条件下,牛角花齿蓟马明显偏好在苜蓿叶片上产卵,在其他牧草叶片上不产卵或产卵量极低。相关性分析表明,牛角花齿蓟马的产卵量与寄主可溶性蛋白含量显著正相关(r=0.722,P=0.002),卵孵化率与可溶性蛋白(r=0.673,P=0.004)和淀粉(r=0.586,P=0.017)含量显著正相关。牛...     

短密木霉新菌株BF06对黄瓜土传病害的防治效果与促生作用

连作导致枯萎病等土传病害发生日益严重,已成为我国黄瓜生产的重要限制因素。采用化学防治和农业措施防治土传根部病害,操作都较为困难,迫切需要开发环境友好的生物防治技术。本研究从森林土壤分离鉴定一株短密木霉菌株BF06,通过对峙培养发现该菌株可以附着和缠绕病原菌的菌丝,对引起黄瓜枯萎病、茎基腐病、菌核病、根腐病和疫病的病原菌Fusarium oxysporum f. sp. cucumerinum,Rhizoctonia solani,Sclerotinia sclerotiorum,F. solani f. sp. cucurbitae,and Phytophthora cryptogea具有较强的拮抗作用。温室盆栽试验发现短密木霉菌株BF06可以迅速附着定殖于黄瓜根部表面,对上述5种黄瓜根部病害的防效达60%以上,对黄瓜枯萎病和茎基腐病的防效分别为90.4和88.8%。此外,利用植物组织培养基培养观察发现BF06显著地促进幼苗黄瓜侧根的形成和生长。本研究的结果表明短密木霉菌株BF06是一种可以有效防治黄瓜根部病害的新生防资源。     

Screening study for potential lead compounds for natural product-based fungicides: I. Synthesis and in vitro evaluation of coumarins against Botrytis cinerea

An efficient, one-pot synthesis of angular and linear dihydropyranocoumarins, along with C-6 and C-8 prenylated coumarins is reported. These compounds, together with single- and furanocoumarins, were tested for their potential antifungal activity against the phytopathogen Botrytis cinerea Pers ex Fr. The results show that furanocoumarins may be able to control the fungus B cinerea.     

Fungicidal potential of methoxylated flavones from citrus for in vitro control of Colletotrichum gloeosporioides, causal agent of anthracnose disease in tropical fruits

Four polymethoxylated flavones (3,5,6,7,3',4'-hexamethoxyflavone, 3,5,6,7,8,3',4'-heptamethoxyflavone, 5,6,7,8,4'-pentamethoxyflavone and 5,6,7,8,3',4'-hexamethoxyflavone) were isolated and characterized from cold-pressed orange oil. Their antifungal activities were evaluated against Colletotrichum gloeosporioides (Penz) Penz & Sacc, a major plant pathogen of fruits that causes significant damage to crops in tropical, sub-tropical and temperate regions. Methoxylated flavones were effective in inhibiting mycelial growth of the fungus. As flavone concentration increased, mycelial growth decreased. 5,6,7,8,3',4'-Hexamethoxyflavone completely inhibited the growth of Cgloeosporioides at a concentration of 100 microg ml(-1).     

In‐field molecular diagnosis of plant pathogens: recent trends and future perspectives

Accurate management practices in crop health and food safety are critical, especially regarding the detection of plant pathogens in the early stages of a disease. To date, specific, fast and sensitive technologies for point‐of‐care diagnosis and simple or grower‐friendly devices are very valuable, as no specialized staff are required for diagnosing a disease in the field. This is especially the case today, when factors such as climate change may cause the appearance of pathogens in areas where years ago they were unexpected. The aim of this research is to review some of the promising techniques that can be applied to in‐field molecular detection of plant pathogens and how these techniques can change the way farmers and pathologists are diagnosing plant diseases. Some of them, like loop‐mediated isothermal amplification and recombinase polymerase amplification, are already being successfully used for routine diagnosis. However, most technologies still need validation in the plant pathology field, where they have a promising future for in‐field diagnosis when combined with simple DNA extraction methods, reagent stabilization techniques and their integration into portable devices.     

植物病原真菌对甾醇生物合成抑制剂类(SBIs)杀菌剂的抗药性研究进展

甾醇生物合成抑制剂类(SBIs)杀菌剂通过抑制植物病原真菌甾醇生物合成途径中不同环节的酶,干扰或阻断病原菌麦角甾醇生物合成而发挥抗真菌作用。综述了植物病原真菌对SBIs杀菌剂的抗药性发生现状、遗传机制、生理生化机制、分子机制及治理策略等方面的最新研究进展。室内及田间有关SBIs杀菌剂抗药性的研究结果表明,植物病原菌对该类杀菌剂的抗药性可能是由1种或多种机制共同作用的结果。ABC和MFS运输蛋白基因及CYP51蛋白基因是植物病原真菌对SBIs杀菌剂产生抗药性的主要分子机制。其中ABC运输蛋白基因能够通过翻转酶将药剂从膜内层转移至外层而排出细胞体外;MFS运输蛋白基因的超表达和本底表达则是导致病原菌产生抗药性的关键因素;而CYP51蛋白基因与药剂作用时易在病原菌体内发生基因点突变或基因超表达,造成编码蛋白与药剂亲和力下降,导致病原菌产生抗药性。随着分子生物学的迅速发展,可从基因水平上寻找出与抗药性直接相关的基因、蛋白及调控途径等信息,同时与其他学科结合,合理设计新的、多作用位点的高效甾醇生物合成抑制剂,从而延长该类杀菌剂的使用寿命。     

Common vole (Microtus arvalis) ecology and management: implications for risk assessment of plant protection products

Common voles (Microtus arvalis) are common small mammals in some European landscapes. They can be a major rodent pest in European agriculture and they are also a representative generic focal small herbivorous mammal species used in risk assessment for plant protection products. In this paper, common vole population dynamics, habitat and food preferences, pest potential and use of the common vole as a model small wild mammal species in the risk assessment process are reviewed. Common voles are a component of agroecosystems in many parts of Europe, inhabiting agricultural areas (secondary habitats) when the carrying capacity of primary grassland habitats is exceeded. Colonisation of secondary habitats occurs during multiannual outbreaks, when population sizes can exceed 1000 individuals ha^?1. In such cases, in‐crop common vole population control management has been practised to avoid significant crop damage. The species' status as a crop pest, high fecundity, resilience to disturbance and intermittent colonisation of crop habitats are important characteristics that should be reflected in risk assessment. Based on the information provided in the scientific literature, it seems justified to modify elements of the current risk assessment scheme for plant protection products, including the use of realistic food intake rates, reduced assessment factors or the use of alternativee focal rodent species in particular European regions. Some of these adjustments are already being applied in some EU member states. Therefore, it seems reasonable consistently to apply such pragmatic and realistic approaches in risk assessments for plant protection products across the EU. © 2013 Society of Chemical Industry     

Induced plant defences in biological control of arthropod pests: a double‐edged sword

Biological control is an important ecosystem service delivered by natural enemies. Together with breeding for plant defence, it constitutes one of the most promising alternatives to pesticides for controlling herbivores in sustainable crop production. Especially induced plant defences may be promising targets in plant breeding for resistance against arthropod pests. Because they are activated upon herbivore damage, costs are only incurred when defence is needed. Moreover, they can be more specific than constitutive defences. Nevertheless, inducible defence traits that are harming plant pest organisms may interfere with biological control agents, such as predators and parasitoids. Despite the vast fundamental knowledge on plant defence mechanisms and their effects on natural enemies, our understanding of the feasibility of combining biological control with induced plant defence in practice is relatively poor. In this review, we focus on arthropod pest control and present the most important features of biological control with natural enemies and of induced plant defence. Furthermore, we show potential synergies and conflicts among them and, finally, identify gaps and list opportunities for their combined use in crop protection. We suggest that breeders should focus on inducible resistance traits that are compatible with the natural enemies of arthropod pests, specifically traits that help communities of natural enemies to build up. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.