Parasitism of arbuscular mycorrhizal fungi: reviewing the evidence.

In order to understand the functioning of mycorrhizal fungi in ecosystems it is necessary to consider the full suite of possible biotic interactions in the soil. While a number of such interactions have recently been shown to be crucially important, parasitism is a highly neglected feature in the ecology of arbuscular mycorrhizal fungi (AMF). A number of studies have classified some interactions between populations of bacteria and fungi with AMF as parasitism, generating discussion about its consequences at both 'parasite' and host population levels. This paper reviews these various publications, and based on a set of criteria that are necessary to demonstrate parasitism, it was concluded that parasitism has not been conclusively shown to exist in AMF, even though some data are highly suggestive of such a relationship. The difficulties in gathering data supportive of parasitism were discussed, and hypotheses for defense were offered. This paper concludes by presenting potential consequences of AMF parasitism at the population/community levels and by discussing applied aspects.     

Colonization of Sclerotinia sclerotiorum sclerotia by a biocontrol isolate of Trichoderma harzianum,and effects on myceliogenic germination

Sclerotia of Sclerotinia sclerotiorum were incubated on cultures of Trichoderma harzianum. Myceliogenic germination decreased by 50% within 1 day and continued to decrease over time. Quantitative PCR showed a decrease in Sclerotinia DNA for older sclerotia, but not fresh sclerotia. Trichoderma DNA increased and persisted inside older sclerotia but not fresh sclerotia.     

Effects of Ph Gene-Associated versus Induced Resistance to Tobacco Cyst Nematode in Flue-Cured Tobacco

Effects of the systemic acquired resistance (SAR)-inducing compound acibenzolar-S-methyl (ASM) and the plant-growth promoting rhizobacterial mixture Bacillus subtilis A13 and B. amyloliquefaciens IN937a (GB99+GB122) were assessed on the reproduction of a tobacco cyst nematode (TCN- Globodera tabacum solanacearum) under greenhouse conditions. Two sets of two independent experiments were conducted, each involving soil or root sampling. Soil sample experiments included flue-cured tobacco cultivars with (Ph(p)+: NC71 and NC102) and without (Ph(p)-: K326 and K346) a gene (Ph(p)) suppressing TCN parasitism. Root sample experiments examined TCN root parasitism of NC71 and K326. Cultivars possessing the Ph(p) gene (Ph(p)+) were compared with Ph(p)- cultivars to assess the effects of resistance mediated via Ph(p) gene vs. induced resistance to TCN. GB99+GB122 consistently reduced nematode reproductive ratio on both Ph(p)+ and Ph(p)- cultivars, but similar effects of ASM across Ph(p)- cultivars were less consistent. In addition, ASM application resulted in leaf yellowing and reduced root weight. GB99+GB122 consistently reduced nematode development in roots of both Ph(p)+ and Ph(p)- cultivars, while similar effects of ASM were frequently less consistent. The results of this study indicate that GB99+GB122 consistently reduced TCN reproduction in all flue-cured tobacco cultivars tested, while the effects of ASM were only consistent in Ph(p)+ cultivars. Under most circumstances, GB99+GB122 suppressed nematode reproduction more consistently than ASM compared to the untreated control.     

褐飞虱与灰飞虱间接种内和种间效应的比较研究

为了明确褐飞虱Nilaparva talugens(Stl)与灰飞虱Laodelphgax striatellus(Fallén)经寄主植物而诱导引起的间接种间效应,在人工气候室内以健康植株为对照,研究了2种飞虱在事先分别经一种稻飞虱危害的汕优63和秀水11上的表现,比较由同种或异种诱导的间接种内和种间效应对该2种稻飞虱主要生物学参数的影响,结果表明在每2株稻苗接20头高龄单一种飞虱若虫危害2d的条件下,褐飞虱存在一定的间接种内竞争,主要表现为在事先由同种危害的寄主上若虫存活率显著下降,但未发现灰飞虱对褐飞虱的正面或负面的间接种间效应。但是,在试验条件下灰飞虱并不存在间接种内竞争,而存在着显著的褐飞虱对灰飞虱诱导的间接种间促进作用,主要表现为在事先经褐飞虱取食危害的寄主植物上灰飞虱若虫的历期缩短、存活率提高、雌成虫寿命延长、每雌产卵量增加。同时,褐飞虱对灰飞虱所表现的间接诱导种间促进效应与寄主品种有显著互作关系,在中抗灰飞虱的汕优63品种上,间接诱导种间促进效应较在感灰飞虱品种秀水10上更为明显。本文对稻飞虱间接诱导种内和种间效应的机制和进化意义进行了讨论。     

Proposed definitions related to induced disease resistance

A clear definition of induced disease resistance is lacking, even though the area has been extensively researched and described. The lack of a precise definition leads to potential confusion on whether an underlying mechanism for biological control is induced resistance. We propose definitions, which were developed at a NATO Advanced Research Workshop on biological control, for induced disease resistance and related terms. These definitions are intended to invoke debate and increase effective communication among investigators of induced resistance.     

Induced resistance by the mutualistic endophyte, Fusarium oxysporum strain 162, toward Meloidogyne incognita on tomato

The non-pathogenic endophytic fungus, Fusarium oxysporum strain 162, originally isolated from the endorhiza of tomato roots, reduces damage caused by Meloidogyne incognita, by inhibiting juvenile penetration of and development in the root. However, little is known about the mode of action of this endophyte fungus against the nematode. This study aimed at investigating how the endophyte affects nematode motility and survival and if induced resistance plays a role in the relationship. In a previous study, F. oxysporum strain 162 decreased nematode penetration of tomato up to 60%. In experiments using a split-root chamber to test for induced resistance, nematode penetration, number of galls, and number of egg masses were investigated 2 and 5 weeks after nematode inoculation. Split-root plants treated with F. oxysporum strain 162 showed 26-45% less nematode penetration, 21-36% less galls and a 22-26% reduction in the number of egg masses in the roots not directly inoculated with the fungus when compared to untreated control plants in repeated tests. In conclusion, inoculation of tomato plants with the non-pathogenic fungal endophyte F. oxysporum strain 162 resulted in a signficant reduction of nematode infection, which was in part due to induced resistance in the first 2-3 weeks after fungal inoculation.     

亚热带森林根系和菌根真菌调控凋落叶分解和主场效应

根系向凋落物层生长是森林生态系统中存在的普遍现象,研究根系和菌根真菌如何调控凋落物分解对理解森林生态系统的养分循环具有重要意义。通过在亚热带楠木(丛枝菌根树种)和格氏栲(外生菌根树种)人工林中进行了2年的凋落物互换和菌根排除实验,研究根系及其共生菌根真菌如何影响森林凋落物的分解速率和主场效应。结果发现:经过720 d的分解,在楠木人工林中,根系的存在促使楠木和格氏栲凋落物的分解速度分别提高了29%和47%,而在格氏栲人工林中,根系存在对格氏栲凋落物分解无显著影响,但增加了楠木凋落物的分解速率。此外,楠木人工林中,有根和无根处理下凋落物分解均无主场效应,而格氏栲人工林凋落物仅在根系存在的情况下显示出负的主场效应。进一步发现格氏栲凋落物的负主场效应归因于楠木人工林凋落物层更大的腐生真菌丰度和更强的磷降解酶活性。结果表明,在亚热带不同菌根类型树种中,菌根真菌与腐生真菌的相互作用(拮抗或促进),很有可能通过影响磷降解酶的活性,进而影响凋落物的分解率和主场效应。     

烟草黑胫病生物防治研究进展(综述)

随着烟草生产向无公害发展,黑胫病作为烟草生产上的主要病害之一,其生物防治取得较大的进展。本文就其诱抗剂、生防菌等生物防治方面的研究作简要综述。     

Beetle grazing reduces natural infection of Rumex obtusifolius by fungal pathogens

In previously reported laboratory experiments, infection of Rumex obtusifolius by the rust fungus Uromyces rumicis was decreased on leaves which had prior herbivory by the beetle Gastrophysa viridula . In this paper we investigate whether this interaction is robust for natural infection by a variety of fungi in field experiments carried out in spring and autumn with plants given different levels of nitrogen fertilization. Grazing by G. viridula led to a decrease in lesion density of Ramularia rubella and Venturia rumicis in the spring and V. rumicis and U. rumicis in the autumn experiment. For V. rumicis and U. rumicis significant reductions in lesion density occurred on the undamaged leaves of damaged plants, compared with similar leaves on undamaged plants, suggesting systemic induced resistance. This induced resistance was usually independent of the amount of nitrogen fertilization, although the inhibitory effect of grazing on R. rubella in the spring and V. rumicis in the autumn experiment was enhanced by increasing nitrogen fertilization and was inhibited by increasing nitrogen fertilization for V. rumicis in the spring. In both experiments, the lesion density of V. rumicis was greater on leaves on which R. rubella was also present, and the presence of U. rumicis in the autumn experiment was linked to a similar but greater effect on V. rumicis lesion density. We found no evidence of induced resistance by fungi against fungi in these experiments. We highlight the complex interactions between inhibitory and facilitatory processes acting on leaf fungal infection. These results are compared with the proposed molecular mechanisms of induced resistance(s) and we consider the benefits of closer integration between molecular and ecological investigations of induced resistances that occur in the field.     

Herbivores and pathogens on willow: do they affect each other?

Abstract 1 Willows often need to cope with attack by both rust fungi and herbivores. We studied whether rust infection on willow affects the herbivore, and vice versa, whether herbivore feeding affects the fungal infection. The system investigated by laboratory bioassays and greenhouse experiments consisted of the willow hybrid Salix × cuspidata, the rust Melampsora allii‐fragilis and the willow leaf beetle Plagiodera versicolora. Effects were studied both on a local scale (rust infection and feeding on the same leaf) and systemically (rust infection and feeding on different, but adjacent leaves). 2 Rust infection was not affected by herbivore feeding on a local scale. Systemically, however, the willow's susceptibility towards rust infection was increased by herbivore feeding, as indicated by a higher number of rust sori on leaves adjacent to feeding‐damaged leaves. The herbivore's performance was detrimentally affected by rust infection: increase of mortality (systemically), decrease of larval weight (locally and systemically) and prolonging of developmental time (locally and systemically). 3 Previous rust infection enhanced systemically the willow's susceptibility towards subsequent fungal infection. Previous herbivore feeding on the willow had no effects on the herbivore's developmental time and mortality. However, feeding upon previously feeding‐damaged willow leaves significantly reduced larval weight.     

稻镰状瓶霉对水稻白叶枯病的生物防治

本文研究了野生稻暗色有隔内生真菌稻镰状瓶霉与水稻的共生关系,通过根部接种DsRED荧光标记菌株,观察稻镰状瓶霉在水稻根系内的定殖,并对其抗白叶枯病特性进行调查,结果发现：经叶部接种白叶枯病菌后,对照组发病严重,病级集中在7级和9级,分别占比43.33%和34.67%,病情指数为79.26;相比之下,接种了稻镰状瓶霉的水稻植株发病较轻,叶片病斑面积小,并伴随零星黑色过敏性坏死斑出现,未发病植株占8%,72%的植株病级为1级,病情指数仅为15.26。稻镰状瓶霉对水稻白叶枯病的防治效果达到80.75%。稻镰状瓶霉的定殖能够引起叶片中超氧化物歧化酶、过氧化氢酶和过氧化物酶活性极显著提高,分别是对照组的5.26、12.08和10.53倍;诱导PR1a和PR1b显著上调表达8.71和3.37倍,AOS、OsSAUR2和EL5基因显著下调表达0.28、0.57和0.65倍。利用野生稻内生真菌防控水稻白叶枯病,在国内外尚属首次,可为水稻白叶枯病的生物防治提供新途径。     

Biological and Chemical Induction of Resistance to the Globodera tabacum solanacearum in Oriental and Flue-Cured Tobacco (Nicotiana tabacum L.)

The effects of acibenzolar-S-methyl (ASM) and four combinations of plant growth-promoting rhizobacteria (PGPR) on the reproduction of a tobacco cyst nematode, Globodera tabacum solanacearum, and growth of Nicotiana tabacum (cv. K326 and Xanthi) were tested under greenhouse and field conditions. The PGPR included combinations of Bacillus subtilis A13 with B. pumilis INR7, B. pumilis SE34, B. licheniformis IN937b, or B. amyloliquefaciens IN937a, respectively. Among the four rhizobacterial combinations, IN937a + A13 exhibited the most consistent reduction in G. t. solanacearum cysts under greenhouse and field conditions. No undesirable effects of IN937a + A13 were observed on tobacco growth under greenhouse and field conditions. Use of INR7 + A13 reduced G. t. solanacearum reproduction on flue-cured tobacco cv. K326 but not on oriental tobacco cv. Xanthi. Application of ASM reduced final numbers of G. t. solanacearum cysts, but also resulted in phytotoxicity mainly under the greenhouse conditions. When oriental tobacco seedlings were pre-grown in a IN937a + A13-treated soil-less medium, a single application of ASM at 200 mg/L one week after transplanting significantly reduced G. t. solanacearum reproduction in the field.     

赤松枯梢病叶内生真菌多样性研究

在微生物层面研究枯梢病与植物针叶内生微生物的互作关系,分析内生真菌的多样性差异,为松枯梢病的防控提供基础数据。利用高通量测序技术测定赤松(Pinus densiflora)不同染病程度的针叶内生真菌的多样性。结果显示,随着病害的加重,P. densiflora针叶内生真菌丰富度呈现出上升的趋势,多样性指数表现为先下降后上升的趋势。无病斑针叶内生真菌中,子囊菌门(Ascomycota)与担子菌门(Basidiomycota)相对丰度最高,优势属为Lapidomyces和Selenophoma,病害导致优势菌相对丰度的降低。通过对不同染病情况的P. densiflora针叶内生真菌的测定,明确了枯梢病不同发病程度的P. densiflora针叶内生真菌的多样性及群落结构组成。     

一株油菜菌核病拮抗真菌的鉴定及生物学特性研究

从兰科植物羊耳蒜根部分离并筛选对油菜菌核病菌Sclerotinia sclerotiorum 具有较强拮抗作用的内生真菌,确定其分类地位,并对其体外培养特性进行研究。利用常规PDA培养法进行内生真菌的分离、培养,采用平板对峙法筛选具有较强抑菌活性的菌株并对其进行种类鉴定,同时设定不同碳源、氮源、温度和pH值条件研究该菌株的生物学特性。通过筛选获得1株对油菜菌核病菌具有较强抑制作用的真菌菌株,结合形态学特征和ITS分子序列分析将其鉴定为多节孢属Nodulisporium sp.。该菌株对碳源要求不严格,以麦芽糖、果糖、葡萄糖和蔗糖为碳源均能良好生长。氮源对该菌株生长具有显著影响,最适氮源为牛肉膏。其最适培养温度为25℃,且温度低于10℃或高于30℃时菌丝生长均受到明显抑制。同时该菌株能耐受较广的酸碱度范围,在pH5-9范围内均生长良好。