Trophic cascades initiated by fungal plant endosymbionts impair reproductive performance of parasitoids in the second generation

Variation in plant quality can transmit up the food chain and may affect herbivores and their antagonists in the same direction. Fungal endosymbionts of grasses change the resource quality by producing toxins. We used an aphid-parasitoid model system to explore how endophyte effects cascade up the food chain and influence individual parasitoid performance. We show that the presence of an endophyte in the grass Lolium perenne has a much stronger negative impact on the performance of the parasitoid Aphidius ervi than on its aphid host Metopolophium festucae. Although the presence of endophytes did not influence the parasitism rate of endophyte-naïve parasitoids or their offspring’s survival to adulthood, most parasitoids developing within aphids from endophyte-infected plants did not reproduce at all. This indicates a delayed but very strong effect of endophytes on parasitoid performance, which should ultimately affect plant performance negatively by releasing endophyte-tolerant herbivores from top-down limitations.     

Expectations for habitat-adapted symbiosis in a winter annual grass

The habitat-adapted symbiosis hypothesis predicts that the most positive effects of symbiosis are expected in the most stressful sites for a plant host. Stress varies with site characteristics but also during the life cycle of a plant, with winter annuals experiencing the most stress after fall emergence. For Bromus tectorum, fecundity can vary tremendously from a few to thousands of seeds per plant. We used endophytic Sordaria fimicola to test the hypothesis in three sites in western Montana. We hypothesized that the effects of S. fimicola inoculation would be most positive in the most stressful site after fall application. As predicted, the most positive effects on growth and fecundity were observed in the most stressful site after fall application of S. fimicola. However, the effects of treatments varied within and between sites considerably, and are best understood as an example of context-dependency in plant-microbe interactions rather than habitat-adapted symbiosis.     

Influence of inoculation on yield ofAlnus glutinosa in the Netherlands

Summary The occurrence and the infectivity of Frankia, the root-nodule endophyte ofAlnus glutinosa, were studied in different kinds of soil in the Netherlands. Both field and pot experiments indicated that many soils, on which alders have not been grown before, had low numbers of endogenous Frankia or none at all. Inoculation of these soils usually enhanced growth and nodulation of alders.The effect of fertilizer treatments on growth and nodulation ofA. glutinosa were studied in experimental plots. Alders grown in sandy soils, dressed with farmyard manure had the highest yield and the most nodules. The influence of inoculation with homogenates of Sp(+) and Sp(–) nodules and with a pure culture of Frankia AvcIl were studied in pot experiments. The quantity of different kinds of inoculum needed to obtain good growth and nodulation of alder was estimated. The results indicated that addition of a nodule homogenate of 90 g fresh AvcIl Sp(+) nodules is sufficient to inoculate one hectare of nursery soil to produce 10 nodules per plant, while a thousand times larger amount of inoculum is necessary when Sp(–) nodules are used. The limitations and the potentials of using nodule homogenates and pure cultures of Frankia for inoculation in forestry are discussed.     

Non-pathogenic Fusarium oxysporum endophytes provide field control of nematodes,improving yield of banana (Musa sp.)

Endophytic colonization by the fungus Fusarium oxysporum can result in increased host resistance to pests and diseases, and greater biomass production. However, few studies have assessed the field performance of this fungus for biological control of pests and diseases in banana. Further to greenhouse assessment, studies were carried out to evaluate the performance of F. oxysporum strains against plant-parasitic nematodes on banana (Musa sp., cv. Giant Cavendish and cv. Grand Nain) in the field using tissue-cultured plants. Plants were inoculated separately with one of three strains (V5W2, Eny 7.11o and Emb 2.4o) before being inoculated with Pratylenchus goodeyi and Helicotylenchus multicinctus in an on-station trial and in an on-farm trial planted in a field naturally infested with the same nematodes. All three endophytic strains significantly suppressed P. goodeyi and H. multicinctus densities and damage in the field. On-station, nematode population densities were reduced by >45% in endophyte-inoculated plants compared to non-inoculated plants, while percentage root necrosis was reduced by >20%. Similarly, on-farm, nematode damage to roots and densities were also significantly lower in endophyte-inoculated plants compared with control plants. Significantly improved yields were observed for plants inoculated with endophytes when compared to the control plants, with inoculation with strains Emb 2.4o and V5W2 resulting in up to 35% and 36% increased banana yields, respectively, for the on-station trial. For the on-farm trial, up to 20% increase in yields were observed for strain Eny 7.11o compared to control plants. This study provides the first report from the field in Africa on the reduction of nematode populations and damage, and the increase in banana production by fungal endophytes. The study shows that endophytes have potential to enhance yields of tissue-cultured banana plants and protect them against pests.     

DTPA soil extractable and plant heavy metal concentrations with soil-added Cd treatments

Summary The numbers, weights, and ages of root nodules were determined in a homogeneous 6- to 7-year-old stand ofHippophaë rhamnoides in a coastal sand-dune area. Large variations in the number of nodules, which ranges from 30 to 281 per m² were found. Most of the nodules occurred between 10 and 60 cm below the soil surface. In the surface layer and lower than 60 cm only small numbers of nodules were present. It is concluded that relatively large samples have to be investigated to obtain an impression of the nodulation of a given stand and to permit a comparison of the contribution of dinitrogen fixation in different stands.Close correlation was found between nodule numbers and the age of the roots, young roots having the highest numbers. However, the wide variation in the number of nodules per square metre could not be explained solely by the age distribution of the roots. The possible role of some other factors is discussed. No relationship was found between the nodule weight and the age of the nodule. The mean dry weight of living nodule material was 5.3 g per m². Most nodules reached an age of up to 3 years. The significance of nodule decay for the distribution of the endophyte in the soil and in the process of nodule formation is discussed.     

Intraspecific variation in Burkholderia caledonica: Europe vs. Africa and soil vs. endophytic isolates

The best-known interaction between bacteria and plants is the Rhizobium-legume symbiosis, but other bacteria–plant interactions exist, such as between Burkholderia and Rubiaceae (coffee family). A number of bacterial endophytes in Rubiaceae are closely related to the soil bacterium Burkholderia caledonica. This intriguing observation is explored by investigating isolates from different geographic regions (Western Europe vs. sub-Saharan Africa) and from different niches (free-living bacteria in soil vs. endophytic bacteria in host plants). The multilocus sequence analysis shows five clades, of which clade 1 with two basal isolates deviates from the rest and is therefore not considered further. All other isolates belong to the species B. caledonica, but two genetically different groups are identified. Group A holds only European isolates and group B holds isolates from Africa, with the exception of one European isolate. Although the European and African isolates are considered one species, some degree of genetic differentiation is evident. Endophytic isolates of B. caledonica are found in certain members of African Rubiaceae, but only in group B. Within this group, the endophytes cannot be distinguished from the soil isolates, which indicates a possible exchange of bacteria between soil and host plant.     

Distribution of phyllosphere fungi within the canopy of giant dogwood

Distribution of phyllosphere fungi within the canopy of giant dogwood (Swida controversa) was examined. Canopies of two dogwood trees (about 8m height) were divided into five parts in relation to the order of shoots within the current-year shoot, the height of leaf layers, and the distance from the main trunk, and leaves were collected from the five positions. A total of 13 and 33 species were isolated from the interior and surface of leaves by surface sterilization and washing methods, respectively. Species composition of fungi was different markedly between interior and surface of an individual leaf, whereas it was similar among five canopy positions in the interior or on the surface. Of 13 frequent species regarded as phyllosphere fungi, 6 species showed no difference in frequencies among five positions within the canopy. The other 7 species showed significant preference within the current-year shoot, between the leaf layer, and/or at the distance from the trunk. The probable effect of leaf properties was detected on 2 of the 7 species, while the frequencies of the other 5 species were not related to the leaf properties but were affected by the order of shoots (leaf age), the height of leaf layer, and/or the distance from the trunk (sunlight intensity).     

白木香内生真菌枝顶孢属两菌株的挥发油成分

采用溶剂萃取法提取白木香内生真菌R1(Acremonium sp.)和R2(Acremonium sp.)的挥发油, 经GC-MS联用技术进行分析, 从R1和R2的挥发油中分别鉴定出20个和16个成分, 均以油酸、亚油酸、棕榈酸等脂肪酸为主要成分, 并且均含有1,8-桉叶油素、姜烯、芳姜黄烯等萜类成分。本研究首次报道白木香内生真菌的挥发油成分。     

植物环肽及其可能的生物合成途径

植物环肽是一个庞大的小分子天然产物家族,通常由4—10个氨基酸残基组合而成。该类化合物广泛存在于全球多种植物的根、茎、枝、叶及种子中,中草药中也时有发现。由于对其生物合成途径及机理研究较少,环肽分子的利用价值尚未得到有效的开发。和常见的非环状基因编码的多肽或蛋白质相比,环肽结构更为复杂。本文将对植物环肽的生物合成途径及其机理做初步探讨。     

Muscodor albus and its biological promise

We have found a novel fungal genus that produces extremely bioactive volatile organic compounds (VOCs). This fungal isolate was initially discovered as an endophyte in Cinnamomum zeylanicum in a botanical garden in Honduras. This endophytic fungus, Muscodor albus, produces a mixture of VOCs that are lethal to a wide variety of plant and human pathogenic fungi and bacteria. It is also effective against nematodes and certain insects. The mixture of VOCs has been analyzed using GC/MS and consists primarily of various alcohols, acids, esters, ketones, and lipids. Final verification of the identity of the VOCs was carried out by using artificial mixtures of the putatively identified compounds and showing that the artificial mixture possessed the identical retention times and mass spectral qualities as those of the fungal derived substances. Artificial mixtures of the VOCs nicely mimicked the biological effects of the fungal VOCs when tested against a wide range of fungal and bacterial pathogens. Potential applications for “mycofumigation” by M. albus are currently being investigated and include uses for treating various plant parts, and human wastes. Another promising option includes its use to replace methyl bromide fumigation as a means to control soil-borne plant diseases.