Plant chemical variation mediates soil bacterial community composition.

An important challenge in the study of ecosystem function is resolving how plant antiherbivore chemical defence expression may influence plant-associated microbes, and nutrient release. We report on a factorial experiment that explores a mechanism underlying this interplay using individuals of the perennial plant Tansy that vary genotypically in the chemical content of their antiherbivore defenses (chemotypes). We assessed to what extent soil and its associated microbial community versus chemotype-specific litter determined the composition of the soil microbial community. Microbial diversity profiles revealed sporadic effects of chemotype litter and soil combinations. Soil source and litter type both explained the microbial communities decomposing the litter with soil source having a more important effect. Some microbial taxa are related to particular chemotypes, and thus intra-specific chemical variation of a single plant chemotype can shape the litter microbial community. But we found that ultimately the effect of fresh litter inputs from a chemotype appeared to act secondary as a filter on the composition of the microbial community, with the primary factor being the existing microbial community in the soil.

Endosymbiotic Bacterial Diversity of Corn Leaf Aphid, Rhopalosiphum maidis Fitch (Hemiptera: Aphididae) Associated with Maize Management Systems.

In this study, different maize fields cultivated under different management systems were sampled to test corn leaf aphid, Rhopalosiphum maidis, populations in terms of total and endosymbiotic bacterial diversity. Corn leaf aphid natural populations were collected from traditionally managed maize fields grown under high agricultural and natural landscape diversity as well as conventionally treated high-input agricultural fields grown in monoculture and with fertilizers use, hence with low natural landscape diversity. Total bacterial community assessment by DNA sequencing was performed using the Illumina MiSeq platform. In total, 365 bacterial genera were identified and 6 endosymbiont taxa. A high abundance of the primary endosymbiont Buchnera and secondary symbionts Serratia and Wolbachia were detected in all maize crops. Their frequency was found to be correlated with the maize management system used, probably with fertilizer input. Three other facultative endosymbionts ("Candidatus Hamiltonella", an uncultured Rickettsiales genus, and Spiroplasma) were also recorded at different frequencies under the two management regimes. Principal components analyses revealed that the relative contribution of the obligate and dominant symbiont Buchnera to the aphid endosymbiotic bacterial community was 72%, whereas for the managed system this was only 16.3%. When facultative symbionts alone were considered, the effect of management system revealed a DNA diversity of 23.3%.

Local Aphid Species Infestation on Invasive Weeds Affects Virus Infection of Nearest Crops Under Different Management Systems - A Preliminary Study.

In the present study, we conducted field surveys to detect the population density of the most important invasive weed species and their associated virus vectoring aphids in crops grown under high input field (HIF) vs. low-input field (LIF) conditions, with and without fertilizers and pesticides. The most frequent invasive weed species were annual fleabane, Erigeron annua (L.), Canadian horseweed, Erigeron canadensis (L.) and Canadian goldenrod, Solidago canadensis (L.). These species were predominantly hosts of the aphids Brachycaudus helichrysi and Aulacorthum solani under both management systems. The 13% higher coverage of E. annua under LIF conditions resulted in a 30% higher B. helichrysi abundance and ∼85% higher A. solani abundance compared with HIF conditions. To reveal the incidence of virus infection in crop plants and invasive weeds, high-throughput sequencing of small RNAs was performed. Bioinformatics analysis combined with independent validation methods revealed the presence of six viruses, but with strikingly different patterns under LIF and HIF conditions. Their presence without symptoms in invasive weeds and crop plants supports the necessity of employing new approaches to those currently employed in invasive weed management. These findings also suggest that invasive weeds could serve as hosts for local aphid species and reservoirs for plant pathogenic viruses, both under low and high input management systems. In this light, as here demonstrated, viruses transmitted by local aphid species were found to differ between the management systems; hence, the importance of B. helichrysi and A. solani as virus vectors in particular clearly needs to be re-evaluated. Altogether, we accept that the present study is a pilot one and individual virus vectoring of aphids still needs to be directly tested. Even so, it represents one of the first contributions to this particular area, and thereby paves the way for further similar applied research in the future.

Effectiveness of the Entomopathogenic Fungal Species Metarhizium anisopliae Strain NCAIM 362 Treatments against Soil Inhabiting Melolontha melolontha Larvae in Sweet Potato (Ipomoea batatas L.).

The effect of fungal entomopathogen M. anisopliae strain NCAIM 362 against M. melolontha larvae in sweet potato was tested under open field conditions when crop management included compost supply and soil cover (agro-foil or agro-textile). Additionally, the effect of M. anisopliae same strain against M. melolontha was compared with the effect of α-cypermethrin under greenhouse conditions. Soil microbial community using Illumina sequencing and soil biological activity were tested as possible parameter influencing M. anisopliae effect. According to the results, compost supply and textile cover may enhance the effectiveness of M. anisopliae under open field conditions, while no effect of fungal treatment was detected under greenhouse conditions. Even if soil parameters (chemical composition, bacterial, and biological activity) were identical, the effect of α-cypermethrin against M. melolontha larvae was significant: lower ratio of larval survival and less damaged tubers were detected after the chemical treatment. Our results suggest that M. anisopliae strain NCAIM 362 is not effective to control M. melolontha larvae, further pieces of research are needed to test other species of the Metarhizium genus to find an effective agent for sustainable pest control in sweet potato.

Arbuscular Mycorrhizal Fungus Rhizophagus irregularis Influences Artemisia annua Plant Parameters and Artemisinin Content under Different Soil Types and Cultivation Methods.

Artemisinin extracted from Artemisia annua has been used efficiently in malaria treatment since 2005. In this study, the variations in plant parameters (plant biomass, glandular trichome density, essential oil total chemical content, artemisinin production, and polyphenol oxidase (PPO) activity) were tested under different soil types (Luvisol, Gleysol, Anthrosol and sterile peat) and cultivation conditions (potted plants in semi-open field, and open field experiments) for plants inoculated with arbuscular mycorrhizal fungus (AMF) Rizophagus irregularis. Under semi-open field conditions, the AMF colonization of A. annua plant roots varied, and presented the highest percentage in Luvisol and sterile peat. The increase in the root colonization rate positively influenced some plant parameters (biomass, glandular trichome density, artemisinin concentration, essential oil quantity and composition), but no effects on PPO enzyme activity were detected. AMF fungus R. irregularis significantly increased the artemisinin content and essential oil yield of plants cultivated in Luvisol, Gleysol, Anthrosol and in peat. These soil types can offer appropriate conditions for A. annua cultivation and artemisinin production even on a smaller scale. Under open field conditions, low (about 5%) AMF colonization was observed. No differences in artemisin contents were detected, but essential oil yield significantly increased compared to control plants. AMF treatment increased beta-farnesene and germacrene D concentrations in Artemisia plants in the open field experiment.

In Vitro and In Vivo Effect of Poplar Bud Extracts on Phytophthora infestans: A New Effective Biological Method in Potato Late Blight Control.

The effect of populin extract from black poplar (Populus nigra) on seven different late blight strains was tested under laboratory and field conditions. The growth rate of hyphae was found to be significantly lower in vitro after 3 and 4 v/v% populin applications. Stain M16 was resistant to populin treatment under lab conditions, however. Both 5% and 10% concentration populin reduced the M16 strain's severity on potato leaves under field conditions and proved to be even more effective than conventionally used fungicides Infinito 687 Sc and Valis M. Higher infection intensity at the 1% level was observed after 24 h using Valis M, and the same trend toward 10% infection remained after 48 and 72 h as well. Low, almost-no-infection intensity was detected after populin 5% and 10% treatment under an open field condition. Altogether, it can be concluded that populin extract can be a low-cost option for growers and an environmentally friendly approach in late blight control.

Current Knowledge of the Entomopathogenic Fungal Species Metarhizium flavoviride Sensu Lato and Its Potential in Sustainable Pest Control.

Fungal entomopathogens are gaining increasing attention as alternatives to chemical control of arthropod pests, and the literature on their use under different conditions and against different species keeps expanding. Our review compiles information regarding the entomopathogenic fungal species Metarhizium flavoviride (Gams and Rozsypal 1956) (Hypocreales: Clavicipitaceae) and gives account of the natural occurrences and target arthropods that can be controlled using M. flavoviride. Taxonomic problems around M. flavoviride species sensu lato are explained. Bioassays, laboratory and field studies examining the effect of fermentation, culture regimes and formulation are compiled along with studies on the effect of the fungus on target and non-target organisms and presenting the effect of management practices on the use of the fungus. Altogether, we provide information to help conducting basic studies, and by pointing out relatively uncharted territories, help to set new research areas.

Intraspecific differences in plant chemotype determine the structure of arthropod food webs.

It is becoming increasingly appreciated that the structure and functioning of ecological food webs are controlled by the nature and level of plant chemicals. It is hypothesized that intraspecific variation in plant chemical resistance, in which individuals of a host-plant population exhibit genetic differences in their chemical contents (called 'plant chemotypes'), may be an important determinant of variation in food web structure and functioning. We evaluated this hypothesis using field assessments and plant chemical assays in the tansy plant Tanacetum vulgare L. (Asteraceae). We examined food webs in which chemotypes of tansy plants are the resource for two specialized aphids, their predators and mutualistic ants. The density of the ant-tended aphid Metopeurum fuscoviride was significantly higher on particular chemotypes (borneol) than others. Clear chemotype preferences between predators were also detected. Aphid specialist seven-spotted ladybird beetles (Coccinella septempunctata) were more often found on camphor plants, while significantly higher numbers of the polyphagous nursery web spider (Pisaura mirabilis) were observed on borneol plants. The analysis of plant chemotype effects on the arthropod community clearly demonstrates a range of possible outcomes between plant-aphid-predator networks. The findings help to offer a deeper insight into how one important factor--plant chemical content--influences which species coexist within a food web on a particular host plant and the nature of their trophic linkages.

Correlations between colonization of onion thrips and leaf reflectance measures across six cabbage varieties.

The main purpose of this study was to reveal if the UV-A, and visible light reflection of leaves of white cabbage varieties is correlated to resistance against onion thrips. The antixenotic resistance (AR) against onion thrips and thrips damage differed between varieties Balashi, Bloktor, Riana - considered resistant - and Green Gem, Hurricane, Quisor - considered susceptible. The solar UV-A (340-400 nm) and visible (401-650 nm) light reflection of white cabbage leaves were recorded. Correlation between AR against onion thrips and reflection of leaves in UV-A and visible range of the studied white cabbage varieties were computed. According to the AR evaluation onion thrips density was always higher on susceptible than on resistant varieties. The UV-A light reflection of head forming leaves and the contrast between head and exterior leaves (H/E) was negatively correlated with onion thrips host preference at an early stage of cabbage head formation. The visible light reflection of both head forming and exterior leaves was also negatively correlated with onion thrips host preference. Susceptible varieties had greater damage ratings at harvest than resistant ones and positive correlations were observed between AR and damage. AR against onion thrips may be affected by differences in reflection of cabbage leaves at an early growth stage. It is suggested that more intensive reflection of leaves and/or higher contrast values between the reflectance intensity of head versus outer leaves made the resistant varieties less attractive to onion thrips. Our results reported here provide the first evidence of negative correlation between UV-A and visible reflection of leaves and AR of white cabbage against a dangerous insect pest, opening new perspectives for understanding the role of reflection by plant leaves in pest management.