http://www.sanger.ac.uk/Projects/S_scabies, http://www.potatodiseases.org/scab.html, http://www.uri.edu/ce/factsheets/sheets/potatoscab.html.

Summary• Root carbon (C) partitioning in two host plant species colonized by one of three arbuscular mycorrhizal (AM) fungal species was investigated.• Split-root systems of barley ( Hordeum vulgare ) and sugar maple ( Acer saccharum ) were inoculated on one side with one of three AM fungi. Leaves were labelled with 14 CO 2 3 wk after inoculation. Plants were harvested 24 h later and the root systems from the mycorrhizal (M) and nonmycorrhizal (NM) sides were analysed separately for 14 C.• Partitioning of 14 C between M and NM sides varied depending on the fungal and host plant species used. Gigaspora rosea showed a strong C-sink capacity with both plant species, Glomus intraradices showed a strong C-sink capacity with barley, and Glomus mosseae did not affect 14 C partitioning. The C-sink strength of the M barley roots inoculated with G. rosea or G. intraradices was linearly correlated with the degree of colonization.• The use of three AM fungal and two plant species allowed us to conclude that C-sink strength of AM fungi depends on both partners involved in the symbiosis.

We investigated in the field the carbon (C) transfer between sugar maple (Acer saccharum) saplings and the spring ephemeral Erythronium americanum via the mycelium of arbuscular mycorrhizal (AM) fungi. Sugar maple saplings and E. americanum plants were planted together in pots placed in the ground of a maple forest in 1999. Ectomycorrhizal yellow birches (Betula alleghaniensis) were added as control plants. In spring 2000, during leaf expansion of sugar maple saplings, the leaves of E. americanum were labelled with CO. Seven days after labelling, radioactivity was detected in leaves, stem and roots of sugar maples. Specific radioactivity in sugar maples was 13-fold higher than in yellow birches revealing the occurrence of a direct transfer of C between the AM plants. The quantity ofC transferred to sugar maple saplings was negatively correlated with the percentage of C allocated to the storage organ of E. americanum. A second labelling was performed in autumn 2000 on sugar maple leaves during annual growth of E. americanum roots. Radioactivity was detected in 7 of 22 E. americanum root systems and absent in yellow birches. These results suggest that AM fungi connecting different understorey species can act as reciprocal C transfer bridges between plant species in relation with the phenology of the plants involved.

The capacity of the spring ephemeral Erythronium americanum L. to grow and absorb nutrient either as nonmycorrhizal (NM) or mycorrhizal (M) plants under the low temperature regime characteristic of its growth period was investigated. Specimens of E. americanum were collected in the field as either NM (early September) or as M plants (late October). Both groups of plants were submitted to different nutrient regimes during the hypogeous growth period at 5 °C, and during the subsequent epigeous growth period conducted at temperature regimes of either 12 °C day : 10 °C night or 17 °C day : 15 °C night. Nutrient regime influenced bulb nutrient content only during the epigeous growth period. The presence of mycorrhizas did not influence nutrient content, but favoured a greater bulb biomass at the final harvest (epigeous growth period), as did the lower temperature regime. Net nutrient uptake was not reduced at lower temperatures and appeared to follow plant demand. These findings confirm that E. americanum is adapted to perform better under a low temperature regime and that mineral nutrition in this species occurs mainly in spring in response to active growth. Arbuscular mycorrhizal fungi benefit E. americanum maybe through less expensive nutrient uptake or sustained carbon sink demand.

A method for quantification of recombinant DNA for Roundup Ready (RR) corn and RR soybean in soil samples is described. Soil DNA from experimental field samples was extracted using a soil DNA extraction kit with a modified protocol. For the detection and quantification of recombinant DNA of RR corn and RR soybean, a molecular beacon and two pairs of specific primers were designed to differentially target recombinant DNA in these two genetically modified crops. Soil DNA extracts were spiked with RR corn or RR soybean DNA, and recombinant DNA was quantified using real-time PCR with a molecular beacon. As few as one copy of RR corn genome or one copy of RR soybean genome was detected in the soil DNA extract.