Genetics of Resistance in Vicia sativa L. to Orobanche crenata Forsk.

The genetics of resistance of common vetch (Vicia sativa L.) to broomrape (Orobanche crenata Forsk.) was studied for two years by using the P₁, P₂, F₁, BC¹, BC₂, F₂ F₃, and F₄ generations obtained from crosses between resistant and susceptible lines. Resistant lines were selected by screening a world collection m a naturally infested plot. Resistance was tested both under field and greenhouse conditions. The best index to measure resistance was the number of emerged broomrapes per host plant. The results fit the additive-dominance model. The main component of the variation was additivity; dominance and interaction effects seemed to depend on the environment. When dominance is expressed, a low number is dominant over a high number of broomrapes per host plant.     

Chloroplast DNA variation in cultivated and wild Prunus avium L: a comparative study

Chloroplast DNA variation in 96 Prunus avium L. cultivars was assessed and compared with the results of a previous study of cpDNA diversity in 23 wild populations of the species. The polymerase chain reaction‐restriction fragment length polymorphism method was used in these studies. Approximately 9% of the chloroplast genome was analyzed, using five universal primer pairs and three restriction enzymes. Ten polymorphic fragments were common to both the wild and sweet cherry; eight polymorphic fragments were found only in the wild cherry. In the cultivars, all mutations were small (5‐30 bp) indels. In the wild populations, a point mutation was also detected in addition to indels. The mutational combinations revealed three haplotypes in the cultivars, which are the main haplotypes in the wild cherry populations. Chloroplast DNA diversity in wild cherry is higher (16 haplotypes) than in sweet cherry cultivars (three haplotypes). The probable wild origin of the sweet cherry cultivars in the maternal line, on the basis of haplotypic similarity, was discussed.     

Characterization of host tolerance to Striga hermonthica

Summary One of the most promising control options against the parasitic weed Striga hermonthica is the use of crop varieties that combine resistance with high levels of tolerance. The aim of this study was to clarify the relation between Striga infestation level, Striga infection level and relative yield loss of sorghum and to use this insight for exploring the options for a proper screening procedure for tolerance. In three pot experiments, conducted in Mali (2003) and The Netherlands (2003, 2004), four sorghum genotypes were exposed to a range of Striga infestation levels, ranging from 0.0625 to 16 seeds cm⁻³. Observations included regular Striga emergence counts and sorghum grain yield at maturity. There were significant genotype, infestation and genotype × infestation effects on sorghum yield. The relation between infestation level and infection level was density dependent. Furthermore, the relation between Striga infection level and relative yield loss was non-linear, though for the most resistant genotype Framida only the linear part of the relation was obtained, as even at high infestation levels only moderate infection levels were achieved. The results suggest that for resistant genotypes, tolerance can best be quantified as a reduced relative yield loss per aboveground Striga plant, whereas for less resistant genotypes the maximum relative yield loss can best be used. Whether both expressions of tolerance are interrelated could not be resolved. Complications of screening for tolerance under field conditions are discussed.     

Effect of simulated acid rain on mycorrhizal infection of Pinus strobus L.

Mycorrhizal infection but not growth of white pine seedlings was reduced by application of simulated rain at pH 3.5 at 3 times ambient rates to plants grown in steamed Mardin soil inoculated with Pisolithus tinctorius. In unsteamed Mardin soil, the simulated acid rain at 3 times ambient rates had no effect on mycorrhizal infection or growth of pine seedlings if the rain was applied to the plants and soil or to only the soil before planting, except that nitrate-containing acid rain increased growth, infection and N content. In limed Mardin soil, the simulated acid rain reduced mycorrhizal infection if applied to the plants and soil as the seedlings were growing but not if applied to the soil before planting. Application of pH 3.5 rain at ambient rates had no detectable influence on mycorrhizal infection in 6 of 9 soils tested, but it stimulated infestion in 3 soils if the simulated rain contained only sulfate and in 1 soil if it had both sulfate and nitrate.     

Ectomycorrhizal fungi identification in single and pooled root samples: terminal restriction fragment length polymorphism (TRFLP) and morphotyping compared

We describe here the results of a study conducted to evaluate a terminal restriction fragment length polymorphism (TRFLP) approach targeting rRNA genes for determination of ectomycorrhizal (ECM) communities colonizing the roots of loblolly pine (Pinus taeda L.). Root tips separated from soil cores were classified according to morphological characteristics and DNA was then extracted from each group of morphotyped tips. Labeled primers were used to generate terminal restriction fragments (TRF) for molecular fingerprinting of root colonizing fungi and to determine how well TRFLP could be used to discriminate between ectomycorrhizal types. Morphotypes generally correlated well with specific TRFs and sequence analysis confirmed that TRFs could be used to discriminate among fungal types. Sequence analysis indicated that important ECM fungi including Russulaceae, Thelephorales, and Tricholomataceae could be fingerprinted with TRFLP. In addition, a fixed proportion of the DNA extracted from each morphotype from the same core was used in a pooling experiment used to assess whether previously identified fungal species types could be distinguished from one another within reconstructed communities. Since some morphotypes share TRFs, dual analysis of ITS1 and ITS2 was necessary for accurate fingerprinting of fungal types. Approximately, 5.0±0.3 phylotypes were detected per core with TRFLP-corrected morphotyping as compared to 4.0±0.4 phylotypes using TRFLP on pooled community samples. TRFLP made on experimental sporocarp communities suggested that reduced ECM richness with TRFLP may be partly caused by differences in the amount of DNA available for PCR and primer bias. Nonetheless, TRFLP on pooled morphotypes accounted for more than 93% of colonized root tips. The method can be used to facilitate analysis of mycorrhizal communities using root tips collected from soil cores.     

El Niño induced local extinction of coral reef bryozoan species from Northern Bahia, Brazil

The 1997-1998 El-Niño Southern Oscillation was the most severe on record and dramatically impacted corals worldwide. However, the effect of this event on the associated community of reef organisms has received much less attention. The composition of the bryozoan assemblage from the coral reefs of Northern Bahia, Brazil were monitored annually from 1995 to 2000, allowing the investigation of the effects of this large-scale stressor on an important, diverse, yet understudied component of the coral reef system. Bryozoan samples (35 replicates/reef) were collected during April/May from four shallow bank reefs (10-40 m depth) located a few kilometres off the coast, together with measurements of the associated environmental parameters. Currently 157 species have been recorded from the study area, but significant reductions in density and diversity were apparent between pre- and post El-Niño Southern Oscillation (ENSO) years, multivariate analysis denoting significant changes in assemblage composition. A total of 61 species were unrecorded following the 1997-1998 ENSO event (22 species from 1997; 25 further species from 1998 and 14 more from 1999). These included several species endemic to Brazil, suggesting that the 1997-1998 ENSO has had a marked influence on the reef bryozoan community, resulting in the local extinction of several species. Bryozoan mortalities were probably initiated by elevated temperatures, but continued disappearance of species for 2 years after ENSO suggests other indirect factors are also influential. These results demonstrate that ENSO events can have severe long-term impacts on the biodiversity of coral reefs, with important conservation consequences.     

Irrigation of Landfill Leachates in Energy Forests — A Technique to Recover Nutrients from Municipal Solid Wastes

From an ecological point of view it is important to close nutrient cycles by recirculating mineral nutrients from the urban society back to agriculture and forestry, and thereby obtaining a sustainable resource utilisation. A part of this cycle is illustrated by irrigation of bioreactor landfill leachates on short rotation forests. This paper presents a budget for nutrients and heavy metals, beginning with the leachates and ending with the harvested tree fraction. The hypotheses were: The applied minerals deliver nutrients to the trees. The nutrient content in the accumulating biomass corresponds to the amount of mineral nutrients applied. The concentrations of heavy metals in the trees will remain low. The uptake of elements in birch was for P 35%, Ca 1. 2%, Cd 64%, Cu 10%, Mn 19%, Ni 0. 11%, and for Zn 26% of the supplied amounts. It was concluded that nutrients, with some exceptions, are supplied in sufficient amounts from the irrigated leachates to achieve optimal biomass growth, that the amounts of ions immobilised by the plants were significantly lower compared to the applied amounts, and that the concentrations of heavy metals are not increasing in the trees after irrigation. The overall conclusion is that a leachate irrigation system is efficient if the available vegetated land area is large enough for effective nutrient uptake, but the nutrient ratio may need to be balanced to meet the needs of the plants.     

Diversity of laccase genes from basidiomycetes in a forest soil

Fungal oxidative exo-enzymes lacking substrate specificity play a central role in the cycling of soil organic matter. Due to their broad ecological impact and available knowledge of their gene structure, laccases appeared to be appropriate markers to monitor fungi with this kind of oxidative potential in soils. A degenerate PCR-primer pair Cu1F/Cu2R, specific for basidiomycetes, was designed to assess directly the diversity of laccase genes in soils. PCR amplification of mycelial cultures and fruit-bodies of a wide spectrum of basidiomycetes, covering all functional groups (saprophytes, symbionts, and pathogens), produced multiple DNA fragments around 200 bp. A neighbor-joining tree analysis of the PCR-amplified laccase sequences showed a clear species-specificity, but also revealed that most fungal taxa possess several laccase genes showing a large sequence divergence. This sequence diversity precluded the systematic attribution of amplified laccase of unknown origin to specific taxa. Amplification of laccase sequences from DNA, extracted from a brown (moder) forest soil, showed a specific distribution of laccase genes and of the corresponding fungal species in the various soil horizons (O_h, A_h, B_v). The most organic O_h-horizon displayed the highest gene diversity. Saprophytic fungi appeared to be less widespread through the soil horizons and displayed a higher diversity of laccase genes than the mycorrhizal ones.