F.F. del Campo

Effects of the microcystin profile of a cyanobacterial bloom on growth and toxin accumulation in common carp Cyprinus carpio larvae

A 12 day growth trial was conducted to compare the effect of the variation in microcystins (MC) composition of two bloom samples of Microcystis aeruginosa on the growth performance and microcystin accumulation in common carp Cyprinus carpio larvae. Two M. aeruginosa natural bloom samples with different MC profiles were collected and larvae were exposed to cyanobacterial cells through their diet. Three diets, a basal control diet and two diets prepared from the basal diet plus the same toxins content (60 ng MC g(-1) diet) of each cyanobacterial bloom, were given at the same ration level to three groups of larvae during the experimental period. Larval mass and standard length from day 9 were significantly different between cyanobacterial treatments and in both cases lower than that of the control. The MC accumulation by larvae, inversely correlated with the growth performance, was also significantly different between cyanobacterial treatments (26.96 v. 17.32 ng g(-1) at the end of the experimental period). These results indicate that MC variants profile may have effects on the toxin uptake and toxicity. To date, this is the first laboratory study to show that fish accumulate MC depending on the toxin profile of the cyanobacterial bloom.

Plant Responses to Parasitic Nematodes: Interaction between Tomato and Root-Knot Nematodes

Meloidogyne genus includes several species of polyphagous sedentary endoparasitic nematodes that infect roots of many plants of agronomical interest. Tomato (Lycopersicon esculentum) is one of the most important targets for root knot nematodes in Spain. Nematode managing practices involve the combined use of nematicides, rotation with non host crops, and resistant tomato cultivars. Nematicides are being abandoned because their non selective biocidal properties pose environmental hazards, and crop rotation is not always desirable. Resistance of tomato to Meloidogyne can be conferred by the Mi gene, which elicits a hypersensitive response by an unknown mechanism. Unfortunately, many Meloidogyne populations overcome this resistance, what probably means that the Mi gene and Meloidogyne avirulence genes have allele-specific interactions. Since most comercial “nematode resistant” tomato hybrids have been selected in breeding programs by their resistance to local or prototype Meloidogyne populations, they behave as susceptible when grown in a different area with new nematode populations. Most stages of the nematode life cycle occur in the host. After egg hatching, the infective juvenile moves in the soil until it reaches a root of a host plant. Once there, it penetrates the root at the elongation zone immediately behind the apical meristem. The nematode migrates intercellularly towards the vascular bundle, where it perforates the wall of a selected cell. This cell is transformed in a multinucleate giant cell that provides food for the biotrophic parasite. The larvae grows and developes, producing a visible swallowing or knot in the root. Reproduction occurs through partenogenetic females, which produce masses of ca. 100–500 eggs each. Pressure from the mature female disrupts the root tissues, and the egg mass is exposed to the soil.