Is the frequency of apomeiosis in the Rhodophyta a genetic character?
The small rhodophyte Antithamnionella sarniensis Lyle (Ceramiaceae), a very common species on the Atlantic coast of France, has a normal Polysiphonia-like life cycle (Sundene, 1964), but some tetraspores can give new tetrasporophytes directly (L'Hardy-Halos, 1985). This phenomenon has now been studied in detail (Magne, 1986). Twenty strains were prepared starting from sterile plants collected in various places along three hundred kilometers of shoreline. The strains were kept in stock cultures at a low temperature (14 C) with dim natural light and were propagated only by cutting. Exceptionally, one of these strains originated from an apomeiotic tetraspore, and another one is the original strain of von Stosch (1969), who kindly provided it. All the strains proved to be tetrasporophytic, in accordance with the dominance of tetrasporophytes in the field. The progenies of the different strains have been investigated. For each, material from the stock culture was cultivated in monitored conditions (20°C with cool white light of 20 tE.-m-2.s 1, 12 h.d ') to produce tetraspores. Plantlets issuing from the spore-sets were picked randomly, individually transferred in small glass jars and cultivated until reproductive organs were formed; one hundred plantlets were used of each strain. In numerous strains, the progeny is a mixture of gametophytes and tetrasporophytes; the proportions of tetrasporophytes differ from one strain to another over a range from 0% to 100% and show many intermediate values (Magne, 1986). It can be sup-
POSSIBILITE D'UNE CULTURE INDUSTRIELLE DE L'ALGUE ROUGE EUCHEUMA SPINOSUM DANS LE GOLFE DE TADJOURAH 'l'
L'algue rouge Eucheuma spinosum (fig. 1) contient en forte proportion un produit de tres haute qualite et relativement rare : le iota carraghenane. Ce compose est isole par les usines d'extraction et utilise, une fois purifie, dans de nombreuses branches industrielles, notamment dans l'industrie alimentaire pour la constitution de la plupart des flans, laits gelifies, glaces, pâtisseries, etc ...
Spatial distribution of root lesion nematodes (Pratylenchus spp.) in a long-term no-till cropping system and their relationship with soil and landscape properties
The Cook Agronomy Farm of Washington State University is a long-term precision agriculture study site. Since 2000, the farm has been in various three-year no-till rotations with winter wheat, spring wheat, and various rotation crops such as barley, canola, peas, lentils, and chickpea. The spatial distribution of root lesion nematodes (Pratylenchus spp.) and their relationships with soil and terrain variables were studied by collecting soil samples at 127 and 124 geo-referenced points in two 12-ha fields during the spring of 2010 and 2011, respectively. Pratylenchus spp. were detected in more than 85% of the sampled locations in both fields. Nematode densities spatially mapped using ArcGIS software occurred in an aggregated pattern. Previous rotation crops had no effect on the spatial distribution. Classification and regression tree analysis (CART) using soil and terrain variables, and nematode density, explained 61 and 34% of the variability associated with nematode density in 2010 and 2011, respectively. Soil edaphic factors, such as organic matter, were stronger predictors of nematode populations than rotation effects.