Mature seed samples from 35 populations ofEchinochloawere collected in fields of the Eastern Iberian Peninsula and evaluated for nine morphologic traits. Four kernels per population were separately assayed for four isozyme systems. Genetic variability components were studied by correspondence analysis and chi-square distance using the isozyme pattern as variables. Genetic uniformity was found within populations as would be expected from their autogamous mating system. Intraspecific isozyme variability covered a wide spectrum, from none inE. colonumto very high inE. oryzoides. All the populations ofE. colonumclustered together based on morphometric and isozymatic characters, and also those ofE. oryzicola, but were distinct from the populations of all other species. Populations ofE. crus-galli, E. hispidula, andE. oryzoidesclustered within species based on morphology, but did not cluster based on isozymatic characters, being mixed in the isozymatic dendrogram. Our results support the hypothesis thatE. hispidulaandE. oryzoidesare infraspecific taxa ofE. crus-galli. The large between-population genetic variability may explain the differential response to herbicides within a given species and indicate that weed specialists should study the differences in response to a wide spectrum ofEchinochloapopulations to several herbicides instead of testing many plants from a small number of populations.
Disappearence of pesticides from field soils results from interactions between various processes such as chemical decomposition, microbiological degradation, volatilization, runoff, leaching, photodecomposition and uptake by plants *Present address: I.V.I.A. Generalitat Valenciana,
Summary:
Soil samples taken in summer 1989 and winter 1990 at different depths from three citrus orchards of the Valencia region (Spain) with a long history of residual herbicide treatments were analysed with bioassays and chromatographic procedures. The herbicides involved were atrazine, bromacil, diuron, simazine, terbuthylazine, terbumetone, terbutryn and trifluralin. Water samples from wells in the orchards were also analysed. The concentrations of the herbicides were very low, often below the limit of determination, and were always highest in the upper layers of soil. After a very unusual period of heavy rain, small quantities of some chemicals were found in the well water. The conclusion was that in these orchards the herbicides applied at currently used rates are unlikely to accumulate in any layers of the soil.
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