Experimental design strategy for the Weibull dose response model.

The objective of this research was to determine optimum design point allocation for estimation of relative yield losses from ozone pollution when the true and fitted yield-ozone dose response relationship follows the Weibull. The optimum design is dependent on the values of the Weibull model parameters. A transformation was developed which allowed the optimum design (by the determinant criterion) for one parametric situation to be translated to any other, and permitted the search for optimum designs to be restricted to one set of Weibull parameters. Optimum designs were determined for the case where the Weibull parameters are assumed known, and effects of deviating from the optimum designs were investigated. Several alternative design strategies were considered for protecting against incorrectly guessing the Weibull model parameters when their true values are not known.

Application of biplot methods to the multivariate analysis of toxicological and pharmacokinetic data.

The biplot technique was applied to aminoglycoside renal toxicological and pharmacokinetic data in beagles. The biplot obtains a two-dimensional approximation to a matrix and plots row effects and column effects jointly, depicting relationships among different observed variables and simultaneously showing the relationship of experimental units as individuals and as treatment groups to those variables. This graphical representation of the matrix allows inspection of relationships, trends, clusters, approximate correlations, and variances existing in the data. Biplots were generated from gentamicin dosage regimen nephrotoxicity data. Six dogs classified as being intoxicated by established indicators of renal toxicity were a distinct cluster. A cluster of nonintoxicated dogs was separated into two groups approximating nephrectomized and normal dogs, thus revealing variables significant in separating toxic and nontoxic as well as nephrectomized and normal dogs. Biplots from pharmacokinetic data were able to separate different renal disease states on the basis of disease-induced changes in gentamicin pharmacokinetic parameters. In conclusion, the biplot technique proved to be a very useful tool in exploring this type of data by revealing clear relationships between nephrotoxicity and physiological and pharmacokinetic variables and by separating different disease states based on these data.

Effects of ferulic acid and some of its microbial metabolic products on radicle growth of cucumber.

An initial survey of the effects of aqueous solutions of ferulic acid and three of its microbial metabolic products at pH 4.5, 6.0, and 7.5 was determined on radicle growth of 11 crop species in Petri dishes. These bioassays indicated that cucumber, ladino clover, lettuce, mung bean, and wheat were inhibited by ferulic, caffeic, protocatechuic, and/or vanillic acids and that the magnitude of inhibition varied with concentration (0-2 mM), phenolic acid, and pH of the initial solution. The pH values of the initial solutions changed considerably when added to the Petri dishes containing filter paper and seeds. The final pH values after 48 hr were 6.6, 6.8, and 7.1, respectively, for the initial 4.5, 6.0, and 7.5 pH solutions. The amounts of the phenolic acids in the Petri dishes declined rapidly over the 48 hr of the bioassay, and the rate of phenolic acid decline was species specific. Cucumber was subsequently chosen as the bioassay species for further study. MES buffer was used to stabilize the pH of the phenolic acid solutions which ranged between 5.5 and 5.8 for all subsequent studies. Inhibition of radicle growth declined in a curvilinear manner over the 0-2 mM concentration range. At 0.125 and 0.25 mM concentrations of ferulic acid, radicle growth of cucumber was inhibited 7 and 14%, respectively. A variety of microbial metabolic products of ferulic acid was identified in the Petri dishes and tested for toxicity. Only vanillic acid was as inhibitory as ferulic acid. The remaining phenolic acids were less inhibitory to noninhibitory. When mixtures of phenolic acids were tested, individual components were antagonistic to each other in the inhibition of cucumber radicle growth. Depending on the initial total concentration of the mixture, effects ranged from 5 to 35% lower than the sum of the inhibition of each phenolic acid tested separately. Implications of these findings to germination bioassays are discussed.

Use of genetic effects and genotype by environmental interactions for the classification of mexican races of maize.

To examine the questions of whether the additive and dominance effects present for morphological characters in racial crosses are of sufficient consistency and magnitude to allow such genetic effects to be used for racial classification, we used a diallel experiment among the 25 well-defined Mexican races of maize, which include the ancestral stocks of most commercial and genetic maize types. With such an experiment, genetic effects and genotype by environmental interactions for one or more characters can be used to measure genetic and adaptational or environmental similarity. We used average parental effects (general combining abilities), specific effects, and genotype by environmental effects of 21 characters from the diallel (grown at three locations) to group the Mexican races of maize. The groupings based upon average genetic effects and upon genotype by environmental interactions are more satisfactory than groupings based upon specific effects. The standard errors for genetic distances based upon specific (largely dominance) effects seem to be too high for practical use. Principal components analyses of the same data suggest a similar conclusion.-The groupings based upon average genetic effects are in general agreement with previous studies, with the exception of Maíz Dulce, which is grouped with the Cónicos, rather than being isolated from the other Mexican races of maize.