The arcsine and square root transformations were tested on 82 weed control data sets and 62 winter wheat winter survival data sets to determine effects on normality of the error terms, homogeneity of variance, and additivity of the model. Transformations appeared to correct deficiencies in these three parameters in the majority of data sets, but had adverse effects in certain other data sets. Performing the recommended transformation in conjunction with omitting treatments having identical replicate observations provided a high percentage of correction of non-normality, heterogeneity of variance, and nonadditivity. The arcsine transformation, not generally recommended for data sets having values from 0 to 20% or 80 to 100%, was as effective in correcting non-normality, heterogeneity of variance, and nonadditivity in these data sets as was the recommended square root transformation. A majority of data sets showed differences between transformed and nontransformed data in mean separations determined using LSD (0.05), although most of these differences were minor and had little effect on interpretation of results.

Hairy nightshade is the most widespread nightshade species in North America. Increased knowledge of hairy nightshade germination biology would facilitate development of an optimum control program. Germination of hairy nightshade seeds as affected by environmental and chemical factors was studied under greenhouse and controlled-environment growth chamber conditions. Hairy nightshade seeds were in an innate dormant state when initially separated from the berries. Moist compared with dry storage was more effective for breaking dormancy at 4 C, but dry storage was more effective at 17 C. Hairy nightshade seeds germinated equally well under both a 14-h photoperiod and continuous darkness. These germinated at constant temperatures ranging from 19 to 39 C, with optimum germination attained between 27 and 33 C. Germination markedly declined as osmotic potential of the germination medium decreased. The optimum pH range for germination of hairy nightshade seeds was between 6 and 8, although some seeds germinated at pH 4 and 9. Maximum hairy nightshade emergence occurred with seeding depths of 2 cm or less. No emergence occurred when seeding depth reached 8 cm.

The rate of CO2 reduction in the S-triazine-resistant biotype of smooth pigweed (Amaranthus hybridus L.) was lower at all levels of irradiance than the rate of CO2 reduction in the susceptible biotype. The intent of this study was to determine whether or not the lower rates of CO2 reduction are a direct consequence of the same factors which confer triazine resistance. The quantum yield of CO2 reduction was 23 ± 2% lower in the resistant biotype of pigweed and the resistant biotype of pigweed had about 25% fewer active photosystem II centers on both a chlorophylH and leaf area basis. This quantum inefficiency of the resistant biotype can be accounted for by a decrease in the equilibrium constant between the primary and secondary quinone acceptors of the photosystem II reaction centers which in turn would lead to a higher average level of reduced primary quinone acceptor in the resistant biotype. Thus, the photosystem II quantum inefficiency of the resistant biotype appears to be a direct consequence of those factors responsible for triazine resistance but a caveat to this conclusion is discussed. The effects of the quantum inefficiency of photosystem II on CO2 reduction should be overcome at high light and therefore cannot account for the lower light-saturated rate of CO2 reduction in the resistant biotype. Chloroplast lameliar membranes isolated from both triazine-resistant and triazine-susceptible pigweed support equivalent rates of whole chain electron transfer and these rates are sufficient to account for the rate of light-saturated CO2 reduction. This observation shows that the slower transfer of electrons from the primary to the secondary quinone acceptor of photosystem II, a trait which is characteristic of the resistant biotype, is nevertheless still more rapid than subsequent reactions of photosynthetic CO2 reduction. Thus, it appears that the lower rate of light-saturated CO2 reduction of the resistant biotype is not limited by electron transfer capacity and therefore is not a direct consequence of those factors which confer triazine resistance.As many as one-half of all commercially available herbicides used in agriculture act by interfering with photosynthetic electron transfer reactions. The margin of selectivity of many of these herbicides between the crop and unwanted plant species is disappointingly low, although the metabolic detoxification of triazines by corn is an exception of immense economic importance. In recent years, dramatically lower sensitivities of photosynthesis to S-triazine herbicides have appeared in populations of numerous weed species growing on agricultural lands (for review, see 16). Investigations into the biochemical basis for the lower sensitivity of these weeds to triazine herbicides have clearly established that the mode of resistance is at the level of the interaction of the herbicide with the photosynthetic electron transport chain (16).Maternal inheritance (9,12) of triazine resistance indicates control by a chloroplast rather than a nuclear gene(s). The implic...

A procedure is described for the rapid analysis of leaf samples to determine triazine resistance. The technique uses a commercially available fluorometer and is based upon the fact that photosynthesis-inhibiting herbicides increase chlorophyll fluorescence (because of dissipation of absorbed radiant energy in the absence of useful photochemistry). Resistant and susceptible biotypes of six weed species were assayed. Fluorescence of susceptible leaf sections increased dramatically over a 1- to 3-h exposure to atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], but resistant leaf sections showed no fluorescence increase. Substantial fluorescence increases of both resistant and susceptible leaf sections were induced by diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. In the absence of herbicides, fluorescence was higher in resistant than in susceptible leaf sections, suggesting that the resistant biotypes are less efficient photosynthetically. Fluorescence analysis was used to characterize atrazine inhibition of photosynthesis in leaf sections of three crop species. Differences in atrazine-induced fluorescence between crop lines were relatively small and were not well correlated with atrazine tolerance. The fluorometer is a convenient device for monitoring photosynthesis inhibition, however, and could be useful in detecting plants having resistance to photosynthesis-inhibiting herbicides.