Research Stution, A,qriculture Cunudu, Lucombe, Alberta T)C 150. Contribution ntt.423, reteivetl I0 Apr. l9Bl, uctepred 23 Feb. 1982. O'Sur-r-rvnN, P. A., Kossrrz,V. C., Wtrss

Data were collected from nine farm fields over 2 yr to determine the relationship between percent yield loss of rapeseed and density of Canada thistle. Regression analyses of the data for percent yield loss of rapeseed and numbers of thistle shoots per square metre, using two representations of the data (untransformed and square root transformation), yielded the following equations:[Formula: see text]and[Formula: see text]where ŷ = estimated percent yield loss of rapeseed, x = the number of Canada thistle shoots per square metre, and 1.48 and 10.42 are the indices of competition for Eqs. 1 and 2, respectively. Equation 1 provides a more accurate estimate of percent yield loss at all levels of thistle infestation. Equation 2 provides acceptable estimates of yield loss at intermediate levels of infestation (5–40 shoots/m2) and is presented for comparitive purposes since the index of competition (10.42) is near the value proposed as a result of extrapolation from earlier studies (10.6) which utilized square root transformation of the data. The significance of this is discussed. The 95% confidence limits for Eq. 1 for the estimated percent rapeseed yield loss when four different samples sizes (n = 1, 5, 10 and 20) are used to estimate the number of thistle shoots per square metre are presented. An example of the utility of the linear equation is presented.Key words: Rapeseed, Canada thistle, crop loss, competition

o'Sur-r-rveNl, P. A. axo Kossarz, v. c. 1982. Selective

Summary Experiments were conducted in a growth cabinet to investigate the absorption and translocation of 14C‐3, 6‐dichloropicolinic acid by Cirsium arvense (L.) Scop. (Canada thistle, creeping thistle), a sensitive species. Applications were made, either to the middle four leaves of 12‐cm‐tall vegetative plants grown under low (40%) and/or high (>95%) relative humidity (r.h.), or to four upper or lower leaves of 30‐cm‐tall flowering plants grown under low r.h. Following application to vegetative plants, absorption and translocation of 14C‐3,6‐dichloropicolinic acid was rapid and was approximately doubled by high r.h. High r.h. increased the amount of radioactivity retained by the treated leaves or translocated to the shoots but did not affect greatly the amount retained in the roots. The herbicide was highly mobile, with over half of that absorbed, translocated out of the treated leaves after two days. The apex accumulated most of the radioactivity, while approximately 8% was recovered from the roots. The absorption and translocation patterns were similar to those reported in the literature for picloram in C. arvense. Absorption of 3,6‐dichloropicolinic acid was greater in vegetative than in flowering C. arvense plants, and placement of herbicide on lower leaves tended to decrease the amount of radioactivity recovered from shoot apex and increase the amount recovered from the roots. Approximately 15% of the applied radioactivity could not be recovered from treated plants by 2 days after treatment.

Peroxidase (EC 1.11.1.7) enzyme units that were recovered by sequential extraction at low and high ionic strength buffer pH 7 from a peanut suspension culture at various intervals of cell growth appeared to increase with culture time. In particular, at the end of a 14-day growth cycle, peroxidase specific activity rose while protein content and the specific activity of porphobilinogen synthase (aminolevulinic acid, dehydratase EC 4.2.1.24) declined. The decrease of the protein content could probably be accounted for by the 95% decrease of protein synthesis at the end of the growth phase. The highest specific activity of aminolevulinic acid dehydratase (ALA dehydratase) appeared to be associated with organelles which could be precipitated at 500 × g and this specific activity appeared to be unaffected by the stage of growth of these cells. It is suggested that the ALA dehydratase activity in nonchlorophyllous peanut cells, which is as high as that found in green tissue, may play a function in the biosynthesis of the hemoprotein peroxidase.