Differential growth and response to atrazine between and within susceptible and resistant biotypes of Chenopodium album L.

Differential growth and response to atrazine were examined in greenhouse experiment with three populations of Chenopodium album from southwestern Ontario: two known susceptible (SI. SII) and one resistant (R). Germination of the resistant biotype was less than SII but the same as SI. R seedlings were not as mature at 16 days and weighed less at 23 days than seedlings of SI and SII. Within SI. early-(ESI) and late-flowering (LSI) variants were recognized. Older plants of R (37 and 44 days) had a greater growth rate than two of the susceptible populations (LSI and SII). In terms of vegetalive, floral, and total biomass. mature individuals of ESI were less productive than the other populations, but devoted a greater percentage of dry weight to floral production. Young plants (37 days old) were sprayed with atrazine at 00125, 0.25, 0.5, 1.25, 2.5 and 5 kg/ha. Population ESI was most sensitive to at razine; height and weight of stems and production of new leaves showed decreases at 0.25 and 0.125 kg/ha. respectively, compared to the untreated. Populations LSI and SII showed greater tolerance and decreases in these characters occurred at a higher rate of atrazine. Leaf weight per plant decreased at 0.25 kg/ha as a result of decreases in weight per unit area of leaf for all susceptible population. Growth of R as measured by the above criteria was not affected by atrazine treatments but leaf weight per unit area was slightly reduced at 2.5 and 5.0 kg/ha Single leaves of 48 day old plants were infused with at razine concentrations of 0.5, 2.0, 3.0 and 20.0 ppm. Leaf chlorosis increased with concentration and injury was greater in populations LSI and SII than in ESI. A small amount of chlorosis occurred in R.