RESPONSES OF ABUTILON-THEOPHRASTI TO AGRICULTURAL MANAGEMENT-SYSTEMS

Seeds of Abutilon theophrasti Medic., collected from plants growing in a continuous maize or soyabean field subjected to herbicide applicati on, cultivation or no weed management for 10 years, differed significa ntly in their weight and germinability. The differences in mean weight and germinability of the progeny seeds were maintained when the paren t plants were grown in a greenhouse under controlled conditions. The o ffspring of plants with or without previous exposure to atrazine respo nded similarly to the herbicide in all the measurements of the growth and development of the plants, except biomass. Significant differences between the two groups of plants were mainly observed in the weight a nd germinability of their seeds. Although plants with or without previ ous exposure to atrazine usually did not differ significantly in their response to the herbicide in terms of individual traits, they differe d both in the amount and pattern of overall response across all traits . The difference in overall response between plants increased with inc reasing rate of atrazine. It is possible that previous exposure to the herbicide had caused minor variation in a group of intercorrelated tr aits or in the strength or pattern of correlation among traits.