Leaf Excision as a Means of Evaluating Picloram Uptake in the Bean Plant

摘要

Eighteen micrograms of 4-amino-3,5,6-trichloropicolinic acid (picloram) were applied to one primary leaf of each 10-day-old Black Valentine bean plant growing in an environmental chamber at 25 C and 50 to 60% RH. The source of the herbicide was then removed by excising all treated leaves at intervals from 15 minutes to 48 hours after treatment. Plants were harvested 14 days after treatment. A marginal 10 to 15% inhibition of height occurred in the 15-minute group of plants. However, the 30-minute uptake period was sufficiently long enough to cause a statistically significant suppression of height. The first epinastic effects occurred within 10 to 12 hours after treatment. This time interval was essentially independent of the length of time allowed for export of the herbicide from the donor leaf for all treatment periods of 2 hours or longer. The severity of injury did not increase with uptake periods greater than 12 hours when evaluated by plant height. Injury, as reflected by a decrease in oven-dry weight, however, did increase with each period greater than 12 hours. This seemingly anomalous effect was caused by the severe injury or death of the terminal bud in all of the treatment groups equal to or longer than 12 hours. (Author)