EFFECTS OF SINGLE AND MULTIPLE EXPOSURES OF FERULIC ACID ON THE VEGETATIVE AND REPRODUCTIVE GROWTH OF PHASEOLUS VULGARIS BBL‐290

Phaseolus vulgaris BBL-290 plants were grown in growth chambers in the Southeastern Plant Environment Laboratory and exposed to either single (at seedling, flower, or podfill) or multiple (biweekly or weekly) treatments of ferulic acid (FA). In the first experiment, plants were harvested one week after FA treatment (0, 1.0, 2.0 mM) and at final harvest (56 days old). FA delayed leaf expansion during the seedling and flowering stages. The total plant leaf area and the plant dry weight of plants treated with 1.0 and 2.0 mM FA as seedlings were reduced one week after treatment by 38-48%. The total plant leaf area and the plant dry weight of plants treated at flowering with 2.0 mM FA were reduced by 25% one week after treatment. Treatment with 2.0 mM FA at podfill caused the senescence and abscission of older leaves and reduced total plant leaf area, plant dry weight and mean pod dry weight by 54, 40, and 48%, respectively, one week after treatment. The plants treated at the seedling and flowering stages recovered by final harvest. In a subsequent experiment, FA (0, 0.50, 1.0, 1.5 mM) reduced total plant leaf area at the seedling and flowering stages but not at podfill. The youngest expanding leaves were most sensitive to FA at flowering. The leaf area of these leaves was reduced by 35 and 25%, one and two weeks after treatment, respectively. Their absolute growth rates were reduced from 31 to 56% one week after treatment at flowering. Their relative growth rates were reduced by 50% one week after treatment. Growth rates then recovered within two weeks after treatment. In the final experiment, biweekly exposures of FA (0.25, 0.50, 0.75, 1.0) reduced total plant leaf area but did not affect any other growth parameters. Weekly exposures of FA (0.25, 0.50, 0.75, 1.0) reduced total plant leaf area up to 34%, absolute growth rate up to 58%, leaf number up to 31% and pod number up to 58%. As the frequency of exposure to FA increased, the concentration necessary to affect bean plant growth and development decreased. ALLELOPATHIC INTERACTIONS between plants have been implicated in the patterning of natural vegetation and in the reduction of crop yields and weed growth in agricultural systems (Putnam, 1983; Putnam, De Frank, and Barnes, 1983; Rice, 1984). Ferulic acid is one of the many allelochemicals that has frequently been identified (Mandava, 1985). Ferulic acid is a product of lignin degradation (Turner and Rice, 1975; Martin and Haider, 1976) and has been isolated from soils (Whitehead, 1964; Lodhi, 1975; Whitehead, Dibb, and Hartley, 1982, ' Received for publication 8 October 1986; revision accepted 11 February 1987. Paper No. 10715 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, North Carolina 27695-7601. Partial support for this research was provided by the North Carolina Agricultural Research Service. We thank Drs. R. C. Fites, D. C. Sanders, and A. D. Worsham for their careful reviews of this manuscript and Mr. John Dunning for supplying all the seeds used in this study. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the products named, nor criticism of similar ones not mentioned. 1983) and plant material (Liebl and Worsham, 1983). Ferulic acid has been used in numerous bioassays and a better understanding ofits mode of action is developing. Exposure of plant roots to ferulic acid reduces plant water utilization (Blum and Dalton, 1985; Blum, Dalton, and Shann, 1985a), turgor and osmotic pressures and closes stomates (Einhellig, Stille Muth, and Schon, 1985). Ferulic acid alters seed germination (Leather and Einhellig, 1984), inhibits radicle growth (Blum, Dalton, and Rawlings, 1984) and decreases leaf expansion, leaf production, dry weight accumulation (Patterson, 1981; Blum and Dalton, 1985; Blum et al., 1985a, b), photosynthetic rates (Patterson, 1981) and leaf chlorophyll content (Einhellig and Rasmussen, 1979; Patterson, 1981). The magnitude of these responses varies with concentration of ferulic acid and environmental conditions such as temperature (Einhellig and Eckrich, 1984) and pH (Blum et al., 1985b; Shann, 1986). Membrane potential and mineral absorption by root tissue are also reduced