DYNAMICS OF GROWTH AND BIOMASS PARTITIONING IN FIELD-GROWN BUSH BEAN (PHASEOLUS-VULGARIS L), TREATED WITH THE ANTIOZONANT ETHYLENEDIUREA (EDU)

The anti-ozonant ethylenediurea (EDU) approach was used to assess the effects of ambient ozone (O-3) air pollution on development, growth an d biomass partitioning in bush bean (Phaseolus vulgaris L. cultivar 'B BL 290') during five staggered plantings in 1989 and 1990. The (EDU) w as applied as a soil drench twice during plant development: after unfo lding of primary leaves and at early flowering. The concentration of E DU used (100 mg l-(1)) was considerably lower than in earlier studies, but had proven to protect bean plants from O-3 injury without alterin g growth in previous greenhouse studies. Plants were harvested in 5 da y intervals from emergence through maturity. Ambient O-3 was low durin g the five plantings (24 h mean: 28-33 nl l-(1); 7 h mean: 45-49 nl-(1 ) O-3), but number of hours and cumulative exposure > 90 nl l-(1) O-3 during the fifth planting was considerably higher compared with the ot her growth intervals. Total plant weight of EDU-treated plants fell be low that of untreated plants after the second application of EDU durin g most of the plantings. During the fifth planting, however, total dry weight of EDU-treated plants was equal to that of untreated ones. Pod dry weight exhibited a similar pattern, and relative pod weight was r educed by EDU during late pod development in two plantings. Patterns o f biomass allocation to other plant organs (foliage, stem, root) were not altered by the EDU treatments. The reduction in pod weight of EDU- treated plants was not due to a reduced number of flowers or young pod s, which was actually slightly increased by the EDU treatments, but wa s caused by an increased rate of pod abscission during maturity. It is concluded that the second EDU soil drench was timed too early to prov ide protection throughout pod development and maturation. Increases in flower and bud duration and a delay in primary leaf abscission demons trated the action of EDU in delaying maturation and senescence. From t hese results it is suggested that repeated soil drenches of EDU may ca use reductions in the total plant weight and pod weight of a O-3-sensi tive bean cultivar if the exposure to ambient O-3 is low. Conclusions for the further use of EDU are discussed.