J. Dixon et al., PHENMEDIPHAM-OZONE POLLUTION INTERACTIONS IN SUGAR-BEET (BETA-VULGARIS L CV SAXON) - A PHYSIOLOGICAL STUDY, Pesticide science, 46(4), 1996, pp. 381-390
Actively growing sugarbeet is treated with the post-emergent herbicide
phenmedipham at times when ozone pollution episodes are likely to occ
ur. There is a possibility of an interaction occurring between ozone a
nd phenmedipham as both treatments produce similar effects in suscepti
ble plants, such as a reduction in growth and photosynthesis and an in
crease in the activities of endogenous antioxidant enzymes. To investi
gate this likelihood, laboratory experiments were conducted in which t
wo- to three-leaf sugarbeet plants (Beta vulgar is L. cv. Saxon) were
exposed to a simulated two-day ozone episode (100 nl litre(-1), 7 h da
y(-1)) followed three days later by treatment with field rate phenmedi
pham (1.14 kg AI ha(-1)). Growth analysis indicated that an interactio
n was occurring in which plants treated with ozone and phenmedipham ha
d less reduction in shoot fresh weight than expected. Exposure to phen
medipham alone or ozone followed by phenmedipham reduced net photosynt
hesis by over 50% and transpiration rate by 30%. The activities of ant
ioxidant enzymes such as catalase, guaiacol peroxidase and superoxide
dismutase were stimulated by both treatments individually, but to a gr
eater extent when ozone and phenmedipham were combined. For example, t
hree days after herbicide treatment, the activity of superoxide dismut
ase increased by 20% in plants treated with ozone alone, 20% in plants
treated with phenmedipham alone and 85% in plants that were treated w
ith ozone followed by phenmedipham. We conclude that ozone pollution m
ay predispose sugarbeet to tolerate the herbicide phenmedipham by enha
ncing the activity of the endogenous antioxidant detoxification enzyme
system.