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Evaluation of Chlorophyll Fluorescence Parameters for an Intact-Plant Herbicide Bioassay¹

The correlations between various chlorophyll fluorescence induction curve parameters and metribuzin [4-Amino-6-(1,1-dimethyl-ethyl)-3-(methylthio)-1,2,4-triazin-5(4/H)-one], diuron [3-(3,4-Dichlorophenyl)-1,1-dimethylurea], and atrazine (2-chloro-4-ethylamino-6- isopropylamino-S-triazine) concentrations were compared in laboratory studies. The ratio of the initial inflection point (I) to the initial peak (P) was the most precise indicator of photosynthetic inhibition over time intervals of 4 to 48 h after an oat (Avena sativa L. ‘Chilocco’) plant was transplanted into herbicide-treated soil. The height of the initial inflection point (I), the peak level (P), and the fluorescence level 30 s after the onset of illumination (T) were also useful at 4 and 8 h after transplanting, but correlated poorly with herbicide concentration at later time intervals. Other variables examined included the slopes from I to P and P to S, the percent decay from P to T, and the complementary area. These parameters did not correlate to herbicide concentration as well, and had a much higher degree of variability associated with them.

Key Words: Metribuzia • Diuron • Atrazine • Photosynthetic inhibitor • Arena sativa L.

² Former graduate research assistant (present address of senior author is Dep. of Plant Pathology and Weed Sci., Mississippi State Univ., Mississippi State, MS 39762), and associate professors, respectively, Dep. of Agronomy, Oklahoma State Univ., Stillwater, OK 74078.

Received for publication June 3, 1985.