Pest Management Science Pest Manag Sci 59:1303–1310 (online: 2003) DOI: 10.1002/ps.763 Linking fluorescence induction curve and biomass in herbicide screening Martin G Christensen, 1 Harald B Teicher 2 and Jens C Streibig 1∗ 1 Department of Agricultural Sciences, KVL, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark 2 Cheminova A/S (Research and Development) PO Box 9, DK-7620 Lemvig, Denmark Abstract: A suite of dose–response bioassays with white mustard (Sinapis alba L) and sugar beet (Beta vulgaris L) in the greenhouse and with three herbicides was used to analyse how the fluorescence induction curves (Kautsky curves) were affected by the herbicides. Bentazone, a photosystem II (PSII) inhibitor, completely blocked the normal fluorescence decay after the P-step. In contrast, fluorescence decay was still obvious for flurochloridone, a PDS inhibitor, and glyphosate, an EPSP inhibitor, which indicated that PSII inhibition was incomplete. From the numerous parameters that can be derived from OJIP-steps of the Kautsky curve the relative changes at the J-step [F vj = (F m - F j )/F m ] was selected to be a common response parameter for the herbicides and yielded consistent dose–response relationships. Four hours after treatment, the response F vj on the doses of bentazone and flurochloridone could be measured. For glyphosate, the changes of the Kautsky curve could similarly be detected 4 h after treatment in sugar beet, but only after 24 hs in S alba. The best prediction of biomass in relation to F vj was found for bentazone. The experiments were conducted between May and August 2002 and showed that the ambient temperature and solar radiation in the greenhouse could affect dose–response relationships. If the Kautsky curve parameters should be used to predict the outcome of herbicide screening experiments in the greenhouse, where ambient radiation and temperature can only partly be controlled, it is imperative that the chosen fluorescence parameters can be used to predict accurately the resulting biomass used in classical bioassays.  2003 Society of Chemical Industry Keywords: Kautsky curve; bentazone; flurochloridone; glyphosate; fluorescence 1 INTRODUCTION Screening for herbicide efficacy in the greenhouse or in the field is usually a lengthy process. 1 The experiments take up much space and the evaluation of results, either quantitatively (biomass) or qualitatively (scoring systems), can usually first be done more than a week after treatment. Several novel methods have been implemented in an attempt to shorten the evaluation time, such as the measurement of herbicide- linked accumulation of intermediates in the plant. 2 If it were possible to apply a cost-effective method shortly after exposure to a herbicide, the costs of screening experiments would be greatly reduced. An option could be to use the shape and form of the fluorescence transition curve, or Kautsky curve. 3–7 The use of various fluorescence parameters, derived from the Kautsky curve, is common in photosynthesis research and in plant stress research. 4,8–11 It is well documented that the shape of the Kautsky curve is affected by various stress factors, such as temperature and water stress, pathogens and herbicides. 8,12 – 16 Measurement of fluorescence is a rapid, non-invasive and simple method to measure a number of parameters linked to the physiological status of the plant. However, as pointed out by Govindjee, 4 the wealth of information contained in the Kautsky curves can be so overwhelming that it may become an ambiguous signal. Consequently, a direct cause-and-effect relationship is sometimes difficult to identify. The most popular parameter derived from the Kaut- sky curve is that of maximum relative fluorescence [(F m − F 0 )/F m ], which measures the relative magni- tude of the fluorescence curve between the O and P steps (see Fig 1). This parameter is effective in providing a snapshot of the physiological status of a plant being exposed to various stress factors, and has been used to measure the effect of photosys- tem II (PSII) inhibitors. 7,17 – 19 Fluorescence has also been used for the study of herbicides with other modes of action than the inhibition of PSII. 5,16,20 The most consistent results have been obtained under controlled conditions in the laboratory or in growth chambers where ambient temperature and light regimes were strictly monitored. 19 If the evaluation of screening experiments for herbicides should utilise the Kautsky curve, then it is imperative to establish well-documented dose–response relationships for the ∗ Correspondence to: Jens C Streibig, Department of Agricultural Sciences, KVL, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark E-mail: jcs@kvl.dk (Received 20 January 2003; revised version received 9 April 2003; accepted 23 May 2003) Published online 5 August 2003  2003 Society of Chemical Industry. Pest Manag Sci 1526–498X/2003/$30.00 1303