title: Leaf Length Tracker: a novel approach to analyse leaf elongation close to the thermal limit of growth in the field.
abstract: Leaf growth in monocot crops such as wheat and barley largely follows the daily temperature course, particularly under cold but humid springtime field conditions. Knowledge of the temperature response of leaf extension, particularly variations close to the thermal limit of growth, helps define physiological growth constraints and breeding-related genotypic differences among cultivars. Here, we present a novel method, called 'Leaf Length Tracker' (LLT), suitable for measuring leaf elongation rates (LERs) of cereals and other grasses with high precision and high temporal resolution under field conditions. The method is based on image sequence analysis, using a marker tracking approach to calculate LERs. We applied the LLT to several varieties of winter wheat (Triticum aestivum), summer barley (Hordeum vulgare), and ryegrass (Lolium perenne), grown in the field and in growth cabinets under controlled conditions. LLT is easy to use and we demonstrate its reliability and precision under changing weather conditions that include temperature, wind, and rain. We found that leaf growth stopped at a base temperature of 0°C for all studied species and we detected significant genotype-specific differences in LER with rising temperature. The data obtained were statistically robust and were reproducible in the tested environments. Using LLT, we were able to detect subtle differences (sub-millimeter) in leaf growth patterns. This method will allow the collection of leaf growth data in a wide range of future field experiments on different graminoid species or varieties under varying environmental or treatment conditions.
authors.affiliation: Institute of Agricultural Sciences, Swiss Federal Institute of Technology, Universitätstrasse 2, 8092 Zurich, Switzerland Institute of Botany, Department of Environmental Sciences, University of Basel, Schönbeinstrasse 6, 4056 Basel, Switzerland sebastian.nagelmueller@usys.ethz.ch.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Nagelmüller
authors.affiliation: Institute of Agricultural Sciences, Swiss Federal Institute of Technology, Universitätstrasse 2, 8092 Zurich, Switzerland.
authors.forename: Norbert
authors.initials: N
authors.lastname: Kirchgessner
authors.affiliation: Institute of Agricultural Sciences, Swiss Federal Institute of Technology, Universitätstrasse 2, 8092 Zurich, Switzerland.
authors.forename: Steven
authors.initials: S
authors.lastname: Yates
authors.affiliation: Institute of Agricultural Sciences, Swiss Federal Institute of Technology, Universitätstrasse 2, 8092 Zurich, Switzerland.
authors.forename: Maya
authors.initials: M
authors.lastname: Hiltpold
authors.affiliation: Institute of Agricultural Sciences, Swiss Federal Institute of Technology, Universitätstrasse 2, 8092 Zurich, Switzerland.
authors.forename: Achim
authors.initials: A
authors.lastname: Walter
mesh_terms: D001467:Hordeum / Q000033:anatomy & histology / Q000254:growth & development*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008129:Lolium / Q000033:anatomy & histology / Q000254:growth & development*; D018515:Plant Leaves / Q000033:anatomy & histology* / Q000254:growth & development*; D013696:Temperature; D013997:Time Factors; D014908:Triticum / Q000033:anatomy & histology / Q000254:growth & development*
keywords: Field conditions; leaf elongation; low temperature; marker tracking; monocotyledons; phenotyping; plant growth.
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