International Symposium “Root Research and Applications” RootRAP, 2–4 September 2009, Boku – Vienna, Austria 1 Model based assessment of barley root ideotypes for breeding strategies in water limited environments Gernot Bodner 1 , Margarita Himmelbauer 2 , Elnaz Ebrahimi Mollabashi 3 , Adel Dabbagh Mohammadi Nassab 3 , Willibald Loiskandl 2 and Hans-Peter Kaul 1 1 University of Natural Resources and Applied Life Sciences, Institute of Agronomy and Plant Breeding (IPP), Gregor-Mendelstraße 33, 1180 Vienna, Austria 2 University of Natural Resources and Applied Life Sciences, Institute of Hydraulics and Rural Water Management (IHLW) Muthgasse 18, 1190 Vienna, Austria 3 University of Tabriz, Faculty of Agriculture, Dept. of Agronomy, 51664 Tabriz, Iran Contact: Gernot Bodner gernot.bodner@boku.ac.at ABSTRACT A simulation study of root effects on barley biomass production under Austrian and Iranian climate conditions was performed using the DAISY model. In Iran deep rooting cultivars provide a general advantage for crop growth. In Austria a rooting depth of 70 cm was sufficient to realize the year specific growth potential. Above a threshold of around 350 mm rainfall, competition for assimilates between roots and shoots even resulted in a lower biomass production of deep rooting cultivars. KEYWORDS: drought, root ideotype, modeling, barley 1. INTRODUCTION Drought tolerance is an increasingly important objective in plant breeding. Cultivars should combine high yield potential under optimum conditions and sufficient adaptation to stress. For this purpose an efficient water and nutrient uptake by the root system is crucial. There are many root traits that could potentially be selected for and target parameters may vary for different regions. Crop models may be a tool to assist plant breeding in defining promising root traits (Ho et al., 2004). Using the DAISY model (Hansen et al., 1990), our study analyses the growth performance of barley under different environmental conditions with varying root characteristics. The objective is to define environmental specific root ideotypes for improved drought tolerance. 2. MATERIAL AND METHODS Two climatic situations were analyzed using ten years weather data from (i) a site in Eastern Austria near Vienna, and (ii) a site in West Iran at Sararood. Two soil types were tested, a silty loam (plant available water 180 mm m -1 ) and a sandy loam (plant available water 100 mm m -1 ). Simulations were made using the DAISY model which considers several root parameters to influence water uptake. The model calculates root water extraction by r Q L S ⋅ = and ∫ − = π ω ω 2 0 ) ( d ) ( f ) r ( v r Q c r r (1) where S (m 3 m -3 s -1 ) is the sink term, L (m m -3 ) is root length density, Q r (m 3 s -1 m -1 ) is water uptake rate per unit root length, r r (m) is root radius, f c (ω) is a function for root-soil contact (0 no contact, 1 full contact), and v(r) (m s -1 ) is the water flow velocity at the root surface. For our simulation analysis we varied (i) maximum rooting depth (range 0.5-1.1 m), (ii) root penetration rate (0.20-0.35 m d -1 °C -1 ), and (iii) specific root length (70-130 m kg -1 ). The effect on