DOI: 10.1007/s11099-011-0010-6 PHOTOSYNTHETICA 49 (1): 98-106, 2011 98 Nondestructive leaf-area estimation and validation for green pepper (Capsicum annuum L.) grown under different stress conditions B. CEMEK *,+ , A. UNLUKARA ** , and A. KURUNC Department of Agricultural Structures and Irrigation, Faculty of Agriculture, Ondokuz Mayis University, 55139 Samsun, Turkey * Department of Agricultural Structures and Irrigation, Faculty of Agriculture, Erciyes University, Kayseri, Turkey ** Department of Agricultural Structures and Irrigation, Faculty of Agriculture, Akdeniz University, 07058 Antalya, Turkey *** Abstract Leaf area of a plant is essential to understand the interaction between plant growth and environment. This useful variable can be determined by using direct (some expensive instruments) and indirect (prediction models) methods. Leaf area of a plant can be predicted by accurate and simple leaf area models without damaging the plant, thus, provide researchers with many advantages in horticultural experiments. Several leaf-area prediction models have been produced for some plant species in optimum conditions, but not for a plant grown under stress conditions. This study was conducted to develop leaf area estimation models by using linear measurements such as lamina length and width by multiple regression analysis for green pepper grown under different stress conditions. For this purpose, two experiments were conducted in a greenhouse. The first experiment focused to determine leaf area of green pepper grown under six different levels of irrigation water salinity (0.65, 2.0, 3.0, 4.0, 5.0, and 7.0 dS m –1 ) and the other under four different irrigation regime (amount of applied water was 1.43, 1.0, 0.75, and 0.50 times of required water). In addition to general models for each experiment, prediction models of green pepper for each treatment of irrigation water salinity and of irrigation regime experiments were obtained. Validations of the models for both experiments were realized by using the measurements belong to leaf samples allocated for validation purposes. As a result, the determined equations can simply and readily be used in prediction of leaf area of green pepper grown under salinity and water stress conditions. The use of such models enable researchers to measure leaf area on the same plants during the plant growth period and, at the same time, may reduce variability in experiments. Additional key words: green pepper; irrigation regime; irrigation water salinity; leaf area estimation; nondestructive methods. Introduction Accurate and simple measurements of leaf area (LA) of a crop are essential to understand the interaction between plant growth and environment since it is an indicator of plant growth and productivity. It is also a determinant factor in mechanisms such as light interception, photo- synthetic efficiency, evapotranspiration, energy exchange and responses to fertilizers and irrigation (De Jesus et al. 2001, Blanco and Folegatti 2005, Demirsoy et al. 2004). The total leaf area of a plant can be obtained by either direct or indirect methods. Direct methods consist of removing and measuring of all leaves in the plant by using instruments, tools and machines such as hand scanners and laser optic apparatuses developed for leaf area measurements. This method requires labor, time, adequate, potentially expensive equipment and the excision of leaves from the plants. Therefore, it may cause problems to other measurements or experiments since plant canopy is damaged. Indirect methods are, however, nondestructive, user-friendly, less expensive, and save time compared with geometric measurements ——— Received 5 February 2010, accepted 6 November 2010. + Corresponding author; phone: +90 0362 312 1919, e-mail: bcemek@omu.edu.tr Abbreviations: AI – amount of applied irrigation water; C AW – water application coefficient; ECi – electrical conductivity of irrigation water; I – water application rate compared to crop water needs; IR – irrigation regime; IWS – irrigation water salinity; L – leaf length; LA – leaf area; LA and LA model – average values of the corresponding variable; LA model – estimated leaf area value; LF – leaching fraction; MAE – mean absolute error; MBE – mean bias error; PS – plant species; PW and PW FC – pot weight just before irrigation and at field capacity; r 2 – coefficient of determination; RMSE – root mean square error; SE – standard error; W – leaf width.