IntroductionThe ultimate object of testing for germination is to gain information with respect to the field planting value of the seed and to provide results that can be used to compare the value of different seed lots (ISTA, 2005). However, the standard germination test often overestimates actual field emergence (Hampton, 2009). The major reason for this overestimation is that germination tests are conducted under conditions that are more favorable than typically encountered in the field. In order to provide a more accurate appraisal of seed quality for estimating field emergence, the concept of seed vigor was established to measure the quality of a seed lot, based on sampled observations of seedling growth (Sako et al., 2002).Vigor testing not only measures the percentage of viable seeds in a sample; it also reflects the ability of those seeds to produce normal seedlings under the less-than-optimum or adverse growing conditions that may occur in the field (ISTA, 2005). Low-vigor lots having poor field emergence may not necessarily be detected by standard germination (Demir and Mavi, 2008). Demir (2007a, 2007b) identified that vigor test regimens correlated well with field emergence potential.Although vigor testing provides useful information, most vigor tests are time-consuming and costly, and they produce variable results from laboratory to laboratory (Sako et al., 2002). In plants that have small seeds, such as Medicago sativa and Onobrychis viciifolia, these problems are serious and have prevented the widespread, standardized use of seed vigor testing. The vigor tests that have been proposed can be grouped into 3 categories (Bennett, 2002): stress tests (e.g., cold test, accelerated aging), biochemical tests (e.g., electric conductivity, tetrazolium test), and germination evaluation and seedling growth tests (e.g., first count of the germination test, normal seedling emergence in peat, image analysis).Accelerated aging is one of the 2 frequently used ISTArecommended vigor tests (

Seedling emergence is one of the most important processes determining yield and the probability of crop failure. The ability to predict seedling emergence could enhance crop management by facilitating the implementation of more effective weed control strategies by optimizing the timing of weed control. The objective of the study was to select a seedling emergence thermal time model by comparing five different equations for tall fescue and wheatgrass in two sites with different climate conditions (semiarid-temperate and humid-warm) in Iran. In addition, seedling emergence between two target species were studied. Among the five models compared, the Gompertz and Weibull models gave more succesful results. In humid-warm conditions, the total emergence of wheatgrass was higher than observed in tall fescue. In contrast, emergence was faster in tall fescue than wheatgrass in both study sites. Given that early-emerging plants have been described as contributing more to crop yield than later-emerging ones, tall fescue is proposed as a more suitable specie for semiarid-temperate conditions in Iran.Additional key words: Agropyron desertorum; Festuca arundinacea; germination; Gompertz model; Weibull model. Resumen Emergencia de las plántulas de lastón y triguilla del desierto bajo condiciones climáticas diferentes en IránEl éxito en el proceso de emergencia de las semillas es un evento determinante en el rendimiento de las cosechas. Por tanto, cualquier mejora en la predicción de este proceso resulta valioso para la mejora de las técnicas de manejo de los cultivos. El objetivo de este trabajo fue la caracterización dinámica del proceso de emergencia de Festuca arundinacea Schreb y Agropyron desertorum (Fisch. ex Link) J.A. Schultes en dos localidades con diferentes condiciones climáticas (semiárido templado y húmedo calido) de Iran. Los análisis realizados indicaron que, de entre los cinco modelos comparados, los ajustes de Gompertz y Weibull proporcionaron los resultados más satisfactorios en la caraterización dinámica de dicho proceso. En condiciones húmedas y cálidas, el porcentaje total de emergencia de A. desertorum fue significativamente superior al observado en F. arundinacea. Por el contrario, en ambos ambientes climá-ticos el proceso de emergencia de F. arundinacea fue más rápido que el observado en A. desertorum. Dado que la emergencia temprana ha sido descrita como un elemento clave en el éxito de las cosechas en condiciones semiáridas, nuestros resultados sugieren que F. arundinacea puede representar una especie más adecuada para su cultivo en los ambientes semiáridos-templados de Iran.Palabras clave adicionales: