Genotype-by-Environment interaction.

KANG M.S; BALZARINI M; GUERRA. J

Genetic Analysis of Complex Traits Using SAS

BBU Press. SAS Institute In A. Saxton (ed.)

Lugar: Cary NC; Año: 2004; p. 78 - 118

Genotype-by-environment interaction (GEI) is a universal issue and relates to all living organisms,9 from bacteria to plants to humans. The subject is important in agricultural, genetic, evolutionary, and10 statistical research. Genotype-by-environment interaction refers to differential responses of different11 genotypes across a range of environments. Gene expression is dependent upon environmental12 factors and may be modified, enhanced, silenced, and/or timed by the regulatory mechanisms of the13 cell in response to internal and external factors. A range of phenotypes may result from a genotype14 when it is exposed to different environments. This phenomenon is called norms of reaction or15 phenotypic plasticity. Norms of reaction represent the expression of phenotypic variability in individuals16 of a single genotype. The lack of phenotypic plasticity is called canalization.17 Genotype-by-environment interaction occurs in all stages of a breeding program. Because of18 the universal presence of GEI, genotype evaluations are carried out in multiple environments in19 planned experiments called multi-environment trials (MET). Especially, quantitative traits, which are20 controlled by several genes, invariably exhibit low heritability. They are, in general, highly influenced21 by environmental factors and display a continuous variation. Most of the agronomically and22 economically important plant traits, e.g., grain yield, and animal traits, such as meat production, are23 quantitative or multigenic in nature. The major objectives of MET are: (1) to compare genotype24 performances in two inference bases, i.e., broad inference ? the general performance of a genotype25 (across environments), and environment-specific or narrow inference, i.e., the performance of a26 genotype within a specific environment, and (2) to estimate the GEI component to gauge heritability27 and its impact on selection, to select test sites and mega-environments, to identify genotypes28 specifically adapted to target environments, and to establish breeding objectives (Yan and Kang,29 2002). Genotype-by-environment interaction has long been an important and challenging issue among30 plant breeders, geneticists, and agronomists engaged in crop performance evaluation (Kang, 1990;31 Kang and Gauch, 1996; Cooper and Hammer, 1996; Kang, 2002). Typical MET in plant breeding32 involve an evaluation of a large number of genotypes for several economically important traits in33 replicated field tests that are conducted across several years (seasons) at several locations in a region34 and/or diverse management systems. At each location, a randomized complete-block design is35 commonly used. Animal breeders also are concerned about GEI in the context of breed evaluation (Montaldo, 2001). Knowledge of genetic effects of breeds and their crosses in various climatic-forage2 systems can be used to identify optimal breed combinations and crossbreeding systems for existing3 markets (Franke et al., 2001)