Contents & Foreword, Characterizing And ... - IRRI books

lar adaptive responses. Thus, the availability of a known reference set of genotypescould greatly assist consideration of whether a new test environment is representativeof the selection target and whether or not a new genotype is preferentially adapted tothat target.In addition to these immediate advantages for the interpretation of breeders’evaluations, we propose that reference lines be used to achieve a rapid and integrativeassessment of environmental characteristics over space and time and to indicate likelycharacteristics of new test environments. This would require evaluation of the referencelines in many locations and seasons to sample a broad cross-section of possibleenvironments. For example, locations distributed across the toposequence would beneeded in order to assess the pattern of environments represented there.Clearly, integration of physical and biological characterization is the ultimategoal for characterization, as this would lead to an improved assessment of whereparticular types of environments are present. The frequency and production risk associatedwith these environments could be assessed using crop simulation (Aggarwal etal 1996, Cooper et al 1999). Since physiological understanding of patterns of genotypeadaptation is required for the identification of useful traits conferring an adaptiveadvantage in particular conditions, widespread use of a set of representative referencelines could provide a first step in this process.This chapter considers the feasibility and methodology for using a set of referencelines to classify sites from multienvironment trials into an identified target populationof environments. We consider strategies for selecting reference lines to capturea wide range of G × E interactions for this purpose. We examine methodologies forassessing the characteristics of new sites from multienvironment trials on the basis oftheir reference line responses. We seek to use these responses to indicate physical andclimatic properties of those new environments.Materials and methodsUsing data from a series of 36 multienvironment trials with 47 entries conductedbetween 1994 and 1998 across South and Southeast Asia by the Rainfed LowlandRice Research Consortium and at the International Rice Research Institute, Wade etal (1999) reported that G × E interactions were repeatable and genotypes and environmentswith similar patterns could be grouped consistently. The genotypes and environmentsthey studied and their groupings and some class properties are listed inFigures 1 and 2. We seek to identify representative individuals from these genotypegroups for use as reference lines and to evaluate whether the G × E classification canbe repeated with just the reference lines. This would indicate whether a new environmentcould be correctly classified based on reference lines alone.In the selection of reference lines, we are concerned with sensitivity of responseof lines to environmental characteristics and would not like this sensitivity to be obscuredby mean genotypic effects (McLaren 1996). Hence, we have used pattern analysisbased on mean polished yield response data (genotypes and environments centeredwith least squares adjustment for imbalance).Using reference lines to classify multienvironment trials . . . 133