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Genotype x environment interaction in tef 149
Stability analysis might require the testing of the genotypes for several years (more
than three years), which might also length the time required to release varieties. To
reduce the time required for genetic improvement, testing at multiple locations in one
year is used as a substitute when climatic conditions among locations are comparable
to differences among years (Fehr 1987). For stability analyses in tef, using each siteyear
combination as a different environment may maximize sampling of the yearly
variation. However, detailed investigations are required for efficient representations
of unpredictable vitiations for use in stability analyses of tef yield trials.
To determine how much of the G x E interaction was due to locations, years and
location x year, the estimated variance components were compared to the estimated
variance component for genotypes (Table 5). The results of such computations have
an important bearing on which dimension to emphasize when dimension to emponent
of the G x E interactions was due to interactions with locations. This indicates that
testing across locations is the most important in each of the three sets to accurately
reveal differences among genotypes. This result once again cells for the evaluation of
early germplasm nurseries in multiple locations for each set of trials.
Table 5. Ration of estimated variance components for the partitioning of
Genotype x environment interaction into genotype x location(δ 2 I).
Genotype x year (δ 2 IY), and genotype x location x year (δ 2 gly) to
The estimated variance component for genotypes (δ 2 g) for three tef
National yield trial sets
Ratio Early set Intermediate set Late set
δ 2 l/ δ 2 g 0.50 0.43 0.64
δ 2 l/y/ δ 2 g 0.20 0.13 0.21
δ 2 gly/ δ 2 g 0.20 0.28 0.29
Causes of G x E
Environmental factors
Legesse (1997) employed multivariate statistical tools in order to study the climatic
(altitude, rainfall, and temperature) and edaphic (nitrogen, phosphorous, pH, organic
matter, and particle size distribution) variables that may account for the variations in
grain yield and yield components of 12 tef genotypes at four locations. The results
indicated that no single variable could explain the variation across locations for the
genotype-environment system studied. Mulu (1994) in another study noted that
moisture stress could cause variation in the relative performance of genotypes in
different environments. Tirunch (1999) also suggested that location differences in
moisture regimes have contributed to the differences in adaptation of 18 genotypes
grown at seven sites. Identifications enable the breeder to look for genetic variation
for resistance/tolerance to the defined production constraint.