differences among or between treatments that were tested over a wide range of environments and where genotype-by-environment interaction was present.
Finlay and Wilkinson (1963) refined and enhanced the Yates and Cochran procedure, and did so apparently without knowledge of the seminal article (p.745). Their most important contribution was to describe the characteristics of varieties with high (> 1.0) and low (< 1.0) stability (regression) parameters and relate these to variety mean yield over environments, Fig. 1.
Figure 1. Relationship of variety regression coefficient and mean yield to stability according to ?inlay and Wilkinson (1963).
..IV.M..W A he a@MV
1.0
Vanety mean yaid
They define varieties with general adaptability as those with average stability (b = 1.0) when associated with high mean yield over all tested environments. However, they also recognize that above average stability (b approaching zero) is associated with increasing adaptability to low-yielding environments, and below average stability with increasing adaptability to high-yielding environment (p.749). They argue in favor of testing over a wide range of environments and not discarding low yielding environments because this "...will bias the selection towards types specifically adapted to high-yielding environments, and will pass over those with general adaptability" (p. 752). As this statement emphasizes, however, their interest ultimately was on generally adapted varieties. In commenting on the varieties included in the tests they were reporting, they stated:
"The varieties with the high phenotypic stability all have low mean yields. They are so stable, in fact, that they are unable to exploit high-yielding environments.
On the other hand, varieties can be too sensitive to environmental change, as is shown by the low mean yields of the varieties with high regression coefficients. The generally adapted varieties balance between these extremes, the actual point of balance depending on the particular genotype and range of environments" (p.752).
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