most successful programs (for example, ICTA in Guatemala) the field testing teams are considered as essential elements of the breeding program and the breeders participate actively in the onfarm activities (McDermott and Bathrick, 1982; Ruano and Fumagalli, 1988). Without these field teams, it would. be difficult for the breeders to have the opportunity for widespread evaluation of their material under the conditions of the small farmers who are the principal clients of the institute. Responses in the field help
orient the direction of the breeding program. In the least
successful programs, field testing teams have no official connection with the breeding program. They have access only to material that has already been released by the breeding program. There is little or no feedback of the results of the field testing program to the breeding program, and there is a low rate of adoption of the tested materials that seldom excel in the conditions of the farmers. Even worse, there is a continual loss
of genetic material that might have excelled under the farmers' conditions.
The number and range of environments under which on-farm tests are conducted depend on 1) the. testing budget (personnel, transportation, and materials); 2) the philosophy of the breeding
and/or testing program leaders; and 3) annual crop production conditions. The range and distribution of environments. is probably more important than number so long as some minimum number (probably around 10) is achieved. As mentioned above, the magnitude of the
range divided by the overall mean yield is a useful measure to usrz as a basis for evaluating this result. A quick search resulted in locating the following ratios:
1) A potato study (reported in Caldwell and Taylor, 1987, p. 353)
on agronomic practices from 20 farms by the International Potato Center in the Mantaro Valley of Peru: 1.42/1.
2) A maize variety study (Poey, n.d., p.58) conducted by the farming systems program in Paraguay on 24 farms: 1.21/1.
3) A maize variety and fertilizer use study (Hansen et al., 1982)
conducted on 14 farms by the farming systems team in Malawi:
1.57/1.
These compare with a ratio of 0.55/1 in the Yates and Cochran study when years are combined (as the authors did) or 0.83/1 when
years and locations are separate. Other cited articles do not show data. However, Eberhart and Russell's recommendation of minimizing genotype-by-environment interaction and then selecting the highest yielding materials would have the tendency to reduce this ratio by either reducing the environmental range used for testing or increasing the overall mean of the materials tested, or both.
CONCLUSIONS AND RECOMM(ENDATIONS
Basic premises of this paper are that:
1) in the developing world, there is an urgent need f or a
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