whether to develop widely or specifically adapted genotypes and (ii) how to allocate resources between tests Sweetpotato [Ipomoea batatas (L.) Lam.] is cultivated across a for yield and nutritional traits. Such an understanding wide range of agrogeographical conditions. The objectives of this study were to analyze genotype ϫ environment (G ϫ E) interactions would also allow informed choices to be made regarding for sweetpotato yield (i.e., storage root yield, biomass, harvest index) which locations and input system should be used in breedand nutritional traits [i.e., root dry matter (RDM), starch (STA), and ing efforts. ␤-carotene (BCR) content; and leaf carotene (BCL) and chlorophyll Prerequisites for the analysis of G ϫ E interactions (CHL) content] in multienvironmental trials (MET) across ecogeoare estimates of variance components relative to genographic regions. Nine clones of diverse origins were tested and comtypes ( G 2 ), G ϫ E interactions ( GϫE 2 ), and the error pared with check clones at seven locations in Peru using two N treatterm ( ε 2 ) from trials conducted across locations. If ments (N ϭ 0 or 80 kg ha Ϫ1 ). The G ϫ E analysis was conducted multilocation trials are conducted that include further with regression, additive main effects and multiplicative interaction environmental factors, such as regions, years, or N input, (AMMI), and cluster analyses. The G ϫ E interactions were smaller then the G ϫ E term can be further partitioned and than the genetic variation of nutritional traits. The G ϫ E interactions were larger or nearly equal to the genetic variation of yield traits corresponding variance components can be estimated. (except harvest index), and were mainly determined by subsets of So far, there is no general theory for a detailed stability genotypes and environments. The contribution of N input to G ϫ E

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Two field experiments were performed to evaluate the nitrogen fixation potential of twenty common bean cultivars and breeding lines during summer and winter seasons of 1986 and 1988, respectively. The ~SN isotope dilution method was used to quantify N 2 fixation. The cultivars and breeding lines were variable in terms of their N 2 fixation. The cv. Caballero was very efficient, with more than 50% N derived from the atmosphere and 60-80 kg N ha -~ fixed in both seasons. Other cultivars were less efficient, since the poorest ones derived less than 30% of their nitrogen from the atmosphere and fixed less than 20 kg N ha -1. After additional testing the best cultivars may be used directly by the farmers for cultivation. The experiments have provided information about which genotypes may be used to breed for enhanced fixation in common bean.

Potatoes are an important cash crop for small-scale producers worldwide. The move away from subsistence to commercialized farming, combined with the rapid growth in demand for processed agricultural products in developing countries, implies that small-scale farmers and researchers alike must begin to respond to these market changes and consider post-harvest treatment as a critical aspect of the potato farming system. This paper presents and assesses a low cost potato-grading machine that was designed explicitly to enable small-scale potato growers to sort tubers by size for supply to commercial processors. The results of ten experiments reveal that the machine achieves an accuracy of sort similar to commercially available graders. The machine, which uses parallel conical rollers, has the capacity to grade different tuber shapes and to adjust sorting classes, making it suitable for locations with high potato diversity. Its relatively low cost suggests that an improved and adapted version of this machine might enhance market integration of small-scale potato producers not only in Peru, but in other developing countries as well.