An econometric approach using international and national yield trial data is employed to estimate a spillover matrix for wheat varietal technology. The global spillover matrix is estimated based on international yield trial data from 1979-80 to 1987-88, that include 195 international trial locations and 209 wheat varieties. The locations were classified across countries using the CIMMYT's wheat megaenvironment system and varieties were classified by both their environmental and institutional origin. The model gave good explanatory power and confirmed the location specificity hypothesis, at least, for the varieties developed by national programs (NARS). The spillover matrix shows that NARS varieties developed in the 'home' environment generally perform better on average than varieties developed in other megaenvironments. Also, the matrix is not symmetric. ClMMYT varieties perform better on average in irrigated and high rainfall environments than NARS varieties developed for these environments. The yield advantage of CIMMYT varieties in many test megaenvironments indicates the potential of CIMMYT varieties to spill-over to these test megaenvironments. Results also indicate that national programs are efficient in selecting from among imported technologies. Analysis of international data is complemented by the analysis of country-level data for Pakistan and Kenya that confirms the above results. The country-level analysis, however, indicates that ClMMYT germplasm does not do so well in some sub-environments, such as the irrigated short-duration environment. The results of the spillover matrix have implications for the design of crop breeding programs both at the national and international levels. Information provided by the spillover matrix can be utilized by national programs to deploy their resources more efficiently by following a mixed strategy of direct importation of technology in some environments and local development of technologies in other environments which are unique to the country.


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