The dendrogram constructed from pattern analysis of those ESWYT locations repeated in two or more years identified four primary clusters at the third-fusion level (Fig.
At Sakha, ESWYT trials were sown in 14 the 20 yr examined.
The individual dendrograms generated from SHMM analysis for each of the 20 yr of ESWYT are summarized in Table 4.
The other highly associated key site, Sakha, although producing two equally important year groupings at the second fusion level, showed that at the third fusion level of the dendrogram derived from pattern analysis, half of the ESWYT years fell into the same primary grouping.
The ESWYT trials sown at this location were fully irrigated thereby reducing genotype x year interactions attributable to variation in rainfall and average yield was high (6.79 [+ or -] 1.96 Mg [ha.sup.-1], data not shown).
The four key clusters observed from pattern analysis of sites repeated at least three times during the 20 yr in which ESWYT was grown are influenced by temperature, rainfall, latitude, altitude, and disease incidence.
This finding is supported by our study as the ESWYT was grown across a range of soil moisture conditions, and cropping season water availability was clearly a primary differentiating factor.
Abbreviations: CIANO, Centro de Investigaciones Agricolas del Noroeste; CIMMYT, Centro Internacional de Mejoramiento de Maiz y Trigo (International Maize and Wheat Improvement Center); COI, crossover interaction; ESWYT, Elite Spring Wheat Yield Trial; GEI, genotype x environment interaction; SHMM, shifted multiplicative model.
Summary of locations used in the analysis of ESWYT trials number 1 to 20 spanning the period 1979-1998, their latitude, altitude, and frequency of occurrence.
We decided to compare the mean of the five highest yielding entries in each nursery as the majority of lines in the ESWYT and SAWYT trials are not expected to be adapted at any specific location.
The significantly greater rates of progress in yield over time recorded for the SAWYT compared with ESWYT for both high and low yielding environments reflects, to some extent, the slightly higher average TM yields recorded for ESWYT.