The Punjab of India is an historical source of key wheat genetic resources in national and global plant breeding, and a focus of concerns about the abandonment of local varieties during the Green Revolution. Much of the wheat area in Punjab was already planted with earlier products of modern plant breeding programs when the Green Revolution began. These cultivars were more genetically similar and less productive than the semi-dwarf wheat varieties that succeeded them. We define, summarize and test indices of variety change and genetic diversity for the modern wheat varieties released and grown in Indian Punjab during the post-Green Revolution period. The first is the area-weighted average of varieties grown, which measures the rate of variety change, important means of counteracting the uniformity that can lead to pathogen mutation and plant diseases. Variety change is determined in large part by variety release and seed industry po licies. The second is the average coefficient of diversity, which measures the extent of dissimilarity among wheat varieties conferred through plant breeding. A generalized Cobb-Douglas production function is estimated with these indices specified as technical efficiency parameters, after testing for the exogeneity of each index. Findings support the hypothesis that slow variety age has counteracted the positive productivity effects brought about through diversifying the genetic base in wheat breeding in the post-Green Revolution period. Policies that speed the rate of variety change and make more equitable the spatial distribution of modern varieties could support, rather than detract from wheat productivity, reinforcing breeding successes.
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