Spring Wheat Diversity in Irrigated Areas of Two Developing Countries

Abstract

Crop genetic diversity may not be apparent from plant phenotypes. Coefficients of parentage were used to examine genetic diversity and compare trends in spring wheat cultivars grown in the Yaqui Valley of Mexico (1972–1991) and the Punjab of Pakistan (1978–1990). Coefficients of parentage estimate probabilities of retaining latent diversity rather than focusing on the apparent diversity of highly heritable traits (e.g., rust resistance alleles). A small trend towards increased genetic diversity was found in the Pakistani Punjab. In the Yaqui Valley, large oscillations in diversity occurred without significant trends. In comparing the two regions, the latent genetic diversity in the Yaqui Valley based on parentage and area of production in a given year (weighted diversity) was 20% less than in the Punjab. However, the lower diversity was partially offset by rapid turnover in germplasm in the Yaqui Valley. The rate of change in germplasm (temporal diversity) was 22% lower in the Pakistani Punjab than in the Yaqui Valley. The temporal diversity of cultivars used by growers in the Yaqui Valley was greater than among cultivars recommended for use by the research services, indicating that growers replace germplasm faster than the changes in recommended cultivars. The opposite was found in the Punjab. In the Yaqui Valley, individual cultivars dominated production for 1 to 3 yr, while in the Punjab, one cultivar, ‘Yecora’ dominated production for 7 yr. We conclude that (i) cultivar improvement programs did not erode genetic diversity in production areas currently growing improved cultivars and (U) patterns of cultivar use by farmers were more important than the composition of recommended cultivars in determining genetic diversity.