Increasing Yields Near the Yield Potential: A Case Study of Rice Breeding in California.

Meeting the challenge of feeding a growing population with increasingly limited resources will require increasing the yield potential of staple crops, such as rice. Yet many high yielding, intensive production systems have experienced slow rates of yield improvement in recent years despite demonstrated increased yield potential of new genetics over old in side-by-side comparisons. We analyzed experimental data from one such system, California (CA) rice production, in order to better understand what improvements have been made in the genetic yield potential via plant breeding. Specifically, the hypothesis that a rice variety’s yield erodes over time after the initial selection was tested as an explanation for how side-by-side comparisons show increased yield while no substantive increases have been seen in farmers’ fields. Side-by-side comparisons under yield erosions will show “false” increases due to the older cultivar decreasing, not due to increased genetic yield potential by the newer cultivar. We confirmed an apparent increase in yield in side-by-side comparisons between old and newer varieties when the yield erosion was not considered. However, we demonstrate this apparent increase in yield can be explained by the differences in the time since selection between cultivars. The impact of yield erosion was estimated to be 29.3 kg ha^-1 year^-1 (90% credible interval -4.4 to -53.3) after initial selection. Once this effect was considered, the apparent yield advantage of newer cultivars over old was uncertain (-3.3 kg ha^-1 year^-1, 90% credible interval -36.1 to 31.5). This underscores the importance of breeding to maintain yield and the challenges of increasing the genetic yield potential.