A framework to characterize the commercial life cycle of crop varieties: Application to the case study of the influence of yellow rust epidemics on French bread wheat varieties
Résumé
We examined the commercial life cycle of varieties of arable crops that could bring a better understanding of the drivers of their commercial success. In the current study, we propose indicators to describe the commercial life cycle of a variety and test their relevance on a case study centered on bread wheat varieties in France. We focus on yellow (stripe) rust, caused by Puccinia striiformis Westend. f. sp. tritici Eriks., an important disease that led to the rapid withdrawal from the French market of susceptible varieties during the last decades. In the present study, we assess how yellow rust pressure influenced the commercial life cycle of 31 bread wheat varieties over the period 1987-1991 which was characterized by the breakdown of resistance based on two race-specific genes Yr6 and Yr9. We defined areas of bread wheat production located in the northern half of France based on homogeneity for yellow rust pressure, virulence frequencies, varietal composition and varietal replacement. We identified four groups of non-redundant indicators and retained one indicator per group based on its biological relevance when considering a priori hypotheses on the influence of yellow rust epidemics on the commercial life cycle of susceptible varieties. These four indicators describe the commercial life-cycle duration, the growth phase duration, the coincidence between an epidemic peak and the end of the growth phase, and the cumulative percentages of acreage of the variety during the growth phase duration. For each homogeneous production area, we calculated these four indicators for a set of varieties and performed a principal component analysis associated with a clustering algorithm. In the northwest coastline production area, known to be highly affected by yellow rust, we identify eight varieties presenting a combination of indicator values suggesting a rapid withdrawal from the market. All these varieties were susceptible to yellow rust, among which five were concerned by the breakdown of resistance based on Yr6 or Yr9 race-specific gene. In contrast, in the northeast production area, much less affected by yellow rust over the period studied, no variety presented a combination of indicator values related to a rapid withdrawal. Beyond the identification of susceptible varieties, our statistical procedure has also permitted to highlight two varieties, Soissons and Scipion, with potential durable resistance in the northwest coastline production area. A promising perspective for breeders could be a more complete identification of varieties with durable resistance that could promote the long-term durability of yellow rust control to face future epidemics.
