Quantitative Trait Loci (QTL) for water use and crop production traits collocate with major QTL for tolerance to water deficit in a fine mapping population of pearl millet (Pennisetum glaucum L. R. Br.)

To increase yield across a range of water stress regimes, we require a precise understanding of biological mechanisms that eventually contribute to it, and an approach to that quest is to assess the degree of co-mapping of genetic regions responsible for traits putatively involved in water stress adaptation and genetic regions responsible for agronomic traits measured in the field. For that, a fine-mapping population of pearl millet, segregating within previously identified quantitative trait locus (QTL) for adaptation to terminal water deficit on chromosome 2 (LG02), was tested across different experimental environments (pot culture, high-throughput phenotyping platform, lysimeters, and field). This population was phenotyped for traits at different levels of plant organization, ranging from water-use traits (transpiration rate, leaf area, plant organ dry weights, etc.) to crop production and agronomic traits (grain yield, tiller number, harvest index, etc.) The linkages between traits across the experimental systems were analyzed using QTL co-localization approach and principal component analysis (PCA). The functional relevance of the phenotyping systems was traced by PCA analysis. Furthermore, four regions within the LG02-QTL underlying substantial co-mapping of water-use related and agronomic traits were found. These regions, identified across the experimental systems, provided genetic evidence of the tight linkages between water-use traits phenotyped at lower level of plant organization and agronomic traits assessed in the field. It suggests that there is much to gain, for the benefits of both genetics and breeding, in combining phenotypic data captured at different levels of plant organization.
Key words: Water stress, GxE interactions, high-throughput phenotyping, vapor pressure deficit