The Inherent Genetic Control of Sesame (Sesamum indicum L.) Root Architecture and the Relationship with Canopy Development

Virtually nothing is known about the root development of sesame and the existing balance between below- and aboveground architecture. This relationship was quantified for non-dehiscent sesame cultivars in 2013 and 2014 in the southeastern U.S. To best represent a range of canopy geometries, six cultivars were utilized that included branched and uniculm types as well as pygmy growth habits. Several root architectural characteristics, including Total Root Length (TRL), were measured repeatedly in situ with a minirhizotron system up to 90 cm in soil depth. Leaf Area Index (LAI) was also repeatedly measured non-destructively. Surprisingly, despite the range in morphological growth habits among cultivars, there were no differences in TRL or LAI in either year. In fact, only in a multivariate assessment utilizing root characteristics over time simultaneously was it possible to distinguish between two cultivars in 2013. This highlights the inherent plasticity of sesame’s ability to maintain root and canopy size in different morphological arrangements. There was an interaction between cultivar and date of measurement for both LAI and TRL, indicating that the rates of leaf and root establishment and senescence differed among cultivars. In fact, most cultivars experienced leaf senescence prior to that of the root system. Overall root architectural patterns across soil depths revealed a consistent zone of high root proliferation between 20 and 50 cm, and the interaction between soil depth and measurement date revealed that the speed of root establishment and senescence was greatest in these same depths. Finally, the ratio of Root Area Index (RAI – calculated as root surface area per soil area) and LAI further indicated high similarity among cultivars and supports the conclusion that LAI was reflective of total root proliferation. This study provides the first critical results in the understanding of belowground sesame dynamics and their relationship with aboveground phenology.