Genetic Analysis of Vegetative Branching and Rhizomatousness in Sorghum

We report a quantitative study identifying genomic regions responsible for vegetative branching patterns and rhizomatousness in sorghum. Initiation and formation of vegetative branches and rhizomes from axillary meristems are important developmental processes in determining plant architecture, which is largely genetically controlled. We have developed a phenotypic system to quantify branching patterns, that integrates morphological positions and physiological status of each branch. Phenotyping of rhizomatousness includes measuring the number of rhizomes as well as distances from rhizome-derived vegetative shoots to the crown. A recombinant inbred line (RIL) population of 161 individuals derived from a cross between the sorghum (Sorghum bicolor) reference cultivar BTx623 and its wild relative (Sorghum propinquum (Kunth) Hitchc), segregating for both branching and rhizomatousness, is suitable for QTL analysis. Branching patterns (i.e. tillers or branches, mature or immature branches) and rhizome growth are each influenced by common genomic regions but also have additional distinct QTLs, indicating that there might be a general control for axillary meristem initiation and separate pathways for its outgrowth. As a complement of QTL mapping, association genetics will identify candidate genes from an established sorghum diversity panel. Better understanding of the genetic determinants of plant architecture, including subterranean structure, will facilitate genetic manipulation of plants for a variety of purposes, and identification of the underlying genes may contribute to plant growth regulation.