Progress in Breeding for Perenniality in Sorghum

Perennial crops may provide consistent food and biomass supplies while preserving ecological capital and reducing water and energy inputs. Sorghum, one of the few multi-purpose crops that provide both grain and biomass in some of the world’s most adverse conditions, has two perennial relatives as well as rich morphological diversity occurring during divergent evolution both in the wild and under domestication, making it a good candidate for breeding for perenniality. Crosses between wild perennials and cultivated sorghums show the feasibility of developing genotypes with varying degrees of investment in perenniality while still providing harvestable food, feed, cellulose, and potentially also sugar. We describe F2, F2:3 and BC1F2 populations derived from an elite cultivar of Sorghum bicolor, and Sorghum halepense, which have displayed tremendous phenotypic variations, including varying degrees of rhizomatousness, winter and spring regrowth, and second-season “ratooning” within a single growing season. Phenotypic evaluation in two different temperate environments, Athens, GA and Salina, KS and in multiple years allows us to investigate effects of genetic and environmental factors and their interactions for traits related to perenniality. A pilot study with an initial assay of 100 SSR markers has detected some QTLs responsible for rhizomatousness and overwintering in F2 and F2:3 populations, and permits comparison to QTLs found in a diploid population derived from annual S. bicolor x perennial S. propinquum (the progenitors of S. halepense). Additional ongoing genotyping by sequencing will offer an opportunity to construct genetic linkage maps in these unusual populations for more comprehensive QTL analyses. Clarifying the genetic control of phenotypic variations in these unusual populations and their progenitors will strengthen our understanding of the evolution of perenniality, and also shed new light on prospects for breeding perennial crops optimized for food and/or biomass production.