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Perennial germplasm derived from crosses between Sorghum bicolor and either S. halepense or S. propinquum is being developed with the goal of preventing and reversing soil degradation in the world's grain sorghum-growing regions. Perennial grain sorghum plants produce subterranean stems known as rhizomes that sprout to form the next season's crop. In Kansas, breeding perennial sorghum involves crossing S. bicolor cultivars or breeding lines to S. halepense or perennial S. bicolor n × S. halepense breeding lines, selecting perennial plants from F 2 or subsequent populations, crossing those plants with S. bicolor, and repeating the cycle. A retrospective field trial in Kansas showed that selection and backcrossing during 2002-2009 had improved grain yields and seed weights of breeding lines. Second-season grain yields of sorghum lines regrowing from rhizomes were similar to yields in the first season. Further selection cycles have been completed since 2009. Many rhizomatous lines that cannot survive winters in Kansas are perennial at subtropical or tropical locations in North America and Africa. Grain yield in Kansas was not correlated with rhizomatousness in either Kansas or Uganda. Genomic regions affecting rhizome growth and development have been mapped, providing new breeding tools. The S. halepense gene pool may harbor many alleles useful for improving sorghum for a broad range of traits in addition to perenniality.

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Social Impact Statement Although tremendously successful at feeding humanity, row crop agriculture based on annuals contributes to numerous ecosystem dis‐services, ranging from soil degradation and aquatic eutrophication to greenhouse gas production. In contrast, perennial grain crops (which produce harvests for multiple seasons from single plantings) have the potential to provide valuable regulating and supporting ecosystem services in addition to food production. In particular, losses of ecological capital that threaten permanent food insecurity such as ~1% of global soil per year are expected to be mitigated or even reversed by crops that combine the high yield realized by scientific breeding via multiple cropping cycles from single plantings. Summary Perennial herbaceous may provide food and biomass while preserving ecological capital and reducing energy inputs. Sorghum has two perennial relatives and rich morphological diversity being used to breed for perenniality. We elucidate genetic determinants of rhizomatousness and survival, in two BC1F2 populations totaling 246 genotypes derived from backcrossing different annual Sorghum bicolor X perennial S. halepense F1 plants to a tetraploidized S. bicolor. RNA‐seq assisted in identifying candidate genes for rhizomatousness. Correspondence of rhizomatousness quantitative trait loci (QTLs) with those from two populations derived from crosses between S. halepense progenitors S. bicolor X S. propinquum suggests either the preservation of interspecific polymorphism or the formation of novel alleles following polyploid S. halepense formation. Correspondence of tillering and branching QTLs further supports their developmental. Identification of genes from RNA‐seq study within QTL intervals provides insight toward discovery of causal rhizomatous genes. An unexpected finding from both S. halepense‐ and S. propinquum‐derived populations is that alleles contributing to late flowering are related to reduced rhizomatousness. Twelve of 16 QTL regions conferring rhizomatousness fall in paleo‐duplicated regions tracing to single ancestral regions 96 million years ago, indicating that corresponding genes in these regions have retained similar functions since the duplication event.