In vitro Rooting of Leguminous Plants: Difficulties, Alternatives, and Strategies for Improvement

Leguminous plants include many of the most important food crops and are also cultivated for forage, used as a rich fiber source, and are important in the manufacture of pharmaceutical compounds. Their ability to biologically fix atmospheric nitrogen enhances soil fertility. Beyond conventional propagation methods, modern in vitro technology offers new means for propagating these plants. Significant progress has been achieved in somatic embryogenesis and embryo rescue, despite legumes' notorious recalcitrance to transformation and regeneration of legumes. The establishment of stable and reproducible regeneration protocols has resulted in commercially successful propagation of some legume species. Still, regeneration protocols for many other legumes have not been successful, primarily due to poor in vitro rooting during regeneration. This review addresses the factors constraining rooting, describes alternative methods to promote in vitro rooting, and provides a summary of in vitro rooting studies performed across a large number of leguminous species.