Crop wild relatives of pigeonpea ( Cajanus cajan (L.) Millsp.): Distributions, ex situ conservation status, and potential genetic resources for abiotic stress tolerance

Pigeonpea (Cajanus cajan (L.) Millsp.) is a versatile, stress-tolerant, and nutritious grain legume, possessingtraits of value for enhancing the sustainability of dry sub-tropical and tropical agricultural systems.The use of crop wild relatives (CWR) in pigeonpea breeding has been successful in providing importantresistance, quality, and breeding efficiency traits to the crop. Current breeding objectives for pigeonpeainclude increasing its tolerance to abiotic stresses, including heat, cold, drought, and waterlogging. Herewe assess the potential for pigeonpea CWR to be further employed in crop improvement by compilingwild species occurrence and ex situ conservation information, producing geographic distribution modelsfor the species, identifying gaps in the comprehensiveness of current germplasm collections, and usingecogeographic information to identify CWR populations with the potential to contribute agronomic traitsof priority to breeders. The fifteen prioritized relatives of pigeonpea generally occur in South and SoutheastAsia to Australia, with the highest concentrations of species in southern India and northern Australia.These taxa differ considerably among themselves and in comparison to the crop in their adaptations totemperature, precipitation and edaphic conditions. We find that these wild genetic resources are broadlyunder-represented in ex situ conservation systems, with 80% of species assessed as high priority for furthercollecting, thus their availability to plant breeders is insufficient. We identify species and highlightgeographic locations for further collecting in order to improve the completeness of pigeonpea CWR germplasmcollections, with particular emphasis on potential traits for abiotic stress tolerance