Gene pool of pearl millet is classified into primary, secondary and tertiary gene pools based on their crossability with cultivated pearl millet. The primary gene pool includes P. glaucum and its wild relatives that can naturally cross with it. The secondary gene pool includes species like P. purpureum that can be crossed with difficulty. The tertiary gene pool includes more distantly related species that cannot be crossed or produce sterile hybrids. ICRISAT genebank conserves over 22,000 pearl millet accessions including 750 wild species accessions from 24 Pennisetum species collected from 51 countries.