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Pearl millet [Pennisetum glaucum (L.) R. Br.] single cross hybrids, bred from high-yielding parental lines in favorable environments, are not well adapted to northwest India’s arid zone. The objectives of these experiments were (i) to measure grain and stover yield heterosis in testcrosses of six landrace-based restorer populations and (ii) to understand how heterosis for biomass and harvest index (HI) affects heterosis for grain and stover yields in Crosses of these populations. Six restorer populations and their testcrosses on 10 to 13 A1 male-sterile lines were evaluated at two arid zone locations of northwest India. Heterosis was calculated as percentage advantage of testcross hybrids over parental restorer population. The range in individual testcross heterosis varied from -3% to +39% for grain yield and from -22% to +17% for stover yield. Variation in biomass heterosis accounted for 55% of the variation in grain yield heterosis and 84% of the variation in stover yield heterosis. Harvest index heterosis accounted for 38% of variation in grain yield heterosis and 13% of stover yield heterosis with a positive heterosis in HI resulting in negative heterosis in stover yield. The testcrosses with the highest biomass heterosis for each restorer population achieved 20% biomass heterosis level (combined with a mean 12% heterosis in HI), resulting in 32% grain yield heterosis and 18% stover yield heterosis. We concluded that heterosis for biomass was the major determinant of grain and stover yield heterosis in pearl millet.