On-farm yield experiments were carried out in the Tombouctou region of Mali in 2009/10 under heat- and drought-prone desert conditions with three local landraces of seed-type watermelons. The landraces, named Fombou, Kaneye and Musa Musa by the farmers, exhibited distinct characteristics for fruit morphology, but in particular for seed traits. On average, the three landraces produced a fruit yield of 11·6 t/ha and an estimated seed yield of 364 kg/ha, with no significant differences among landraces. Kaneye showed the highest stability of fruit number/ha in different field environments, suggesting this landrace is the best among the three for a poor growing environment, whereas Fombou and especially Musa Musa responded positively to more favourable environments. Seed weight revealed a different trend, with Fombou as the most responsive to favourable conditions, while Kaneye and Musa Musa were less responsive. The yields obtained suggest that these local landraces of watermelon are valuable plant genetic resources for securing food supply in arid, heat- and drought-prone areas.