Adjacent but separate trials of `Oroblanco' and `Melogold', both triploid pummelo [Citrus grandis (L.) Osbeck] × grapefruit (Citrus paradisi Macf.) hybrids, were established on nine rootstocks in the Indian River citrus region of Florida in 1993. The trees on the citrandarin rootstock ×639 [Cleopatra mandarin (C. reticulata Blanco) × trifoliate orange (Poncirus trifoliata L.)] were significantly more productive than trees on any other rootstock tested for `Oroblanco' and all rootstocks except Swingle citrumelo (C. paradisi × P. trifoliata) and Cleopatra mandarin for `Melogold'. Cumulative production of `Oroblanco' on ×639, through year 9, was 50% higher than for Swingle or Volkamer lemon [C. limon (L.)], which were the next highest in yield. `Melogold' displayed extremely low yield, with 45% of trees producing fewer than 50 fruit total in the 9 years of this study. Carrizo citrange (C. sinensis Osbeck × P. trifoliata) produced the smallest trees with both scion varieties, reflecting poor adaptation of this rootstock to the calcareous soil at the trial site. As expected, acidity of `Oroblanco' and `Melogold' was much lower than would be observed for grapefruit when fall harvested, with similar total soluble solids (TSS), and much higher TSS: titratable acidity ratio. Some rootstock effects on internal quality were observed.
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