Acidity and Total Soluble Solids in Citrus Hybrids and Advanced Crosses Involving Acidless Orange and Acidless Pummelo1

Titratable acidity and total soluble solids were measured in F 1 hybrid citrus populations involving an acidless pummelo [ Citrus grandis (L.) Osbeck] and an acidless orange [ Citrus sinensis (L.) Osbeck] respectively, as one parent. Three advanced crosses were also studied. Crosses of the pummelo with 5 medium acid cultivars produced no acidless individuals but many with low to medium acidity and a few with acidities above 1.6% in their main seasons of use. The overall mean titratable acidity was 1.1%. Crosses of the acidless orange with 4 medium-acid cultivars produced only a few low to medium-acid individuals, and many with acidities above 1.6%; the overall mean acidity was 2.0%, significantly higher than with the pummelo. Mean levels of total soluble solids had a range which was similar between the 2 types of crosses, although the overall mean was significantly higher in the orange crosses. There were significant correlations between acid and total soluble solids levels in only 2 out of 11 progenies among all of the crosses. Twelve of 40 individuals were essentially acidless in an F 2 population involving the acidless pummelo as a grandparent. There were no acidless individuals, but there were many moderately-acid ones in 2 populations of acidless pummelo hybrids backcrossed to acid cultivars. These proportions suggest simple inheritance for the acidless character of the pummelo. In contrast, the high acid levels of the F 1 populations with acidless orange imply a different basis for the latter’s lack of acidity.