US SuperSour 4

Bowman (2023) reports US SuperSour 4 as a Florida Hirado pummelo seedling × Cleopatra cross. Tardivo et al. (2025) identify experimental rootstock US-1688 as SS4 and report the same named parents. Neither paper identifies the exact seedling accession used; Bowman gives only a collective 2000–2006 crossing window for SS2–SS5, not an SS4-specific cross year.^⁠[1]⁠[3]

The CRDF Project 21-008 report states that SS4 and SS5 were released in September 2023 and propagated for demonstration plantings and field trials. Bowman (2023) lists SS4's release year as 2023 but gives no month or day. In a separate 2025 nursery study, none of 24 tested seed-derived seedlings was true-to-type by SSR markers, although 89% of 50 looked visually similar; field-trial plants were propagated by cuttings.^{⁠[2]⁠[1]⁠[3]}

In the randomized 2014 Picos/St. Lucie County trial, grafted Valencia on SS4 produced 56.8 kg fruit/tree cumulatively in 2018–21 (65% above Swingle). The later six-season economic analysis reports 638 additional lb solids/acre and $2,307/acre more cumulative revenue than sour orange in 2022 dollars at 10% interest. These results describe grafted Valencia at this site; the later analysis revisits the same cohort.^⁠[1]⁠[4]