XXX-639

XXX-639 is the name used in a 2022 report for a recovered mutant rootstock from one unusually vigorous tree in a commercial planting of HLB-positive Valencia on X-639. SSR markers matched standard X-639; flow cytometry measured less DNA and suggested possible deletion mutations. The recovered rootstock tested negative for CLas and was being propagated for advanced trials. This early report does not establish a replicated performance result or commercial release.^⁠[1]

A 2025 SWFREC presentation describes a putative X-639 mutant labeled “STR-4-1” and reports a vigorous Valencia scion on X-639 rootstock with about 50 fruit. The talk does not name XXX-639. This may be the selection called XXX-639 in the 2022 report, but that connection is an inference; the presentation is an early account, not a replicated performance trial.^⁠[2]