Genetic impoverishment and cross-incompatibility in remnant genotypes of Ziziphus celata (Rhamnaceae), a rare shrub endemic to the Lake Wales Ridge, Florida

The loss of genetic diversity in fragmented populations ofself-incompatible plant species may result in sexual reproductive failure andlocal extinctions. Florida ziziphus (Ziziphus celata) is aself-incompatible clonal shrub known only from five genetically depauperatepopulations on the Lake Wales Ridge, Florida, USA. Recovery of this speciesrequires identification of cross-compatible genotypes that can be used to createviable (i.e., sexually reproducing) populations. To further development of arecovery program for this highly imperiled species, we investigated its geneticstructure and sexual reproductive viability. We used random amplifiedpolymorphic DNAs (RAPDs) to investigate genetic variability within remnantpopulations and we conducted experimental compatibility trials to determine thecross-compatibility of remnant genotypes. One hundred and ninety-nine uniquestem samples collected from one ex situ and fivein situ populations were assayed for the presence orabsence of a band for 32 RAPD markers. Based on unweighted pair-group meancluster analysis (UPGMA), only 11 multi-locus genotypes (MLGs) were identified.Eight of these MLGs correspond to MLGs identified in an earlier allozyme study.In addition, we identified three new RAPD-based MLGs. Three of the five naturalpopulations consisted of only one MLG, while the largest and most geneticallydiverse population comprised only four MLGs. Coefficients of similarity rangedfrom 96.6% for the most closely related MLGs to 20.7% for the most distantlyrelated. The compatibility trials demonstrated that most MLGs arecross-incompatible. With 69% of all possible one-way crosses tested (38/55), wehave identified only eight compatible crosses via germination trials. Based onthe results of the compatibility trials, we assigned MLGs toself-incompatibility (SI) mating types. On present evidence, the currentbreeding population of Florida ziziphus may comprise as few as two SI matingtypes. These SI mating types will be used to guide future breeding efforts andan experimental introduction.