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 populntions of self-incompalible plant species may result in sexual mproductive f%lure and local extinctions. Florida ziziphus (Ziziphus c&m) i s a self-incompetiblc clonal shrub known only from five genetically depaupemre populations on the Lake Wales Ridge. Florida, USA. Recovery of thix spccics rcyuirex identification of cross-compatible genotypes that can be used to create viable (i.e., sexually reproducing) pqxdalinns. To further development of a recovery program for this highly imperiled species, we invesrigatcd its genetic strucntre and sexual reproduclive viability. We used random amplified polymorphic DNAs (RAPDs) to investigate genetic variability within remnant populations and we conducted experimental compatibility trials IO determine the truss-compatibility of rtxlnanf genotypes. One hundred and ninety-nine unique slem ~amplcs collected from one ex sirrr and tivc irt rite populations wcrc assayed for the presence or absence ol‘a band for 32 RAP0 markers. Based on unweightcd pair-group mean cluster analysis f UPGMA), only I I multi-locus genotypes (MLGs) were identified. Eight of these MLGn correspond lo MLGs identltied in an earlier all~zyme stndy. In addition. we identified three new RAPD-based MLGs. Three of the five natural populations consisted of only one MLG, while the largest and most genetically diverse population comprised only four MLGs. Coefficients of similarity ranged tiom 96.6% for the most closely related MLGs to 20.7% fix the most distantly related. The compatibility trials detnon~hated that most MLCs are cross-incompatible. With 69% of all possible one-way crosses tested (3X/5.5 1 . we have identified only eight compatible crosses via germination t&is. Based on the results of the compatibility trials, we assigned MLGs to self-incompatibility (3) mating types. On present evidence. the current breeding population of Florida ziziphus may comprise as few as two Sl mating types. These SI mating types will be used to guide future breeding efforts and an expcrimentnl introduction.