MATING SYSTEM OF PACHYCEREUS-PRINGLEI - AN AUTOTETRAPLOID CACTUS

The mating system of the Mexican subdioecious columnar cactus, Pachyce reus pringlei (Cardon), was examined by allozyme analysis. Tetrasomic patterns of inheritance were found for all polymorphic loci, indicatin g that the species is an autotetraploid. A model is presented that exp ands Ritland's (1990a) mixed mating model for autotetraploids to incor porate an arbitrary number of alleles per locus. This model is applied to the progeny arrays of several female and hermaphroditic individual s of P. pringlei. P. pringlei exhibited a complex breeding system; the multilocus estimate of outcrossing, t(m), for female cacti was 0.949 and for hermaphrodites was 0.301. These results are discussed in the c ontext of inbreeding depression and the evolution of the breeding syst em of this species.