THE GENETIC-BASIS OF MALE-STERILITY IN SCHIEDEA (CARYOPHYLLACEAE), AN ENDEMIC HAWAIIAN GENUS

Interspecific crosses of Schiedea and Alsinidendron (Caryophyllaceae), endemic Hawaiian genera, produced segregation patterns of females, males, and hermaphrodites consistent with nuclear control of male sterility. Female excesses, typical in hybrids when mismatches occur between cytoplasmic factors controlling male sterility and nuclear factors restoring fertility, were not observed in any crosses. The nuclear gene controlling expression of the male (or hermaphroditic) sex in Schiedea is dominant; females are homozygous recessives. Results from intraspecific crosses and segregations among progeny raised, from field-collected seeds were largely consistent with results obtained from interspecific and intergeneric crosses. In Schiedea gynodioecy is likely to represent an early stage in the evolution of dioecy. The transition from gynodioecy to full dioecy may be a relatively rapid event favoured by nuclear control of male sterility, a view supported by the occurrence of gynodioecy, subdioecy, and dioecy in Schiedea.