ECOLOGICAL DIFFERENTIATION IN PERENNIAL, OCTOPLOID SPECIES OF FRAGARIA

Plants of octoploid Fragaria (2n = 56) were collected from 19 natural sites supporting strawberry colonies in California, grown in a common greenhouse and analyzed for 25 quantitative traits and 2 enzyme systems. Inter-populational variation was measured by using analysis of variance and genetic identity techniques. Microand macro-environmental measurements were made at each site. Stepwise multiple regressions were completed on the morphological-environmental variations and the allozyme frequency-environmental variations. Clonal propagules were compared under three controlled environmental conditions. Octoploid Fragaria appears to have undergone considerable ecological differentiation. Significant amounts of inter-populational variation were observed in a number of polygenic and monogenic traits. Numerous significant correlations were found between environmental and character variations, and in many cases, only a few environmental variables were necessary to "explain" significant amounts of that variation. Inter-populational differences were also found in the abilities of plants to accumulate biomass and survive under salt, nutrient and shade stress. It has been suggested that ecological differentiation plays a minor role in determining the eco-geographical range of allopolyploids due to the effects of polyploidy on the generation of mutational and recombinational variability. Clearly, this has not been the case in Fragaria. A NUMBER of workers have suggested that the broader ecological amplitudes of polyploid species are the result of dissimilar genomes being incorporated into single cytoplasms (Stebbins, 1950, 1971; Grant, 1971). Gottlieb (1976) pointed out that if the progenitors carry different alleles located on homeologous chromosomes, "fixed heterozygosities" may result, producing individuals with the combined adaptations of their progenitors or novel combinations of both. The fact that allopolyploids often express the enzyme genes of their progenitor species is well documented. This has been reported in wheat (Mitra and Bhatia, 1971; Hart, 1969, 1970, 1973, 1975), cotton (Cherry, Katterman, and Endrizzi, 1972), tobacco (Smith et al., 1970; Reddy and Garber, 1971; Sheen, 1972), safflower (Efron, Paleg, and Ahori, 1973), beans (Garber, 1974), and Tragopogon (Roose and Gottlieb, 1976). Novel heterodimeric enzymes were described in many of these studies. Similar relationships have also been shown by using phenolic compounds (Levy and Levin, 1974; Brehm and Ownbey, 1965; Bringhurst, Khan, and Voth, 1964). Polyploids have traditionally been described as less efficient than diploids in ecotypic differentiation because polyploidy places restrictions on the generation of mutational and recombinational variability. In polyploids, a change in a I Received for publication 26 June 1978; revision accepted 6 December 1978. single gene may have little effect on the plant as a whole because of the presence of a number of other similar alleles, while polysomic inheritance greatly reduces F2 variance in quantitative traits (Stebbins, 1950, 1956; Grant, 1971). In allopolyploids, the formation of new recombiant types is restricted by gene duplications and preferential synapsis. Genic variations may be present in these individuals, but if different "alleles" are located on nonpairing, homeologous chromosomes they will not segregate. Polyploids can still undergo considerable amounts of genetic differentiation, however. Large amounts of intraand inter-populational variability have been observed in tetraploid Avena barbata (Hamrick and Allard, 1972), hexaploid Aegilops (Zohary, 1965), tetraploid Sedum (Smith, 1946) and in a number of segmental allopolyploids (Stebbins, 1950). Heterogenetic associations which give rise to genetic segregation can occur in allopolyploids (Huskins, 1941, 1946; Stebbins, 1950), and single gene changes may arise which are not masked completely by homologous alleles. This study was designed to evaluate ecotypic differentiation in octoploid Fragaria (2n = 56). Two-taxonomic species are widely distributed in California: F. chiloensis (L.) Duchn. and F. virginiana (L.) Duchn. ssp. glauca Staudt. These taxa are completely inter-fertile autoallopolyploids and share diploid F. vesca (2n = 14) or a close relative as one of their progenitors (Sen-