CONSEQUENCES OF LONG-TERM ARTIFICIAL SELECTION, INBREEDING AND ISOLATION IN PHLOX. II. THE ORGANIZATION OF ALLOZYMIC VARIABILITY.

Recent electrophoretic surveys of soluble proteins have demonstrated that most natural populations of plants contain remarkable stores of genic variation (cf. Allard and Kahler, 1971, 1972; Levin 1975a). Correlatively these surveys have demonstrated that protein polymorphism and heterozygosity are maintained within and among cultivated strains in spite of severe inbreeding (e.g., barley, Allard et al., 1972; Weir et al., 1972; Weir et al., 1974) or selection (e.g., maize, Brown, 1971; Brown and Allard, 1971; Stuber and Moll, 1972). The various studies to date have dealt either with populations subject to the exigencies imposed by the plant breeder on the one hand, or the natural environment on the other. We do not know the effect of tens of generations of inbreeding, divergent selection and bottlenecks upon the allozymic constitution of a wild self-incompatible species. If the information from barley and maize is representative, we would expect the wild species to resist the depletion of polymorphism and heterozygosity wrought by the aforementioned factors. The present investigation was undertaken to determine the effect of long-term artificial selection, inbreeding and isolation on populations of Phlox drummondii Hook., which is a common self-incompatible element of the spring flora of central and south Texas. The treatments in question were not performed by the author, but rather by horticulturalists during the past 140 years. According to Kelly (1915) this Phlox was collected in 1835 by Thomas Drummond, who sent its seeds to Great Britain. Subsequently they were distributed to nurserymen in several European countries. The nurserymen breached the self-incompatibility barrier, developed truebreeding strains which displayed different statures, branching patterns, corolla colors and eye markings, and corolla outlines and sizes. During the 79 generations from the time P. drummondii reached Europe to 1915 over 200 true-breeding lines had been established. Many of the lines are still available from European nurseries. Since Drummond's foray in 183 5, the native populations ostensibly have undergone little change, if one can judge from the descriptions of P. drummondii as it appeared to several observers before the turn of the century (cf. Kelly, 1915), and as it appears today. Although the precise phylogeny of the P. drummondii cultivars is unknown, the "Grandiflora" strains were derived from the native foundation seed, and these strains served as the source of the "Dwarf" strains. This scheme is based upon the morphological similarity of these groups of cultivars to the native Phlox, and upon the sequence of their appearance in horticultural catalogues (Kelly, 1915). First we shall examine the extent of allozymic polymorphism, heterozygosity and genetic diversity within each cultivar. Then we shall examine the pattern of genetic variation among cultivars using F statistics analyses developed by Wright (1943, 1951, 1965). Specifically we will determine the total amount of inbreeding among the cultivars treated collectively and within each cultivar, and the level of gene frequency hetero-