PARENT SESSION
Oral Session #65: Evolutionary Ecology/ Population Genetics. Presiding: G. Gerrish.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Hall of Ideas J.
Subtlety will get you everywhere: differential response of Louisiana Iris hybrids to flooding, shade and drought.
Johnston, Jill1, Arnold, Michael1, Patterson, Charles1, Donovan, Lisa1, 1
ABSTRACT- Plant breeding has shown that hybridization followed by artificial selection can generate novel phenotypic variation. Recent studies in natural plant populations show that novel hybrid phenotypes can persist in habitats that allow higher hybrid fitness relative to parental species. Thus, contribution of hybrids to future generations may depend upon subtle differences in physiological tolerance among hybrid genotypes. We studied the potential for hybridization to generate novel variation in photosynthesis, growth, and biomass allocation between two native Louisiana Iris species. Previous descriptive studies showed that Iris brevicaulis (IB) and I. fulva (IF) and hybrids are differentially distributed across wetland gradients. Shade, flooding, and drought treatments were imposed on seed, seedling and adult Iris plants, and the synthesis of those results is reported here. Adult photosynthetic rates of all genotypic groups were reduced by shade and drought. Hybrids achieved larger biomass than either parent in flood treatments. Shade had little effect on adult plants, but drought significantly reduced growth overall. Seed and seedling stages differed from adults in sensitivity to abiotic factors. In moist conditions, IF seeds germinated more than IB or hybrids, whereas shade stimulated germination of IB. Taken across all vegetative life stages, drought, flooding, and shade explain much of the natural distribution pattern for these Iris groups.
KEY WORDS: Louisiana Iris, hybridization, hybrid novelty, physiological tolerance