A. Dan Wilson

Cytology and Genetics of Sexual Incompatibility in Didymella rabiei

Mating crosses in all possible combinations between 15 monoascosporic isolates ofDidymella rabiei (Ascomycotina, Dothideales), derived from diseased chickpea stems collected at a single location in Genesee, Idaho, were prepared on sterile chickpea stem pieces incubated on moist sterile filter papers in glass petri dishes for 5-6 weeks at 10 C or in nylon mesh bags placed on the soil surface outdoors to overwinter for 6 months. The discharge of large numbers of viable ascospores from mature pseudothecia forming on the chickpea stems was indication of successful matings. Pairings between sympatric isolates demonstrated that the fungus is heterothallic with a unifactorial (bipolar) homogenic mating incompatibility system. Papazian test pairings between tester strains and mating types from three locations in Idaho and Washington indi? cated the absence of complete interfertility between allopatric populations and provided strong evidence that the fungus is biallelic, lacking multiple alleles at the single mating locus. The nuclear content of so? matic and reproductive cells at all phases of the life cycle was examined using Giemsa stain. Ascospores and conidia were commonly multinucleate and ap? peared to undergo multiple mitotic divisions prior to germination. Somatic hyphae derived from ascospores and conidia were predominately uninucleate. The importance of sexual reproduction, sexual incompati? bility, and the teleomorph in the disease cycle is dis? cussed relative to environmental factors required for their occurrence and implications for disease control.

Growth and intraspecific competitive abilities of the dioecious Lindera melissifolia (Lauraceae) in varied flooding regimes.

Abstract The contribution of sexual dimorphism to male-biased colony ratios observed in field populations of the federally endangered Lindera melissifolia was investigated. Growth characteristics and intraspecific relative competitive abilities were determined for first-year male and female L. melissifolia plants grown at varied densities and receiving three flooding treatments. In the no-flooding and 30-day-flooding treatments, stem height, stem diameter, and total leaf area for male plants were significantly greater than that of higher density male plantings and of female plants without respect to density. In both male and female plants, stem growth ceased and leaves were abscised in response to flooding. Although density effects in combination with hydrologic regime influenced intersexual competition, male-bias from competitive exclusion was not indicated. Growth characteristics for male plants grown alone suggest potential for greater interspecific competitive abilities than that of female plants. Therefore, male plants may be better adapted for colonizing suitable habitat, thus contributing to male-biased colony ratios observed in naturally occurring populations.

Flooding Facility Helps Scientists Examine the Ecophysiology of Floodplain Species Used in Bottomland Hardwood Restorations

Bottomland hardwood ecosystems, important for their unique functions and values, have experienced considerable degradation since European settlement through deforestation, development, and drainage. Currently, considerable effort is underway to restore ecological functions on degraded bottomland sites. Restoration requires a better understanding of the biological components, especially plants, and their interactions with other biotic and abiotic components of the ecosystem. Previous experimental approaches have focused on the effects of stress on floodplain plant species in controlled, small-scale studies or large, uncontrolled ecosystem-scale studies. We describe a facility, named the Flooding Research Facility (FRF), where hydrologic regimes can be manipulated to study ecophysiology of floodplain species. Key features of the FRF include the ability to establish experiments on a scale larger than would be possible in a greenhouse, but small enough to control key abiotic variables, such as flood frequency, duration, and light availability on native bottomland soil. Design of the FRF allows for random and replicated treatment applications. Additionally, we provide an example of ongoing research on the effects of flooding and light availability on pondberry (Lindera melissifolia), a federally endangered shrub found in the southeastern United States.