The 2011 ASHS Annual Conference

It has long been established that soil-incorporation of char, the product of pyrolysis of organic material, can provide benefit to agricultural systems through the improvement of water and nutrient retention, drainage, and positive effects on the microbial soil community.  In addition, several studies suggest the possibility of decreased plant disease severity as a result of char incorporation into soil or potting mix.  The cause of this decrease in disease severity may be an indirect effect of one or more of the factors mentioned above, but recent work has shown that incorporation of char into potting mix resulted in a reduction of two different foliar diseases, indicating some level of systemic induced resistance in the plant.  Pathogens in the genus Phytophthora cause some of the most important diseases of ornamental and forest plants throughout the world.  These root and crown rot pathogens are also a major limiting factor in nursery production and cause great expenditures for disease management.  In order to determine if char can induce a systemic resistance to this group of pathogens, we tested a species known to penetrate stem tissue and cause above ground lesions in order to eliminate the indirect effects of char on soil-borne organisms.   One of the most important diseases of various beech species (Fagus spp.) is bleeding canker caused by Phytophthora cactorum.  The purpose of this study was to examine the possibility of induced resistance to this pathogen through incorporation of char into the potting mix.  By using an above-ground canker pathogen, and providing ample water and nutrients to all plants, many potential indirect effects of char on disease resistance were eliminated.  30 seedlings of European beech (Fagus sylvatica) were planted in either pure potting mix, or potting mix thoroughly blended with 10% or 20% char by volume.  Five weeks following leaf expansion, half of plants in each treatment group were stem-wound inoculated with an isolate of P. cactorum using standard agar-plug inoculation procedures.  Various parameters of plant growth, health, and water status were monitored throughout the experiment, including stem water potential, biomass accumulation and allocation, chlorophyll fluorescence, and necrotic lesion development.  The effects of char incorporation on seedling growth, plant health, and disease progression will be presented.