Increased plant resistance to stem-lesions caused by Phytophthora spp. following biochar amendment

Background/Question/Methods

It has long been established that soil-amendment with biochar can provide benefit to agricultural systems through improvement of soil nutrient retention, improvement of soil physical properties, and positive effects on the soil microbial community, in addition to being a long-term sink for atmospheric carbon dioxide. Studies also suggest the possibility of decreased plant disease severity as a result of biochar amendment of soil or potting mix. The decrease in disease severity may be the result of increased plant vigor; however, recent work has shown that amendment with biochar resulted in an apparent induction of systemic resistance against several biotic stresses. Pathogens in the genus Phytophthora cause some of the most important diseases of trees and crops worldwide, and require extensive chemical input for management. The purpose of this study was to examine the possibility of induced resistance to this genus of pathogens through incorporation of biochar into potting media. By using an above-ground canker pathogen, and providing plants with ample water and nutrients, many potential indirect effects of biochar on disease resistance were eliminated. Seedlings of red oak (Quercus rubra) and red maple (Acer rubrum) were planted in either pure horticultural potting mix, or potting mix amended with 5%, 10%, or 20% biochar by volume. In the maple experiment, a non-inoculated control and a chemical treatment were also included. Plants were stem-wound inoculated with an isolate of Phytophthora cinnamomi (Q. rubra) or P. cactorum (A. rubrum) using standard agar-plug inoculation procedures.

Results/Conclusions

Treatment effects were assessed by measuring the expansion of necrotic lesions from the point of inoculation, biomass accumulation, mid-day stem water potential (oak), and carbon assimilation (maple). Amendment of potting media with 5% biochar reduced mean vertical expansion of lesions in both host x pathogen combinations, though only significantly so in the maple experiment. In the oak experiment, amendment with 5% biochar resulted in significantly less negative mid-day stem water potential compared to inoculated control. In the maple experiment, amendment with 5% biochar significantly increased above ground biomass. Seedlings of either species growing in potting mix amended with 10% or 20% biochar did not differ from the non-amended inoculated control for most factors. Overall, the results indicated that incorporation of 5% biochar into potting media or soil may be a useful management option for plant disease caused by Phytophthora spp. while also serving as a sink for atmospheric carbon dioxide.