Further studies on Phomopsis convolvulus, a bioherbicide candidate for field bindweed (Convolvulus arvensis L.)

摘要

Field bindweed (Convolvulus arvensis L.) is a perennial plant that can be found in many agricultural areas of the world except the tropics. This weed not only reduces crop yield but also interferes with manual and mechanical harvesting. The presenceof an extensive root system makes this species particularly difficult to control even with commonly used herbicides such as 2,4-D, glyphosate, and dicamba. Phomopsis convolvulus Ormeno is a Coelomycete (Deuteromycotina) fungus that causes lesions on stems and leaves of C. arvensis. High seedling mortality and shoot biomass reductions were obtained when C. arvensis plants were inoculated with spore suspensions containing the infectious alpha-conidia of this fungus or when the spores were delivered alongwith fungal mycelia on barley grains. In one phase of the research, the effect of inoculum storage on conidia germination rate was tested. The germination rate of conidia decreased from 91 percent to 10-42 percent (depending on the size of container used) in only 9 weeks. These findings suggest that the present method of storage is not adequate to maintain high levels of conidia viability. Future research should focus on the effect of initial inoculum water content on conidia germinability and viability under different storage conditions. A second phase of the research examined the inoculum dose response of Phomopsis convolvulus on Convolvulus arvensis seedling growth under growth chamber conditions. The objective of the work was to determine the optimum inoculum dose for pre-emergence application. A high degree of variability in the response of C. arvensis seedlings to pre-emergence inoculum applications was found. The highest inoculum dose used (i.e., 0.9 g per pot) resulted in over 60 percent necrosis and mortality of C. arvensis seedlings. At this same dose, shoot biomass was reduced by approximately 40 percent. The final phase of the research evaluated the efficacy of Phomopsis convolvulus to suppress the growth of vegetatively derived Convolvulus arvensis plants in spring wheat under field conditions. Six days after pre-emergent application of the barley-based inoculum, lesions were observed on C. arvensis leaf and stem tissue. Although the fungus killed lower leaves, lesions never spread over entire plants. No significant reductions in C. arvensis population densities were found following application of Phomopsis convolvulus inoculum.