Extruded seed pelleting offers an alternative direct seeding option to rehabilitate forested ecosystems impacted by a soil-borne plant pathogen

Abstract

The high cost of native seeds and low seedling establishment percentages after seed broadcasting are major constraints for seed-based rehabilitation. This study examines whether extruded seed pelleting can be used as a tool to distribute seeds more effectively (e.g. distribute small seeds in a precise manner) while maintaining or enhancing seedling emergence and establishment of Australian shrub species used in the rehabilitation of Phytophthora cinnamomi infested Jarrah (Eucalyptus marginata) forest sites. Pellet formulation was first tested using five different formulations of dry ingredients and the addition of seeds from four Phytophthora-resistant species under glasshouse conditions. The best performing formulation from this work was then adopted to compare laboratory-produced and field-deployed pellets. Seedling emergence of the larger seeded species, Raspberry Jam Wattle (Acacia acuminata) and Pin-cushion Hakea (Hakea laurina), was highest using field-deployed pellets and emergence was statistically similar to the non-pelleted seeds. Seedling emergence reached 100% for the small seeded species, Silky-leaved Bold Flower (Calothamnus sanguineus) and Melaleuca seriata, from laboratory-produced pellets and was significantly higher than non-pelleted seeds. These results indicate that extruded pelleting offers an alternative direct seeding option that can result in greater or equal seedling emergence than that observed with non-pelleted seeds, yet the responses are species-specific. These species-specific pelleting techniques must now be tested under field conditions to confirm whether pellet production method and delivery improve seedling establishment under field conditions.