Trichoderma harzianum as a growth enhancer of pot and cut floriculture crops

Trichoderma species have been used extensively for biocontrol of soilborne pathogens. These fungi may also have a growth-enhancing effect independent of mechanisms associated with biocontrol. Although several plants are responsive to growth enhancement by Trichoderma spp., cut and potted flower production applications remain largely uninvestigated. Optimization of rate and delivery method is necessary to facilitate commercial use of this fungus. Integrating Trichoderma into current greenhouse production schedules could serve to decrease use of fungicides, growth regulators, and labor in the greenhouse, hence lowering costs and environmental impact.

Specific goals of my research were: (i) to optimize rate of media amendment with Trichoderma harzianum-isolate T-12 (T- 12) as a powdered peat-bran formulation; (ii) to compare amending the rooting medium with T-12 to treating unrooted cuttings with IBA to promote rooting; (iii) to compare the powdered peat-bran formulation to an alginate pellet preparation of the fungus as methods of delivery; (iv) and to investigate T-12 as a growth enhancer of several cut and pot floricuture crops.

Zero, 5, or 25 g of T-12 peat-bran amendment was added per kilogram medium in an effort to enhance the rooting of four chrysanthemum [Dendranthema X grandiflorum (Ramat.) Kitamura] cultivars, two considered easy-to-root (‘Davis' and 'White Marble') and two considered hard-to-root (‘Dark Bronze Charm' and ‘Golden Bounty'). The experiment was repeated with the same rates and cultivars with and without dipping cuttings into a 0 or 7.4mM solution of IBA. We also investigated an alternative method of delivering the fungus to the medium, adding T-12 either as a powdered peat-bran amendment at the rates of 0, 5, or 50g*kg^-1 or as alginate pellets at 0, 80, or 800g*kg^-1 produced by reacting a mixture of aqueous sodium alginate containing T-12 powder with Ca⁺⁺. Finally, we amended the growing medium of several cut flower species and potted poinsettias with T-12 as a powdered peat-bran amendment to investigate enhanced growth.

Addition of the powdered T-12 amendment at 5 and 25 g*kg^-1 increased root and shoot fresh weights during 21 days of rooting. Midway between transplant to flowering, increases in height, shoot dry weight, and root fresh and dry weight were detected in ‘Dark Bronze Charm' with T-12 relative to the control; increases in height, shoot fresh and dry weight, and number of nodes were detected in ^Golden Bounty' with T-12. Amending medium with 5g-kg^-1 was equivalent to treating ^White Marble' cuttings with 7.4mM IBA with regard to root length, fresh and dry weight, and ^Davis' for root length. Both pellet treatments gave increased shoot height on day 14 and 21, with 800g*kg^-1 being more effective, over all other treatments, which were similar to controls. Amendment with 50g T-12 powder kg^-1 increased root length, 80g T-12 pellets kg^-1 medium resulted in decreased root dry weight compared to other treatments, and 800g T-12 pellets-kg^-1 medium increased shoot dry weight. In the cut flower study, we saw increases in height due to T-12 treatment in zinnia (Zinnia elegans) and dill (Anethum graveolens) and increased flower number in zinnia. Poinsettias treated with T-12 had greater heights or widths than controls periodically throughout the study, although these differences may not be of commercial interest.