Effect of delivery method and population size of Trichoderma harzianum on growth response of unrooted chrysanthemum cuttings.
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In a previous study, addition of Trichoderma harzianum Rifai isolate T-12 to a propagative medium resulted in improved performance of chrysanthemum cuttings. However, root and shoot growth of one cultivar, 'Dark Bronze Charm', were more responsive to a lower (5 g T-12/kg medium) than higher (25 g T-12/kg medium) rate of fungal propagules, suggesting potential phytotoxicity at higher concentrations. The objectives of this study were to investigate higher rates of T-12 medium amendment for phytotoxicity, and to examine an alternative method of delivering the fungus to the propagative medium in order to obtain a more uniform response from cuttings. Isolate T-12 was added to the propagative medium as either a powdered peat-bran amendment (0, 5, or 50 g T-12/kg medium) or as alginate prills (80 or 800 g T-12/kg medium). There were no differences among treatments on day seven, but by day 21, shoot fresh weight and heights were significantly greater for plants treated with prills at 800 g T-12/kg medium. Both prill treatments resulted in greater shoot height on day 14 and 21 than all other treatments, which were similar to controls. Amendment with T-12 powder at 50 g/kg increased root length, but 80 g/kg medium added as prills decreased root dry weight compared to the control. The highest rate of T-12 (800 g prills/kg medium) had no effect on root growth. This suggests that moderate, rather than high rates of T-12 are more effective in promoting rooting of unrooted chrysanthemum, and that there is a potential for phytotoxic effects on root growth with higher rates.
