Preliminary Studies On Autotoxicity Of Chrysanthemum

Under field conditions, chrysanthemum(Dendronthema morifolium Tzvel.)cultivars 'Gaoyataizi' has poor establishment and less productivity when seedlings are replanted to the same area more than 3 years, which is one of the main problem puzzled on the growth of chrysanthemum. Autotoxic effect, as one of continuous cropping obstacle factors, has not been widely reported in chrysanthemum. Laboratory and greenhouse experiments were conducted to determine if the autotoxic effect is responsible for continuous cropping obstacle of chrysanthemum ' Gaoyataizi' and the autotoxic effects of different parts from continuous cropping chrysanthemum on seed germination and seedling growth, cuttings rhizogenesis and the growth of potted-chrysanthemum 'Gaoyataizi' . Different parts of continuous cropping 'Gaoyataizi' chrysanthemum, roots, stems, litter, leaves, root exudates and rhizospheric soil were extracted with distilled water separately and bioassayed to detect any possible autotoxic activity. Bioassays revealed several conclusion as follows:1. It is suggested that the autotoxicity of chrysanthemum 'Gaoyataizi' is one of causes obstructing its continuous cropping.2. Aquatic extracts of different parts from continuous cropping chrysanthemum ' Gaoyataizi ' inhibited seed germination, potted-chrysanthemum growth, cuttingrhizogenesis of the same species with increasing concentrations of tissue extracts, however, had weak effect at lower concentration.3. Autotoxic effect was depended on the type and concentration of the tissue extracts. Autotoxic effects of aquatic extracts of different parts from continuous cropping chrysanthemum 'Gaoyataizi' on seed germination, potted-chrysanthemum growth, cutting rhizogenesis had the following order by response index: litter(2.585) > leafs(2.019) > stems (2.019)> rhizospheric soil (1.949)> roots (1.169)> root exudates(1.128), which was suggested autotoxic effects of extracts was mainly depended on aerial parts.4. The physiological and biochemistry mechanism of autotoxicity of chrysanthemumDamage to stability of membraneAquatic extracts significantly inhibited the activities of POD, SOD, CAT, and stimulated creation of MDA, and damaged the normal balance between the activity of anti-oxidation enzymes and peroxidation of membrane lipids, changed the structure and function of membrane, which were one of the main mechanisms of autotoxicity. 4.2 Influence on activity of enzymes and inhibition of metabolism of nutrition Aquatic extracts significantly inhibited the activities of root dehydrogenase, nitrate reductase and PAL, anabolism of soluble sugars and soluble protein. However, aquatic extracts induced and activated the activity of indicator amino acid oxidation(IAAO),promoted IAA decomposing, and inhibited cuttings rhizogenesis itself.Inhibition of photosynthesisAquatic extracts significantly inhibited the chlorophyll content, net photosynthetic rate, intercellular CO2 concentrations, stomatal conductance, promoted transpiration rate, or inhibited the photosynthesis activeness of leaves, which appeared to inhibit the efficiency of photosynthesis.5. Autotoxicity was not significant when aquatic extracts amended by active carbon, 4% and 0.4%(w/v) Polyvinlpyrrolidone (PVP). Bioassays revealed that phenolic compounds appear to be related to the autotoxicity of chrysanthemum 'Gaoyataizi' .Based on this research, several measures were advised to overcome autotoxicity of continuous cropping 'Gaoyataizi' chrysanthemum.Preliminary studies on autotoxic effects of chrysanthemum 'Gaoyataizi' would supply theory foundations for the solution of continuous cropping obstacle for chrysanthemum and other horticultural crops.