Study On Allelopathic Mechanism In Different Pumpkin (Cucurbita Moschata M.) Varieties

Continuous cropping is a common agricultural phenomenon, Crop yield loss during the continuous cropping of leguminaceous crops and the cucurbitaceae vegetable is extremely serious, in which cucurbitaceae vegetables continuous cropping obstacles is mainly due to autotoxic effect. In the facility cucumber cultivates, pumpkin (Cucurbita moschata M. Var. Heizi) seedling is generally used as grafted material. However, grafted seedlings may avoid autotoxic effect of the cucumber root system, but the serious continuous cropping obstacles were occurred. Whether the pumpkins have the allelopathy effects? Academic search for the pumpkin allelopathy research reports are really rare.The tissue culture technology was used to prove pumpkin root system allelopathy effects. Meanwhile, from the nutritional pressure point of view, the characteristics of pumpkin tissue cultured roots exudates were studied under the nutrient elements stress. The hydroponic culture experiments were carried out for study on whether root exudates have significant difference in the grafted seedlings and scion-root seedlings, and determine whether the allelopathy effects is one of the main factors for cucumber continuous cropping obstacles. And the result of the tissue culture was utilized in sandy culture experiment to analyze allelopathy effects of sandy cultured pumpkin under the nutritive elements regulation. Soil which has been continuously cropped pumpkin for three years and soil which the previous crop are maize were used to carry on soil culture experiment in order to study the different allelopathy effects of pumpkin seedlings in different soils under the nutritional elements regulation. The results of this study could provide important guidance for removing the obstacles of continuous cropping by applying fertilizer, using grafting technique and crop rotation. In addition, it can provide important reference for the problem of continuous cropping obstacle based on the allelopathy effects. The main results are as follows:1. Different elements showed various effects on growth of acceptors plant seedlings, which depended significantly on their corresponding contents and varieties of the accepting plants. Pumpkin cultured roots filtrates exhibited significant inhibition under deficit (1/2 B5) and normal (B5) nutrient circumstance. And under enhanced nutrients conditions (3/2 B5and 2 B5), it generally showed significant stimulation effects. Fe and B redundancy would lead to certain inhibition. On the other hand, under the most redundant condition (2 B5), B element causes strong autotoxic effects of Var. Jingou. In addition, Fe displayed inhibitory effect of Var. Jingou cultured roots on seedlings growth of Var. Heizi. In conclusion, it was preliminarily derived that both P and Mg elements could eliminate phytotoxic activity of pumpkin cultured roots. However, Fe, Cu, and B elements showed allelopathy regulation of pumpkin, which depend on acceptors varieties. The results of this study could provide important reference and guidance for removing the obstacles of continuous cropping by fertilizer manipulations in modern sustainable agriculture.2. In the different time, root exudates of the grafted seedlings inhibited cucumber radicle growth and inhibition effects enhance with increasing the number of hydroponic culture times. The inhibitory effects of root exudates of the grafted seedlings on cucumber radicle growth enhanced with the concentration increasing. The inhibitory effects of root exudates of the scion-root seedlings on cucumber were greater than that of the grafted seedlings. This indicated that grafting techniques can reduce the intraspecific allelopathy effects, but cannot completely eliminate interspecific allelopathy effects.3. In sandy culture experiment, root exudates of pumpkin (Var. Heizi) significantly inhibited their radicle and coleoptile growth as well as branching roots number. Inhibition effects were enhanced as the prolongation of cultivation times. The range of inhibition effects on their radical length and branching roots number enhanced with the prolongation of culture times, but on coleoptiles length is was decreased as the prolongation of culture times. After the 3rd cultivation, root exudates of pumpkin (Var. Heizi) could significantly inhibit their radicle and coleoptiles length as well as branching roots number.4. Under Fe element regulation, the first cultured root exudates of pumpkin (Var. Heizi) inhibit their radicle and coleoptile growth as well as branching roots number, but after the second cultivation the root exudates of pumpkin (Var. Heizi) significantly promoted them, compared with the distilled water control. It is suggested that the Fe element regulation cannot displays in application time, therefore, Fe fertilizer should be applied in each time. Under the B element regulation, the first cultivation root exudates of pumpkin (Var. Heizi) promote their radicle and coleoptile growth as well as branching roots number, but after the second cultivation root exudates of pumpkin (Var. Heizi) inhibit them, but inhibition was strengthened in the third time cultivation.5. When the pumpkin (Var. Heizi) were planted in the soil of the continuous cropping pumpkin three years, the maximum leaf area, stem height, stem diameter, fresh and dry weight of shoot were significantly smaller than those in the soil which the preceding crop were maize. Under 3/2P and 3/2Mg regulation, the soil which the preceding crop were maize, can significantly promote seedling's growth, but the soil of the continuous cropping pumpkin three years can reduce auto-toxic effect, but cannot eliminate them completely.