Studies On Growth Regulation And Cold Resistance Improvement Of White Clover On TEDA Green Belt

The growth and cold resistance of white clover (Trifolium repens L.} treated with 250, 500, 750, 1000 and 1250ppm paclobutrazol solution at rate of 200ml/m2 were investigated in a field trail in Tianjin Economy and Development Area (TEDA) at four different times: May 23, June 20, Sep. 13 and Nov.12, 2001. The result showed that early three paclobutrazol treatments delayed the growth, and the Nov. 12, 2001 treatment had no significant effect because of low temperature.40 days after paclobutrazol treatments, the plant height of white clover reduced significantly with increasing paclobutrazol application rate. The length and the width of leaves reduced significantly. However, when the application rate reached 1000 ppm and above, the leaflets had unacceptable discoloration about three weeks. The Nov. 12, 2001 treatment had no obvious changes at the plant height and the leaflet size, but retarded the growth of white clover significantly the following year.The chlorophyll content of leaf increased with the application rate of paclobutrazol (under 1 000 ppm) increasing, and the chlorophyll content increased significantly by the treatment. When the application rate of paclobutrazol reached 1 000 ppm and above, the chlorophyll content of leaf reduced slightly. The Nov. 12. 2001 treatment had no significant effect on the chlorophyll content of leaf.The internode length reduced and the stem diameter increased by paclobutrazol treatments in the three early treatments. The content of soluble sugar and the nitrogen content of leaf and stem were increased in the three early treatments.The cold resistance of white clover treated with paclobutrazol at May 23, June 20. and Sep. 13. 2001 were improved, and the rate of electrolyte leakage of leaf and stem were reduced significantly after the first thick frost. But the regermination of white clover treaded by paclobutrazol was not improved or retarded significantly at the following year. The Nov. 12, 2001 treatment had no significantly effect on white clover's cold resistance, and the treatment retarded the regermination of white clover significantly in the spring of 2002.The results showed that the paclobutrazol treatment had significant concentration effect and the concentration of paclobutrazol for growth regulation of white clover was suitable at 750ppm, no more than 1 000ppm. The paclobutrazol treatment should be processed at midseason of thegrowth of white clover; otherwise, the retarding effect was small and the regermination and growth of white clover in the 2nd year were retarded significantly.The results of the comparison of variety showed that Haifa > Riverdale, Persistent and Huia , the four varieties of white clover were differently in growth characteristics. The three other varieties' leaf sizes were smaller than Haifa, and the heights were also lower. The rate of electrolyte leakage of stem and leaf and the LTso of Riverdale and Persistent were significantly lower than Haifa and Huia in seedling stage after low temperature treatment. Considering the growth characteristics and cold resistance, Riverdale and Persistent are the more suitable varieties to grow in TEDA green belt than the other two varieties.