| Camellia is one of ten famous flowers in China and also a famous woody ornamental plant, which has very high ornamental value and performs excellent prospects of industry development. Because most of camellia resources are naturally distributed in South China and along the Yangtze River valley, the cold resistance of the cultivars genetically derived from Camellia japonica and C. reticulata is generally lower and most commercial camellias cultivars are difficult to survive in the winter season when planted outdoor in the north of the Yangtze River.The potential of cold resistance has been already regarded as one of the main restricting factors to industry's development for camellias at present. This thesis systematically deals with the cold hardiness for 142 camellia species and 19 high-quality camellia cultivars by the methdology such as physiological biochemistry indeses and field cold injury index etc, and its results are expected to play an important role of utilizing the cold-resistant camellia resources and breeding new cold-resistant camellia cultivars. This thesis also conducted the experiment of the low temperature acclimation and its influences for callus of immature embryos from 3 camellia species. The results indicate that low temperature acclimation can improve cold-resistant capacibility of the camellia callus to some extent, and thurthermore does not obviously influence their later growth within one month after low temperature treatment. Thus this method performs excellent prospects to breeding new cold-resistant camellia cultivars at the cell level. Camellia species showed significant difference of the relative electricity coeffient (REC) after exposed by-5 ℃for 8 hours, and the greatest REC is 3 times of the minimum REC. There were significant difference for MDA among the camellia species after exposed to the gradient low temperature (-5℃, -10℃, -15℃) for 8 hours, but the camellia species performed 5 types of MDA variation, namely slow-rapid increase type , rapid-slow increase type , flat increas type at low level, flat increase type at high level and the linear increase type. These variation patterns for MDA content indicate that cold resistant camellias may differently response to low temperature. The differences for rate of free base of ultra oxygen anion are very significant among the camellia species. The camellia species differ significantly for the POD activity, but not for SOD activity. Furthermore there were also significant differences for POD and O2 ? in 26 camellia species leaves between the January and February. The field freeze injury was systematically investigated for 142 camellia species in the Jinhua International Camellia Species Garden in January of 2005, after heavy snowfall and the rarely severe freeze. The results indicated that 75% of camellia species in the garden did not suffer from any freeze injury or slight freeze injury, and most of them can tolerate the natural low temperature of -5 ℃. There were very significant positive correlation between the 2 physiological index and the field freeze injury index after treated by low temperature,and this correlation indicated that the assessment for cold –hardiness based on the 2 physiological indexes was highly reliable. There were negative correlation between geographical latitude and the 2 physiological indexes, and the camellia species naturally grown in north distribution perform highly cold-hardiness. The 142 camellia species were divied into 4 types, namely as cold-resistance, medium cold-resistance, low-temperature sensitivity, low temperature significant sensitivity, based on the multiple statistical cluster analysis by REC and MDA combined with the field freeze injury. The results also indicates that the only C.liberistyloides is distributed in high altitude range in Yunnan Province and the other 4 camellia species distributed in the further north latitude 28.34°among the 5 cold resistant camellia species. Some 84 percent of the medium cold resistant camellia species are grown between north latitude 25°and north latitude 28.34°,and about 68 percent of low temperature sensitivity and low temperature significant sensitivity camellia species distributed between north latitude 22°and 25°. The REC and MDA content were measured for the 19 camellia high-value cultivars. It was found that there were significant differences for these two indexes among 19 cultivars. Furthermore the ranks of cold-hardiness for the 19 cultivars were approximately same whether by REC or MDA. But there was no close correlation between the cold resistance and flower patterns. There was obvious effect to improve cold resistance of callus induced from the immature embryos after low temperature acclimation for 16 days at 4℃with 8 hours lighting per day. The REC and MDA content for the acclimated callus exposed to low temperature were declined, compared with the control. The LT50 for the acclimated callus of C.chekiangoleosa,C.yuhsienensis and C.semiserrata were lower 0.77℃, 0.73℃, 0.62℃than those control respectively. The results indicated that the potentials of cold-hardiness for camellia callus after low temperature are improved. The capacibility of metabolization from camellia callus was declined whether the callus were exposed to low temperature or not, but there were no significant differences for growth at later stage, based on the data of TTC test.
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