Experiments And Evaluations Of Physiological Characteristics Of The Cold-injury And The Cold-hardening Of Eucalypt Clones

The plantation of eminent eucalypt clones is obviously expecting a bright future in our province, but eucalypts' sensitivity to low temperatures stands in the way as a main barrier for them to be widely planted. After many years of related researches, researchers noticed that the cold-resistance of eucalypts varies from breed to breed, and from clone to clone too. So, it's of great significance for more studies to be done on selecting cold-resisting clones of eucalypts.Recently, researches on cold-resistance of eucalypts are developing rapidly as profits from eucalypts plantation increased. Thus, the cold-injury experiments of eucalypts are developing from only field experiments to mostly laboratory experiments, and more knowledge about the laboratory modeling methods of cold-treatment and cold-hardening process is greatly needed. But recent experiments reported on that subject are quite rare while most researchers tend to use some randomly selected temperatures for their laboratory cold-treatments. However, the time and the temperature in a laboratory cold-treatment model are of significant influence on the reliability of results attained. In a word, great importance lies in more systematic experiments studying these two factors' relations with cold-injury and cold-resistance of eucalypts.Another aspect of cold-resistance rarely concerned in national researches reports is the cold-hardening of eucalypts. Cold-hardening process with temperatures above OX^ is necessary for plants to induce their cold-resistance, and in natural conditions this process appeared in autumn before the temperature drop to values below 0°C. Without a preceding treatment of cold- hardening, the direct suffering to very low temperatures can make the cold- resistance of plants different from otherwise, leading to wrong knowledge about the cold-resistance of plants which should have reflect its genotypes. In this way, the researches on genes related to cold-resistance can't be conducted if no cold-hardening is treated to experimental materials. And the evaluation of cold-resistance concluded without knowledge of this process could hardly meet with the results from relative genetic researches, causing great difficulties for the conducting of cold-resisting eucalypt genotypes selection.According to information from recent researches on cold-related genes, the basic cold-resistance and the hardening-related cold-resistance are different for plants. With different mechanisms, these two kinds of cold-resistance are of similar importance. After all, high basic cold-resistance is not necessarily foretell a high level of hardening-related cold-resistance, and a so-called cold-resisting plant can possibly appeared to be non- cold-resistant under wrong cold-acclimation conditions. However, if we say a plant is cold-resistant, it's probably indispensable to explain that in what cold-acclimation conditions could this plant be cold-resistant. Otherwise, plants with cold-resisting genotypes could become disappointing when applied to industry.