| Dendrobium hybrida is one of the most ornamental value and the most excellent accessions of Dendrobium. Being beautiful, colorful, flowering and bottle inserted a long period of time, Dendrobium is loved by most people, as well as an important orchid ornamental flowers and potted flowers, which has great market potential. However, Den. hybrida is produced in tropical or subtropical regions, demanding high temperature and humidity in the whole growth period, of which the suitable growth temperature is 25-30 ?, while the suitable growth humidity is 60-70% or more. In China , only part of province like Guangdong, Hainan, Yunnan, Fujian, Guizhou can produce Den. hybrida, even in Hainan,some of the winter temperatures are below 15 ?, can't reach the minimum growth temperature of Den.hybrida. The development of Den.hybrida are required to invest a lot of money to build winter heating facilities, such as greenhouses, increasing the cost of production. The low temperature in winter not only caused the decline in cut flower production, seriously affected the quality of cut flowers, also because of the growth stopped affecting the cut flower production of next year of Den. hybrida. Therefore, it is the key to solve the problem of improving the cold tolerance of Den. hybrida to reduce the loss of winter low temperature injury. Although the introduction and cultivation of more accessions in China recent years, the lack of systematic evaluation of cold tolerance limited the selection of cold-resistant accessions. So it is a great significance for the development of Den. hybrida in China to evaluate the cold tolerance of Den. hybrida.In this study, under result cold resistance survey in the field in the condition of natural low temperature, we evaluated the cold tolerance of adult seedlings and seedling of Den. 'Sonia Hiasakul' and Den. 'hongzhenzhu', and the 4 kinds of test materials were selected as the research object. The low temperature treatment was carried out after low temperature treatment. The determination of physiological indexes, including soluble protein, soluble sugar,MDA, free proline, chlorophyll and LT50, were carried out. The significant,correlation, principal component, membership function and other comprehensive analysis were carried out on the measure results of the indicator, the initial construction of Dendrobium comprehensive cold tolerance evaluation system was established. Then, Den.'699#' and Den. 'Burana Crystal'were used as experimental materials to check the comprehensive cold tolerance evaluation system of Den. hybrida. Finally, total of 38 Den.hybrida accessions were tested for the comprehensive evaluation of cold tolerance. The main results are as follows:(1) According to cold resistance survey in the field, comprehensive analysis of yellow leaf rate, leaf rate and falling rate analysis, cold tolerance of Den. 'Baby Burana Crystal'?Den. 'zixia'?Den. 'Burana Jade'?Den. 'mini hongbai'?Den. 'Burana Crystal' was better, and cold tolerance of Den. '41#',Den. '709#',Den. '513#', Den. '699'was quite poorer, other Dendrobium accessions were in common.(2) The physiological indexes such as soluble protein, soluble sugar, MDA, free proline, chlorophyll and LT50 of Den. 'Sonia Hiasakul' and Den. 'hongzhenzhu' were measured and the morphological indexes such as yellow leaf rate, leaf rate and falling rate were measured. The results showed that with the temperature and time changing, the soluble protein and the soluble sugar were positively correlated with the LT50, but the contents of MDA, free proline, chlorophyll and yellow leaf were significantly affected by the treatment of temperature and time. The change trend was obvious and correlated with LT50, which could reflect the change level of Den. hybrida with low temperature stress and the difference of cold tolerance among different accessions. The determination of MDA,free proline, chlorophyll, yellow leaf rate and LT50 at 5 ? for 8 days were used as the determination index of cold tolerance system of Den. hybrida, and the evaluation system of cold tolerance of Dendrobium hybrid was established by membership function analysis.Den. '699' and Den. 'Burana Crystal' were used as materials to check the system. The results showed that the cold tolerance of Den. '699' and Den. 'Burana Crystal' in the comprehensive analysis was in accordance with cold resistance survey results in the field,that is, the evaluation system was effective.(3) The results of cold tolerance evaluation system in Den. hybrida showed that there were some differences in the cold tolerance of 38 Den. hybrida accessions, Den,'863#', Den. 'NPR969',Den.'911#', Den. 'pomo', Den. 'Burana Crystal' were in grade?,which were the most-cold tolerence accessions;Den. 'mini hongbai',Den. '956#',Den.'Lisa', Den. 'Raibow compactum', Den. 'shuifurong',Den. 'shuijingjing', Den.'Xl',Den.'hongzhenzhu'(adult seedling), Den. 'X2' were in grade ?,which were more-cold accessions; Den. 'NPR2183' Den. 'tianelan',Den. 'Sonia Hiasakul', Den. '913#',Den.'zixia', Den. 'shuimitao',Den. 'hongzhenzhu (seedling), Den. 'Malaysia Green' (adult seedling), Den. 'Noppom pink', Den. 'huanglv', Den. '915#', Den. '727#' were in grade?, which were middle-cold accessions; Den. 'Nopporn green star', Den. '709#',Den.'Sonia Hiasakul' (adult seedling), Den. 'white diamond',Den. '844#',Den. 'Malaysia Green' (seedling), Den. 'Lucy' were in grade ? 5 which are less-cold accessions; Den.'zhonghuahong', Den.'699#', Den. '962#',Den. 'Burana Green',Den. 'Sonia Hiasakul'(seedling), Den. 'Green NP1062' were in grade V,which are non-cold accessions.(4 ) Compared to the results of survey in field of Den. hybrida and LT50, the evaluation system was comparatively reliable and accorded with local practice. It could be used for the germplasm resources of Den. hybrida in Hainan area, and the results were in good agreement. The results of cold tolerance evaluation system in Den. hybrida provided an accurate and objective basis for the evaluation, and could provide the basis for selection of accessions of Den. hybrida, had an important guiding significance. |
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