Studies On The Isolation And Identification Of INA Bacteria From Tea Plant In Shandong And Its Relationship With Frost Injury Of Tea Plant

Tea plant, as a leafy crop and grow in the temperate, subtropical area, is originated in southwest part of China, low-temperature damage is one of agro-meteorological disasters which is often encountered in tea area. With the north-expanding of tea area and the popula -rizing of early-sprouting cultivars in tea production in recent years, tea plants were frequently suffered from the frost damage. After the tea production damaged from the frost injury, the growth potential of tea plants were seriously influenced, on the one hand, resulting in the severe reduction even total destruction of the tea production, on the other hand, the quality including the taste and aroma of the made tea from the damaged tea plants were reduced significantly. Investigation showed that the severity of tea plants suffered by the frost not only related to the intensity and duration of low temperature as well as the frost resistance of tea plants, but also related to the amounts of INA bacteria on the leaf surface of tea plant. The existence of ice nucleation active bacteria on tea leaves could induce and increase the occurrence of frost injury, ice nucleation active bacteria(referred to INA bacteria) could induce the water in plant cells frozen in -2℃～-5℃,while those plants lack of INA bacteria on the leaf surface are generally tolerated -7℃～-8℃low temperature and without the occurrence of frost. The purpose of this study is to isolate and identify INA bacteria on tea plants in Shandong, to study the distribution and dynamics of INA bacteria, the relationship between tea plant and INA bacteria, and suggest the method in controlling INA bacteria. The results obtained are as follows:The investigation and isolation of the INA bacteria in the main producing areas of Rizhao, Qingdao, Tai'an in Shandong were conducted. Investigation showed that there were 22 INA bacteria strains isolated from tea plants in Shandong province, according to 16SrDNA sequence analysis and biochemical characteristics of culture, two species of INA bacteria i.e. Pantoea ananatis and Pantoea agglomerans, were identified on the tea plants in Shandong. Fifteen strains of Pantoea ananatis were isolated in tea areas in Shandong province, accounting for 68.2% of the total, and seven strains of Pantoea agglomerans were isolated, accounting for 31.8% of the total. These two kinds of strains distributed in Tai'an, Rizhao, Qingdao tea areas, and the dominant species is Pantoea ananatis.According to the investigation on ice nucleation activity of isolated INA bacteria, it was showed that these ice nucleation active bacteria separated from tea plants in Shandong can be divided into two kinds: strong ice nucleation active strains(103～104/ice nuclei) and middle ice nucleation active strains(105～106/ice nuclei). The distribution density and the frequency of INA bacteria in different parts of tea plant is not the same. It is easy to isolate the INA bacteria from tea buds, and its frequency was 83.3%, while it would be much more difficult to be isolated from the mature and old leaves, its frequency is only 14.3%. Secondly, the amounts of ice nucleation bacteria were different on the various leaves with different age, and it was decreased as the follows: tea buds>tender leaves >mature leaves. With regarding to the INA bacteria isolated in different tea areas, Qingdao is more easier to isolate INA bacteria compared to that in Tai'an.In view of INA bacteria distribution in annual cycle, there was a high density of INA bacteria isolated in the autumn frost period and the spring frost period, especially in the spring frost period with high humidity and more rainfall.The supercooling temperature was determined on the tea leaves inoculated with INA bacteria and uninoculated tea leaves. Investigation showed that the inoculation of INA bacteria could significantly raise the supercooling temperature of tea leaves, the supercooling temperature were -1.4℃and -3.0℃in the inoculated tea leaves and uninoculated tea leaves respectively, the supercooling temperature was 1.6℃higher after the INA bacteria was inculated.The existence of INA bacteria showed an aggravation on the damage of cell membrane of tea leaves, it expressed in the increased permeability and the relative electric conductivity of cell membrane, The SOD and POD activity were activated in the initial period and decreased gradually, the contents of malondialdehyde(MDA) were increased also.Using indoor and outdoor potted seedling experiments to explore the methods of the prevention and control of INA bacteria, results showed that some pesticides could inactivate the ice nucleation active substances and caused lethal to INA bacteria. Two fungicides of Mancozeb and Thiram were screened and possessed the controlling effects on the ice nucleation bacteria.