Physiological Characteristics Of Four Water-stressed Camellia Species Grafted With Camellia Oleifera At The Seedling Stage

By artificial control of watering to simulate natural water stress, the drought resistance and flooding tolerance of one-year-old seedlings in C. oleifera, C. vietnamensis, C. semiserrata and C. osmantha were studied. Meanwhile, the physiological and biochemical characteristics of the one-year-old graft plantlets were determined. C. oleifera (as control), C. vietnamensis, C. semiserrata and C. osmantha were used as rootstocks. Xianglin 11 clone, Changlin 4 clone and Cenruan 3 clone of C. oleifera were used as scionwood to be grafted on each of the four species respectively. The physiological characteristics studied included such as the leaf osmotic regulation substances, the activity of the protective enzymes and the membrane lipid per oxidation products in the grafted seedlings. The main component analysis and subordinate function method were used to comprehensively evaluate the drought resistance or flooding tolerance of each of the clone grafted seedlings. The important role of the rootstock to enhance the drought resistance and flooding resistance of C. oleifera grafted seedlings has been studied for the first time, which laied the foundations for enhancing the drought-resistance and flooding resistance of seedlings and for further guidance on drought and flooding area of C. oleifera silviculture. The main results are as follows:1. The permanent wilting coefficient in C. oleifera, C. vietnamensis, C.semiserrata and C. osmantha were 1.71%,1.85%,3.11% and 1.10% respectively. The ability of drought resistance from strong to weak was C. osmantha> C. oleifera> C. vietnamensi-s>C.semiserrata. There was a degree separation of drought resistance in individuals among the four species studied. According to the magnitude of wilting coefficient, the drought-resistant capacity were divided into five types in total:0%-l%,1%-2%, 1%-3%,3%-4% and 4%-5%. Among them, C. semiserratawas classified at 3-5 level; C. oleifera and C. vietnamensis were only found todistribute at the 2 and 3 levels; C. osmantha only distributed at the 1 and 2 levels. The results laied a foundation for further screening of drought-resistant rootstock for production.2. The plants in C. semiserrata and C. oleifera were all dead at flooding processing 32 days, while a small number of plants in C. vietnamensis and C. osmantha still survived at the flooding treatment duration of 60 days, of which the damaged index were 97 and 96 respectively. The ability of waterlogging tolerance from strong to weak was C. osmantha> C. vietnamensis> C. semiserrata> C. oleifera. There was a degree separation of waterloging tolerancein individuals among the four species studied, where C. osmantha’s waterlogging tolerance separationwas the largest, and C. vietnamensis ensued. The results laied a foundation for further screening of flooding-resistant rootstock forproduction.3. In drought stress condition, although there were differences at the change range of the physiological and biochemical indexes of grafted seedlings with different Camellia rootstocks, the certain trend was presented:Leaf relative water content showed a trend of decline, with the extension of drought stress time, the symptoms of injured leaves did worsen; During the whole period of drought stress, the MDA content was on the rise, while the soluble protein content, proline concentration, SOD and POD activity were on the whole increased. All changes were in the direction of enhancing the grafted seedlings drought resistance.4. Under waterlogging stress, although there also were differences at the change range of the physiological and biochemical indexes of grafted seedlings with different Camellia rootstocks, the certain trend was presented:The chlorophyll content showed a downward trend, with the extension of flooding stress time, the symptoms of injured leaves did worsen; During the whole period of flooding stress, the MDA content showed an increased trend at first, and then dropped down. The SOD activity was on the increase as a whole. The POD activity of the seedlings grafted with Xianglin 11 clone for each of the four species markedly rose at the beginning stage but declined sharply later on, whereas the change of POD activity of the seedlings grafted with Changlin 4 clone and Cenruan 3 clone was not obvious. But all changes were in the direction of enhancing grafted seedlings flooding resistance.5. In drought stress condition, with the extension of time, new leaves of all grafted seedlings began to wilt first, and then old leaves started to wilt, curl, dry, or even fell off. Comprehensive evaluation with subordinate function method indicated that C.osmantha as rootstock had better performance than C. oleifara rootstockin terms of improving the drought resiatance of Xianglin 11 clone, Changlin 4 clone and Cenruan 3 clone grafted seedlings, while C. semiserrata was the best rootstock for improving the drought resistance of Changlin 4 clone and Cenruan 3 clone grafted seedlings.6. Under waterlogging stress, new leaves of all grafted seedlings turned into slightly yellow. However, one week later, there was a new shooting phenomenon in all grafted seedlings when C. oleifera, C. vietnamensis and C. osmantha were used as rootstock, while C. semiserrata did not generate new shoots. After three months of flooding stress, the symptoms of injured leaves did not worsen, which showed a strong waterlogging resistance. Comprehensive evaluation by subordinate function method showed that, compared with C. oleifera as rootstock, C. osmantha or C. vietnamensis as rootstock was more able to improve flooding tolerance in Xianglin 11 clone, and C. vietnamensis was the best rootstock for Changlin 4 clone.