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Relationship between Plant Growth and Tree Vigor in Kyoho Grapevines
Summary The grape production in Taiwan has multiple harvest in a year. But in the second harvest, tree vigor was decreased, inflorescence was shorter and the berry size was smaller. In order to understand the relationships between plant growth and tree vigor of this unique cultural model in Taiwan, the variation of physiology of root growth and tree growth vigor in two harvest crops were investigated, and the influence of vineyard management on the root growth was discussed in this study. It will provide the information for the improvement on the plant physiological condition and vineyard management technique, and serves as reference for the plant physiological research of other deciduous fruit tree that grew in high temperature area. The growth of root system in different growth stages of two harvests ‘Kyoho' grapevines(Vitis vinifera L. ×Vitis labruscana Bailey cv. Kyoho) was observed by means of excavated method and glass-walled rhizotron method. The results showed that the young roots were began to grow before budbreaking in the spring. The growth amount of young roots was measured the area of the young roots on the glass face was also calculated at different growth stages. It revealed that a mass growth of root system in first harvest was occurred often the slowdown of the shoot growth at the varison stage, and the flush growth of young roots was observed at the berry coloration stage. The young roots ceased to grow at the budbreaking stage that followed the pruning for the second harvest, another flush growth was started at the varison stage, whereas the growth amount was lower than that of in the first harvest. According to the investigation of this experiment, a correlative relationship is existed between the growth of the young roots and the shoots, and neither the first nor the second harvest had flush growth in the post-harvest periods. This result was different from the one-harvest per year in the temperate-zone area. The growth physiology in different growth stages of two harvest grapevines was investigated. The results showed that the first harvest had longer shoot length and more leaves, and thicker shoot diameter than that of second harvest. The leaf photosynthetic rate was higher during flowering stage to varison stage and declined after coloration, whereas the chlorophyll content was decreased till maturation stage. Both in the first and the second harvest, the physiological activities of root and shoot were increased following budbreaking, and reached the peak at fruit-setting stage, declined after maturation, the physiological activities in the first harvest were higher as comparing in the same growing stage. In the analysis of plant carbohydrates, the contents of total soluble sugar and starch in the early growing stage after pruning were higher for the first harvest than the second harvest, and the contents were higher in the roots than in the above part. The plant starch content was gradually increased in the late growing stages in the second harvest, in which the root had the higher content. The contents of free amino acids and soluble protein were also higher in the root, the contents of free amino acids in the early growing stages in the first harvest were higher, whereas there was no difference in the contents of soluble protein between two harvests. The plants were treated with different duration of chilling in 5℃ in the summer. The results showed that treatment of 5℃ chilling for 300 hours could promoted the budbreaking and shoot growth in the second harvest, prolong the chilling duration could not accelerate the budbreaking but enhanced the shoot growth after budbreaking. Chilling treatment in the summer could increase the plant physiological activities, and the activities in the pre-budbreaking stage were higher in treatment with chilling or hydrogen cyanamide. Chilling treatment in the summer, from July to August, could increase the content of total soluble sugars after pruning to budbreaking in the second harvest, and decreased the starch content. The content of soluble protein was decreased, and the content of free amino acids decreased at the early stage of chilling, but increased as the chilling was prolong to 900 hours. The investigation of water absorption in two-harvest model was carried out under the control of 30% soil water content. The results of two years showed that the amount of root absorption was increased with the shoot growth. The peak root absorption of the first harvest occurred in late June to early July, right before ripening, and decreased after pruning of the second harvest. The absorption decreased as the shoot growth of the second harvest, the second peak absorption was reached at early October, and decreased thereafter. Comparing the difference of the amount of water absorption between the two harvests, the first harvest was higher than the second harvest. The peak absorption of the first harvest lasted longer whereas the peak absorption of the second harvest decreased sharply owing to the decrease of temperature. The result of the investigation on the model of root growth in one harvest showed that two flush growths were appeared in varison stage and post-harvest, which was different from two-harvest. The root growth during maturation stage was affected by the yield of the fruit, the area of young roots have negative correlation with the yield. The root water absorption amount during plant growth ceasing period from February to March had no difference among three soil water content, 30%, 26% and 22%. Following by the increase in shoot growth and leaf area after budbreaking, the plant water absorption was increased gradually, the plants in higher soil water content had high absorption amount and thus increasing vine growth. In the same soil water content, the total water absorption was 50-83% higher in the first harvest than that of the second harvest. The influence of bud-forcing on water absorption was low at the early period, but the absorption in the bud-forced plant was higher at 18-19days after bud-forcing. Based on the results of this study, the growth of above part and the root were mutually co-related, an alternation of growth appeared between the root and the shoot in two harvest ‘Kyoho' grapevines. As the plant carbohydrate contents at early growth stage was higher in the first harvest, thus the winter chilling could help the conversion of the insoluble carbohydrate and the early shoot growth. Therefore, the growth of the above part and the root were both higher in the first harvest than that of the second harvest, and higher TTC viability and root water absorption were also occurred in the first harvest. The chilling condition could enhanced budbreaking and the shoot growth. The probable reason is that the chilling accelerate the decomposition of starch into soluble sugars thus enhance the plant vigor after budbreaking.
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