| Summary: | 博士 === 國立中興大學 === 農藝學系 === 87 === The original source of potato index virus-free tubers can be obtained through either by in vitro nodual culture and /or by in vitro tuberization. In vitro potato mass propagation and tuberization system of have been established, however, the multiplication rate and seedling/microtuber quality were still need to improve. These phenomena could result from the lower carbon dioxide exchange rate of seedlings and / or inadequate nutrient supplies of medium. The main objective of this study was designed to examine whether changing the carbon dioxide concentration in culture vessel could influence seedling growth, multiplication rate during subculture and subsequent tuber production. For improving the in vitro tuber quality, this study was also designed to examine whether the tuber initiation could be shorten and dry mass accumulation can be enhanced by regulating the culture environment and medium nutrition during tuber development.
It was found from this study that seedling photosynthesis in vitro tends to be considerably lower because of physiology stress, abnormal plant morphogenesis, or both. Carbon dioxide enrichment could change the leaflets structure, leaf chlorophyll content, soluble protein and Rubisco activity. These physiology improvements resulted in increase carbon dioxide exchange rate and multiplication rate. The plants derived from that grown on high carbon dioxide concentration environment also tend to produce larger and heavier tuber.
In vitro tuberization experiments results showed that jasmonic acid in concentration of 2-6 ppm stimulated tuber formation. The enhancement of tuberization was position dependent and special note on the upper nodes. Under dark condition, the tuber could be induced within 10-12 day after culture by using basal-node segment as an explantlets and culture on medium containing jasmonic acid and high concentration sucrose.
The results in this study also indicated that the lower weight of in vitro tubers was due to inadequate nutrition supply and pH environment of medium during tuber development. Tuber grown on high nitrate-ammonia medium exhibited higher rate of sucrose use and dry matter accumulation than tubers grown on lower nitrate-ammonia medium. Regulating the sucrose concentration when concentration was dropped to 30 % of initial, and/or adjusting pH value maintain at 5 during culture also enhanced the tuber dry matter accumulation.
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