| Summary: | 碩士 === 中興大學 === 園藝學系所 === 99 === When waterlogged, plants suffer two injuries: accumulation of toxic metabolites and lack of energy caused by the shortage of oxygen. Papaya (Carica papaya L.) is severely waterlogging intolerant and was used to study two methods of sorting seeds for waterlogging tolerance. The first method exposed papaya seeds to ethanol, a toxic metabolic that is the product of anaerobic respiration. The second was to establish an accelerated method of sorting by exposing papaya seeds and leaves to hypoxic (lack of oxygen) stress which was simulated by nitrogen gas.
Results showed that the ethanol treatment of ‘TN2’ papaya seeds reduced their germination percentage and extended their germination time in direct correlation to the amount of ethanol and duration of the treatment. The most significant results were seen at 1.0 mL/ 4L ethanol for 3 days in which 66% of the seeds did not germinate and few that did required 15 days to germinate, a process that only takes 10 days under normal conditions. This suggested that the physiological function of seed was obstructed by ethanol. Twelve cultivar seeds were then sorted using this treatment (1.0 mL/4L ethanol for 3 days). The mean germination time of the seeds was increased significantly but the changes in germination were non-significant when compared to the control group. This may indicate that germination of the seeds, which were pretreated with ethanol, might also have been affected by other factors, but this requires further study to confirm. After the ethanol-germination tests, the resulting seedlings underwent waterlogging experiments in which the seedlings were immersed in water for 2 days. The appearance of the seedlings and chlorophyll fluorescence of the leaves did not change significantly.
Nitrogen gas created an oxygen deficient (oxygen concentration was below 5%) condition to which ‘TN2’ papaya seeds were exposed at 0, 5, 10, 15, and 20 days after being sown. The germination decreased significantly while the mean germination time increased, especially in the seeds that were exposed to nitrogen on the 10th day after being sown. This is the point in the germination process when the seeds are the most sensitive to oxygen deficiency. Therefore, this treatment can be used as an indicator for sorting. In the nitrogen gas treatment of leaves, the membrane stability index and chlorophyll fluorescence of the leaves of adult papaya plants decreased significantly after 36 hours, more so for mature leaves than for new and older leaves. Changes in the membrane stability index and chlorophyll fluorescence showed a positive correlation; therefore, chlorophyll fluorescence test were used to quickly sort 17 cultivars of papaya for possible waterlogging tolerance. ‘PPI x ML-F2’ was found to maintain the highest chlorophyll fluorescence and ‘Exotica’ showed the lowest chlorophyll fluorescence.
|
|---|
