Effects of Papaya Ringspot Virus on Photosynthesis Among Papaya (Carica papaya L.) Populations

• Main Authors: Ren-Hoang Wang, 王仁晃
• Other Authors: Loong-Sheng Chang
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/76353221954664026529

碩士 === 國立臺灣大學 === 園藝學研究所 === 89 === Chapter1 Effects of papaya ringspot virus on photosynthetic characteristics of papaya leaf Summary The lines of papaya used in this experiment is ringspot tolerant line ''NTU hybrid (AE)'' bred by by Department of Horticulture, NTU and ringspot sensitive line ''Tainung 2'' . SMN-PRSV virus was firstly purified then inoculated on the plant material. The photosynthetic rate of infected leaves were measured under fixed vapor pressure deficit (VPD)、temperature、CO2 and phyllotaxy but different level of light intensity by portable gas exchange system. In contrast with healthy leaves, the net photosynthetic rate (Pn) and photo quantum yield (Φ) of infected leaves of ''Tainung 2'' were decreased to 56 % and 66 % of healthy leaves respectively, and respiration rate (Rd) and photocompensation point were increased significantly while total chlorophyll and Fv/Fm value were decreaseed. The results suggest PRSV resulted in serious damage to photosynthesis mechanism on ''Tainung 2''. In contrast, infected leaves of ''NTU hybrid (AE)'' only showed minor rise in respiration and no effects on photosynthesis. Thus, photosynthesis of ''NTU hybrid (AE)'' can maintain normal photosynthesis after infection of the virus. The stomatal conductance (gs) and transpiration rate (Tr) of infected leaves of ''Tainung 2'' were both lower than those of the healthy leaves and the intercellular CO2 concentration (Ci) increased, thus the stomata were very likely an expression parameter of poorer photosynthesis of infected leaves of virus sensitive varieties. The virus infected leaves of ''NTU hybrid (AE)'', on the other hand, although showed slight increment in Ci, neither stomata conductivity (gs) nor transpiration rate (Tr) was affected. The above results showed that the infected leaves of ''NTU hybrid (AE)'' kept normal photosynthetic parameters thus prove ''NTU hybrid (AE)'' virus resistant. Chapter2 Effects of papaya ringspot virus on photosynthetic parameters and growth characteristics of papaya leaf Summary The objective of this study was to learn the PRSV tolerance ability of papaya line ''NTU hybrid (AE)'' bred by Department of Horticulture, NTU. The PRSV sensitive culivar ''Tainung 2'' and tolerance cultivar ''Tainung 5'' were compared and used as controlled group. The differences of photosynthetic parameters were measured on the 12th leaf of all plants by portable gas-exchange system. The viral titer of leaves among phyllotaxy and its effects on photosynthesis were examined and compared. The viral expansion rate was fastest in ''Tainung 2'' and the chlorophyll meter reading (CMR) was observed lower among different phyllotaxy. Further the occurrence of photoinhibition (decrease in Fv) and decrease in gs resulted in lower Pn. On the other hand, the leaf area、leaf duration and leaf number were decreased significantly, light interception was severely affected as a consequence in controlled group. The infected leaves of virus tolerant line showed superior performance to ''Tainung 2'' in various parameters of photosynthesis. The tolerance line ''NTU hybrid (AE)'' viral titter is lower than the tolerant ''Tainung No.5'', and susceptible ''Tainung No.2''. Further, Pn、leaf duration and survived/remaining leaf number was less affected than that in its counterparts. It is therefore concluded that the ''NTU hybrid (AE)'' expressed the strongest virus resistance among three entries. Chapter3 Effects of improving the resistance of papaya ringspot virus on photosynthesis and fruiting Summary The lines of papaya used in this experiment are papaya ringspot virus disease tolerant lines bred by Department of Horticulture, NTU and sensitive line ''Tainung 2''. Between the open field and net-house, effects of papaya ringspot virus on photosynthetic parameters, fruit numbers and total soluble solid were discussed. There are no significant different on net photosynthetic rates among healthy lines or cultivars. After infection of papaya ringspot virus, the tolerant line ''NTU A line'', parents of ''NTU hybrid (AE)'', and ''NTU hybrid (AE)'' respectively maintaining 90% and 97% of net photosynthetic rate compared to the healthy control in the field, but the ''Tainung 2'' was reduced to 40%. Therefore, the tolerant lines can keep the normal net photosynthetic rate and inherit the resistance after infection viruses. Furthermore, the tolerant lines have little effects on radiation interception parameters, chlorophyll contents and leaf area, and show slight disease rating. The above results showed that the tolerant lines kept normal radiation use efficiency, photosynthesis, and radiation interception, thus had good total soluble solids and crop load. Because of high significant correlation among Pn , disease rating and total soluble solids, we can apply Pn measurement and disease rating estimation to resistant selection.