Ho Jeong

Chlorophyll Fluorescence as a Diagnostic Tool for Abiotic Stress Tolerance in Wild and Cultivated Strawberry Species

Chlorophyll (Chl) fluorescence analysis was used to assess stress tolerance in wild and cultivated strawberry species. We found that the parameters, photochemical quenching (1-qP), non-photochemical quenching (qN), and maximum quantum yield (Fv/Fm), can serve as stress indicators because they are sensitive to early responses to stress. The most sensitive region used for measuring Chl fluorescence in strawberry leaves was the upper surfaces of leaflets located in the middle of new leaves. An analysis of the Chl fluorescence characteristics of strawberry species showed that octoploid species had greater stress tolerance than diploid species. The ‘Whiteberry’ maintained high levels of 1-qP and qN through the dissipation of excess excitation energy as heat during early stress treatment. These results suggest that ‘Whiteberry’ has a photoinhibition system that allows it to respond to stress in a more sensitive manner than other cultivars. Therefore, among the Chl fluorescence parameters examined, 1-qP and qN, can serve as good indicators for comparing stress tolerance, and they can be used to simultaneously screen many plants for stress tolerance in strawberry breeding programs.

Effects of backcrossing on quality of strawberry fruit

American/European strawberry cultivars are morphologically different from Asian cultivars with American cultivars generally having higher yields, fruit weight, and fruit hardness and Asian cultivars tending to have higher sugar content. In this study, we performed backcrossing to improve the fruit qualities of Asian varieties of strawberries using American cultivars as the donor parent. The F1 progeny derived from crosses between Asian and American cultivars tended to have lower sugar content and higher fruit weight and yield than Asian cultivars, but fruit hardness did not differ between the Asian cultivars and the progenies. The percent germination and survival ratio were not significantly different between the BC1F1 and BC2F1 generations, whereas the percent germination decreased rapidly with advancing backcross generations. The BC1F1 generation had slightly higher sugar content and the sugar content of the BC2F1 generation increased significantly over the BC1F1 generation, but fruit weight and yield decreased. However, there was variability among individual progeny from the same cross. With advancing generations of backcrossing (BC3F1, BC4F1, BC5F1), sugar content tended to improve while fruit weight and yield tended to decrease, and hardness tended not to change. Therefore, to develop new cultivars with the combined qualities of Asian and American cultivars, we concluded that generations beyond the BC2F1 are not necessary, and that the selection efficiency of superior individual plants can be improved if the number of seedlings is increased in generations before the BC1F1 or BC2F1.

Effect of EC Level of Irrigation Solution on Tomato Growth and Inorganic Ions of Root Zone in Soilless Culture of Tomato Plant Using Coir Substrate

In hydroponics, the nutrient solution is supplied considering the water and nutrient uptake characteristics of crops. However, as the ionic uptake characteristics are changed as a result of the weather conditions or the growth response of the crops, the root zone can not be maintained in optimal condition. In addition, the coir substrate has been used mainly for the tomato cultivation in place of the inorganic substrate, there are few studies on long-term cultivation using coir substrate. Therefore, this study was conducted to investigate the effect of EC level of irrigation solution on tomato growth and inorganic ions of root zone in soilless culture using coir. Coir substrate mixed with 5 : 5 chip and dust was used. EC level of irrigation solution was 1.0, 1.5, 2.0, and 3.0 dS·m. At the initial stage, NO3N, P, Ca and Mg in the drainage were lower than the irrigation level at 1.0 and 1.5 dS·m. However, EC 2.0 dS·m or higher, all the ions except P were highly concentrated in the drainage. The average fruit weight was not significantly different between 1.0 and 1.5 dS·m until 3th cluster, but from the next cluster, the higher the EC level, the smaller the weight. The number of fruit and yield to 6th cluster was the highest at 1.5dS·m. From the next cluster, The yield was decreased with the higher EC level. At the early stage of growth, BER occurred only in EC 3.0 dS·m, but increased in all treatments with increasing irradiation. The incidence rate of EC 3.0 dS·m was higher than that of the lower EC level treatment. Additional key words : EC, drainage, blossom-end rot(BER), soluble solids content