Study On The Selection Of Cell Mutant Lines Resistant To Phytophthora Infestans In Potato

The research used stem and leaf of three potato cultivar, Favorite, Dongnong 303 and Zaodabai as explant and the culture filtrate of Phytophthora infestans as the selective agent. The bioactivities and culture condition of the crude toxin were assayed at the beginning of the study. Then the callus resistant to Phytophthora infestans was selected by using one-step and multi-step screening method at different concentration of the crude toxin. The disease resistant mutant selection system was established and several mutant plants were obtained. 1 The crude toxin was obtained by means of liquid culture of Phytophthora infestans with rye liquid medium. Using the crude toxin, the study investigated the effect of Phytophthora infestans on the leaf and callus of potato, the germination of tomato seeds and the growth of tomato radicel. The results showed that the effect of crude toxin on four types of explants were consistent. The higher the concentration of crude toxin was, the stronger the toxicity would be. The effects of crude toxin on seed germination and the radicel growth of tomato were more distinct than on potato leaf and callus. Therefore, the germination rate of tomato seeds could be used to study the culture condition of crude toxin in the following study.2 The toxin production of Phytophthora infestans was studied in different culture conditions, such as liquid medium, light, temperature, pH value and shaking. It was appropriate for toxin production that pH value and temperature of culture medium were 6-7 and 20-22℃ respectively with darkening and shaking 24h every day among 14 and 18 day in the rye liquid medium. At above conditions, the crude toxin showed more inhibitive effects on seed germination of tomato.3 The crude toxin of Phytophthora infestans had the capacity of thermal stability and could not only extremely inhibit the germination of tomato seeds but also do great harm to the growth radicel.4 Crude toxin as the selected agent, some cell mutant lines resistant to Phytophthora infestans were screened by leaf, stem and callus from them in three cultivars by means of one-step and multi-step methods. The experimental results showed the resistance of three cultivars to Phytophthora infestans was different. The highest resistant concentration to Phytophthora infestans crude toxin for Favorite was 40%, and for Dongnong 303 and Zaodabai were 50%. With the increase of the crude toxin concentration, the relative growth of callus decreased and the its colour appeared brown. The callus from stem was more resistant to Phytophthora infestans than callus from leaf. The great harm of crude toxin to the growth of buds differentiated from the callus was also found. 5 The plantlets of the control and from the screened mutant were cultured on medium with crude toxin. The results showed that the rooting rate was higher on medium without crude toxin. On the medium with crude toxin, the rooting rate of mutant was higher than 20%, but the control was zero. Therefore, the resistance of mutant was thought persistent.6 The regenerated plantlets were obtained and their resistant stability was detected. Theresult showed that the resistant cell mutant lines had a stable resistance to Phytophthora infestans. The mutant plantlets showed resistant to the disease of Phytophthora infestans compared to the control in the pot test.