BIOLOGICAL AND BIOCHEMICAL STUDIES ON IRRADIATED POTATO TUBERS

SUMMARYThe present investigation aimed to study and overcome two important diseases which attacks potato plant, using some chemical and physical treatments. The first disease was preharvest brown rot caused by Ralstonia solanacearum and the second was postharvesFirstly brown rot:1- Foliar treatment of salicylic acid or calcium chloride on potato plants leads to increasing in plant height and number of potato tubers, since salicylic acid give the highest value of plant height and also calcium chloride give the highest number of po2- The bacteria Ralstonia solanacearum isolated from infected tubers obtained from The Project of Brown Rot, Ministry of Agriculture, Egypt, added with irrigate water to the pots this bacteria could infect healthy potato plant and the symptoms of brown ro3- Concerning D10-value determined from the relation between dose rate of gamma ray (k-rad) and log count of bacterial number it was found that the D10-value for R. solanacearum was 0.25 kGy.Secondly dry rot:1- Exposing to dry heat treatment at 40ºC for 72hr or dipping in hot water at 55ºC for 7 min could decrease the growth of Fusarium oxysporum in vitro but not inhibit it.2- Dipping infected potato tubers with F. oxysporum in hot water at 55ºC for 7 min or holding in hot air at 40ºC for 72 hr retard dry rot incidence but not prevent it.3- Lemongrass essential oil at 1.0 ppm or caraway essential oil at 2.0 ppm followed by peppermint oil at 4.0 ppm and fennel oil at 6.0 ppm could inhibit growth of F. oxysporum, the causal agent of dry rot.4- Dipping potato tubers in 1.0 ppm lemongrass oil or in 2.0 ppm caraway oil prevented dry rot for more than four months.5- Scan and transmission electron micrographs showed distortion of hyphae, conidiophores and chlamydospores, changes in ultrastructure of cell wall, plasmamembrane, cytoplasm, cell organelles and hyphal tips of fumigated mycelium of F. oxysporum by sublet6- One of the most important results appeared during this study is the ability of lemongrass and caraway oils at sublethal dose to prevent mycotoxin production from F. oxysporum.7- Gamma irradiation treatment at doses 0.1, 0.25 and 0.35 kGy could retarded the appearance of dry rot to the third month but the dose of 0.15 kGy retarded the appearance of the same disease to the fourth month of storage at room temperature.8- Studies the effect of different doses of gamma radiation on sugar content, starch, free amino acid, phenol content and vitamin C showed that radiation minimized the decreasing of total soluble sugar content, starch and phenol contents but increased in 9- The interaction effect of gamma radiation at 0.15 kGy and lemongrass (1.0 ppm) or caraway (2.0 ppm) oils could retard the appearance of dry rots caused by F. oxysporum to the fourth month of storage.10- Foliar treatment of salicylic acid or calcium chloride on potato plants leads to increasing in potato tubers resistance to dry rots caused by F. oxysporum decreasing severity of infection from 55.06 to 25.8 or from 55.06 to 37.3 by using 1.0 mM of sal