Genetic diversity studies and screening for rice stem borer (Chilo Agamemnon) resistance in six Egyptian rice cultivars (Oryza sativa L.) using DNA based-markers

Genetic Resources and Crop Evolution - In order to assess the genetic diversity among six Egyptian rice cultivars and developing cultivars resistant to different rice stem borers, random amplified...     

Plant regeneration from hypocotyl and cotyledon explant of tomato (Lycopersicon esculentum Mill.)

Three tomato cultivars were used to examine the influence of the genetic background on the regeneration efficiency. White embryonic calli were formed within two weeks of culture. Shoots emerged either directly from the explant or indirectly from the embryonic callus. Multiple adventitious shoots were formed by clonal propagation of somatic embryos in the presence of 2 mg zeatin L^-1. The meristematic end of the hypocotyl of the cultivar Pontaroza showed a high regeneration frequency (70.2%) compared with the cotyledonary leaf explant (35.3%). The plants grown in the green house and the regenerants obtained showed a similar peroxidase banding pattern. The combined analysis of variance indicated that the difference in shoot induction between cultivars was highly significant. Shoot induction frequency was 57.2%, 43.5%, and 35.5% for the cultivars UC-97, Pontaroza, and Zuishi, respectively. The regeneration frequency was 50%, 28%, and 20% for the cultivars UC-97, Pontaroza, and Zuishi, respectively. The observed differences in shoot induction between cultivars were due to the genetic difference between them.     

Characterization of salt tolerance in tomato plant in terms of photosynthesis and water relations

Three commercial tomato cultivars (UC-97, Momotaro, and Edkawi) were subjected to a gradual increase of NaCI concentrations and the effect on biomass production and its parameters was compared. The data indicated that salinity reduced plant growth and the reduction was more pronounced in UC-97 and less in Edkawi. The apparent photosynthetic rate (P _o) was also depressed by the salt treatment and the depression was more remarkable in UC-97 and less in Edkawi. Edkawi shoot showed a much higher concentration of sodium ion and proline compared with the other cultivars, which may result in the maintenance of a higher turgor potential. In all the cultivars examined the stem diameter decreased after the beginning of exposure to light and recovered after the light was turned off. The decrease in the stem diameter during day light was enhanced and the recovery at night decreased after 1 d of salt treatment and the changes in the stem diameter were less conspicuous in Edkawi than in the other cultivars. These results suggest that Edkawi is more tolerant to salinity than the other cultivars due to a higher ability of maintaining the root function for the uptake and supply of water to shoot under salinity conditions but not due to the adjustment of transpiration from stomata.