Development of Hardy Sorghum Cultivars for the Arid and Semi Arid Regions

Tissue culture is the starting point of many techniques in biotechnology aimed at genetic modification of plant cells and whole plants. Plant tissue and cell culture was used to induce and maintain embryogenic calli established from young embryogenic explants of three sorghum bicolor cultivars (Mtama 1, EI Gardam and Seredo) selected basing on tannin content. Embryogenic calli were obtained by culturing young embryos on Linsmaier and Skoog's (LS) medium containing 2mg/12, 4-dichlorophenoxyacetic acid (2, 4-D) and 0.5 mg l^-1 Kinetin. Calli were subjected to various NaCl concentrations to screen for salinity tolerance. Calli subjected to 0.0 mM NaCl served as controls. Calli with tolerance to salinity stress had a higher activity of succinate dehydrogenase, which reduced trimethyl tetrazoliumn chloride (TTC) to formazan. From the TTC viability test, 1000 mM NaCl was selected as the optimum concentration, which was incorporated into LS media to select salt tolerant calli. Random amplified polymorphic DNA (RAPDs) technique showed that variation existed between NaCl treated plants and the controls in the individual and pooled DNA samples. This may indicate that somaclonal intra-cultivar variation had resulted in some of the cell lines becoming tolerant to salinity. A measure of CO2 assimilation rate, synchoronised with Photosynthetic Active Radiation (PAR), stomata conductance (SC) and Transpiration Rate (TR) using infrared gas analyzer (IRGA), along with titratable acidity and malate content were used to assess productivity under stress. The treated plants significantly (P<0.05) had higher CO2 assimilation rate, higher levels of titratable acidity and malate than the controls in the 3 cultivars. The three parameters had a day pattern of increasing starting from morning, reach a peak at noon and decreased as the afternoon progressed in parallel with PAR. High positive regression correlations (r² ≥ 0.7) existed between titratable acidity and malate content; malate and CO2 assimilation rate (r² ≥ 0.6) illustrated that these parameters were interdependent.