Barley, sorghum, and maize plants were grown in nutrient culture with increasing concentrations of bicarbonate supplied as NaHCO 3 (0-20 mM) and harvested at 0, 2, 4, and 8 days of treatment. Bicarbonate induced symptoms of iron (Fe) deficiency (chlorosis) in all three plant species, but sorghum and maize were more sensitive than barley. Increases in the concentration of HCO 3 -ions in the nutrient medium markedly decreased dry weight of roots and shoots in all three crop species. These effects became more distinct with time, particularly at 10 and 20 mM of bicarbonate supply. In contrast to root dry weight, however, root length was depressed by 'Present address:

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The present research work has been carried out to study the response of three genotypes of sugarcane (Saccharum species hybrids) for callus induction, embryogenic callus production and their in vitro salt tolerance.For callus induction and embryogenic callus production, leaf base segments were subjected to in vitro culture on Murashige and Skoog (MS) medium supplemented with 3 mg l -1 2,4 Dichlorophenoxyacetic acid for 4 weeks. To evaluate salt tolerance of the varieties, cultured calli were exposed after two subsequent subcultures (4 weeks each) to different concentrations of NaCl (0, 17, 34, 68 and 102 mM) added to the culture medium for 4 weeks. Comparison of genotypes was based on callus induction percentage, embryogenic callus production percentage and relative fresh weight growth. For salt tolerance, necrosis percentage and relative fresh weight growth of callus were used. The three genotypes responded well to callus induction with about 82, 84 and 100 percentage of induction for GT 54-9(C9), NCo310 and Co 413, respectively. The high per cent of embryogenic callus obtained for the three varieties indicated that these genotypes have a high capacity for embryogenic callus production. Relative fresh weight growth of callus was about 1.076, 1.282 and 0.925 for GT 54-9, NCo310 and Co413, respectively. The effects of NaCl resulted in calli necrosis and a reduction of their growth. Growing calli derived from genotypes GT 54-9 and NCo310 showed less necrosis percentage and less relative fresh weight growth reduction under salt stress. They appeared to be more salt tolerant in vitro than Co 413.The finding of superior genotypes GT 54-9 and NCo 310 and inferior one Co 413 for salt tolerance together with their high potential for embryogenic callus induction may be a model varities to study physiological mechanisms associated with in vitro salt tolerance and in vitro selection for salt tolerance in sugarcane.

Seeds of sorghum [Sorghum bicolor (L.) Moench cv 'Wrangler'] dressed with three increasing concentrations of an iron ethylenediamine-di-O-hydroxphenylacetic acid (FeEDDHA) product up to 480 mg Fe kg −1 seed as a sole source of iron supply as well as a treatment without any dressing were grown for 19 days after germination in sand culture buffered to pH 8 by calcium carbonate. Nitrogen was supplied either as ammonium (NH 4 )-N or nitrate (NO 3 )-N, the former being supplemented with nitrapyrin (N Serve) to prevent nitrification. Chlorosis of the younger leaves was evident in all treatments except at the two higher levels of NH 4 -supplied plants. Dry matter yields of the shoots were raised only relatively slightly by the increasing levels of Fe supply and at each level the NH 4 form was superior to that of NO 3 -N. At the end of the growth period the pH of the sand around the roots had fallen by about 0.5 of a unit for NH 4 -fed plants and increased by about 0.2 of a unit for NO 3 -fed plants. At each level of Fe supply, NH 4 nutrition approximately doubled the micronutrient [Fe, zinc (Zn), copper (Cu), manganese (Mn)] shoot concentrations and uptakes as compared with NO 3 -nutrition. For the NO 3 -fed plants, increasing rates of Fe seed dressing had little effect on shoot Fe concentrations or uptakes, the concentration values determined (about 40 µg g −1 dry wt.) being below the range of critical deficiency concentration. Similarly concentrations of Mn were also in the deficiency range in the seed dressed NO 3 -fed plants (11-12 µg g −1 dry wt) so that in the NO 3 treatments chlorosis may have resulted from a lack of 1855 1856 R. A. Alhendawi et al.Mn as well as Fe. Dressing sorghum seeds with Fe chelates in conjunction with NH 4 fertilization supplemented with an inhibitor to prevent nitrification would appear to be a worthwhile approach to ensure an initial source of Fe to the young developing plant in the avoidance of iron-induced chlorosis in the growth of sorghum on high pH calcareous soils.

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