الملخص
This work aimed at investigating the morphological, physiological and biochemical adaptations of some sorghum cultivars (the yellow, white and red) in Asser region. The seeds were grown under the greenhouse conditions located in KKU, then the plants were subject to through the course of germination. Morphological measurements (i.e. leaf area, stem elongation and root growth), physiological changes (plant water status by RWC; leaf diffusive resistance to water vapour) and biochemical determinations (proline concentration, total carbohydrates) due to drought were taken. The results showed that the RWC of the yellow cultivar continued to significantly decline from the onset of drought onwards, followed by thatof the white cultivar whose RWC started declination as from about 15 days from drought onwards. Regarding the red one, however, its RWC remained unchanged by drought in most of the measurement dates. The actual values for the yellow and white at the end of the experiment were fixed at 48% compared with 77% for the red one. Regarding the LDRWV, the drought plants showed significant increases when values of 113, 89 and only 58 s.cm-1 were obtained by the yellow, white and red cultivars respectively. The chlorophyll content of the yellow, white cultivars were also significantly reduced under drought by 23.7%, 37.9% and 24.6% respectively. The leaf area results revealed significant decreases under drought in the case of the yellow CV from the onset of drought on. This trend was followed by those of the other two CVs. The values at the end of the experiment i.e. after 37 days from drought were similar at about 77 and 70 cm2 for the white and the red ones which were significantly higher than that of the red CV (58 cm2). With respect to the data of the shoot: root components, the shoot dry weights for the yellow, white and red CVs significantly decreased by 79.8%, 69.3% and 55.8% respectively. On the other hand, the root dry weights significantly increased by 64.4% and 87.9% for the yellow and white CVs respectively, with no significant change in the case of the red one. These results clearly showed that the yellow and white CVs managed to increase the dry weights of their root systems, perhaps as a measure of adaptation to drought.The levels of proline under drought for the yellow, white and red CVs increased to concentrations of about 19.9, 14.7 and only 6.6 µmole proline.g-1 DW respectively. The value shown for the red cultivar dropped to its control level after 2 days from re-watering of the drought plants, while remaining significantly higher for the other two cultivars on the same date. The TNC values of all cultivars significantly increased under drought. The typical values for the yellow, white and red CVs were 88.5, 72.1 and 77.8 mg.g-1 DW. These values significantly decreased after re-watering. The WSC concentrations for the yellow, white and red cultivars also significantly increased under drought by 57.6% and 90.6% and only 20.4% respectively. The results showed significant drops in the all carbohydrate parameters after 10 days from re-watering, reflecting their redistribution to targeted plant sinks. With respect to starch concentration, it was also significantly increased under severe drought condition, but after rewatering significantly declined to values of 6, 3.4 and only 0.8 mg.g-1 DW for the yellow, white and red cultivars respectively. All in all, the results reflected that the yellow cultivar was the most susceptible to do drought, perhaps its high root dry weight and low leaf area under drought were in favor of some drought tolerance for this cultivar. However these characteristics were far behind help survival of the plants which were observed to die before end of the experiment. On the other hand, the red cultivar remained green over the whole of the experimental period, thus possessing the stay green character known to be an effective adaptation tool under severe drought.
