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>PHYSIOLOGICAL AND MORPHOLOGICAL MECHANISMS OF DROUGHT RESISTANCE IN SORGHUM AND PEARL MILLET. I. EFFECTS OF LEAF TREATMENT WITH ABSCISIC ACID. II. SEED PRE-TREATMENT WITH ABSCISIC ACID. III. COMPARATIVE SHOOT AND ROOT DEVELOPMENT. IV. LEAF SURFACE MORPHOLOGY (WATER USE EFFICIENCY, EPICUTICULAR WAX, CUTICULAR TRANSPIRATION, STOMATA).
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PHYSIOLOGICAL AND MORPHOLOGICAL MECHANISMS OF DROUGHT RESISTANCE IN SORGHUM AND PEARL MILLET. I. EFFECTS OF LEAF TREATMENT WITH ABSCISIC ACID. II. SEED PRE-TREATMENT WITH ABSCISIC ACID. III. COMPARATIVE SHOOT AND ROOT DEVELOPMENT. IV. LEAF SURFACE MORPHOLOGY (WATER USE EFFICIENCY, EPICUTICULAR WAX, CUTICULAR TRANSPIRATION, STOMATA).
The differential effects of exogenously applied abscisic acid (ABA) on leaves of stressed and non-stressed sorghums was investigated. In general, root to shoot ratios were increased by the treatment in well-watered plants. Shoot heights, rooting depth, and total shoot and root dry weights were nearly unaffected in water stressed plants, while grain yield and seed number were increased. Application of gibberellic acid and kinetin counteracted the effects of the ABA. A technique was also developed for treating sorghum seeds with ABA solutions which induced greater drought resistance. The ABA seed treatment increased plant heights and grain yields in droughted plants. With well-irrigated plants, the effects of the seed treatment were variable in that it increased yields in some genotypes and markedly decreased them in others. A comparative study of shoot and root development in sorghum and pearl millet showed the millets to have smaller leaf areas and a larger number of main adventitious roots that the sorghums under both well-watered and water-stressed conditions, and shorter maximum root depth than sorghums when water stressed. Droughted millets used less water, but their water use efficiency was higher than the sorghums. The millets had lower root dry weights than the sorghums except in the 20 to 40 cm depth zone where the millets had greater root dry weights than the sorghums. A comparison between glossy and non-glossy sorghums showed the glossy lines to have less leaf area, lower number of main roots, shorter maximum rooting depth and lower total dry weights than non-glossy types. Leaf surfaces of sorghum, maize and pearl millet were studied by scanning electron microscopy. The glossy character was correlated with a reduction or absence of observable wax deposits on the leaf surfaces. The pearl millets showed no glossiness even on the twelfth leaf, whereas sorghum and maize leaves were generally glossy after the fifth leaf. Glossy leaves had higher cuticular water loss than non-glossy leaves.
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