Effect of drought stress on ovules of Phaseolus vulgaris L.

Drought stress is an important environmental factor which limits bean yield in rainfed areas. Bush-type bean (Phaseolus vulgaris L.) plants grown in a greenhouse were subjected to soil-water deficit until leaves reached permanent wilting condition (PWC: turgidity was not recovered overnight) at 13, 17, 21, 25 (preanthesis) and 30 (anthesis) days after emergence (DAE). An age when a treated plant reached the PWC constituted a treatment. The plants remained in PWC 56 h before watering was resumed. Preanthesis treatments were sampled at 31 DAE, anthesis treatment at 33 DAE. Preanthesis and anthesis unstressed controls were watered to maintain the soil at field capacity. Approximately 60 ovules from flower buds or from flowers at anthesis per treatment or control were observed under the microscope and scored for abnormalities. Conclusions: 1) Water stress retards the development of some ovules and might arrest their further growth. 2) Necrosis of the embryo sac is the only abnormality which occurs in unstressed controls but it is much more frequent in water-stressed plants. 3) Retarded and shriveled embryo sacs, and necrosis in the nucellus and chalaza are abnormalities that might be specifically related to water stress, since they do not occur in the unstressed controls. 4) There seems to be a relationship between the age of the plant at which the water stress is imposed and the kind and frequency of ovule abnormalities.