Two field experiments were carried out in two successive seasons (2001 and
2002) at the middle of Delta. EI-Mahalla El-Kobra region, Gharbia Governorate to
study the physiological responses of cotton plants to bioregulators uniconazole at 20.
40 and 60 ppm or coumarin at 50, 100 and 200 ppm. This work aimed at studying the
effect of these bioregulators on vegetative growth parameters, some biochemical
constituents (e.g. endogenous hormones, photosynthetic pigments. oil and fatty acids
composition of the produced seeds) and the reflection of all these physiological
changes on the yield and fiber properties of colton (Gossyp < /em>ium barbadense, Cv. Giza
86) plants.
The obtained results revealed that plant height. internode length and the
number of internodes/ptant were significantly decreased mostly at all the used levels
of bioregulators. Meanwhile, number of leaves/plant and the number of branches/plant
were Significantly increased at 40 or 60 ppm of uniconazole and at 100 or 200 ppm of
coumarin. Application of uniconazole at the rate of 40 or 60 ppm and coumarin at the
rate of 100 or 200 ppm led to mostly significant increases in number of flowers/plant.
number of bolls/plant, boll set1ing %, number of open bolls/plant. seed cotton
yield/plant and seed cotton yield/(ed. Also. the fiber properties, e.g. uniformity, fiber
length, fiber strength. elongation and micronaire reading of the produced cotton. were
improved and increased mostly at all used leve's
The application of bioregulators ill ali the used levels led to decreases in the
content of endogenous hormones indole acetic acid (1M) and gibberellic acid (G~).
but the endogenous content of scscisrc acid (ABA) was increased. While the
photosynthetic pigments (chI. a. chi band carotenoids) were significantly increased
mostly at all the used le;,els of unicooazole. Oil percentage and fatty acid comoos.uon
of the produced seeds were improved mostly at all the used levels of uniconazole and

coumarin