This investigation was carried out at Mallawi Agric. Res. Station, Minia
Governorate during 2001 and 2002 seasons to study the response of Giza !b cotton
cultlvar to the application of gibberellic acid (GAJ) and mepiquat chloride (pix applied
in sequential foliar applications as follows: 1· Control. 2· Spraying GAJ at seedling stage (SES) + pix at ear1y floweqpg stage
(EFS). 3· Spraying GAJ at squaring stage (SaS) + pix at EFS 4- Spraying GA3 twice
at SES and sas + pix at EFS. The used concentration of both GA3 and pix was 50
ppm. However, results showed that the application of GA:! once at SES 0 at sas
with sequent spray of pix at EFS positively influenced growth characters; pia t height,
number of nodes per stem and number of sympodia per plant. producing vigorous but
balanced plants with greater both fruiting capacity and reproductive eflicien~ through
enhancing number of total fruiting sites, nowers, open bolls and total bolls !per plant
along with reducing fruil shedding% leading to a significant increase in sead cotton
yield per feddan. The appucanon of GA:! twice at SES and sas + pix at EFS enhanced plant
growth and Its fruiting capacity by increasing significantly plant height, numbej of main
stem nodes, number of sympodia, lotal fruiting sites, flowers and total bolls ~er plant
but it failed to increase seed cotton yield due to the Significant increase in umopened
bolls per plant and delaying crop maturity associated with this treatment. The results of chemical constituents of leaves obtained from treat d cotton
planls showed that application of GAJ once at SES or at sas and then sprayi g pix at
EFS increased significantly chlorophyll (a, b and total). carotenoides, carbohydrate
contents (reducing sugars, non-reducinq sugars and total soluble sugars) and
phenolic compounds. Gibberellic acid and mepiquat chloride treatments had no significant effects on
internode length, number of days from sowing to either first flower or first open boll,
boll weight, tint % and fiber quatity. Only in 2002 season, seed index was sigmificantly
increased by the treatments included one spray of GAJ at sas or two sprays of GAJ,
followed by spraying Pix al EFS.