Two field experiments were conducted at the Experimental Farm of Agric. Minufiya University, during 1999 and 2000 seasons, to study the effect of Jasmonic
acid (JA) rates namely i.e. 00, 500 and 1000 mg L·¹ at two times of application on the
rice development, paddy yield and grain chemical composition were investigated. It
was found that JA strongly reduced plant height and increased number of tillers and
main culm diameter. The higher rate of JA applied at the early time of application
(stage 7) was the most retarding treatments. Spraying JA at the rate of 1000 mg L" at
growth stage 7 decreased the length of the middle and upper internodes of plant
culm. Early JA application at the higher level was more effective in reducing rice lodging
by increasing plant shortening. JA application at growth stage 7 tended to decrease
flag leaf area, and chlorophyll concentration. JA application decreased 1M and GA
whereas cytokinin and ABA increased when rice plants sprayed at growth stage 7.
Paddy yield and starch and protein content were increased with the lowest rates of JA
at growth stage 9. N, P and K in grains were increased by JA application at growth
stage 9.