Introduction Directory UMM :Data Elmu:jurnal:E:Environmental and Experimental Botany:Vol44.Issue1.Aug2000:

1. Introduction

Cotton is the most important fiber crop in the world as well as in Egypt. Increasing cotton production and quality is an urgent national goal to meet the consistent demand for this crop. Plant development is influenced by various endogenous and exogenous factors. The result- ing physiological processes regulate the rhythm of growth and development. A group of sub- stances that is of particular interest in this re- spect are the bioregulators. Plant growth regulators PGRs usually are defined as organic compounds, other than nutri- ents, that at low concentrations, affect the phys- iological processes of plants Glemas, 1982. For practical purposes, PGRs can be defined as ei- ther natural or synthetic compounds that are applied directly to a plant to alter its growth processes or structure in some beneficial way Luib and Schott, 1990. Growth and development processes in plants are coordinated by phytohormones Bruinsma, 1980. They can also be influenced, however, by the exogenous application of specific bioregula- tors. The specific effect of a bioregulator de- pends on the application rate, time of treatment, and the developmental stage of the plant at the time of application Do¨rffling, 1982. The cytokinins CK play an important role in all phases of plant development, from cell division, and cell enlargement up to the forma- tion of flowers, fruit set and dry matter forma- tion in plants Mayeux, 1985; Cothren, 1994. The basis for foliar application of cytokinins to field plants is inferred from the improved growth of plants in cytokinin-containing solu- tions Hedin and McCarty, 1994b. Cytokinins may not always be active unless other hormones are present Hedin and McCarty, 1994b. How- ever, cytokinins alone can often evoke a variety of physiological, metabolic, biochemical, and de- velopmental processes when applied to plants Elliott, 1982; Taiz and Zeiger, 1991. Cytokinins are synthesized in root tips and are active in the maintenance of ongoing pro- cesses and nutrient mobilization in the shoot Hearn and Constable, 1984. Thus they inhibit shedding by stimulating auxin production. Peak CK activity in bolls is at 4 – 9 days after flower- ing, declining to little or none at 18 days Sand- stedt, 1971. It is hoped that if the endogenous concentration of cytokinin can be increased by exogenous application, it may reduce the unde- sirable shedding of squares and bolls which may lead to an increase in seed cotton yield. The use of PGRs on cotton has been investi- gated by many workers including McCarty et al. 1987, Hedin and McCarty 1991, 1994b. Fo- liar spraying revealed that the synthetic cy- tokinin, kinetin 6-furfurylaminopurin, tended to increase yield of cotton. Hedin and McCarty 1991, 1994b found that kinetin applied in the field increased cotton yield by 26. Deng Ji- anXiu 1996 spraying cotton plants with a mix- ture of 4 PU-30 synthetic cytokinin and DPC mepiquate chloride increased lint yield by mainly 17 compared with water only, and by mainly 7 compared with spraying DPC only. Foliar application of this cytokinin products was reported to promote bud initiation and develop- ment that caused an increase in plant fruitful- ness and increased efficiency of the plant to develop and fill that fruit Mayeux, 1985. Oost- erhuis et al. 1997 found that Maxon cy- tokinin application produced a significantly greater number of open bolls 7 weeks after first flower. El-Aggory et al. 1982 reported that kinetin significantly increased seed cotton yield and number of mature bolls. Lint strength or fineness did not change with any of the kinetin treatments. Since most plant growth and development processes are regulated by natural plant hor- mones, many of these processes may be manipu- lated either by altering the plant hormone level or enhancing the capacity of the plant to its natural hormones. Thus, PGR chemicals could become a useful tool for cotton producers re- serve to ensure efficient production. To attain high productivity of Egyptian cottons and to preserve the superior quality of their fibers, promising approaches should be investigated. We tested the hypothesis that the application of kinetin will stimulate germination, seedling vigour, and cotton yield.

2. Materials and methods