| In order to clarify the effects of the chemical control at different leaf stages on the population dry matter production and leaf cell morphology of winter wheat, a field experiment was carried out during 2008-2009 in Gaocheng County, Hebei Province with a winter wheat cultivar'Ji 5265'as materials. Four plant growth regulators (PGRs), multiple effect triozole (MET), uniconazole, Mai Ju Jin (a commercial PGR) and Mai Ye Feng (another commercial PGR) was sprayed at 1st, 2nd and 3rd leaf before winter, and 2nd, 4th and 6th (flag) leaf stage in spring with conventional (recommended) and double concentration. The population and individual growth parameters, photosynthetic performance, leaf cell morphology and yield components of winter wheat of PGRs treatments and control (CK) were determinated. The main results were summarized as follows:1 The dry matter accumulation of winter wheat was firstly inhibited, but then accelerated when sprayed with the four PGRs at different leaf stages with two concentrations. The leaf area index (LAI) of all the treatments including CK reached the peak at booting stage then decreased. The LAI of wheat sprayed with the four PGRs of double concentration at 2nd, 4th and 6th leaf stage in spring decreased slower than that of CK, and kept 4 or larger at 20 days after anthesis. The dynamics of population culms per ha of different treatments were different. The spikes per ha of the two treatments, sprayed with MET of conventional concentration at 2nd leaf stage and with uniconazole of double concentration at 3rd leaf stage, were the highest among all the treatments.2 Two kinds of concentration treatment of 4 PGRs reduce the plant height at second leaf stage, four leaf stage, and six leaf stage in spring, but internodes which are reduced significantly are different. After the treatments of second leaf stage in spring, the length of the first and the second internodes at the base is remarkably shorter than CK, the third and the fourth internodes at the base is of almost the same length, but the fifth internode is obviously longer than CK. The length of the first and the second internodes at the base is shorter than CK at fourth leaf stage, the fifth internode is longer than CK. Under the condition of conventional concentration treatment, the length of caulis internodes differs little at sixth leaf stage. Under the condition of double concentration treatment, the length of the first, second and third internodes varies unobviously, the length of the fourth internode is much shorter than CK, and that of the fifth is longer than CK.That is, double concentration treatment has former inhibiting and latter promoting effect on the length of the upper two internodes. After two kinds of concentration treatment of 4 PGRs at second and fourth leaf stages in spring, the diameter of all basal internode increase, but that of only individual increase remarkably. After the concentration treatment of 4 PGRs at sixth leaf stage in spring, the diameter of all basal internode differs little. All in all, the concentration treatment of 4 PGRs at second, fourth, and sixth leaf stages in spring has former inhibiting and latter promoting effect on the length of the shaped internodes, but the length of basal internodes is shorter obviously, especially the concentration treatment at second leaf stage is of great advantage to the formation of plant shape with short and thick basal internodes and long top internodes. Of all the 4 PGRs concentration treatment, multiple effect triozole reduces the length of internodes on the top of the list.3 The control measures at the different leaf stage and four plant growth regulators (PGRs)can prolong the functional period of flag, and increase chlorophyll content further. Compared with the control , the peak emergence time of photosynthetic rate of flag leaf was later and extended4 Four PGRs, with conventional concentration, had a significant effect on the 4th leave cells; the mean cell links of the third and the fourth leave of double concentrations were increased some what than that of CK at the 2nd leaf emergence in spring. For the treatment of the 4th leaf emergence, there was no significant effect on mean cell links of the fifth leave with conventional concentration, however, the sixth leaf cell was affected significantly by mai ye feng. Under the treatment of multiple effect triozole,, mai ye feng and mai ju jin with double concentration, the mesophyll cell links of fifth leave were influenced, obviously, and showed more than that of CK; but the effeces of sixth leave's cell links of multiple effect triozole and mai ye feng were significant. The 6th leave emergence in spring affected cell links of the sixth leave.With mai ju jin of conventional concentration and multiple effect triozole ofdouble concentration, the mesophyll cell links were significantly with that of CK.5 The effects of four PGRs, sprayed at the 2nd leaf emergence in spring, on morphology cell at different positions of winter wheat were as follows: the cell length of different leave position had not been affected obviously in conventional concentration, but for cell width, mai ye feng was obviously narrow. There was no obvious effect of four PGRs on cell length; but for cell width, Uniconazole, multiple effect triozole and mai ju jin was narrow with doubled concentration. In contrast to cell width was affected apparently by mai ye feng and mai ju jin, at the 4nd leaf emergence in spring, the cell length was obviously narrow in conventional concentration, the same to the cell length as concentration doubled when cell width became narrower with multiple effect triozole and mai ye feng. Cell length and cell width of the sixth leave were significantly narrower than that of CK with conventional concentration of mai ju jin. For the double concentration treatment, Uniconazole, multiple effect triozole and mai ye feng decreased significantly the cell width, and only multiple effect triozole cell length was shorter. At the 6th leaf emergence in spfing, cell length and cell width were both smaller, especially for cell width. Mai ju jin in conventional concentration made cell width narrower significantly than that of CK and other PGRs. And cell length and cell width with multiple effect triozole in double concentration were both smaller significantly than that of Ck and other PGRs.6 The leaves thickness of flag leaf of winter wheat had no obvious effect for four PGRs at the 2ed leaf emergence in spring, but increased significantly with Uniconazole in double concentration. At the 4th leaf emergence in spring, Uniconazole,mai ju jin and mai ye feng in conventional concentration made flag leaf thickness increase significantly, and it was same consequence occurred to four PGRs in double concentrations. Under the treatment of the 6th leaf emergence, flag leaf thickness were increaser than that of CK, significantly or very significantly, with four PGRs in conventional or double concentration both7 After two kinds of concentration treatment of 4 PGRs, the grain yeild is affected by the combined interaction of the 3 yeild components. Under the condition of conventional concentration treatment of uniconazole at first, second and third leaf stages before winter, double concentration treatment of uniconazole at second and third leaf stages before winter, and conventional concentration treatment of Mai Ye Feng at second and third leaf stages, the yeild is much higher than CK. After two kinds of concentration treatment of Mai Ju Jin at second, fourth and sixth leaf stages in spring, the yeild increases, the concentration treatments increases remarkably expect the double concentration treatment at sixth leaf stage in spring. After two kinds of concentration treatment of Mai Ye Feng at sixth leaf stage in spring, the yield rises significantly. After the conventional concentration treatment of uniconazole at second leaf stage in spring and the double concentration treatment of uniconazole and multiple effect triozole at second and sixth leaf stages in spring, the yield goes up obviously. Thus, although two kinds of concentration treatment of 4 PGRs both decrease the plant height, especially shortening the length of basal internodes and forming better plant shape, we can draw a conclusion that uniconazole or recommended Mai Ju Jin could be used to avoid the occurrence of vigorous growth at second and third leaf stages before winter. In order to control the length of basal internodes and prevent lodging, uniconazole, multiple effect triozole and Mai Ju Jin should be used at second leaf stage in spring. However, if the vigorous growth still occurs, we can also use growth regulators for emergency.
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