| ABSTRCT A systematic study and comprehensive analysis on phasic development and apex morphogenesis in wheat will help elucidate the dynamic of apex development and support cultural regulation and growth modeling. The present study was conducted on the experiment station of Nanjing Agric. Univ. (32°N ) in two growing seasons from 1996 to 1998. The study included two types of varieties: winter type variety (WV) "Jing 411" and spring type variety (SV) "Yangmai 158" and three sowing dates: Sept. 30 (EP), Oct. 30 (MP), Mar. 2 (LP). By time-course sampling and dissecting, the development progress of apex was observed and analyzed. The major results were as follows.1. Near-S, regular-S and half-parabola-S shape curves could describe accumulated numbers of leaf, bracteal and spikelet primordia in relation to GDD( Growing Degree Days ) after sowing, respectively. The logistic equations of the three types of S curves were all highly significant with R~2 greater than 0.74. The patterns of apex primordium differentiation were similar patterns in winter- and spring-type varieties and on main stem and tillers.2. Thermalchrons of apex primordium differentiation were reduced greatly in the order of leaf, bracteal and spikelet. Thermalchrons of different types of apex primordium differentiation and duration of bracteal and spikelet primordium differentiation in GDD were near the same in winter- and spring-type varieties in MP treatments, but were different significantly in EP and LP treatments. Measured with GDD, differences between different sowing dates for the end of bracteal primordium differentiation and beginning of spikelet primordium differentiation were much greater than for the beginning of bracteal primordium differentiation. Also, leaf primordium number was highly correlated with bracteal and spikelet primordium numbers on main stems and tillers in spring-type variety, but not in winter-type variety. Bracteal primordium number was significantly correlated with spikelet number in the two types of varieties, as well as in main stems and tillers.3. Parabolic curve (rise stage) and straight line could describe respectively floret differentiation and degeneration in relation to GDD on MS, Tl and T2 (MS for main stem;Tl, T2 for first and second tillers on main stem, respectively) of MP in wheat. The floret differentiation and degeneration models on T3 (third tiller on main stem) of all planting and on MS of EP with spring-type variety and LP with winter-type variety appeared abnormal. Total floret number of LP was less than EP and MP significantly in both varieties. Difference of total floret number between two varieties was not significant in MP, but highly significant in EP and LP. Also, the differences of GDD from sowing to initiation of floret differentiation among different sowing dates and between the varieties were all highly significant, so did the mean thermalchrons of tloret differentiation between MP and LP, but showed an opposite pattern.4. Two-phase linear model equations ( quick rise, slow rise ) divided by glum differentiation stage could describe leaf emergence progress in relation to GDD after sowing in wheat. This pattern was consistent on main stems and tillers of normal development on both winter-and-spring type varieties. The beginning of slow rise phase shifted to an earlier development stage on main stems of winter type varieties of EP and LP, and on T3 of both varieties of EP, MP and LP due to their abnormal development. The thermal rate of leaf emergence on main stem was relatively high and steady during development for winter type variety of MP, and became higher with later sowing in spring type variety. Phyllochrons of EP and MP were higher in winter type variety than in spring type variety, although the difference between the two varieties of LP was not significant.5. Emergence of tiller was mainly regulated by the ecological factors rather than genetic effect in wheat. For winter-type variety, most variable growth duration throughout the entire growing cycle occurred from tillering to jointing. In contrast, timing of single ridge stage was determined by genotypic effect rather than ecological factors. Single ridge to double ridge stage was most sensitive to vernalization progress For spring sowing of winter-type variety, vernalization process could last till floral primordium differentiation stage The corresponding relationships existed between the phenological stages and spike development stages in different sowing dates, although a little variable. Winter-type variety had more ecologically variable leaf primoudia due to itsstronger vernalization requirement. For winter-type variety, the primordium numbers of reproductive organs were not apparently related to the GDD accumulated prior to vernalization completion. Yet for spring-type variety, numbers of different apex primordia including vegetative and reproductive organs were significantly related to the accumulated GDD during the entire phenological stages as well as before anther separation stage.6.Leaf ages (Haun stages) on main stem of winter type variety of MP were significantly less than those of EP and LP at all major spike differentiation stages (MSDS). In spring type variety, leafage of MP were less than those of EP and LP before double ridge stage, but after then, that of LP was the lest. Also, leaf ages of winter type variety of all sowing date treatments were significantly higher than those of spring type variety at all MSDS. Although differences of remaining leaf primordium number between different sowing dates became less with later spike differentiation stages in both winter and spring-type varieties, they were still significant up to stamen and pistil primordium differentiation stage. Remaining leaf primordium numbers of winter and spring-type varieties were very similar at all MSDS. Differences of leaf age indexes on main stems at MSDS between different sowing dates were small in the same variety. But leaf age indexes of winter type variety were significantly higher than those of spring type variety at MSDS. |
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