This study was undertaken to determine the time-course of floret primordium initation and degeneration in relation to thermal time after sowing in various cultivars and tiller position sof wheat (Triticum aestiveum L.). The field experiment was carried out on the experiment station of Nanjing Agricultural University of China. and included three sowing dates: carly planting of 30 September. middle planting of 30 October and late planting of 2 march and two wheat cultivars: winter type 'Jing 411' and spring type 'Yangmai 158'. Quadratic and linear relationships could deseribe floret initiation. degeneration and abortion in response to growing-degree-days after sowing for main stem and first and second tillers of middle planting plants of both cultivars. The floret fertility. The growing-degree-days from sowing to floret intiaion were significantly diffeent between the thre sowing dates and between the two cultivars. These results help quanitfy the dynamic processes of apical development and explain differcnes in floret development of wheat with different environments. cultivars and tiller development and explain the diffences in floret development of wheat with different environments. cultivars and tiller positions.

Simulationg of phasic development in wheat is necessary in constructing wheat growth and yield models. It is also useful for evaluating culvivar adaptation and scheduling cultural practices. This paper describes a conceptual model of wheat development based on phenological principles, as affected by vernalization, photoperiod, thermal response and intrinsic earliness, and also reports the results of ensitivity analysis and validation of the model. The model predicts when the plant will reach double ridge, termianl spikelet and heading. In tthe model, the daily thermal sensitivity of development following emergece is determined by and interacton of relative vernalization comptetion and relative photoperiod effectiveness for that day. After complete vernalixation is reached, the daily thermal sensitivity is determied only by relative photoperiod effectiveness, which gradually increases from terminal spikelet to heading. A multiplication between the daily thermal sensitivisty and thermal effectiveness generated daily flowering were characterized as vernalization requirement, photoperiod sensitivity and intrinsic earliness. The model showed a sensitive response to environmental varibles of temperature and daylength. and to gentic parameters of vernalizaion requrement and photoperiod sensitivity. Evaluation of the model using multiple experimental data involving varous cultivars and planting dates exhibited a marked goodness of fit between simulation and observation with a root mean square error<5 days. The results indicate that the model can be used a prdictor for the major flowering stages. as well as functioning as dnowledge for understading the characteristics of different develoment componcets in wheat.

The effect of environmental changes on the rate of leaf emergence in wheat Triticum aesiveum L. must be understood to accurately simulate the development of the crop canopy. We determined the phyllochron for 'stephens' winter wheat plants in growth chambers at two constant temperatures (10 and 18℃) at a daylength of 14h and at two constant daylengths (8 and 18h) at a temperature of 20℃, and for plants transferred between the two temperatures and between the two daylengths at the first-, second--, third-, and fourth. leaf stages. The phyllochron of all plants transferred from low to high temperature increased to that of plants kept continually at the high timperature. The phyllochron of plants transterred from high to low temperature at the one-leaf stage was identical with the phyllochron of plants kept continually at the low temperature, but was intermedite between that of the high and low temperatures for gransfers at the second-, third, or fourth-leaf stage. The phyllochron of plants transferred from short to lone days decreased to values identical to those plants transferred from long to short daylengths increased to values equal to or greater than that of plants kept continually at the short daylengths. Thus. plants adapted to either tmperature or day length environments that favor rapid leaf environment for leaf growth than plants that were kept continually in the less favorable environment. The results help explain why the phyllochron is often constant for a particular field planting where plants are subject to seasonal changes in tmperature and daylength.

Accumulation of protein and starch in grain is a key procss determining grain yield and quality in wheat. Under drought or waterlogging, endogenous plant hormone levels will change and may have and impact on the yield and quality of wheat. In a greenhouse experimnet, four winter wheat (Triticum aestivum L.) varieties differing in grain protein conternt. Heimai 76. Wanmai 38. Yangmai 10 and Yangmai 9, were subjected to drought (SRWC=45～50%, DR). waterlogging (WL) and moderate water supply (SRWC=75～80%, CK), beginning form 4 days post-anthesis (DPA) to maturity. On the 10 (grain enlargemet stage) and 20 (grain filling stage) DPA. endogenous in sink and source organs of wheat plants by enxymc linked immunosorbent assay (ELISA). The patterns of hormonal changes were similar in four varieties. The ABA levels were much higher under DR and WL than under CK. Compared with CK, GA1+3 levels in whole-plant under DR and WL changed a little at 10 DPA, but markedly dectrease under DR and WL at 20 DPA. Changes of enodgenous IAA level under DR and WL exhibited a complicated pattern, depending on organs and growth stages. Particularly at the 20 DPA, the mean levels of IAA in roots. leaves and grains decreased significantly under DR and WL. In comparison with CK. ZR levels in all organs significantly decreased under DR and WL at both stages. The correlation analyses between yiclds and contents of starch and protein in grains and levels and rations of four hormones in source and sink organs indiated that the changes in yield and content of grain starch and protein under DR and WL were associated with the reduced IAa, ZR and GA, levels and elevated ABA level in plants, expecially in grains. It was proposed that the changed levels of endongenous hormones under post-anthesis DR and WL might indirectly affect protein and starch accumulation in grains by influencing the regulatory enzyines and rpocesses.

Nondestructive moitoring and diagnosis of plant N status is necessary for precision N management. The present study was conducted to determine if canopy reflectance could be used to evaluate leaf N status in rice (oryza sativa L.). Ground-based canopy spectral reflectance and N concentration and accumulation in leaves were measured over the entire rice growing season udner various treatments of N feritlization, irrigation, and plant population. Analyses were made on the relationships of seasonal canopy spectral reflectance, ratio indices, and normalized difference indices to leaf N concentration and N accunulation in rice under different N treatments. The results showed that at each sampling date, leaf N concentration was negatively related to the reflectance at the green band (560nm) while positively related to ration index, with the best correlation at jionting. However, the relationships between leaf N accumulation and reflectance at green band and ration index were consitent across the whole growth periold. The ratio of near infraed (NIR) to green (R480/R560) was especiallly linearly related to total leaf N accrmulation, independent of N level and growth stage. Tests of the linear regression model with different field experiment data set involving diffeent plant densities, N fertilization, and irrigation treatments exhibited good agreement beweent the prediceted and boserved values, with an estimation accuracy of 96.69%, root mean square error of 0.7072, and relative error of -0.0052. These results indicate that ratio inex of NIR to Green (R06/R560) should be useful for nondestructive monitoring of N Status in rice plants.