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.

Quantifying dry mattcr partitioning into individual organs of plants is a key component for simulating crop growth and yicld formation. This study was undertakcn to develop a dynamic module of biomass partitioning over the entire duration of growth in wheat. The paritioning fraction of shoor or rool was defined as the fraction of its dry weight in plant biomass, and partitioning fraction of green leaf, stem or ear as the fraction of its dry weight in shoot mass of wheat. The functional relationships of the partitioning fraction with physiological development time for the entire growth period were established, in which harvest indes (HI) regulated partitioning fraction of ear to shoot biomass as a genetic parameter. The dry weight of individual organ was the product of the respective partitioning fracton and plant weight or shoot weight. Test of the model with the field experiment data sets involving differen sowing dates, plant weight of shoot weight. Test of the model with the field experiment data sets involving different sowing dates, plant densities and nitrogen fertilization strategies indicated a good agrecment between the predicted and observed values.

Weight of individual grains is a major yield component in wheat. The non-uniform distribution of single grain weight on a wheat spike is assumed to beelosely associatted with starch synthesis in grains. The preseint study was undertaken to determine if the enzymes involved in starch synthesis caused the difference in single grain weight between superior and inferior grains on a wheat spike. Using two high-yield winter wheat (Tritieum aestivum L.) varieties diffeing in grain weight and theree nitrogen rates for one varity, the contents of amylse and amylopection, and activities of enzymes involved in starch synthesis in both superior and inferior grains were investigated during the entire periol of grain filling. Superior grains showed generally higher starch accumulation tates and actieties of enzymes ineluding SS (sucrose synthaes), UDPGP Pase (UDP-glucose pyrophosphorylase), ADPGPPase (ADP-gluceose pyrophosphorylase), SSS (soluble starch synthase) and GBSS (starch granule bound starch synthase) and subsequently produced much higher single grain weigth than inferior grains. Nitrogen inereased enzyme activities and starch accumulation rates.and thus improved individual grain weight, especially for inferior grains. The SS. ADPGPPase and SSS were significantly correlated to amylopectin accumulation, while SS, ADPGPPase, SSS and GBSS were signinficantly correlated to amylose accumulation. This infers that SS, ADPGPPase and starchsynthase play key roles in regulating starch accumulaition and grain weight in superior and inferior grains on a wheat spike.

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.

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.