Photosynthetic ability in terms of CO2 exchange rate and leaf area, dry matter accumulation(dry weight)and other important growth components along with yield and yield contributing characters in two F1 hybrids of Akebono × Chiyonishiki(A×C)and Zenith × Akebono(Z×A)were studied. The photosynthetic rate at the flowering stage was lower than that at the panicle initiation stage in all the inbred parent cultivars and F1 hybrids. Heterosis in photosynthetic rate was higher at the panicle initiation stage than that at the flowering stage. Pre-anthesis leaf area in the F1 hybrid was significantly larger than that in the parent cultivars. However, the post-anthesis decline in leaf area was more rapid in the F1 hybrids than in the parent cultivars and its magnitude was the highest in the F1 hybrid of Z × A which was tall having long and curved panicles. Pre-anthesis dry matter accumulation in both hybrids was significantly higher in the F1 plants than the parental cultivars, but post-anthesis dry matter accumulation in the F1 hybrid was lower than the mid-parental value in Z × A. The degree of heterosis in grain yield varied with the hybrid combination, an average heterosis being 1.03. Heterosis in grain yield was closely associated with heterosis in harvest index.
Penetration of the roots deep into soil layer(deep roots)may alleviate growth inhibition under various soil stress conditions. In this study, the nodes from which deep roots had emerged were examined at the heading stage in rice and maize grown in a 2 m long tube. The effect of soil mechanical stress on the rooting nodes of deep roots was also examined. The roots that emerged in a relatively early growth stage, that is, the roots from coleoptilar, 1st and 2nd node in rice, and the seminal root and roots from the coleoptilar, 1st and 2nd nodes in maize, penetrated into the deep soil layer. The node which produced the highest number of deep roots was the 1st node in rice and the coleoptilar node in maize. Seminal root of rice and seminal adventitious roots of maize did not penetrate into the deep soil layer although they emerged at an early growth stage. In the rice root system, the nodal roots, emerged from the upper portion of the node, tended to penetrate deeper than the nodal roots emerged from the lower portion of the same node. Soil compaction did not affect these tendencies.
A non-destructive method for measurements of spatial root elongation in soil, using acoustic emission(AE)sensors, was developed. Growing roots passing in close proximity to soil particles generate AE pulses, which are detectable as counts by AE sensors. Previously, vertical maize(Zea mays L.)root elongation in soil was successfully measured using AE sensors. The method was expanded to measure spatial maize root elongation in a rectangular stainless steel container. Three AE sensors were placed vertically at 15mm intervals on each of the four side walls of the container. Spatial root tip position was expressed by the three axes(x, y, z). Relative AE counts on the x axis and y axis(Rxp and Ryp)were obtained from three sensors on the same and opposite planes as a fraction of total AE counts on both sides of this plane. Rxp and Ryp were linearly related to root tip positions on the x axis and y axis, respectively. The relationship was expressed by the equation:Y=0.740-0.0420X(r=0.861**)where X is the actual distance from the sensor to root tip position and Y is Rxp or Ryp. Spatial root tip positions can be estimated by the relative AE counts using this regressing equation. Thus, spatial root tip positions were expressed as a function of time. The trajectory of root tip position estimated by AE sensors was consistent with that obtained from actual measurements after excavation of the root from soil. This method can be used to give continuous and three-dimensional information of root tip movements, the rate and direction of root elongation.
The rate of leaf development in wheat is related to time and temperature in units of degree-days(DD)leaf-1(phyllochron). Experiments were conducted in controlled environment chambers to study the effect of day to night variation in temperature on leaf development in two wheat cultivars, Penawawa and Stephens. Plants were grown at constant 20°C, and in eight day/night temperature ranges as wide as 8/32°C to 32/8°C, all with a mean temperature of 20°C. The leaf number on the main stems was counted(in Haun units)every other day, from the emergence of the 2nd leaf until the emergence of the 5th leaf. Leaf phyllochron values were derived from the inverse of the slopes of the linear regression of leaf number on DD. Phyllochron values ranged from 99 to 153 DD leaf-1. The phyllochron values were greater when higher temperatures were imposed at night under extreme day to night temperature treatment.
The spike development in three spring wheat genotypes was studied under various cultural conditions. Two genotypes weakly responsive to cultural conditions in spikelet number per spike(T1 from Nepal and Haruyutaka from Japan)and one weakly responsive to cultural conditions in spike length(U6 from Xinjiang Uygur district of China)were grown under three cultural conditions with different seeding density and fertilization levels:680 seeds m-2 without fertilizer(unfavorable), 340 seeds m-2 with common fertilizer(common)and 170 seeds m-2 with double fertilizer(favorable). The durations of the vegetative phase, spikelet phase and the spike elongation phase were scarcely influenced by these cultural conditions, although the leaf number was influenced. The development of spikelets seemed to be determined by several factors other than those affecting the developmental processes of the spike. In U6, the increase in shoot apex length during the floral initiation period under the favorable condition was accompanied with an increase in double ridge number and spikelet number per spike, but such a relationship was not observed in T1 and Haruyutaka. T1 and Haruyutaka had a higher rate of spikelet formation under the favorable condition than under the unfavorable condition, but U6 showed a rather lower rate of spikelet formation under the favorable condition. Thus, the effects of the cultural conditions on the spikelet number per spike differed with genotype. At the time of terminal spikelet formation, U6 tended to have a longer spike than T1 and Haruyutaka. However, since the rate of spike elongation was higher in T1 and Haruyutaka than in U6, the spike length at anthesis was shorter in U6.
Seed weight(weight per seed)is an important trait in soybean[Glycine max(L)Merr.]that affects its production, processing, marketing and consumer preferences. To determine the effects of nitrogen fertilizers and climatic conditions on seed weight, a five-year field experiment was conducted by growing four nodulating cultivars and 13 non-nodulating lines at 4 levels of nitrogen fertilizer(0, 2, 10 and 20 g m-2). The variation in seed weight due to the difference in the fertilizer level and climatic condition of the year was greater in non-nodulating lines than in nodulating cultivars. This resulted in a lower heritability estimate in non-nodulating lines(0.49)than in the nodulating cultivars(0.85). Nitrogen fertilizer increased the seed weights of non-nodulating lines but did not affect the seed weights of the nodulating cultivars. The high response of the non-nodulating lines to nitrogen fertilizer may be attributed to their strong dependence on fertilizer and soil nitrogen due to their lack of ability to fix nitrogen in symbiosis. The small seeds produced during the years with low temperatures and early onset of frost may have been caused by the slow seed growth rate and short seed filling duration.
Spectral reflectance of differentially-managed rice canopies was measured over an entire growing season and analyzed with special attention to linking remotely sensed information with a simple growth model. The fraction of absorbed photosynthetically active radiation(fAPAR), which is often used as a key variable in simple process models, was well correlated with spectral vegetation indices(VI). VIs, such as NDVI and SAVI, were derived from the ratio of reflectance at two wavelengths(R660 nm and R830 nm)and a new VI, termed the normalized difference ND[R1100 nm, R660 nm], was derived from the difference of R1100 nm and R660 nm divided by their sum. These close relations between fAPAR and VIs were expressed by exponential formulae with different parameters for the periods before and after heading. These indices became less sensitive to fAPAR when fAPAR was larger than 0.4. The use of R1100 nm and R1650 nm with R660 nm and R830 nm in multiple regression significantly improved the prediction accuracy of fAPAR. A close linear relation was found between a spectral ratio R830 nm/R550 nm and leaf nitrogen content during the ripening period although it was not the case before heading. Results suggested that R830 nm/R550 nm was effective for estimation of leaf nitrogen content when the paddy field was regarded as a big leaf. The total amount of leaf nitrogen was well correlated with ND[R1100 nm, R660 nm];nevertheless, the sensitivity was lost when the total amount of leaf nitrogen was greater than 3 g m-2. Multiple regression analysis showed that a combination of four spectral bands R550 nm, R830nm, R1650 nm and R2200 nm was useful for estimation of the total amount of leaf nitrogen. Remotely-sensed nitrogen variables would be a potential model parameters in a simple model. A real-time recalibration module based on a simplex algorithm was developed and proved effective in linking the remotely-sensed fAPAR with a simple model. This approach was also useful for inferring the physiological parameters such as radiation use efficiency for each rice canopy without destructive sampling. The re-parameterization and/or re-initialization with remotely-sensed information was demonstrated to be a practical and effective approach, especially for operational purposes.
Lodging is a major cause of yield loss in the rice production systems using direct seeding. In this study, several characteristics of 80 F4 breeding lines and 10 check cultivars were examined in connection with lodging resistance to establish a technique suitable for screening a large number of lines efficiently for breeding rice for direct seeding. Experiments were conducted over a 2-year period in puddled wet-fields and in seed pack growth pouches(SPGP). Among the root parameters of SPGP seedlings, only root thickness had a significant positive correlation(r=0.495**)with pushing resistance, which is the force to bend rice culm to a designated angle and is correlated with lodging resistance. The root thickness of SPGP seedlings was also positively correlated with root thickness in the field at 18(r=0.346**)and 30(r=0.512**)days after seeding. For selected lines and check cultivars, positive correlations were found between pushing resistance and culm thickness in the field(r=0.809**), between pushing resistance and root thickness in SPGP(r=0.694**). Culm length and panicle number were negatively correlated with pushing resistance (r=-0.454**, r=-0.563**, respectively). Among the characteristics related to lodging, root and culm thickness were higher in selected breeding lines than in check cultivars. Grain yield was positively correlated with panicle weight(r=0.601**)and harvest index(r=0.586**)but not with panicle number(r=-0.007ns). Thus the low-tillering, panicle-weight type plants with thick roots and culms seem to be suitable for direct seeding. Some promising lines and candidate parental lines for the next crossing cycle for direct seeding were identified.
Ultrastructural changes during the fusion of the protoplasts isolated from wild viola callus(without chloroplasts)and pansy mesophyll cells(with chloroplasts)were examined by scanning electron microscopy(SEM)and transmission electron microscopy(TEM). The presence of pansy protoplasts in the fusion products was proved by the presence of chloroplasts lying beneath the plasma membrane identified by SEM. Involvement of pansy chloroplasts in the fusion products was confirmed by TEM. Thus it was possible to distinguish between viola protoplasts and pansy protoplasts by SEM. During the process of protoplast fusion, adhesion of two protoplasts, the rupture and recovery of the membrane between them, and a single-paired spherical fusion body were clearly observed by SEM using our preparation method. Fused protoplasts divided and a microcolony was produced.
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