Information on the ecological and physiological status of crops is essential for growth diagnostics and yield prediction. Within-field or between-field spatial information is required, especially with the recent trend toward precision agriculture, which seeks the efficient use of agrochemicals, water, and energy. The study of carbon and nitrogen cycles as well as environmental management on local and regional scales requires assessment of the spatial variability of biophysical and ecophysiological variables, scaling up of which is also needed for scientific and decision-making purposes. Remote sensing has great potential for these applications because it enables wide-area, non-destructive, and real-time acquisition of information about plant ecophysiological conditions. With recent advances in sensor technology, a variety of electromagnetic signatures, such as hyperspectral reflectance, thermal-infrared temperature, and microwave backscattering coefficients, can be acquired for both plants and ecosystems using ground-based, airborne, and satellite platforms. Their spatial and temporal resolutions have both recently been improved. This article reviews the state of the art in the remote sensing of plant ecophysiological data, with special emphasis on the synergy between remote sensing signatures and biophysical and ecophysiological process models. Several case studies for the optical, thermal, and microwave domains have demonstrated the potential of this synergistic linkage. Remote sensing and process modeling methods complement each other when combined synergistically. Further research on this approach is needed for a wide range of ecophysiological and ecosystem studies, as well as for practical crop management.
Northern Japan, Hokkaido has cold weather damage in agriculture almost every four years. Cold weather damage to soybeans [Glycine max (L.) Merr] during flowering is especially severe and is caused by both low temperature and insufficient sunlight. Therefore, the damage should be analyzed from both aspects. We analyzed the effects of low temperature and shading during the flowering season on seed yield and yield components in two varieties of soybeans : cv. Hayahikari, an excellent cold weather tolerant variety, and cv. Toyomusume, a cold weather sensitive variety. The soybean plants were exposed to a low temperature of 18°C day/13°C night, shaded (50%) without low temperature treatment, or shaded at a low temperature, during the four-week flowering season. The control plants were kept under normal conditions. The results indicated that cold weather damage is mainly caused by the low temperature, which severely reduced the number of pods per plant, in Toyomusume. However, shading also reduced the number of pods per plant in both varieties. All of the yield components examined were reduced by cold weather more severely in Toyomusume than in Hayahikari. Furthermore, shading combined with low temperature treatment caused greater damage in both Hayahikari and Toyomusume than either a low temperature or shading treatment alone.
In snap bean (Phaseolus vulgaris L.), flower and pod abscission causes yield reduction under high-temperature conditions. A high temperature enhances transpiration and thus may induce temporal water deficiency in plants in the daytime. The objective of this study was to clarify the effect of a high temperature on the water status of floral organs at their most heat-sensitive stage. We compared the water potential and its components as well as gas exchange between the heat-tolerant cultivar, Haibushi, and heat-sensitive cultivar, Kentucky Wonder, grown under optimal (control) and high-temperature conditions. Haibushi showed higher pollen fertility under high temperature than Kentucky Wonder. Transpiration was enhanced under a high temperature, causing decrease of water potential in leaves and flower buds. The deterioration of water status in floral organs was larger in Kentucky Wonder than in Haibushi. We conclude that temporal deterioration of the water status in flower buds is one of the factors causing pollen damage.
The International Rice Research Institute (IRRI) has developed a new plant type (NPT) and F1 hybrids to further increase rice yield potential. In this study we compared yield and yield-related traits among four genotypic groups : indica inbreds, F1 hybrids, NPT and NPT×indica lines; and determined the contribution of biomass partitioning and translocation to grain yield under sub-optimum growing conditions. Field experiments were conducted in 1998 wet season (WS) and 1999 dry seasons (DS) in the Philippines. Forty-seven genotypes in the WS and 46 genotypes in the DS were studied. Growth analyses were done at flowering and physiological maturity and yield, and yield components were measured at physiological maturity. Among the genotypic groups, average grain yield of the F1 hybrids was the highest and that of the NPT lines was the lowest. Grain yield was highly associated with harvest index (HI) with an r2 of 0.73-0.84 in both seasons. The relationship between grain yield and biomass production was relatively weak. A negative relationship was observed between T, the amount of biomass accumulated before flowering and translocated to the grains during grain filling and Wr the biomass accumulation from flowering to physiological maturity. The NPT lines had the highest average Wr but had the lowest T among the genotypic groups, which was opposite of that of the F1 hybrids. Compared to Wr, T was more closely related to HI and grain yield. Results suggest that under sub-optimum growing conditions such as low total solar radiation increasing T and HI is vital for achieving high actual grain yield in irrigated rice.
Brassinolide (BL), a brassinosteroid, applied to rice plants in pots promotes panicle ripening. In this study, we examined the effect of BL applied at the meiosis and flowering stages on endogenous levels of various plant hormones in the panicles of the rice plant (cv. Nipponbare) grown in a field-temperature(F-temp; 25°C on average ranging from 22 to 33°C during ripening periods) condition and low-temperature(L-temp; in phytotron kept at 22°C/17°C) condition in rice cultivation season in Japan. The content of either free- or bound-IAA in the rice spikelet at the milk-ripe stage (10 - 15 days after heading) was higher in the F-temp condition than in the L-temp condition. BL applied twice, 10 days before and on the day of heading, slightly increased the free-IAA content and greatly increased the bound-IAA content at the milk-ripe stage in both condition. BL slightly decreased the ABA content of the spikelet at the milk-ripe stage in the F-temp condition, and slightly increased it in the L-temp condition. The rate of ethylene production was measured only in the F-temp condition. It was markedly high at the milk-ripe stage and low at the dough-ripe stage (21 days after heading). BL treatment clearly increased the rate of ethylene production from the panicles under both light and dark conditions at the milk-ripe stage. These results suggest that BL, which promotes rice ripening, influences in the levels of endogenous plant hormones to play an important role in controlling the sink function during grain-filling.
Two varieties of mungbean (Vigna radiata L.), BARImug 2 (M2) and BARImug 3 (M3) were grown under 1) 12-h light at 700 μmol m-2 s-1 (HL) at 30°C/12-h darkness at 25°C (HL+LT), 2) 12-h HL at 40°C (HT)/12-h darkness at 25°C (HL+HT) and 3) 12-h light at 200 μmol m-2 s-1 (LL) at HT/12-h darkness at 25°C (LL+HT), and their growth, yield and photosynthetic activities were analyzed. The plants grown under LL+HT were the tallest followed by those grown under HL+HT and HL+LT, in this order. The leaf area was the largest under HL+LT followed by LL+HT and HL+HT. In general, the plants grown under HT had lower biomass compared with those grown at LT. Grain yield was zero (no pod setting) under HL+HT in both varieties, but that under LL+HT was 30-40% of that under HL+LT. M3 produced higher grain yield as well as higher biomass than M2 under both HL+LT and LL+HT. The yield reduction under LL+HT was primarily due to the substantial reduction in the number of pods per plant as well as number of seeds per pod. HT decreased the photosynthetic CO2 assimilation rate (Pn), and the plant under HL+HT had lower Pn than those under HL+LT. The heat acclimation of photosynthetic apparatus was considered to proceed more easily under HL than under LL, because the photochemical efficiency of PSII (Fv/Fm) and quantum yield of PSII electron transport (FΔ/F’m) after heat shock at 50°C were greatly higher in the plants grown under HL+HT than those under HL+LT. It was concluded that HL at HT inhibited pod setting but accelerated the heat acclimation of photosynthetic apparatus of mungbean.
We monitored the effects of elevated atmospheric CO2 concentrations on the photosynthetic carbon metabolism in the flag leaves of rice plant (Oryza sativa L. cv. Akitakomachi) before and after heading. The plants were grown under ambient (350 ppm : control) or elevated (650 ppm) CO2 conditions. Flag-leaf blades grown under high CO2 accumulated more starch than control leaf blades before heading, but the level of starch declined to almost zero under both CO2 concentrations as soon as the development of ears began. Before heading, the transcript level of sucrose-phosphate synthase (SPS) (EC 188.8.131.52), a key enzyme in the sucrose synthesis in flag-leaf blades was significantly higher under elevated CO2 conditions than under elevated CO2 (P<0.01). The difference in the expression of SPS decreased after heading, coinciding with a change in starch contents in both groups. These results showed that the effects of elevated CO2 concentration on rice plants might vary with the growth stage of the leaf blades. We also discussed the influence of the changes in the carbohydrate metabolism of rice plants caused by elevated CO2 concentration on yield.
Recently, rice varieties having large panicles with many spikelets are expected to produce high yield. However, the ripening, growth pattern, priority to photoassimilate partitioning and final grain weight in each spikelet vary with the position of the spikelet in a panicle. Therefore, not only the panicle size but also rachis-branching system in a panicle is an important factor determining the yield. In this report, we performed principal component analysis to characterize the rachis-branching system in 65 japonica varieties. In the principal component analysis, the proportions of variability explained were 49.6 and 22.2% for the first two attribute components. The first principal component was assumed as the factor of size in number, and the second principal component was assumed as the factor of shape of panicle. The distribution of the scores for each variety in the scatter diagram showed a large diversity in panicle characteristics in japonica varieties. A small number of varieties had scores distributed in the first quadrant of the scatter diagram. These varieties would be high-yielding because the number of spikelets is high in the panicle having a relatively large number of primary rachis-branches compared with the secondary rachis-branches. Some clusters in the scatter diagram were related with their origins.
The effects of planting density and cutting frequency on dry matter productivity and overwintering ability were compared in the years following establishment among dwarf varieties (early-heading, DE and late-heading, DL) and normal varieties, Wruk wona (Wr) and Merkeron (Me), in the southern part of Kyushu, Japan. The planting densities examined were high (16 plants m-2, 25 cm×25 cm of spacing), medium (8 plants m-2, 50 cm×25 cm), and low (4 plants m-2, 50 cm×50 cm) for Wr, DE and DL, and was only medium for Me. The cutting frequency was three times at about 60-day intervals in 1999 and two times at about 90-day intervals in 2000. Irrespective of the planting density, dwarf varieties were higher in tiller number (TN), leaf area index (LAI) and dry weight percentage of leaf blade (PLB) than normal varieties, but lower in plant height (PLH), mean tiller dry matter weight (MTW) and total dry matter weight at all planting densities in both years. With the increase in planting density, TN and annual herbage dry matter yield (HDMY) increased. The annual HDMY was higher in 2000 (cut twice) than in 1999 (cut three times), and the difference in annual HDMY between the dwarf and normal varieties was reduced by planting at a high density and cut twice. This was due to higher MTW in dwarf varieties than in normal varieties at the higher TN conditions. The percentage of overwintered plant (POP) tended to be higher in DL than in other varieties and was higher in 2000 than in 2001 for all varieties, while it tended to decrease with the increase in planting density. Even though the dry matter productivity was higher in the normal varieties than in the dwarf varieties at any planting density and cutting frequency, DL tended to show a stable productivity with high PLB irrespective of planting density and cutting frequency. In addition, it had a high overwintering ability compared with the other varieties.
For improving the yield of drilled sugar beet (Beta vulgaris L. ssp. vulgaris), it is important to promote germination and early growth. In this study, the priming of sugar beet seeds was examined in six cultivars to improve their germinability in cool conditions. The optimum water content of sugar beet seeds (which botanically are fruits) during priming was 24 to 25% when they were kept at 20°C for 5 d. In further experiments, after the water content of seeds was adjusted to 24% by adding distilled water, the primed seeds were air-dried to below their original water content. The primed true seeds contained 0.5 to 4% more soluble sugar, by dry weight, than the control true seeds. The levels of amylase activity of the primed true seeds were 1.9 to 11.5 times higher than those of the control true seeds, though there was little change in α-glucosidase activity. Priming shortened the average germination period at 8°C by 1.6 to 4.0 d and seedlings from the primed seeds emerged significantly faster than did seedlings from the control seeds in the field. The advanced emergence in the primed seeds brought about a significant increase in early growth compared with control seeds, and the root yield from the primed seeds tended to exceed that from the control seeds by 3% on average at harvest time. Priming did not affect the sugar, potassium, sodium or amino nitrogen content in the root.
Effects of planting depth on emergence, growth, development and yield of turmeric (Curcuma longa L.) in dark red soil (Shimajiri Mahji) were evaluated in Okinawa, Japan. Turmeric planted at the depths of 8, 12 and 16 cm emerged earlier and more evenly than that planted at a shallower depth in both glasshouse and field experiments. Weed growth was unaffected by the planting depth of turmeric until 50-60 days after planting (DAP), but affected thereafter due to mutual shading with the canopy. Weed biomass at 90-140 DAP was significantly smaller in the fields where turmeric was planted at the depths of 8, 12 and 16 cm than in the field where it was planted at a shallower depth. The turmeric rhizome (yield) developed earlier when planted at 8, 12 and 16 cm depths than at 4 cm. In a glasshouse study, shoot biomass and yield of turmeric were significantly greater when planted at the depths of 4, 8 and 12 cm than that of 2 cm. In field experiments, they were also significantly greater when planting depth was 8 or 12 cm than 4 cm. Even in turmeric planted at a 16 cm depth shoot dry weight and yield were greater than that planted at a 4 cm depth, but it was comparatively difficult to harvest rhizomes in this field. About 30% of turmeric in the field planted at a 4 cm depth was uprooted by a typhoon, but not at the depths of 8, 12 and 16 cm. The over all results suggested that rhizomes of turmeric should be planted at a depth of 8 to 12 cm in dark red soil for a higher yield and lower weed competition.
Paclobutrazol (PB), an inhibitor of endogenous gibberellin synthesis, was applied to peanut plants altered dry-matter distribution and increased seed yield. PB solution at a concentration of 100, 200 or 400 ppm was sprayed on foliage at the beginning of the pod formation stage (BPFS), the early pod filling stage (EPFS) and the middle pod filling stage (MPFS). The height of the plants treated with PB at BPFS and EPFS was shorter than that of the control plants by more than 10 and 5 cm, respectively. The pod number of the plants treated with 100 or 200 ppm PB at any developmental stage was higher than that of the plants treated with 0 or 400 ppm PB. The seed yield was increased by PB applied at any stage, and the yield after the treatment with 100 or 200 ppm PB at BPFS or EPFS was approximately 370 g m-2.
Breeding programs for rainfed lowland rice normally use large plot sizes for accurate estimation of yield. Resource requirements are reduced and more genotypes can be tested if a small plot size can be used. A total of 4 experiments was conducted at high and low soil fertility locations in Thailand to determine the influence of plot size and arrangement of tall and short genotypes in small plots on the estimation of yield of genotypes differing in height. Ten to sixteen genotypes were grown in different orders of tall and short genotypes within 2-row plots and also in random arrangements in 4-row, 6-row and 16-row plots. Results showed that taller genotypes tended to suppress the performance of the neighboring shorter genotypes. Consequently the yield results from 2-row plots, in which genotypes were randomly allocated, were unreliable at the high soil fertility location with more vigorous growth, although they were sufficient at the low soil fertility location. Thus plot sizes of 4 and 6-rows appear necessary for accurate estimation of yield across environments. However, when all short genotypes were grouped together and formed a block, and all tall genotypes grouped to form another block, yield results from 2-row plots showed a rather small effect of the competition between the neighbouring genotypes. The yield estimation was improved further by adjusting yield according to the height of each genotype by using covariance analysis. With these modifications, 2-row plots were found to be sufficient for accurate estimation of yield.