Temperature limits productivity and kernel quality of rice grains. Water status of rice (Oryza sativa L. cv. Hinohikari) grains grown at 20, 25 and 30°C was evaluated by NMR relaxation times (T1 and T2) in relation to kernel quality during the period of grain development and maturation. During milky and dough stages, 7 to 15 days after flowering (DAF), T1 values of long and short fractions in rice grains grown at 20°C slightly increased but those grown at 30°C decreased markedly. In rice grains grown at 25 and 30°C, T2 values of long and short fractions were about 100 and 10 ms, respectively, until 22 DAF but rapidly decreased to about 1 ms and 20 μs, respectively, at 29 DAF (yellow-ripe stage). This means that these grains had free water until 22 DAF , but only loosely bound water and bound water thereafter. On the other hand, in the grains grown at 20°C, T2 values of long and short fractions were about 100 and 10 ms, respectively, until 29 DAF, indicating that free water was maintained for seven days longer than at higher temperatures. The grains grown at 30°C had white-back kernels in 85% of them and no perfect kernels, while the grains grown at 25 and 20°C had perfect kernels in 68 and 27% of them, respectively. In contrast, the grains grown at 20°C had notched-belly kernels in 28% of them though the grains grown at 25 and 30°C had only a few and no notched-belly kernels, respectively. The present study revealed that the changes in T1 of rice grains closely related with the quantity of water until mid-mature stage, while T2 was more sensitive diagnostic indicator for accumulation of dry matter and quality of kernels, which were influenced by low/high temperature stresses.
The practice of intercropping pearl millet with cowpea is widespread among subsistence farmers in northern Namibia. In this region, the scarce and erratic rainfall may enhance competition for the limited soil water between intercropped plants. Trials were conducted on a field of the University of Namibia (on-station) and on a farmer’s field (off-station) to determine the effects of competition between pearl millet and cowpea on the water sources and plant growth of each crop. The deuterium analysis showed that pearl millet, intercropped with cowpea, significantly increased its dependence on the recently supplied labeled irrigation water. Intercropped cowpea also showed an increased trend of the dependence but it was not statistically significant. At the university field, intercropped pearl millet showed higher dependence on the irrigation water than monocropped pearl millet. At the farmer’s field, the dependence of intercropped pearl millet on the irrigation water was low in the pearl millet-dominant zone. In contrast, the dependence on the irrigation water was high in the cowpea-dominant zone, indicating that the dependence on the irrigation water changes according to the size of the pearl millet canopy. The water sources of cowpea did not show a significant difference at either pearl millet-dominant or cowpea-dominant zone, indicating a stable water uptake trend under competitive conditions. Competition with cowpea significantly increased the root-weight density of intercropped pearl millet in the deep soil layers, but decreased that in the shallow layers. The root-weight density of intercropped cowpea, however, was reduced in most of the soil layers. In conclusion, cowpea has a higher ability to acquire existing soil water, forcing pearl millet to develop deep roots and shift to the surface irrigation water.
Acclimation to light condition is associated with change in water transport system in napiergrass. In this study, the effects of shading on shoot hydraulic resistance and morphology of napiergrass (Pennisetum purpureum Schumach.) were investigated. In the plants under shading (to 30% of full sunlight) for 30 days (S plants), total hydraulic resistance of a shoot (Rshoot) increased from that of full sunlight (control). In the plants grown under shade condition for 24 d followed by full sunlight conditions for 6 d (SF), the Rshoot value was intermediate between that of control and S plants. A similar response to shading was found in total hydraulic resistance of a stem (Rstem), which accounted for more than 60% of Rshoot, but the total hydraulic resistance of the leaves was not significantly affected by shading. Leaf length, leaf area and stem length were larger, but the stem cross-sectional area (SA) was smaller in S and SF plants than in the control plants. SF plants showed similar leaf length, leaf area and stem length to those in S plants, but the SA in SF plants was slightly larger. Normalization of Rstem by SA and stem length decreased the difference among the treatments, indicating the increase of Rshoot and Rstem under shading resulted from the decrease of SA and the increase of stem length.
The yielding ability of a new rice cultivar Akisayaka was compared with that of a standard rice cultivar Yumehikari. The refined grain yield was 9 % larger in Akisayaka than in Yumehikari since Akisayaka had more panicles and spikelets per unit area but had a similar percentage of ripened grain. Although the leaf area index (LAI) in Akisayaka was similar to that in Yumehikari, the leaf area of the flag leaf per unit area of Akisayaka was smaller than that of Yumehikari at the full heading stage. This indicates that Akisayaka had a larger number of smaller upper leaves than Yumehikari. The refined grain weight of Akisayaka was similar to that of Yumehikari at 30 days after heading. This implies that the plant type of Akisayaka is not so important for increasing dry matter production from early to middle ripening period although small upper leaves seems to suppress overluxuriant growth. Accordingly the most important factor for the high yield of Akisayaka was considered to exist in the late ripening stage. The refined grain weight of Akisayaka increased more rapidly than that of Yumehikari from 30 to 45 days after heading. In addition, the leaf chlorophyll content estimated with chlorophyll meter (SPAD) and top dry weight of Akisayaka exceeded those of Yumehikari at the late ripening stage. These results suggest that the large number of spikelets per unit area and the continuation of sink and source ability during the late ripening stage caused the high yielding ability of Akisayaka.
The varietal difference of pod dehiscence in 25 soybean cultivars consisting of 16 Japanese and 9 Thai cultivars was examined at 3, 5, 7, 14, 21, 28 and 35 days after placing in a desiccator (desiccator method) and 2, 4 and 7 hrs after placing in an oven at 60°C (oven-dried method). The cultivars examined were divided into susceptible and resistant groups according to the degree of pod dehiscence. Most of the Japanese cultivars (excepting Suzuotome) and NS1 were susceptible while most of the Thai cultivars (excepting NS1) and Suzuotome were resistant to dehiscence. The degrees of pod dehiscence measured by the desiccator and oven-dried methods were nearly the same, and the moisture content of the pods not dehisced was always higher than that of the dehisced pod. The effect of ambient humidity on pod dehiscence was examined in five soybean cultivars SJ5, Shirotae, Tamahomare, CM60 and Fukuyutaka. When the pods were exposed to 15 or 25% relative humidity (RH), the pods of susceptible cultivars, Shirotae, Tamahomare and Fukuyutaka, started to dehisce at 24 hrs after the start of the treatment, but those of resistant cultivars, SJ5 and CM60, did not dehisce for 72 hrs. None of the cultivars dehisced under 50 and 60% RH. These results revealed that placing the pods in the desiccator for 14 days (desiccator method) or exposing the pods to 60°C for 7 hrs in an oven (oven-dried method) were useful methods for checking the degree of dehiscence.
Effects of anoxia on the levels of free-amino acids were investigated in the coleoptiles of rice (Oryza sativa L.) seedlings. Rice coleoptiles are able to grow in extremely low oxygen conditions. Anoxic stress increased the concentration of total free-amino acids in the coleoptiles. Alanine (Ala) and γ-aminobutyric acid (Gaba) were the main amino acids accumulated. After 48 h, Ala and Gaba concentrations in anoxic coleoptiles were 3.4- and 11.2-fold greater than those in non-stressed coleoptiles, respectively. Ala and Gaba represented 19 and 23 % of the amino acid pool in anoxic coleoptiles, respectively. Submergence stress also increased Ala and Gaba concentrations in rice coleoptiles. Since Ala and Gaba are bio-compatible solutes and their accumulation is known to stabilize osmotic potential and/or cytoplasmic pH in plant cells, these stress-induced amino acids may allow rice coleoptiles to make biochemical adjustment that enable them to cope with the stress conditions. Therefore, the ability to increase the concentrations of Ala and Gaba may be important for anoxic and submergence stress tolerance of rice seedlings.
The mesocotyl and lower internodes of seedlings are underground organs that play a possible role in water absorption and transport. The aim of this study is to reexamine and understand further the anatomy and morphology of mesocotyls and lower internodes in rice, especially in terms of the existence of Casparian bands. Anatomical structures of mesocotyl and lower internodes tissue of rice seedlings were observed by light and fluorescence microscopy. The rice mesocotyl had two central cylinders, one is large and the other small, in the cross section. Casparian bands were observed in both the endodermis and exodermis of the mesocotyl, and also in the endodermis of the first internode. Furthermore, some bundles with intermediate xylem differentiation were observed between the exarch and endarch arrangement in the first internodes. Casparian bands were identified in the radial walls of cells surrounding each of these bundles. The second internode is quite similar to that of upper internodes in adult plants with respect to internal structure; scattered vascular bundles were seen as in monocotyledons. In the second internode, Casparian bands were seen in the radial cell walls of the bundle sheaths in each vascular bundle. Unlike the mesocotyl, Casparian bands were not observed in the hypodermis of the first or second internodes. The results show that the histological features of the mesocotyl and lower internodes of rice seedlings widely differed. In addition, the present study provides anatomical evidence for the existence of Casparian bands in both the mesocotyl and lower internodes of rice seedlings.
We evaluated the varietal difference in the flood tolerance of germinated seed in 17 Japanese varieties of common buckwheat (Fagopyrum esculentum Moench), including both local varieties and bred varieties or lines of different agroecotypes. Germinated seeds were flooded for 1 day in a growth chamber in June, July and August. The mean rate of seedling emergence from the seeds sown on different dates varied with the variety ranging from 20.4 to 57.4%. The mean emergence rate of summer agroecotypes (29.9%) was significantly lower than that of intermediate and late-summer agroecotypes (42.8 and 40.1%, respectively), and that of local varieties (44.2%) was significantly higher than that of bred varieties or lines (31.2%). These results suggest that inherent variation in flood tolerance was decreased by breeding as a result of a bottleneck effect. The local variety ‘Kitou zairai’ which exhibited a high and stable seedling emergence rate, may be a suitable choice in breeding for flood tolerance during germination. We also attempted to select for flood tolerance under mild selection pressure. Mass selection after four generations increased seedling emergence rate in five of six selected lines (with the exception of ‘Kitawasesoba’ compared with those of unselected populations, although the results varied with the line. These results indicate the possibility of breeding for flood tolerance during the germination period.
The experimental site (Shihezi, Xinjiang, China) is located in an arid area of central Asia with abundant solar radiation of almost 10 daily sunshine hours from April to September. The yield potential in this area appears to be high if sufficient water is supplied. The yields of five soybean (Glycine max (L.) Merr.) cultivars including three semi-indeterminate Chinese cultivars (Shidadou 1, Xindadou 1 and Suinong 11) and two determinate Japanese cultivars (Toyomusume and Toyokomachi) were evaluated over three years. These cultivars were grown under drip irrigation, a high planting density (22.2 plants m-2) and heavy applications of farmyard manure (15 t ha-1). Each cultivar showed a high leaf area index (LAI). In particular, the maximum LAI was greater than 7 over the three years in Shidadou 1 and Toyokomachi. The three Chinese cultivars with a high plant height had a low LAI in the upper layers of the canopy, but the two Japanese cultivars with a short plant height had a higher LAI in the middle or upper layers. Toyokomachi and Shidadou 1 had the highest seed yield, followed by Toyomusume. In particular, the seed yield of Toyokomachi was as high as 8.67 t ha-1 on the average of the three years. These high-yielding cultivars had more than 60 pods per plant (1350 m-2). The high yields in this experiment could be due to the large amount of intercepted radiation owing to the high LAI and abundant solar radiation, frequent and sufficient irrigation by the drip irrigation, and large number of pods as a sink.
To assess the potentiality of edible canna (Canna edulis Ker-Gawl.) as economically and environmentally sound animal feed, the feeding value of silage prepared from aboveground parts was examined, in parallel with studies on in situ digestion in the rumen among three local varieties. Contents of crude protein, acid and neutral detergent fibers and crude ash in canna silage were significantly higher, and that of nonstructural carbohydrate was significantly lower than in corn silage. The pH of corn and ‘yellow flower’ canna silages were significantly lower (3.8—3.9) than either ‘green stem’ or ‘red stem’ canna silage (4.4—4.9). The contents of lactic acid, acetic acid, total organic acid and the Flieg’s score of ‘yellow flower’ canna silage were equivalent or superior to those of corn silage. The rate of disappearance of dry matter in the rumen was significantly higher for corn silage than for canna silage, while the disappearance of neutral detergent fiber in canna silage was more rapid during the first 12 hours of incubation, but less rapid thereafter. The effective degradability of dry matter and organic matter of canna silage in the rumen was significantly higher than that of corn. Silage made from edible canna has a potential as a feed for ruminants.
The effect of water stress caused by alternate furrow irrigation (AFI) on the yield of maize may be alleviated by applying every-furrow irrigation (EFI) at stress sensitive growth stages. This research was conducted in two different areas with deep and shallow water tables to examine the amount of water used, yield, yield components and water use-efficiency of maize under AFI at 7-day intervals supplemented with EFI at different stages. AFI resulted in significant reduction in grain yield and in both Bajgah and the Kooshkak areas with deep and shallow water tables, respectively. This occurred due to probable water stress and reduction in 1000-grain weight. However, under AFI supplemented with EFI once or twice at the tasseling or silking stage grain yields were statistically equal to those obtained in EFI although the amount of water used was about 30% smaller in both Bajgah (deep water table) and Kooshkak areas (shallow water table). In both areas the water-use efficiency for grain yield under these irrigation treatments was 1.04 and 0.97 kg grain per m3 of water, respectively.
The total water supply (irrigation plus rainfall) would determine biomass production. This study aimed to elucidate the effects of water supply and cultivar differences on the dry matter production of rice grown under upland conditions. Three rice cultivars (‘Yumeno-hatamochi’, YHM; ‘Lemont’, LMT; ‘Nipponbare’, NPB) were used on an upland site with three water regimes (rain-fed, RU; irrigated, IU; water deficit during the panicle-formation stage, WD) and in a flooded lowland (FL) in Japan from 2001 to 2003. The total amount of aboveground dry matter (TDM) of NPB in RU (1101 g m-2) was 15% lower than that in FL (1302 g m-2) in 2001, when dry spells occurred frequently, but was comparable to FL in 2003 (1313 vs. 1324 g m-2) under favorable soil water conditions with ample rainfall before heading. The nitrogen (N) content of the aboveground part at maturity in RU in 2003 was similar to that in FL, but the growth duration was 9 days longer in RU. The amount of total water supply during the crop growth differed greatly (419 to 1132 mm) among water regimes and years under upland conditions, where TDM and aboveground N content generally increased with increasing water supply. We detected a cultivar – water regime interaction in TDM at maturity in both 2002 and 2003. In FL and under the upland conditions with adequate water supply in 2003, TDM was the largest for NPB, but it was the smallest in this cultivar in 2002 when rainfall was less frequent. The small TDM of NPB in 2002 resulted from a smaller amount of N uptake associated with shallower root system development. In contrast, YHM had a deeper root system and thus the amount of N uptake was larger and TDM was smaller under upland conditions with limited water supply. Our results indicate that the three cultivars responded differently to the water conditions, and that the total water supply greatly affected TDM in uplands through its effects on the amount of N uptake, which was associated with the depth of root development.
Upland rice production has great potential as a water-saving form of agriculture if yield can be increased and stabilized across a range of environments with different levels of water supply. The objective of this study was to clarify the effects of water supply and plant characteristics on grain yield of rice (Oryza sativa L.) grown under upland conditions. We compared grain yield (ranging from 346-685 g m-2) and yield components of three rice cultivars (‘Yumeno-hatamochi’, YHM; ‘Lemont’, LMT; ‘Nipponbare’, NPB) grown under upland conditions with three water regimes (rain-fed, RU; irrigated, IU; and water deficit during the panicle-formation stage, WD) with those of rice grown under flooded lowland (FL) conditions (ranging from 394-649 g m-2) from 2001 to 2003 at Nishitokyo, Japan. Grain yield and each yield component of NPB in RU were comparable to those in FL when there was ample rain during the 40 days before heading in 2003. However, grain yield of NPB decreased with decreasing water supply during the period of 20-40 days before heading under upland conditions (r = 0.93) as a result of reduced number of spikelets per unit area and reduced harvest index. Water productivity (grain yield per unit water supply) in rice in RU and IU ranged from 0.43 to 1.05 kg m-3 in the three cultivars across the 3 years, and was more than twice the corresponding value in FL. We found a cultivar – water regime interaction for grain yield within each year and a cultivar × environment interaction across all the 5 upland conditions in 2002 and 2003. In FL, NPB and LMT had higher yields than YHM, while LMT had the highest yield under all upland conditions and NPB grain yield under the suboptimal upland environments (i.e. RU and IU in 2002) decreased to the largest extent compared with that under optimal upland environment, i.e. IU in 2003 among the three cultivars. The reasons for the highest grain yield of LMT across upland conditions were maintenance of large panicle and high harvest index. Maximum yield was lowest in YHM. In WD, yield potential and growth recovery, rather than crop growth during water stress, affected the cultivar ranking in terms of grain yield. We conclude that water supply during panicle development is important for maintenance of high yield and that a high potential yield and harvest index, as well as yield stability under different water regimes, are important putative plant characters for developing new elite varieties for water-saving upland rice production.
Higher water requirements and increasing labor costs are the major problems of the traditional rice production system. Direct seeded rice culture, growing rice without standing water, can be an attractive alternate. However, poor emergence and seedling establishment, and weed infestation are the main hindrances in the adoption of this culture. An attempt to improve the performance of direct seeded rice by seed priming was made in the present study. Priming tools employed were traditional soaking (soaking in tap water up to radicle protrusion), hydropriming for 48 h, osmohardening with KCl or CaCl2 (osmotic potential of ’ –1.25 MPa) for 24 h, vitamin priming (ascorbate 10 ppm) for 48 h and seed hardening for 24 h. All the priming techniques improved crop stand establishment, growth, yield and quality except traditional soaking, which resulted in impaired germination and seedling establishment that ended in reduced kernel yield and lower harvest index than that of control. Early and synchronized germination was accompanied by enhanced amylase activity and total sugars. Osmohardening with CaCl2 resulted in the best performance, followed by hardening and osmohardening with KCl. Osmohardening with CaCl2 produced 2.96 t ha-1 (vs 2.11 t ha-1 from untreated control) kernel yield, 10.13 t ha-1 (vs 9.35 t ha-1 from untreated control) straw yield and 22.61% (vs 18.91% from untreated control) harvest index. Mean emergence time and emergence to heading days, germination percentage and panicle bearing tillers; plant height and straw yield, 1000-kernel weight and kernel yield, α-amylase activity and total sugars, kernel proteins and kernel water absorption were correlated positively.