Salinity tolerance has been extensively studied in Oryza sativa, but little is known about the salt tolerance levels in Oryza glaberrimaand the interspecific progenies including New Rice for Africa (NERICA). In this study, the salinity tolerance of the three cultivated rice species, O. glaberrima (54 genotypes), the interspecificprogenies (21) including NERICA (7) and O. sativa (41) mainly grown in West Africa were examined comparatively. At 10 days after sowing (DAS) 80 mM NaCl was added to the culture solution, and the plants were grown for 10 more d. The ratio of shoot biomass in the 80 mM NaCl solution to that in the control was significantly higher in the interspecific progenies than in the other two species, and the relative root biomass was significantly lower in O. glaberrima than in the others. The vegetative growth of six genotypes including the salt tolerant Pokkali, and NERICA4 and its parents were evaluated further in pot experiments irrigated with 80 mM NaCl solution from 22 to 52 d after sowing. At 30 d of the salt stress, CG14 and Mala noir IV (O. glaberrima) were killed by salt, while WAB56-104 and NERICA4 survived; Pokkali maintained the highest relative shoot biomass growth at all sampling times of 10 d intervals. These results indicate that O. glaberrima is relatively weaker to NaCl salinity, while the interspecific progenies are fairly tolerant during the seedling stage, and that the relatively high salt stress tolerance of NERICA4 is derived from the O. sativa parent, WAB56-104.
The energy partitioning in photosystem II (PSII) and the susceptibility to photoinhibition in PSII were investigated in flag leaves of two rice cultivars, Shirobeniya (a traditional japonica) and Akenohoshi (an improved japonica-indica intermediate) grown under standard-nitrogen (N) (SN) and low-N (LN) conditions. N-deficiency resulted in significant decreases in total dry weight, net photosynthetic rate (PN), the energy flux via carboxylation (Jc), and content of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in flag leaves in the two cultivars, and these parameters of Shirobeniya were lower than those in Akenohoshi under the LN condition. In the two cultivars, the energy flux via alternative electron flow was significantly increased by N-deficiency, which was accompanied by enhanced activity of superoxide dismutase (SOD). Although under the LN condition no cultivar differences were found in Ja and SOD, ascorbate peroxidase activity in Shirobeniya was lower than that in Akenohoshi. N-deficiency resulted in more significant increases in the susceptibility to photoinhibition (the degree of decrease in maximum quantum yield of PSII), hydrogen peroxide (H2O2) content and malondialdehyde content after exposure to high irradiance in Shirobeniya than those in Akenohoshi. These results indicated that the increased susceptibility to photoinhibition in the LN plants of Shirobeniya was mainly due to oxidative damages to chloroplasts, resulting from lower carboxylation and H2O2-scavenging capacities. Therefore, both carboxylation and H2O2-scavenging capacities could be important factors in determining the cultivar difference in the productivity of rice under LN conditions.
Flower opening in the early morning helps to avoid sterility of rice (Oryza sativaL.) caused by heat stress at anthesis. Although flower opening time (FOT) is under genetic control, it is also affected by weather, particularly by air temperature (Ta). However, the effects of Ta, solar radiation (R s), and vapor-pressure deficit (VPD) on rice FOT are unclear, making it difficult to predict FOT. Therefore, we investigated the correlation of FOT with Ta, R s, and VPD during various periods before anthesis under field conditions. By photographing spikelets at 10-min intervals, we determined the FOT of five cultivars. To evaluate the individual effects of cultivar, Ta, R s, and VPD on FOT, we constructed general linear models (GLMs) and calculated mean Ta, R s, and VPD every 3 hr from 0000 to 1200. The GLMs revealed that the average Ta, R s, and VPD between 0600 and 0900 significantly affected FOT (adjusted R 2=0.399; P<0.001). The standardized partial regression coefficients of Ta and R s were negative and those of VPD were positive, indicating that higher Ta, higher R s, and lower VPD in the early morning result in earlier FOT. Moreover, multiple-regression analysis showed that the period affecting FOT the most, and the relative contributions of Ta, R s, and VPD to FOT differ with the cultivar.
Flower opening in the early morning helps avoid sterility induced by heat stress at anthesis in rice (Oryza sativa L.). A pot experiment was conducted to reveal the effects of methyl jasmonate (MeJA) on flower opening time (FOT), sterility, pollination, and anther dehiscence. Four mmol L−1 MeJA solution (3 mL per panicle) and water, as a control, was applied to the panicles of the japonica type rice cultivar ‘Hinohikari’ at 0900, 1000, or 1100. By photographing flowers at 4-min intervals, we determined the FOT. Flower sterility, pollination, and anther dehiscence were also examined. Application of MeJA solution at 0900 advanced FOT about 2 hr compared with that without application, and 1.5 hr compared with that after application of water. MeJA application at 1000 also advanced FOT, but that at 1100 did not. Application of MeJA solution significantly increased the numbers of flowers opening on the day of treatment and decreased that on the day after treatment. Application of MeJA solution at 0900 significantly increased flower sterility compared with that without treatment. More than 40% of the flowers that were treated with MeJA and opened on the day of treatment were those expected to open on the next day. These results suggest that sterility induced by application of MeJA is caused by the early opening of flowers expected to open the day after treatment.
Rice yield is reduced by a short period of water stress at the early panicle-development stage. This study was conducted to examine the factors that reduce the panicle dry weight of rice subjected to water stress and the alleviating effects of top dressing after the stress. Akihikari, Nipponbare and Akebono were grown in 4-L pots under submerged soil conditions. One half of the pots were subjected to the same degree of water stress during panicle development and the other half was grown without water stress. On the day after the stress treatment, chemical fertilizer was applied to one half of each water treatment. Panicle dry weight at maturity was decreased by water stress and the top dressing after the stress alleviated the decrease. The top dressing increased panicle dry weight under the two water treatments in all three cultivars. Increase of panicle dry weight was dependent on that of total dry weight from drainage to full heading, from full heading to maturity, and from drainage to maturity. Leaf area duration (LAD) and net assimilation rate (NAR) were responsible for changes in total dry weight. Effect of water stress was prominent before full heading, while that of top dressing after full heading. It was concluded that reduction of LAD and NAR may be involved in reduction of panicle dry weight by water stress at the early panicle-development stage, and that top dressing after the water stress may mitigate the effect of water stress on panicle dry weight through the improvement of LAD and NAR.
Reactive oxygen species (ROS) play an important role in seed germination. Although hydrogen peroxide (H2O2), a type of ROS, enhances the germination rate of various plant seeds, little is known about the mechanism. NADPH oxidases catalyze the production of superoxide anion (O2-) that is one of the ROS and the enzymes regulate plant development. We, therefore, investigated the role of NADPH oxidases in seed germination and seedling growth in barley (Hordeum vulgare L.). The production of O2- was observed both in embryo and aleurone layers in barley seeds treated with distilled water (DW). However, it was suppressed in seeds treated with diphenylene iodonium (DPI) chloride, NADPH oxidase inhibitor. Moreover, DPI markedly delayed germination and remarkably suppressed α-amylase activity in barley seeds, indicating the importance of NADPH oxidases in germination of barley seeds. The gene expression and the enzyme activity of NADPH oxidases gradually increased after imbibition, and the enzyme activities were closely correlated with seedling growth after imbibition. Besides, DPI markedly suppressed the seedling growth. These results indicated that NADPH oxidases perform a crucial function in germination and seedling growth in barley. These facts clearly reveal that O2- produced by NADPH oxidases after imbibition regulates seed germination and seedling growth in barley.
The photosynthetic rate in the flag leaf of rice at the full heading stage was examined in three japonica varieties, Koshihikari, Aikoku and Asanohikari, and the indica high-yielding variety Takanari at the same level of leaf nitrogen. At an ambient CO2 concentration of 350 µL L-1, Takanari had a higher photosynthetic rate and stomatal conductance than the japonica varieties when plants were compared at a leaf nitrogen content of approximately 1.5 g m-2. Stomatal conductance increased considerably with increases in leaf nitrogen content in the japonica varieties. As a result, at a leaf nitrogen content of approximately 2.0 g m-2, differences in terms of the photosynthetic rate among varieties were small. By contrast, there were no clear varietal differences in Rubisco content at any identical nitrogen content of leaves. We conclude that stomatal conductance is responsible for the varietal differences in photosynthetic rate examined at the same leaf nitrogen content.
Biomass production and lodging resistance in the new long-culm forage cultivar ‘Leaf Star’, developed using a precise evaluation method for lodging resistance, were evaluated by comparing these properties with those of its parents and recently improved forage rice cultivars. Leaf Star had a higher biomass production of above-ground parts than its parents, and its straw yield was 13 t ha-1. The bending moment of the basal internode at breaking in Leaf Star was three times higher than that in Koshihikari, owing to a large section modulus and a high bending stress. Biomass production of above-ground parts of Leaf Star did not differ significantly from that of other forage cultivars. However, Leaf Star had the highest straw yield of all forage cultivars. Leaf Star accumulated a large amount of starch in straw. Bending moment of the basal internode was the highest among forage cultivars owing to a large section modulus. These results show that the traits related to lodging resistance such as culm thickness and culm stiffness could be introduced into long-culm cultivars by using the precise evaluation method for the traits related to lodging resistance. The results also show that Leaf Star has a large biomass and high quality, which are suitable properties for feed and biofuel production.
The effects of reducing plant height by the growth retardant chlormequat on radiation interception and radiation-use efficiency in field-grown wheat were studied in southwest Japan. Chlormequat was applied to wheat cultivar Sanukinoyume 2000 at the beginning of jointing. The cumulative total solar radiation intercepted by the plant canopy (Si) was determined by continuous measurements of total solar radiation above the canopy with a dome pyranometer and below the canopy with tube solarimeters. Nondestructive measurement of leaf area index (LAI) and mean tip angle of the canopy (MTA) using a plant canopy analyzerwas performed weekly. Chlormequat application shortened the culm length by 12.6% compared with the control, but did not affect the aboveground dry matter (AGDM), LAI, yield or yield components except for the harvest index (HI). The extinction coefficient in canopy (K) was not affected by chlormequat, so that Si at heading and anthesis were not significantly different. Radiation-use efficiency (RUE) of chlormequat treated plants estimated from the slope of a linear regression of Si vs AGDM was 1.34 g MJ-1 for the period up to heading and 1.57 g MJ-1 for the period up to anthesis. The RUE values were not significantly different between chlormequat-treated and control plants. Although the effect may be restricted to the duration from heading to the premature ripening stage, a higher MTA in chlormequat should provide a more even distribution of radiation within the canopy, which should increase the photosynthetic performance. These results suggested that shortening the culm length of this wheat cultivar by about 12% is beneficial in reducing the risk of lodging without affecting light interception characteristics or RUE.
Arbuscular mycorrhizal fungi (AMF) improve the uptake of immobile mineral nutrients such as phosphate, thereby improving plant growth. In acid sulfate soil (ASS), AMF spore density is generally low which impacts root colonization and phosphate uptake. Thus, inoculation may help increase AMF colonization of crops grown in ASS. AMF spore density decreases after cultivation of a non-host crop or bare fallow. In addition, preceding crops affect the growth and yield of subsequent crops. The production of AMF inocula requires AMF-compatible plants. The objective of the present study is to elucidate the effect of preceding crops on the persistence of inoculated AMF and growth of succeeding maize under an ASS condition with lime application. Spore density of AMF after cultivation of preceding crops (soybean or job’s tears) was maintained in comparison to fallow leading to higher AMF colonization of maize and improved plant growth. Thus, maintenance of AMF spore density, either through selection of preceding crops or application of AMF inoculum, may be a viable strategy to improve maize growth in limed ASS of Thailand.
Characterization of the release of degradable components of cover crops is important for determining the quality of soil nutrients for the following crop and weed occurrence. We have examined the temporal changes in soil phenolic carbon (C) and nitrogen (N) after incorporation of cover crops (hairy vetch and rye) with different C to N ratio and their effects on subsequent weed occurrence in the. Cover crops, hairy vetch (Vicia villosa Roth. cv. Hungvillosa) and rye (Secale cereale L. cv. Winter-green), grown in a glass house for 60 days, were harvested and incorporated into soil at the rate of 35 and 25 ton ha-1, respectively. The contents of total phenolics (TP) in hairy vetch- and rye-incorporated soil increased from 45.5 to 21.3 μg g-1 DW and decreased from 17.7 to 37.0 μg g-1 DW, respectively, from 10 to 50 d after incorporation (DAI). Inorganic nitrogen (InN) was substantially released from hairy vetch residues, and it remained over four-fold greater than those in the control or rye-incorporated soil at 30 DAI. In the correlation analysis, the TP content of soil correlated negatively (r=−0.55, P<0.01) with total carbon (TC), but TP content of soil did not correlate with total nitrogen (TN) or inorganic nitrogen (InN) contents of soil. Occurrence of weed species was not significantly different among the treatments, whereas weed density was decreased by the incorporation of hairy vetch- or rye-residues. Weed dry weights observed at 50 DAI revealed that the growth of weeds on hairy vetch-incorporated soil was about ten- and four-fold greater than that on rye-incorporated and control soil, respectively. It is concluded that incorporation of hairy vetch did not suppress weed growth, but incorporation of rye significantly suppressed the emergence and growth of weed.
The moisture of paddy soil after rice cropping is a major impediment to the establishment, tillering and yield of winter wheat in the rice−wheat (R−W) cropping system. We examined the seedling establishment ratio, based on soil moisture at seeding by path analysis of nine soil/plant traits in the farmer’s fields in Western Japan where the R−W cropping system was being used, to establish a strategy for improving tiller density by optimizing the seedling establishment ratio. The clod size of surface soil, which showed a significant positive correlation with soil moisture at seeding, had a significant negative direct effect on the seedling establishment ratio. The reduction in seedling establishment ratio, together with fewer tillers per plant, resulted in a significant decrease in tiller density. The sum total of contribution of soil moisture contents to tiller density via clod size was smaller than that of seeding rate, and similar to that of the amount of nitrogen (N) basal dressing. This indicates that manipulating clod size based on soil moisture at seeding provides an opportunity for maintaining tiller density, as well as changing the amount of N basal dressing with the soil moisture conditions after rice cropping.
: This study was conducted in 2003−2004, 2005−2006 and 2006−2007 in Okinawa, Japan (24−28ºN and 126−130ºE) to evaluate the effects of harvest time on biomass accumulation pattern in shoots and rhizomes (yield) of turmeric (Curcuma longa) for determining critical harvest time. Four lines/cultivars, Aki Ukon, Ryudai Gold, Ryudai-11 and Ryudai-44 were tested. Turmeric was planted in April every season, and biomass was monitored at different dates. Shoots of all turmeric lines/cultivars remained green until November, thereafter turned yellow and completed drying in January every season. Turmeric shoot biomass increased until November and decreased thereafter. Fresh yield of turmeric harvested in November, December and January was almost the same, but dry yield increased significantly with the delay in harvest until January. Percentage (%) of dry yield to fresh yield was 7−10 in September and October, 10−16 in November, 14−22 in December and 15−24 in January; and yield-shoot ratio in dry weight was 0.2−0.5, 0.5−1.2, 0.9−2.2 and 1.3−3.0, respectively. All the lines/cultivars maintained a similar biomass accumulation pattern during the harvest time in each season. These results suggest that maximum dry yield is obtained when turmeric shoots wither completely, and turmeric should be harvested in January for higher dry yield in Okinawa.
The crop management in direct-seeded rice to promote growth during the reproductive stage was evaluated in weed-controlled toposequentially intermediate fields in a small watershed in Northeast Thailand. In 2004, the effectiveness of topdressing with 21 kg ha-1 of nitrogen at the panicle initiation stage were examined using two genotypes, KDML105 and IR57514-PMI-5-B-1-2 (IR57514) seeded at the rates of 500, 250 and 125 seeds m-2. In 2005 and 2006, the effectiveness of a new management (seeding rate of 125 seeds m-2 and nitrogen application of 90-101 kg ha-1; CM2) was compared with that of conventional management (seeding rate of 500 seeds m-2 and nitrogen application of 50 kg ha-1; CM1) using 3 genotypes (KDML105, IR57514 and HY71) seeded in May and June. In 2004, the number of spikelets on the tertiary pedicel at a low seeding rate in KDML105 was greatly increased by topdressing. In 2005 and 2006, CM2 had higher grain yield than CM1 (346 vs. 235 g m-2), owing to its larger spikelet number per panicle, heavier shoot dry weight and greater nitrogen uptake. May-seeding resulted in longer non-flooded period in the seedling to tillering stage, lower SPAD reading value around heading and less shoot dry weight increase from heading to maturity, and had lower grain yield than June-seeding (253 vs. 328 g m-2). This reduction in grain yield was larger for late-heading KDML105 than in early heading IR57514. These results indicated the effectiveness of the new crop management (CM2) for direct-seeded rice in toposequentially intermediate fields with less weed infestation or weed-controlled conditions.
In northern Laos, weeds are a major constraint to upland rice production in slash-and-burn systems. Two experiments were conducted to assess genotypic variation in ability to recover from weed competition at the early vegetative stage. Three traditional and two improved (IR 55423-01 and B6144F-MR-6-0-0) cultivars were grown with or without maize as an artificial weed. Maize was seeded at the same time as rice and removed at 37 d after rice sowing. The two improved cultivars out-yielded the traditional cultivars without weed competition. Larger yield loss due to the competition was associated with longer delay in days to flowering and smaller plant height at 37 d after sowing. The use of B6144F-MR-6-0-0 with high yield potential as well as strong ability to recover from weed competition appears to improve and stabilize rice productivity in this region.