In sub-Saharan Africa, the demand for higher rice production continues to grow rapidly. Although there is a huge potential for increasing rice production through expansion of the rice cultivation area in wetlands, iron (Fe) toxicity tends to occur and consequently results in low rice yield. Development and deployment of varieties tolerant to Fe toxicity is one of the practical options to overcome this constraint. Several tolerant varieties have been developed through conventional breeding but progress in breeding has been generally slow mainly due to large genotype × environment interaction and field heterogeneity, which make rice selection ineffective. In addition, there are no valid managed-stress screening protocols which are highly efficient and that can predict rice performance in the diverse target environments of West Africa. Many O. glaberrima accessions have superior tolerance, but only a few of them have been utilized in breeding programs. The known quantitative trait loci (QTLs) related to Fe toxicity, have not been used for marker-assisted selection (MAS), as they gave small effects with a large confidence interval. Accelerating rice breeding efficiency for tolerance to Fe toxicity requires establishment of reliable screening protocols, use of O. glaberrima accessions as donors, identification of large-effect QTLs and MAS using such QTLs. This paper reviews the past and current efforts in West Africa to develop new varieties with superior tolerance to Fe toxicity.
During sago palm cultivation, many suckers appear from the mother stem as it grows. Some suckers are thinned out, but the rest are left to grow to be harvested several years later after harvesting of the mother stem (trunk). Proper management of the suckers from the mother stem is important to obtain successive sago trunks from a single transplantation. Nevertheless, little scientific knowledge exists about the sucker growth, even the development of its primordium. Our objective is to clarify the differentiation position and the development of the sago palm lateral bud, which is the sucker bud. Results show that in sago palm, the sucker bud differentiates inside of the connate part of the leaf petiole, which is opposite to the axil side. Swelling of tissue is first visible inside of the third leaf from the growth point (rbL 3). Sucker bud initiation is visible at almost all leaf positions lower than rbL 5. Furthermore, at each leaf position, one or two (rarely three) buds are observed. Differentiated buds usually elongate exponentially. Some develop more than two times on average. These sucker buds differentiate inside of the connate part of the thin leaf petiole, which split toward the base gradually as new leaves emerge. The differentiation position of the sucker buds and the thin leaf petiole are expected to be related closely to the further growth of the large sucker buds.
Seed deterioration by ageing caused by natural and artificial treatments lowers germinability and viability. Seed priming is a technique used to relieve seed deterioration from ageing. We evaluated the effect of seed priming with 5-aminolevulinic acid (ALA) at various concentrations on the seed germination capacity, seedling growth, antioxidant enzyme activities, and lipid peroxidation in the rice seedling cultivar Pathum Thani 1 with or without exposure to artificial ageing treatment. Seeds were subjected to accelerated ageing treatment by exposure to high relative humidity and high temperature conditions for 84 hr (aged seeds). The shoot length was significantly reduced and the injury index and H2O2 formation were increased in the seedlings emerged from the aged seeds. Priming of the aged seeds with 0.5 μg mL–1 ALA significantly enhanced the seed germination capacity and seedling relative growth rate to values higher than those obtained by priming with water (hydropriming). However, there was no significant difference in superoxide dismutase, peroxidase and ascorbate peroxidase activity as compared with hydropriming. In the seeds not given ageing treatment priming with ALA significantly increased the superoxide dismutase and peroxidase activities in the seedlings by 144% and 282%, respectively, as compared with the hydropriming treatment. Seed priming with ALA at 0.2 μg mL–1 significantly increased the relative growth rate of seedling and lowered seedling water content as compared with the values without priming or with hydropriming. Seed priming with ALA was confirmed to enhance rice seed germination capacity, seedling growth, and antioxidant enzyme activity in rice seedlings.
We investigated the effects of soaking temperature and duration on the germinability of seeds of rice (Oryza sativa L., cv. Koganemochi, Gohyakumangoku, and Koshihikari) that had been stored for a long period. The germinability of the seeds soaked at 5ºC for 5 d was markedly lower than that of seeds soaked at 12ºC for 5 d. The germinability of the seeds soaked at 5ºC for 24 hr was not increased by subsequent soaking at 12ºC for 4 d. On the other hand, the germinability of the seeds soaked either at 12ºC for 24 hr or at 30ºC for 80 min was similar to that of seeds soaked at 12ºC for 5 d, even when followed by treatment at 5ºC. Thus, the soaking temperature during the first 24 hr was most important for the germination of rice seeds that had been stored for a long period. Western blotting analysis revealed characteristic expression patterns of α-amylase isoforms in cultivars correlating with the germinability after soaking at a low-temperature.
The effects of calcium concentrations in the growth medium on oxalate content of leaf blades, petioles and corms and the involvement of guttation in the regulation of oxalate homeostasis were investigated in eddo (Colocasia esculenta (L.) Schott var. antiquorum Hubbard & Rehder). The plants were grown hydroponically in solutions containing 0 mM calcium, 1 mM calcium nitrate (control), 15 mM calcium nitrate or 15 mM calcium chloride. Total oxalate content (soluble plus insoluble) of leaf blades, petioles and corms did not differ with the calcium concentration in solutions containing 1 mM or 15 mM calcium nitrate or 0 mM calcium. The soluble oxalate content of these parts decreased as the calcium concentration of the solution was increased. Solutions containing 15 mM calcium nitrate or 15 mM calcium chloride gave a significantly lower proportion of soluble oxalate content to total oxalate content in each part, especially in leaf blades than 0 mM calcium or 1 mM calcium nitrate. In contrast, a positive correlation was found between insoluble oxalate content and calcium concentration in the solution. These results demonstrate that high calcium concentrations in the growth medium reduce soluble oxalate content of the plant. Soluble oxalate was detected in eddo guttation fluid. Soluble oxalate content in this fluid (mg mL−1) and the amount of soluble oxalate exuded by guttation (mg leaf−1 night−1) were significantly lower in the solutions containing 15 mM calcium than in those containing 0 mM and 1 mM calcium. These results indicate that guttation may affect the concentration of soluble oxalate in the plant bodies although not strongly contributing to a decrease in soluble oxalate content in eddo grown under high calcium conditions.
We investigated the morpho-physiological traits of rice (Oryza sativa L.) during the germination and post-germination phases to explore avoidance of hypoxic conditions. We compared four lines selected for anaerobic germination (AG lines) with the variety IR42. The germination capacity of AG lines was higher than that of IR42. The germination percentages and coleoptile elongation differed among the four AG lines; IR06F459 showed the fastest germination and rapid coleoptile elongation. The coleoptiles of IR06F459 were significantly longer than those of IR42. The α-amylase activity in germinating seeds was significantly higher in IR06F459 than in IR42. At 2 days after sowing, the sucrose and glucose concentrations in germinating seeds were higher in IR06F459 than in IR42. These results show that IR06F459, an AG line with a long coleoptile, has high α-amylase activity and high sucrose and glucose concentrations in germinating seeds. These attributes partly explain its vigorous germination and coleoptile growth under hypoxic conditions.
Polyamines acid extracted from roots, stems, leaves, flower buds, flowers and seeds of eight Brassica crop plants (cabbage, broccoli, cauliflower, Komatsuna, Chingensai, turnip, Aburana and Seiyou-aburana) with or without clubroot disease were analyzed by high-performance liquid chromatography and gas chromatography. Endogenous concentrations of polyamines per wet weight of the organ were calculated. In cabbage, broccoli and Komatsuna clubroot galls, the levels of putrescine, spermidine and spermine were increased whereas the levels of agmatine levels were decreased after the infection with a protist, Plasmodiophora brassicae. The levels of 2-phenylethylamine and homospermidine found in the normal healthy roots were decreased in the clubroots. The thermospermine level in broccoli was higher in the sprout stem than in the sprout root or other organs. A high agmatine level was found in the healthy sprouts and flower buds of broccoli and cauliflower flower buds. Diaminopropane, cadaverine and norspermine were detected in some Brassica organs as a minor polyamine. The seeds of the eight Brassica plants were rich in spermine and spermidine.
The grain yield of two high-yielding rice varieties, Kita-aoba and Tachijobu, was examined in a field experiment by using swine compost at a rate of 0, 1 and 2 kg m-2 and chemical fertilizer at a rate of 5.25, 7.35, and 10.5 g N m-2 in 2010, and 5.25 and 10.5 g N m-2 in 2011 (Exp. 1). The grain yield of Tachijobu was also evaluated by applying compost at a rate of 0 or 2 kg m-2 and chemical fertilizer at a rate of 5.25, 10.5, and 15.75 g N m-2 from 2011 to 2013 (Exp. 2). Tachijobu had a lower grain yield than Kita-aoba under the same fertilizer management in Exp. 1 due to its lower sink production efficiency, but it showed the highest grain yield of 1085 g m-2 at the highest fertilizer level in Exp. 2. A significant interaction between compost application and nitrogen fertilizer level was observed in grain yield and nitrogen uptake in Tachijobu in Exp. 2, and the nitrogen uptake in Tachijobu reached its maximum at around 15 g m-2 at maturity. In addition, the apparent nitrogen use efficiency of compost (NUEcompost) was higher at a lower nitrogen fertilizer level. From the nitrogen uptake and NUEcompost at each fertilizer level, the optimum rates of compost and fertilizer were discussed. The compost also increased the concentration of protein in Tachijobu (significantly in 2013).
Rice has a vital role in food security but the production is limited in infertile and degraded soils. Rice is cultivated on acid sulphate soil in the coastal area of Peninsular Malaysia. Soil amendment using biological charcoal (biochar) increases the soil fertility. Thus, empty fruit bunch biochar (EFBB) was applied in a pot experiment under a controlled environment using an organic system of rice intensification (SRI) practice and its effects on the floodwater pH, acid sulphate soil properties and growth performance of rice and yield of rice MR219 were preliminarily investigated. EFBB increased grain yield by 141 to 472%. Plant growth and yield parameters in EFBB amended soils were significantly higher than in soil without biochar. The number of tillers increased significantly with the increase in biochar applied; 28 tillers were produced in the control, while up to 80 tillers were produced in the plots applied 40 t ha–1 EFBB. Moreover, the decline of Al3+ in flood water indicated that EFBB mitigated Al3+ toxicity. Soil water pH increased from 3.5 to 6 with increasing EFBB application rates. The grain yield was linearly correlated to the application rate of EFBB. This pot study demonstrates that the application of EFBB combined with organic fertilization and intermittent irrigation has the potential to improve rice yield on acid sulphate soil. Further study in the field is warranted to determine the effect of EFBB on large scale rice production.
The aerobic rice system is a new promising water-saving cultivation technique; however, rice sensitivity to aerobic conditions limits its use. We investigated morphological and physiological responses of seedlings of two upland rice genotypes (Beodien and Sensho) and two lowland rice genotypes (KD18 and Koshihikari) to flooded condition (control) and three aerobic conditions (32, 22, and 14% soil moisture content (SMC), w/w) in 2013 and to a flooded condition and aerobic condition (32% SMC) in 2014. Under aerobic conditions, shoot growth was limited because of a reduction in water uptake. Water uptake capacity was highly controlled by root traits such as root dry weight and root length. Under aerobic conditions, leaf water potential, stomatal conductance, and root hydraulic conductance declined. We found that the 32% SMC condition was the most favorable aerobic condition whereas 22% and 14% SMC conditions strongly suppressed rice growth. Genotypic variations in physio-morphological traits were more clearly detected under well-irrigated conditions (32% SMC) than other two aerobic conditions. In both years, cultivar Sensho adapted to the 32% SMC condition, whereas Koshihikari did not adapt to the aerobic rice system, probably because of its limited root growth and lower root plasticity. The positive correlation between root traits and water uptake indicate that root traits are important for improving rice performance under an aerobic rice system.
The aim of this study was to determine the effect of seed size and shape on germination characteristics of SC701 maize at different temperature regimes. Seeds were grouped according to shape and size and germinated using constant (30ºC and 20ºC), and two alternating (30/20 and 15/20ºC; 12/12hrs) temperatures. A factorial experiment arranged in completely randomized design with three replications was used. Highly significant differences (P < 0.001) were observed for daily germination percentage, germination rate, mean germination time, germination velocity index and vigor index. Germination rate, and germination velocity index showed that flat seeds germinated faster than round seeds at constant temperatures while, small seeds germinated faster than large seeds. A similar trend was observed for vigor index which was higher in the small and flat seeds having a higher vigor index than large and round seeds. However, the vigor index was higher at the alternating temperature (20/30ºC) than at constant temperatures in all seed groups. Highly significant differences (P < 0.001) were observed in the root: shoot ratio, seedling dry mass and fresh mass. Small seeds had higher germination speed than large seeds. Higher temperatures (30ºC constant and 20/30ºC) were associated with better germination. It is concluded that the temperature regime has a major influence on seed morphology and its seed quality parameters. These findings are useful for selection of seed size and determination of soil temperature conditions to grow maize under field conditions.
The contents of major nutrient components, and the composition and contents of medicinal substances were examined in Houttuynia cordata cultivated under field conditions and treated with natural light at full intensity, 40% intensity, and 20% intensity from sprouting to harvesting. The results indicated that the yield of the aboveground portion per unit area was highest at a 40% intensity and lowest at 20% intensity. The yield of the underground portion per unit area was highest under full intensity and lowest at a 20% intensity. As light intensity was reduced, protein and water content increased, while the contents of soluble sugar and fat, the contents of volatile oils both the aboveground and underground portion decreased. The total flavonoid content in both the aboveground and underground portions decreased with diminishing light intensity, but the composition of these flavonoids was hardly affected. In summary, although proper shading can increase the yield and the contents of some nutrients in H. cordata, this treatment reduces the net contents of medicinal components such as volatile oils and flavonoids, as well as the contents of active components. Therefore, it is necessary to provide sufficient light when growing H. cordata for medicinal and functional food purposes, but the crop may be treated with appropriate shading or intercropped when grown as food.
Experiments were conducted to evaluate the nitrogen (N) balance in forage rice cultivation using animal manure in 1/2,000a Wagner pots in a greenhouse. The cattle manure and poultry manure were applied at 3 levels of N (0, 14, 28 g available N m–2) without additional chemical fertilizer application. The pots were designed to simulate the fluid percolation in the paddy field. The results indicated increasing levels of N input improved plant height, tiller number, SPAD value and biomass (straw, grain and root) production, however, N leaching from soil (Andosols) due to percolating water also increased. The planting of rice plants proved to reduce 30% of the N leaching loss. N use efficiency, the ratio of N uptake by plant per unit N application, decreased in higher N application. The N uptake by the above-ground parts occupied about 66% of the whole plants.
Sweet sorghum bagasse (SSB) is a soil amendment with potential for biofuel production. This study was conducted to determine the appropriate techniques for application of SSB and the effect of incorporation of inorganic fertilizer (IF) on the production of komatuna (Brassica rapa) plants. SSB was applied to the surface of the plant or incorporated into soil. The N fate of IF was evaluated by using 15N-labeled IF. The combination of surface application of SSB and incorporation of IF to soil decreased the N uptake by komatsuna plants but increased dry weight, whereas the incorporation of IF and SSB gave lower komatsuna dry weight than IF treatment alone. Moreover, the application of SSB tended to increase the N distribution from IF to komatsuna with decreased N loss from the plant-soil system. These results showed that surface application of SSB is effective for increasing crop production due to reduction of N loss and improved N use efficiency.
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