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  • 1
    ISSN: 1432-0789
    Keywords: Adverse soil conditons ; Aeschynomene ; Green manure ; Lowland rice ; Nitrogen fixation ; Sesbania ; Forming system development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Poor adoption of sustainable pre-rice green manure technology by lowland farmers is frequently associated with unreliable legume performance under adverse environmental conditions such as marginal soils, short photoperiod, and unfavorable hydrology. A series of field and microplot experiments were conducted at the International Rice Research Institute (IRRI) in 1991 and 1992 to screen and evaluate 12 promising flood-tolerant legumes for adaptation (N accumulation and biological N2 fixation) to a range of environmental stresses, frequently encountered in rice lowlands. Legumes belonging to the genera Sesbania and Aeschynomene were grown for 8 weeks at 10×10 cm spacing: (1) in a fertile control soil and in four marginally productive irrigated lowland rice soils (sandy Entisol, P-deficient Inceptisol, acid Ultisol, and saline Mollisol); (2) during short- (11.7h) and long-day (12.3 h) seasons in a favorable irrigated lowland soil; and (3) in an aerobic soil (drought-prone rain-fed lowland) and a deep-flood-prone lowland soil (1 week seedling submergence). A large variability in N accumulation was obsersed among legume species and across different environments, ranging from less than 1 to over 70 mg N plant-1. The nitrogen derived from the atmosphere (Ndfa) accounted on average for 82% of total N accumulation. Sesbania virgata was least affected by unfavorable soil conditions but its Ndfa was the lowest among the tested species (less than 60%). Stem nodule formation did not convey a significant advantage to legumes grown under adverse soil conditions. However, flooding reduced N2 fixation less in stem-nodulating than in solely root-nodulating species. Most species drastically reduced N accumulation under short-day conditions. Aeschynomene afraspera and S. speciosa were least affected by photoperiod. The considerable genetic variability in the germplasm screened allows the selection of potentially appropriate legumes to most conditions studied, thus increasing N accumulation in green manures.
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  • 2
    ISSN: 1432-0789
    Keywords: Azospirillum lipoferum ; Mucigel ; Oryza sativa ; Root colonization ; Scanning electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Seedlings of rice (IR42 and IR50) were aseptically dipped into Azospirillum lipoferum strain 34H suspension under dark, and the presence of bacteria on the differentiating regions of rice roots was observed by scanning electron microscopy. The bacterium did not colonize the root tips of IR42, while it colonized this region in the case of IR50, within 24 h after inoculation. In the early stages, most of the bacteria were embedded in the ruptured mucigel below the root cap cells of IR42. Mucigel was hardly detectable in IR50. While the root hair primordia of IR50 were colonized heavily with the bacterium within 24 h, the root hairs of IR42 were colonized 48 and 72 h after inoculation. This phenomenon in relation to plant varietal differences was discussed.
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  • 3
    ISSN: 1432-0789
    Keywords: Sesbania rostrata ; Green manure ; Biofertilizer ; Nitrogen fixation ; Stem nodule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Ratooning and stem cutting were compared with seeding in order to reduce the amount of seeds of Sesbania rostrata for green-manure growth. Both methods increased the biofertilizer yield highly significantly within a 6-week growth period.
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  • 4
    ISSN: 1432-2242
    Keywords: Oryza sativa L ; Spikelet fertility ; Non-allelic interaction ; Restriction fragment length polymorphism (RFLP)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Significant segregation of spikelet fertility occurred in an F2 population derived from a spikelet fertility-normal F1 hybrid produced by a cross between ‘Palawan’, a japonica variety, and ‘IR42’, an indica variety. To identify factors controlling the fertility segregation, we used 104 RFLP markers covering all 12 rice chromosomes to investigate the association of spikelet fertility and marker segregation. We found that the segregation of two sets of gene pairs was significantly (P 〈 0.001) associated with fertility segregation. The first pair of genes was linked to RFLP marker RG778 on chromosome 12 and RFLP markers RG690/RG369 on chromosome 1. A significant reduction in fertility was observed when the plants were homozygote at RG778 with the indica allele as well as homozygote at RG690/RG369 with the japonica allele. The second pair of genes was linked to RG218 on chromosome 12 and RG650 on chromosome 7, respectively. The recombinant homozygote at these two loci showed a significant reduction on spikelet fertility. The non-allelic interaction effect was further modified by a gene linked to RG778, resulting in even lower fertility. The results of this study provides the first evidence of chromosomal localization of sporophytic sterility genes whose interaction can result in a reduction of spikelet fertility in the F2 derived from fertility-normal F1.
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  • 5
    ISSN: 1432-2242
    Keywords: Oryza sativa L. ; Atom 15N% excess ; N2 fixation ; Restriction fragment length polymorphism (RFLP)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An F2 population, consisting of 231 individuals derived from a cross between rice cultivars with a similar growing duration, Palawan and IR42, was utilized to investigate the genetic nature of rice varietal ability to stimulate N2 fixation in the rice rhizosphere. To assess rhizospheric N2 fixation, an isotope-enriched 15N dilution technique was employed, using 15N-stabilized soil in pots. IR42, an indica variety, had 23% higher N derived from fixation (Ndfa) than Palawan, a javanica genotype. Normal segregation of atom% 15N excess was obtained in the F2 population, with an average of 0.218 with 8% of plants below IR42 (0.188) and 10% of plants above Palawan (0.248). One-hundred-and-four RFLP markers mapped on 12 chromosomes were tested for linkage to the putative QTLs. Significant (P〈0.01) associations between markers and segregation of atom% 15N excess were observed for seven marker loci located on chromosomes 1, 3, 6 and 11. Four QTLs defined by the detected marker loci were identified by interval-mapping analysis. Additive gene action was found to be predominant, but for at least one locus, dominance and partial dominance effects were observed. Significant (P〈0.01) epistatic effects were also identified. Individual marker loci detected between 8 and 16% of the total phenotypic variation. All four putative QTLs showed recessive gene action, and no phenotypic effects associated with heterozygosity of marker loci were observed. The results of this study suggest that rice genetic factors can be identified which affect levels of atom% 15N excess in the soil by interacting with diazotrophs in the rice rhizosphere.
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  • 6
    ISSN: 1432-0789
    Keywords: Sesbania rostrata ; Sesbania cannabina (syn. Sesbania aculeata) ; Non-N2-fixing reference ; Biological N2 fixation ; 15N dilution ; 15N atom % excess
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A field experiment in concrete-based plots was conducted to estimate the contribution of N derived from air (Ndfa) or biological N2 fixation in Sesbania rostrata and S. cannabina (syn. S. aculeata), using various references, by the 15N dilution method. The two Sesbania species as N2-fixing reference plants and four aquatic weed species as non-N2-fixing references were grown for 65 days after sowing in two consecutive crops, in the dry and the wet seasons, under flooded conditions. Soil previously labeled with 15N at 0.26 atom % 15N excess in mineralizable N was further labeled by ammonium sulfate with 3 and 6 atom % 15N excess. The results showed that 15N enrichment of soil NH 4 + -N dropped exponentially in the first crop to half the original level in 50 days while in the second crop, it declined gradually to half the level in 130 days. The decline in 15N enrichment, in both N2-fixing and non-fixing species, was also steeper in the first crop than in the second crop. Variations in 15N enrichment among non-fixing species were smaller in the second crop. The ratio of the uptake of soil N to that of fertilizer N in N2-fixing and non-fixing species was estimated by the technique of varying the 15N level. In the second crop, this ratio in non-fixing species was higher than that in N2-fixing species. Comparable estimates of % Ndfa were obtained by using 15N enrichment of various non-fixing species. There was also good agreement between the estimates obtained by using 15N enrichment of non-fixing species and those by using soil NH 4 + -N, particularly in the second crop. By 25 days after sowing, the first crop of both Sesbania spp. had obtained 50% of total N from the atmosphere and the second crop had obtained 75%. The contribution from air increased with the age of the plant and ranged from 70% to 95% in 45–55 days. S. rostrata fixed substantially higher amounts of N2 due to its higher biomass production compared with S. cannabina. Mathematical considerations in applying the 15N dilution method are discussed with reference to these results.
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  • 7
    ISSN: 1432-0789
    Keywords: Sesbania rostrata ; Echinochloa crus-galli ; 15N atom% excess ; Soil NH inf4 sup+ -N ; 15N dilution ; Biological N2 fixation ; Fertilizer use efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A pot experiment in the greenhouse was conducted to compare the contribution of N derived from the atmosphere or from biological N2 fixation by Sesbania rostrata inoculated with Azorhizobium caulinodans, applied either to roots or to roots and stems (single or multiple stem inoculation). Two subsequent crops were grown for 50 days under flooded conditions. N derived from air was estimated by 15N dilution using 15N enrichment of soil NH inf4 sup+ -N and of Echinochloa crusgalli as the non-N2-fixing reference datum and compared with estimates obtained by the N-difference method. The first crop was grown to stabilize the 15N into the soil organic N fraction. The 15N enrichment of soil NH inf4 sup+ -N in the second crop declined slowly. The extractability ratio (15N enrichment of extractable soil N to 15N enrichment of total soil N) decreased from 4.8 to 4.1 50 days after planting. The enrichment of soil NH inf4 sup+ -N was comparable to that of E. crus-galli, resulting in similar estimates of N derived from air when either soil NH inf4 sup+ -N or enrichment of E. crus-galli was used as a non-fixing reference. The N-difference method did not always provide reliable estimates of N derived from air; percentages ranged from 75 to more than 80 by 50 days after planting in both crops and did not differ among treatments. The study demonstrates the potential of using 15N enrichment of soil NH inf4 sup+ -N as a non-N2-fixing reference for reliable BNF estimates of crops in lowland puddled soil.
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  • 8
    ISSN: 1432-0789
    Keywords: Azospirillum lipoferum inoculation ; Rice yield ; Acetylene reduction assay ; 15N feeding and dilution techniques
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A spontaneous mutant ofAzospirillum lipoferum, resistant to streptomycin and rifampicin, was inoculated into the soil immediately before and 10 days after transplanting of rice (Oryza sativa L.). Two rice varieties with high and low nitrogen-fixing supporting traits, Hua-chou-chi-mo-mor (Hua) and OS4, were used for the plant bacterial interaction study. The effect of inoculation on growth and grain and dry matter yields was evaluated in relation to nitrogen fixation, by in situ acetylene reduction assay,15N2 feeding and15N dilution techniques. A survey of the population of marker bacteria at maximum tillering, booting and heading revealed poor effectivety. The population of nativeAzospirillum followed no definite pattern. Acetylene-reducing activity (ARA) did not differ due to inoculation at two early stages but decreased in the inoculated plants at heading. In contrast, inoculation increased tiller number, plant height of Hua and early reproductive growth of both varieties. Grain yield of both varieties significantly increased along with the dry matter. Total N also increased in inoculated plants, which was less compared with dry matter increase.15N2 feeding of OS4 at heading showed more15N2 incorporation in the control than in the inoculated plants. The ARA,15N and N balance studies did not provide clear evidence that the promotion of growth and nitrogen uptake was due to higher N2 fixation.
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  • 9
    ISSN: 1432-0789
    Keywords: Key words Adverse soil conditons ; Aeschynomene ; Green manure ; Lowland rice ; Nitrogen fixation ; Sesbania ; Forming system development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Poor adoption of sustainable pre-rice green manure technology by lowland farmers is frequently associated with unreliable legume performance under adverse environmental conditions such as marginal soils, short photoperiod, and unfavorable hydrology. A series of field and microplot experiments were conducted at the International Rice Research Institute (IRRI) in 1991 and 1992 to screen and evaluate 12 promising flood-tolerant legumes for adaptation (N accumulation and biological N2 fixation) to a range of environmental stresses, frequently encountered in rice lowlands. Legumes belonging to the genera Sesbania and Aeschynomene were grown for 8 weeks at 10×10 cm spacing: (1) in a fertile control soil and in four marginally productive irrigated lowland rice soils (sandy Entisol, P-deficient Inceptisol, acid Ultisol, and saline Mollisol); (2) during short- (11.7 h) and long-day (12.3 h) seasons in a favorable irrigated lowland soil; and (3) in an aerobic soil (drought-prone rain-fed lowland) and a deep-flood-prone lowland soil (1 week seedling submergence). A large variability in N accumulation was observed among legume species and across different environments, ranging from less than 1 to over 70 mg N plant–1. The nitrogen derived from the atmosphere (Ndfa) accounted on average for 82% of total N accumulation. Sesbania virgata was least affected by unfavorable soil conditions but its Ndfa was the lowest among the tested species (less than 60%). Stem nodule formation did not convey a significant advantage to legumes grown under adverse soil conditions. However, flooding reduced N2 fixation less in stem-nodulating than in solely root-nodulating species. Most species drastically reduced N accumulation under short-day conditions. Aeschynomene afraspera and S. speciosa were least affected by photoperiod. The considerable genetic variability in the germplasm screened allows the selection of potentially appropriate legumes to most conditions studied, thus increasing N accumulation in green manures.
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  • 10
    ISSN: 1432-0789
    Keywords: Sesbania rostrata ; Green manure ; Stem nodulation ; N2 fixation ; Azorhizobium caulinodans ; Inoculation ; Rice ; Yield ; N balance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Root and stem nodulation, nitrogen fixation (acetylene-reducing activity), growth and N accumulation bySesbania rostrata as affected by season and inoculation were studied in a pot experiment. The effects ofS. rostrata as a green manure on succeeding wet-season and dry-season rice yields and total N balance were also studied.S. rostrata grown during the wet season showed better growth, nodulation, and greater acetylene-reducing activity than that grown during the dry season. Inoculation withAzorhizobium caulinodans ORS 571 StrSpc® (resistant to streptomycin and spectinomycin) on the stem alone or on both root and stem significantly increased N2 fixation by the plants. Soil and seed inoculation yielded active root nodules under flooded conditions. Plants that were not inoculated on the stem did not develop stem nodules. The nitrogenase activity of the root nodules was greater than that of the stem nodules in about 50-day-oldS. rostrata. S. rostrata incorporation, irrespective of inoculation, significantly increased the grain yield and N uptake of the succeeding wet season and dry season rice crops. The inoculated treatments produced a significantly greater N gain (873 mg N pot−1) than the noinoculation (712 mg N pot−1) treatment. About 80% of the N gained was transferred to the succeeding rice crops and about 20% remained in the soil. The soil N in the flooded fallow-rice treatment significantly declined (−140 mg N pot−1) but significantly increased in bothS. rostrata-rice treatments (159 and 151 mg N pot−1 in uninoculated and inoculated treatments respectively). The N-balance data gave extrapolated values of N2 fixed per hectare at about 303 kg N ha−1 per two crops forS. rostrata (uninoculated)-rice and 383 forS. rostrata (inoculated)-rice.
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