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PubMed2006

Genetic analysis of agricultural traits in rice related to phosphorus efficiency.

Relative tillering ability, available spike, biomass, and grain yield of P1, P2, F1, and F(2,3) were used to study the genetic development of rice related to phosphorus efficiency with a quantitative genetic model. The results indicated that under a low-P condition, the relative tillering ability and the relative available spike were apt to the additivity-dominance-epistasis model with two couples of major genes, between which additive, dominant and epistatic effects existed, and with multi-gene modifications. Their maximum major gene effect mostly indicated additivity, but sub-maximum major gene effect mostly indicated dominance. Relative biomass and grain yield were apt to the additivity-dominance-epistasis and multi-genes model. The heritabilities of the major genes were 60.08% and 37.70%, and those of the multi-genes were 32.15% and 58.9%, respectively. This meant that the heritabilities of the relative tillering ability, the relative available spike, and the relative biomass were high, so they were ideal indexes for rice breeding tolerating to low-P stress; whereas, the heritability of the relative grain yield was low, which meant that the grain yield was easily affected by the environment.

Biomass↗
PubMed1988

Exploring the limits of crop productivity. I. Photosynthetic efficiency of wheat in high irradiance environments.

The long-term vegetative and reproductive growth rates of a wheat crop (Triticum aestivum L.) were determined in three separate studies (24, 45, and 79 days) in response to a wide range of photosynthetic photon fluxes (PPF, 400-2080 micromoles per square meter per second; 22-150 moles per square meter per day; 16-20 hour photoperiod) in a near-optimum, controlled-environment. The CO2 concentration was elevated to 1200 micromoles per mole, and water and nutrients were supplied by liquid hydroponic culture. An unusually high plant density (2000 plants per square meter) was used to obtain high yields. Crop growth rate and grain yield reached 138 and 60 grams per square meter per day, respectively; both continued to increase up to the highest integrated daily PPF level, which was three times greater than a typical daily flux in the field. The conversion efficiency of photosynthesis (energy in biomass/energy in photosynthetic photons) was over 10% at low PPF but decreased to 7% as PPF increased. Harvest index increased from 41 to 44% as PPF increased. Yield components for primary, secondary, and tertiary culms were analyzed separately. Tillering produced up to 7000 heads per square meter at the highest PPF level. Primary and secondary culms were 10% more efficient (higher harvest index) than tertiary culms; hence cultural, environmental, or genetic changes that increase the percentage of primary and secondary culms might increase harvest index and thus grain yield. Wheat is physiologically and genetically capable of much higher productivity and photosynthetic efficiency than has been recorded in a field environment.

Biomass↗
PubMed2005

Rhizosphere competent Pseudomonas aeruginosa GRC1 produces characteristic siderophore and enhances growth of Indian mustard (Brassica campestris).

Pseudomonas aeruginosa GRC1, an isolate of potato rhizosphere, was known to have several plant growth-promoting activities, including production of phytohormone and antibiotic substance. The isolate was found to have prolific production ability of hydroxamate siderophore in iron-deficient conditions. The siderophore of GRC1 was purified and characterized. The purified siderophore appeared to be of pyoverdin type with typical amino acid composition. In field trials, P. aeruginosa GRC1 enhanced the growth of Brassica campestris var Pusa Gold (Indian mustard). Significant increase in root and shoot weight, length, grain yield per plant, and total grain yield was recorded. Root colonization was studied with Tn5-induced streptomycin-resistant transconjugants of spontaneous rifampicin-resistant GRC1 (designated GRC1(rif+strep+)) after different durations. The strain was significantly rhizopheric competent and stabilized in the rhizosphere, without disturbing the normal indigenous bacterial population.

Anti-Bacterial Agents↗
PubMed1992

Identification of genetic factors contributing to heterosis in a hybrid from two elite maize inbred lines using molecular markers.

The use of molecular markers to identify quantitative trait loci (QTLs) affecting agriculturally important traits has become a key approach in plant genetics-both for understanding the genetic basis of these traits and to help design novel plant improvement programs. In the study reported here, we mapped QTLs (and evaluated their phenotypic effects) associated with seven major traits (including grain yield) in a cross between two widely used elite maize inbred lines, B73 and Mo17, in order to explore two important phenomena in maize genetics-heterosis (hybrid vigor) and genotype-by-environment (G x E) interaction. We also compared two analytical approaches for identifying QTLs, the traditional single-marker method and the more recently described interval-mapping method. Phenotypic evaluations were made on 3168 plots (nearly 100,000 plants) grown in three states. Using 76 markers that represented 90-95% of the maize genome, both analytical methods showed virtually the same results in detecting QTLs affecting grain yield throughout the genome, except on chromosome 6. Fewer QTLs were detected for other quantitative traits measured. Whenever a QTL for grain yield was detected, the heterozygote had a higher phenotype than the respective homozygote (with only one exception) suggesting not only overdominance (or pseudooverdominance) but also that these detected QTLs play a significant role in heterosis. This conclusion was reinforced by a high correlation between grain yield and proportion of heterozygous markers. Although plant materials were grown and measured in six diverse environments (North Carolina, Iowa and Illinois) there was little evidence for G x E interaction for most QTLs.

Crosses, Genetic↗
PubMed2004

An approach to the genetics of nitrogen use efficiency in maize.

To study the genetic variability and the genetic basis of nitrogen (N) use efficiency in maize, a set of recombinant inbred lines crossed with a tester was studied at low input (N-) and high input (N+) for grain yield and its components, grain protein content, and post-anthesis nitrogen uptake and remobilization. Other physiological traits, such as nitrate content, nitrate reductase, glutamine synthetase (GS), and glutamate dehydrogenase activities were studied at the level of the lines. Genotypexnitrogen (GxN) interaction was significant for yield and explained by variation in kernel number. In N-, N-uptake, the nitrogen nutrition index, and GS activity in the vegetative stage were positively correlated with grain yield, whereas leaf senescence was negatively correlated. Whatever N-input, post-anthesis N-uptake was highly negatively related to N-remobilization. As a whole, genetic variability was expressed differently in N+ and N-. This was confirmed by the detection of QTLs. More QTLs were detected in N+ than in N- for traits of vegetative development, N-uptake, and grain yield and its components, whereas it was the reverse for grain protein content and N-utilization efficiency. Several coincidences between genes encoding for enzymes of N metabolism and QTLs for the traits studied were observed. In particular, coincidences in three chromosome regions of QTLs for yield and N-remobilization, QTLs for GS activity and a gene encoding cytosolic GS were observed. This may have a physiological meaning. The GS locus on chromosome 5 appears to be a good candidate gene which can, at least partially, explain the variation in nitrogen use efficiency.

Chromosome Mapping↗
PubMed2025

UAV-based multispectral image analysis revealed stay-green haplotypes in wheat specific for different soil nitrogen levels.

BACKGROUND: The so-called stay-green trait, a delay in onset and progression of leaf senescence, is associated with slower chlorophyll degradation and higher photosynthesis rates during maturation resulting in higher crop yields. Understanding the genetic and physiological basis of the stay-green trait and breeding cultivars with stable stay-green behaviour across a range of different nitrogen (N) conditions and specifically under low N availability can contribute to ensuring wheat yields and reducing N fertilizer application. The goal of this study was therefore to identify haplotypes associated with high stay-green capacity under different N availability conditions in wheat. A diverse set of 221 wheat cultivars was grown under three different N levels and phenotyped by uncrewed aerial vehicle (UAV)-based multispectral imaging to characterise genetic and environmental variation in stay-green. Haplotypes associated with stay-green were identified across N levels and specifically under low N availability. RESULTS: The plant senescence reflectance index (PSRI) calculated from multispectral images was identified as the most specific stay-green indicator allowing for differentiation of genotypic effects due to its greater sensitivity to senescence-related changes in pigment composition and its higher reliability. We found genetic variance for stay-green and a consistent genetic correlation between stay-green and grain yield at all imaging dates and N levels within the utilised diversity panel confirming its potential as a future breeding target. Haplotype analyses revealed two favourable major allele haplotypes present in 95% of the stay-green cultivars, i.e. the top 25% of the diversity set based on PSRI values, which significantly enhance stay-green performance and grain yield. In addition, we identified a favourable minor allele haplotype specifically associated with stay-green under low N availability and capable of further increasing stay-green and grain yield when stacked onto the two favourable major allele haplotypes. CONCLUSIONS: The newly identified stay-green haplotypes can be further used for fine-mapping and identifying the underlying genes as well as for selecting for higher stay-green and grain yield. Thereby our results can contribute to improving our understanding of the complex genetic regulation underlying stay-green in different environments and to breeding new cultivars with stable performance across N levels or specifically under low N availability.

Triticum↗
PubMed2000

Analogue-resistant mutants of Azotobacter chroococcum derepressed for nitrogenase activity and early ammonia excretion having potential as inoculants for cereal crops.

Spontaneous mutants resistant to methionine sulfoximine (Msx), methyl alanine (Mal) and methyl ammonium chloride (Mac) were derived from A. chroococcum strain A103. Msx and Mal-resistant mutants expressed 1.73 to 10.98% of the fully derepressed nitrogenase activity when grown in Burk's medium containing ammonium acetate. Mac-resistant mutants did not express nitrogenase activity in ammonium acetate supplemented medium. The mutants excreted ammonia even after 2 days of growth and some mutants excreted more ammonia as compared to the parent. Selected mutants were inoculated on wheat (Triticum aestivum) and barley (Hordeum vulgare) under field conditions. Majority of the derepressed mutants increased grain yield of wheat and barley varying from 1.2 to 33.3%. However, host-dependent effects on grain yield were observed with different mutants. Two mutants, Mal 27 and Mac 19 showed significant increase in grain yields of both the crops. The results suggest that metabolic analogue-resistant mutants of Azotobacter have potential for use as a biofertilizer for cereal crops.

Alanine↗
PubMed2002

Effect of sequential applications of foliar nutrients, biofertilizers and sowing dates on the incidence of corn stem borers in Egypt.

In this study either early sown (May 1st) or lately sown (June 2nd) corn plants were treated with Phosphorin & Rhizobactrin as biofertilizers and sprayed with six selected foliar nutrients, i.e. Polymex; Greenzit SP100, Greenzit NPK, Potasin-F, Copper sulphate and Ascorbic acid; in mono-, bi-, and/or tri-sequential applications. Such practices were conducted to show their beneficial effects compared with the chemical treatment in checking the incidence of the stem borers and hence increasing the corn yield. The obtained results could be summarized in the following chief points: (a) the lately sown biofertilized plants showed somewhat higher levels of infestation than the early planted ones., (b) in general, spraying the biofertilized corn plants in both sowing dates with the tested foliar nutrients, significantly decreased the rate of the stem borers infestation than the untreated plants of control., (c) the foliar sprays of Greenzit NPK alone, bi- or tri-sequential applications of Potasin-F, Polymex, Ascorbic acid and Copper sulphate achieved considerable success in reducing larval numbers of the borers species. For example, in case of using the bi-sequential nutrients (Polymex/Ascorbic acid) the numbers were 1.2, 1.5 and 1.2 larvae/5 plants, whereas the numbers were 1.3, 1.0 and 0.7 larvae/5 plants as a result, of the tri-sequential applications (Potasin-F/Ascorbic acid/Polymex) for the pink stem borer, Sesamia cretica, (Led.), the purple lined borer, Chilo agamemnon, (Bels.), and the European corn borer Ostrinia nubilalis (Hb.), in respect, vs. 4.8, 4.5 and 2.9 larvae/5 plants for the same stem borers, respectively, in case of the untreated corn plants. In addition, the other trisequential applications (Polymex/ascorbic acid/Copper sulphate), (Potasin-F/Copper sulphate/ascorbic acid) and (Potasin-F/Copper sulphate/Polymex) reduced the stem borers infestation; (d) from the view point of the interaction effects of sowing dates and the tested foliar nutrients, it was found that the tri-sequential sprayings (Potasin-F/Copper sulphate/Polymex) and/or (Potasin-F/Copper sulphate/Ascorbic acid) have lowered the rate of the stem borers infestation to 3.3 and 3.3 and 5.7 and 4.3 larvae/5 plants for the tri-applications in the 1st and 2nd sowing dates, respectively. Such reductions in the levels of infestation led to an increase in the grain yield up to 6.9 and 7.2 and 5.4 and 5.8 ton/fed, for the early and lately sown corn plants, in respect, and (e) All the foliar nutrients, with no exception, proved to be efficient in managing the stem borers infestation as compared with the insecticide treatment using Polytrin. Although the chemical application had lowered the level of infestation to 2.3 and 5.7 larvae/5 plants in the 1st and 2nd sowing dates as compared with 9.7 and 14.7 larvae/5 untreated plants for the same sowing dates, lesser grain yield of 5.6 and 4.4 ton/fed. was obtained in the first and second dates of planting, successively, in comparison to the grain yield resulted from the tri-applications of Potasin-F/Copper sulphate with either Polymex or Ascorbic acid. The abovementioned results assured the profitable effects of using foliar nutrients as well as the biofertilizers for attaining healthy corn plants, which would be capable of tolerating the injury inflicted by the studied stem borers and compensating for the harmful effects of insects infestation, so high grain yields could be obtained than those of the untreated and/or the insecticide treated plants.

Agrochemicals↗
PubMed2004

Comparative effectiveness of cattle manure, poultry manure, phosphocompost and fertilizer-NPK on three cropping systems in vertisols of semi-arid tropics. I. Crop yields and system performance.

A field experiment was conducted on deep vertisols of Bhopal, India to evaluate the manural potential of three organic manures: farmyard manure (FYM), poultry manure (PM), phosphocompost (PC) vis-a-vis 0%, 75% and 100% recommended dose of fertilizer-NPK and to find out the most productive cropping system at various combinations of organic manures and chemical fertilizers. The seed yield of intercrop soybean (population converted to 100%) was 8.7% less than sole soybean whereas the grain yield of intercrop sorghum was 9.5% more than that of sole sorghum. However, the productivity in terms of soybean equivalent yield (SEY) was relatively high in intercropping system. The increasing NPK dose from 0% to 100% significantly improved SEY in sole sorghum and soybean/sorghum intercropping system and the integrated use of organics and inorganics recorded significantly more SEY than inorganics. The effect of nutrient management followed the order; 75% NPK + 5 t FYM ha(-1) > 75% NPK + 1.5 t PM ha(-1) > 75% NPK + 5 t PC ha(-1) > 100% NPK. Sorghum, both as sole and intercrop, responded more to PM while soybean to FYM. Application of 75% NPK in combination with PM or FYM or PC to preceding rainy season crops (soybean and sorghum) and 75% NPK to wheat produced significantly higher grain yield of wheat than those in inorganics and control indicating noticeable residual effect on the succeeding wheat crop and saving of 25% fertilizer-NPK. The effect of PC on rainy season crops was not as prominent as those of FYM and PM, but its residual effect on grain yield of wheat was comparable to those two organic manures. Among the cropping systems, soybean as preceding crop recorded the highest seed yield of wheat and was on a par with that of soybean/sorghum intercropping system. The yield of wheat following sorghum was the lowest. The total system productivity (TSP) was the highest in sorghum + soybean-wheat system and the lowest in the soybean-wheat system.

Agriculture↗
PubMed1977

Effect of lime-pelleting on nodulation and yield of soybean grown in acid soil.

An experiment for studying the effect of lime-pelleting of inoculated seed of soybean [Glycine max. (L.) Merr.] on nodulation, growth, and grain yield was undertaken in red sandy loam of Bangalore, having a pH of 4.0. The results indicated that inoculation alone increased significantly nodulation, plant dry weight, and grain yield. But inoculation plus lime-pelleting significantly increased the dry weight of nodules and plants, but not the grain yield. However, lime-pelleting was found to be beneficial though not essential in acid soils.

Acids↗
PubMed2006

Environmental and production consequences of using alum-amended poultry litter as a nutrient source for corn.

Field trials were established to compare alum-treated poultry litter (ATPL), normal poultry litter (NPL), and triple superphosphate (TSP) as fertilizer sources for corn (Zea mays L.) when applied at rates based on current litter management strategies in Virginia. Trials were established in the Costal Plain and Piedmont physiographic regions near Painter and Orange, VA, respectively. Nitrogen-based applications of ATPL or NPL applied at rates estimated to supply 173 kg of plant-available nitrogen (PAN) ha(-1) resulted in significantly lower grain yields than treatments receiving commercial fertilizer at the same rate in 2000 and 2001 at Painter. These decreases in grain yield at the N-based application rates were attributed to inadequate N availability, resulting from overestimates of PAN as demonstrated by tissue N concentrations. However, at Orange no treatment effects on grain yield were observed. Applications of ATPL did not affect Al concentrations in corn ear-leaves at either location. Exchangeable soil Al concentrations were most elevated in treatments receiving only NH4NO3 as an N source. At N-based application rates, the ATPL resulted in lower Mehlich 1-extractable P (M1-P) and water-extractable soil phosphorus (H2O-P) concentrations compared to the application of NPL. A portion of this reduction could be attributed to lower rates of P applied in the N-based ATPL treatments. Runoff collected from treatments which received ATPL 2 d before conducting rainfall simulations contained 61 to 71% less dissolved reactive phosphorus (DRP) than treatments receiving NPL. These results show that ATPL may be used as a nutrient source for corn production without significant management alterations. Alum-treated poultry litter can also reduce the environmental impact of litter applications, primarily through minimizing the P status of soils receiving long-term applications of litter and reductions in runoff DRP losses shortly after application.

Alum Compounds↗
PubMed2006

The genetics of nitrogen use in hexaploid wheat: N utilisation, development and yield.

A genetic study is presented for traits relating to nitrogen use in wheat. Quantitative trait loci (QTLs) were established for 21 traits relating to growth, yield and leaf nitrogen (N) assimilation during grain fill in hexaploid wheat (Triticum aestivum L.) using a mapping population from the cross Chinese Spring x SQ1. Glutamine synthetase (GS) isozymes and estimated locations of 126 genes were placed on the genetic map. QTLs for flag leaf GS activity, soluble protein, extract colour and fresh weight were found in similar regions implying shared control of leaf metabolism and leaf size. Flag leaf traits were negatively associated with days to anthesis both phenotypically and genetically, demonstrating the complex interactions of metabolism with development. One QTL cluster for GS activity co-localised with a GS2 gene mapped on chromosome 2A, and another with the mapped GSr gene on 4A. QTLs for GS activity were invariably co-localised with those for grain N, with increased activity associated with higher grain N, but with no or negative correlations with grain yield components. Peduncle N was positively correlated, and QTLs co-localised, with grain N and flag leaf N assimilatory traits, suggesting that stem N can be indicative of grain N status in wheat. A major QTL for ear number per plant was identified on chromosome 6B which was negatively co-localised with leaf fresh weight, peduncle N, grain N and grain yield. This locus is involved in processes defining the control of tiller number and consequently assimilate partitioning and deserves further examination.

Ammonia↗
PubMed2001

Productivity and carbon isotope discrimination in durum wheat organs under a Mediterranean climate.

For durum wheat, we promote the use of carbon isotope discrimination (delta) as an indirect selection criterion for transpiration efficiency and grain yield (GY), and we identify the most effective organ for characterising delta genotypic variation. A field experiment was conducted in the South of France on 144 accessions, with a drought period occurring from February to June. Harvest index (HI), GY and delta (delta L, flag leaf; delta A, awn, delta G grain) were measured. Significant positive genetic correlations were noted between delta and both GY and HI. A larger genotypic variation and a higher broad-sense heritability were noted for delta G compared to delta L and delta A. delta G correlated better with GY and HI than delta L and delta A, showing that delta G could provide a better assessment of genotypic behaviours under drought during grain filling. Moreover, the indirect selection based on delta G (even when evaluated with one replicate) appeared more efficient than the direct selection for grain yield. This result emphasised the potential value of grain carbon isotope discrimination as a criterion for grain yield improvement under stressed Mediterranean conditions.

Carbon Isotopes↗
PubMed1999

[Favorable genes and favorable genic interactions enhancing F1 fertility in indica/japonica hybrids].

Two test cross populations were developed by crossing a set of DH lines as male parents to two wide compatibility rice lines, photoperiod-sensitive genic male sterile (PGMS) line-N422S and thermosensitive-genic male sterile (TGMS) line-Peiai64S. Polymorphism of the cross parents and another set of diverse indica or japonica lines (as a control) was assayed by using 92 RFLP markers. 41 RFLP markers were detected highly associated with indica and japonica phenotypes, which can be used as diagnostic markers to differentiate indica and japonica. Our results indicated that 87.8% of the diagnostic markers were also highly associated with grain yield and its components in at least one of the test cross populations, suggesting parallel relationships between the genes involving in evolution and QTLs controlling grain yield and yield components in the process of differentiation of rice (O. sativa L.). Further analysis indicated that fertility was a main factor affecting the heterosis for grain yield in inter-subspecific rice hybrids. The fertility was conditioned by both intra-locus and inter-locus gene interactions and favorable genic interactions could raise it accordingly.

Fertility↗
PubMed2005

[Yield-formation and source-sink characteristics of rice genotypes under two different eco-environments].

With nine Japanese varieties and two local cultivars of rice as test materials, this paper studied the characteristics of their yield-formation and source-sink characteristics under different eco-environments of Nanjing and Lijiang. The results showed that eco-environment had an obvious effect on rice grain yield and dry matter accumulation. High-yielding rice genotypes could accumulate more dry matter, especially in their late growth period. They had higher total spikelet number, leaf area index (LAI) and crop growth rate (CGR), as compared with other genotypes. The grain yield increased with increasing total dry matter accumulation, and significantly positively correlated with dry matter accumulation after heading, total spikelet number, LAI, and spikelet/leaf area ratio. The results suggested that the lower grain yield in Nanjing than in Lijiang was mainly resulted from the lower LAI, total spikelet, dry matter accumulation and CGR after heading.

Biomass↗
PubMed2004

Grouping of tropical mid-altitude maize inbred lines on the basis of yield data and molecular markers.

The classification of maize inbred lines into heterotic groups is an important undertaking in hybrid breeding. The objectives of our research were to: (1) separate selected tropical mid-altitude maize inbred lines into heterotic groups based on grain yield data; (2) assess the genetic relationships among these inbred lines using amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers; (3) examine the consistency between yield-based and marker-based groupings of the inbred lines. Thirty-eight tropical mid-altitude maize inbred lines were crossed to two inbred line testers representing the flint and dent heterotic pattern, respectively. The resulting testcrosses were evaluated in a trial at three locations for 2 years. Significant general combining ability (GCA) and specific combining ability (SCA) effects for grain yield were detected among the inbred lines. The tester inbred lines classified 23 of the 38 tested inbred lines into two heterotic groups based on SCA effects and testcross mean grain yields. This grouping was not related to endosperm type of the inbred lines. The outstanding performance of testcrosses of the remaining 15 inbred lines indicates the presence of significant genetic diversity that may allow the assignment of the lines into more than two heterotic groups. Diversity analysis of the 40 maize inbred lines using AFLP and SSR markers found high levels of genetic diversity among these lines and subdivided them into two main groups with subdivision into sub-groups consistent with breeding history, origin and parentage of the lines. However, heterotic groups formed using yield-based combining ability were different from the groups established on the basis of molecular markers. Considering the diversity of the genetic backgrounds of the mid-altitude inbred lines, the marker-based grouping may serve as the basis to design and carry out combining ability studies in the field to establish clearly defined heterotic groups with a greater genetic similarity within groups.

Altitude↗
PubMed1996

Effects of enhanced O3 and CO2 enrichment on plant characteristics in wheat and corn.

The effects of CO(2) enrichment and O(3) induced stress on wheat (Triticum aestivum L.) and corn (Zea mays L.) were studied in field experiments using open-top chambers to simulate the atmospheric concentrations of these two gases that are predicted to occur during the coming century. The experiments were conducted at Beltsville, MD, during 1991 (wheat and corn) and 1992 (wheat). Crops were grown under charcoal filtered (CF) air or ambient air + 40 nl liter(-1) O(3) (7 h per day, 5 days per week) having ambient CO(2) concentration (350 microl liter(-1) CO(2)) or + 150 microl liter(-1) CO(2) (12 h per day.). Averaged over O(3) treatments, the CO(2)-enriched environment had a positive effect on wheat grain yield (26% in 1991 and 15% in 1992) and dry biomass (15% in 1991 and 9% in 1992). Averaged over CO(2) treatments, high O(3) exposure had a negative impact on wheat grain yield (-15% in 1991 and -11% in 1992) and dry biomass (-11% in 1991 and -9% in 1992). Averaged over CO(2) treatments, high O(3) exposure decreased corn grain yield by 9%. No significant interactive effects were observed for either crop. The results indicated that CO(2) enrichment had a beneficial effect in wheat (C(3) crop) but not in corn (C(4) crop). It is likely that the O(3)-induced stress will be diminished under increased atmospheric CO(2) concentrations; however, maximal benefits in crop production in wheat in response to CO(2) enrichment will not be materialized under concomitant increases in tropospheric O(3) concentration.

Journal Article↗
PubMed1998

Trifolitoxin Production Increases Nodulation Competitiveness of Rhizobium etli CE3 under Agricultural Conditions.

A major barrier to the use of nitrogen-fixing inoculum strains for the enhancement of legume productivity is the inability of commercially available strains to compete with indigenous rhizobia for nodule formation. Despite extensive research on nodulation competitiveness, there are no examples of field efficacy studies of strains that have been genetically improved for nodulation competitiveness. We have shown previously that production of the peptide antibiotic trifolitoxin (TFX) by Rhizobium etli results in significantly increased nodule occupancy values in nonsterile soil in growth chamber experiments (E. A. Robleto, A. J. Scupham, and E. W. Triplett, Mol. Plant-Microbe Interact. 10:228-233, 1997). To determine whether TFX production by Rhizobium etli increases nodulation competitiveness in field-grown plants, seeds of Phaseolus vulgaris were inoculated with mixtures of Rhizobium etli strains at different ratios. The three nearly isogenic inoculum strains used included TFX-producing and non-TFX-producing strains, as well as a TFX-sensitive reference strain. Data was obtained over 2 years for nodule occupancy and over 3 years for assessment of the effect of the TFX production phenotype on grain yield. In comparable mixtures in which the test strain accounted for between 5 and 50% of the inoculum, the TFX-producing strain exhibited at least 20% greater nodule occupancy than the non-TFX-producing strain in both years. The TFX production phenotype had no effect on grain yield over 3 years; the average yields reached 2,400 kg/ha. These results show that addition of the TFX production phenotype significantly increases nodule occupancy under field conditions without adverse effects on grain yield. As we used common inoculation methods in this work, there are no practical barriers to the commercial adoption of the TFX system for agriculture.

Journal Article↗