P Utilization Efficiency Research Articles

Phosphorus absorption and use efficiency by Lotus spp. under water stress conditions in two soils: A pot experiment

The response to P and water deficiencies of forage Lotus species has not been sufficiently studied in the Andisol and Vertisol soil orders in Chile’s marginal areas. A pot experiment under cover was carried out between October 2007 and March 2008 to study the effects of P and soil water availability (SWA) on DM production, P absorption, and P use efficiency in Lotus spp. The experiment included three Lotus ( L. corniculatus L., L. tenuis Waldst. & Kit. ex Willd., and L. uliginosus Schkuhr) species, two soils (Andisol and Vertisol), two contrasting P levels (low and high), and two SWA levels (10% and 100%). A completely randomized design with a 3 × 2 × 2 × 2 factorial arrangement with four replicates was used. Accumulated shoot and root DM, P absorption and efficiency, and arbuscular mycorrhizal (AM) colonization were measured. Phosphorus absorption was significantly higher in Andisol with 100% SWA and high P in the three species, which was reflected in P efficiency where the species exhibited higher P absorption efficiency (PAE) and P utilization efficiency (PUE) with low P, and mean of the three species with low P and high SWA. When the P level was low, L. uliginosus showed the highest PAE and L. corniculatus exhibited the highest PUE. Phosphorus efficiency was also influenced by AM colonization since on the average mycorrhization in the three species was significantly higher in the low P treatments. Differences existed among species for DM production, response to P, P absorption, PAE, and PUE.

Effect of elevated CO<sub>2</sub> and temperature on phosphorus efficiency of wheat grown in an Inceptisol of subtropical India

In a phytotron experiment, wheat was grown under two levels of atmospheric CO<sub>2</sub> [ambient (385 ppm) vs. elevated (650 ppm)], two levels of temperature (ambient vs. ambient +3°C) superimposed with three levels of phosphorus (P) fertilization: 0, 100, and 200% of recommended dose. Various measures of P acquisition and utilization efficiency were estimated at crop maturity. In general, dry matter yields of all plant parts increased under elevated CO<sub>2</sub> (EC) and decreased under elevated temperature (ET); however, under concurrently elevated CO<sub>2</sub> and temperature (ECT), root (+36%) and leaf (+14.7%) dry weight increased while stem (–12.3%) and grain yield (–17.3%) decreased, leading to a non-significant effect on total biomass yield. Similarly, total P uptake increased under EC and decreased under ET, with an overall increase of 17.4% under ECT, signifying higher P requirements by plants grown thereunder. Although recovery efficiency of applied P fertilizer increased by 27%, any possible benefit of this increase was negated by the reduced physiological P efficiency (PPE) and P utilization efficiency (PUtE) under ECT. Overall, there was ~17% decline in P use efficiency (PUE) (i.e. grain yield/applied P) of wheat under ECT.  

Response of Soybean to Phosphorus Fertilization in Brazilian Oxisol

Soybean is an important grain crop for Brazil, and phosphorus (P) plays an important role in improving yield of this crop in Brazilian Oxisols. Data are limited on influence of P sources and rate on soybean yield, yield components, and P-use efficiency. A field experiment was conducted for 3 consecutive years to determine response of soybean to three fertilizers (single superphosphate, Yoorin, and Arad) with 0, 17.5, 35, and 52.5 kg P ha−1 (0, 40, 80 and 120 kg P2O5 ha−1). Grain yield was significantly influenced by phosphorus fertilization. Overall, maximum grain yield was produced by application of single superphosphate, followed by Yoorin and Arad. Number of grains per pod and 100-grain weights were also influenced significantly by P fertilization. Shoot dry weight, number of pods per plant, and grain harvest index had a significant positive association with grain yield. Phosphorus uptake in grain was about six times more than uptake in shoots, and P uptake in grain had a significant positive association with grain yield. Phosphorus-use efficiency (kg grain/kg P applied or uptake) decreased with increasing P rate, and it was greater for single superphosphate than for Yoorin and Arad sources of P fertilization. However, P-utilization efficiency (kg grain plus straw yield / P uptake in grain plus straw) was greater under Yoorin treatment compared to the two other sources of P.

Phosphate utilization efficiency correlates with expression of low-affinity phosphate transporters and noncoding RNA, IPS1, in barley.

Genetic variation in phosphorus (P) efficiency exists among wheat (Triticum aestivum) and barley (Hordeum vulgare) genotypes, but the underlying mechanisms for the variation remain elusive. High- and low-affinity phosphate (Pi) PHT1 transporters play an indispensable role in P acquisition and remobilization. However, little is known about genetic variation in PHT1 gene expression and association with P acquisition efficiency (PAE) and P utilization efficiency (PUE). Here, we present quantitative analyses of transcript levels of high- and low-affinity PHT1 Pi transporters in four barley genotypes differing in PAE. The results showed that there was no clear pattern in the expression of four paralogs of the high-affinity Pi transporter HvPHT1;1 among the four barley genotypes, but the expression of a low-affinity Pi transporter, HvPHT1;6, and its close homolog HvHPT1;3 was correlated with the genotypes differing in PUE. Interestingly, the expression of HvPHT1;6 and HvPHT1;3 was correlated with the expression of HvIPS1 (for P starvation inducible; noncoding RNA) but not with HvIPS2, suggesting that HvIPS1 plays a distinct role in the regulation of the low-affinity Pi transporters. In addition, high PUE was found to be associated with high root-shoot ratios in low-P conditions, indicating that high carbohydrate partitioning into roots occurs simultaneously with high PUE. However, high PUE accompanying high carbon partitioning into roots could result in low PAE. Therefore, the optimization of PUE through the modification of low-affinity Pi transporter expression may assist further improvement of PAE for low-input agriculture systems.

Growth Behavior, Nitrogen-Form Effects on Phosphorus Acquisition, and Phosphorus–Zinc Interactions in Brassica Cultivars under Phosphorus-Stress Environment

Phosphorus (P) and zinc (Zn) interact both in plants and soils and hence may affect the availability and utilization of each other. To investigate P and Zn nutritional status and P–Zn interactions, two genetically diverse Brassica cultivars classified as P tolerant (Brown Raya) and P sensitive (Sultan Raya) were grown in a sand-based pot culture. Jordan rock phosphate (RP) and monocalcium phosphate [Ca(H2PO4)2] were used as P sources, and ammonium nitrate (NH4NO3) or nitrate (NO3 --) only were used as nitrogen (N) sources. Two Zn levels [0.25 (low Zn) and 2.5 (high Zn) mg zinc sulfate (ZnSO4·5H2O) kg−1 sand, respectively] were applied along with recommended doses of other essential nutrients in the culture media. Cultivars differed significantly for their response to added P for biomass accumulation, but Zn supply had little effect. Cultivar Brown Raya had greater P uptake and P-utilization efficiency (PUE) than Sultan Raya under a P-stress environment, irrespective of Zn and N supply. Zinc supply had little effect on tissue P concentration and P uptake per unit of root dry matter (RDM) in either cultivar, irrespective of N supply. An increase in P supply caused a significant reduction in specific Zn uptake (Zn uptake per unit of RDM; SZnU) and tissue Zn concentration of both cultivars. The reduction in tissue Zn concentration cannot be ascribed entirely to a dilution effect. Zinc concentrations and uptake by P-efficient cultivar Brown Raya were significantly lower and more sensitive to P uptake than those of P-sensitive Sultan Raya cultivar. It is suggested that high PUE may depress plant Zn uptake and therefore cause a reduction in Zn concentration of Brassica grown in low-P and possibly low-Zn soils. In NH4NO3 nutrition, plants had significantly lower cation concentrations compared to NO3 -- nutrition only. Brown Raya consistently had lower cation concentrations than Sultan Raya under P stress. The differences in cation concentrations decreased with increased P availability, but Zn supply had no significant effect. In Brown Raya, the ratio of potassium in roots to shoots was always greater than in Sultan Raya. This suggested that lower cation concentrations in Brown Raya were due to root carboxylate exudations, which in turn were related to better P acquisition and PUE under insufficiently buffered P-stress environment.

Mobilization and Acquisition of Sparingly Soluble P‐Sources by Brassica Cultivars under P‐Starved Environment I. Differential Growth Response, P‐Efficiency Characteristics and P‐Remobilization

Phosphorus (P) starvation is highly notorious for limiting plant growth around the globe. To combat P-starvation, plants constantly sense the changes in their environment, and elicit an elegant myriad of plastic responses and rescue strategies to enhance P-solublization and acquisition from bound soil P-forms. Relative growth responses, P-solublization and P-acquisition ability of 14 diverse Brassica cultivars grown with sparingly soluble P-sources (Rock-P (RP) and Ca(3)(PO(4))(2) (TCP)) were evaluated in a solution culture experiment. Cultivars showed considerable genetic diversity in terms of biomass accumulation, concentration and contents of P and Ca in shoots and roots, P-stress factor (PSF) and P use efficiency. Cultivars showed variable P-stress tolerance, and cultivars depicting low PSF and high P-efficiency values were better adaptable to P-starvation. In experiment 2, after initial feeding on optimum nutrition for 12 d after transplanting (DAT), class-I (low P-tolerant (Oscar and Con-II)) and class-II (low P-sensitive (Gold Rush and RL-18)) cultivars were exposed to P-free environment for 25 d. All of the cultivars remobilized P from above ground parts to their roots during growth in P-free environment, the magnitude of which was variable in tested cultivars. P-concentrations ([P]s) at 37 DAT were higher in developing compared with developed leaves. Translocation of absorbed P from metabolically inactive to active sites in P-stressed plants may have helped class-I cultivars to establish a better rooting system, which provided a basis for enhanced P-utilization efficiency (PUE) and tolerance against P-stress. By supplying TCP and RP spatially separated from other nutrients in split root study, class-I cultivars were still able to mobilize RP and TCP more efficiently compared with class-II cultivars. To compare the growth behavior under P-stress, cultivars were grown in pots for 41 d after sowing, using a soil low in P (NaHCO(3)-extractable P = 3.97 mg/kg, Mehlich-III-extractable P = 6.13 mg/kg) with (+P = 60 mg P/kg soil) or without P addition (0P) in study 4. Tested cultivars showed genetic diversity in PUE, P-efficiency (PE), P-efficiency ratio (PER) and PSF. P-stress markedly reduced biomass and plant P contents. Cultivars that produced higher root biomass accumulated higher total P-contents (r= 0.98**), which in turn was related negatively to PSF (r=-0.95**) and positively to shoot and total biomass. PER and PE showed significant correlations with shoot P-contents and biomass. Cultivars depicting high PUE and PE, and low PSF values showed better growth behavior under low soil P-environment. Systematic analysis and deployment of the plant rescue traits underlying the nutrient acquisition, assimilation, utilization and remobilization under P-starvation will bring more sparingly soluble P into cropping systems and will help to scavenge more P from plant unavailable bound P reserves.

Nutritional and management strategies on nitrogen and phosphorus use efficiency of lactating dairy cattle on commercial farms: An environmental perspective

Dairy farm activities contribute to environmental pollution through the surplus N and P that they produce. Optimization of animal feeding and management has been described as a key strategy for decreasing N and P excretion in manure. Sixty-four commercial dairy farms were studied to assess the efficiency of N and P use in lactating herds and to identify dietary and management factors that may contribute to improving the efficiency of nutrient use for milk production, and decrease N and P excretion. The average ration was formulated to 50:50 forage:concentrate ratio with grass silage and corn silage as the main forage sources. Mean N and P intakes were 562 g/d [16.4% crude protein (CP)] and 84.8 g/d (0.40% P), respectively. Milk yield averaged 29.7kg/d and contributed to 25.8% (standard deviation±2.9) of N utilization efficiency (NUE) and 31.9% (standard deviation±4.5) of P utilization efficiency (PUE). Dietary N manipulation through fitting the intake of CP to animal requirements showed a better response in terms of decreasing N excretion (R2=0.70) than that estimated for P nutrition and excretion (R2=0.30). Improvement in NUE helped increase PUE, despite the widespread use of feedstuffs with a high P content. Management strategies for lactating herds, such as the use of different feeding groups, periodical ration reformulation, and selection of feeding system did not show any consistent response in terms of improved NUE and PUE. The optimization of NUE and PUE contributed to decreasing the N and P excretion per unit of milk produced, and therefore, reductions in N and P excretion of between 17 and 35%, respectively, were estimated. Nevertheless, nutritional and herd management strategies were limited when N and P excretion were considered in relation to the whole lactating herd and farmland availability. Dietary CP manipulation was estimated to decrease herd N excretion by 11% per hectare, whereas dietary P manipulation would be decreased by no more than 17%. We conclude that the correct match between the ingested and required N and P, together with an increase in milk productivity, may be feasible strategies for decreasing N and P excretion by lactating herds on commercial farms.

Genetic Variability in Phosphorus Acquisition and Utilization Efficiency from Sparingly Soluble P‐Sources by Brassica Cultivars under P‐Stress Environment

AbstractPlants display an array of classical strategies to maximize phosphate (Pi) acquisition from sparingly soluble P sources. Acclimation to Pi‐stress via elegant Pi‐starvation induced (PSI) adjustments would reduce our current overreliance on expensive, polluting and non‐renewable Pi‐fertilizers. Nevertheless, differences in the ability of various species to solubilize sparingly soluble P‐sources have been often evidenced; inter‐cultivar variations are scarcely documented. Brassica is known as an effective, non‐mycorrhizal user of sparingly soluble P‐sources. Various growth parameters and biomass accumulation by genetically diverse Brassica cultivars were determined in four experiments using hydroponics and quartz sand culture media. Role of PSI root mediated pH changes, organic anions (OAs) exudation and altered root architecture in mobilization and acquisition of sparingly soluble P‐forms [Jordan rock‐P (RP) at 2 g l−1 and Ca3(PO4)2 (TCP) at 0.2 g l−1 respectively] was investigated. Cultivars showed considerable genetic variations in biomass accumulation, various growth parameters and root–shoot ratio. Concentration and total uptake of P, specific absorption rate of P, P‐transport rate and P‐utilization efficiency (PUE) were also significantly (P < 0.001) different for various cultivars and their dry matter was significantly correlated with P‐uptake [r = 0.94** (significant at 1% level)]. P‐tolerant cultivars showed substantial decrease in solution media pH because of H+ efflux and exuded more carboxylates than low P‐sensitive cultivars under P‐starvation. P‐uptake by cultivars increased linearly with decreasing pH. The amount and types of OAs exuded from the roots of P‐starved plants differed from those of plants grown under P‐sufficient environment. In split pot study, with TCP and RP supplied spatially separated from other nutrients, efficient cultivars were still able to mobilize RP and TCP more efficiently than inefficient cultivars. In rhizobox study, the elongation rates of primary roots decreased but the elongation rates of the branched zones of primary roots and the length of lateral roots increased under P‐starvation. Tested cultivars showed genetic diversity in accessing, mobilization, acquisition and utilization of Pi from sparingly soluble P forms. An arrange marriage of plant traits can explain cultivar’s access to different forms of sparingly soluble P, and in addition to altered lateral root topology and enhanced P‐uptake and PUE, enhanced H+ efflux and OAs exudation are key factors in Pi scavenging from extra cellular sparingly soluble P‐forms.

Intraspecific Variations of Phosphorus Absorption and Remobilization, P Forms, and Their Internal Buffering in Brassica Cultivars Exposed to a P‐Stressed Environment

Translocation of absorbed phosphorus (P) from metabolically inactive sites to active sites in plants growing under P deprivation may increase its P utilization efficiency (PUE). Acclimation to phosphate (Pi) starvation may be caused by a differential storage pool of vacuolar P, its release, and the intensity of re-translocation of absorbed P as P starvation inducible environmental cues (PSIEC) from ambient environment. Biomass assay and three P forms, namely inorganic (Pi), organic (Po), and acid-soluble total (Ptas) were estimated in Brassica cultivars exposed to 10 d P deprivation in the culture media. Considering that -delta Pi/delta t denotes the rate of Pi release, Pi release velocity (RSPi) was determined as the tangent to the equations obtained for Pi f(t) at the mean point in the period of greatest Pi decrease, whereas the inverse of the RSPi was an estimate of the internal Pi buffering capacity (IBCPi). Inter cultivar variations in size of the non-metabolic Pi pool, RSPi, re-translocation of Pi from less to more active metabolic sites, and preferential Pi source and sink compartments were evaluated under P starvation. The cultivar 'Brown Raya' showed the highest Pi storage ability under adequate external P supply, and a more intensive release than 'Rain Bow' and 'Dunkled' under P stress. Cultivar 'B.S.A' was inferior to 'Con-1' in its ability to store and use Pi. Roots and upper leaves were the main sink of Pi stored in the lower and middle leaves of all cultivars and showed lower IBCPi and larger RSPi values than lower and middle leaves. In another trial, six cultivars were exposed to P-free nutrition for 29 d after initial feeding on optimum nutrition for 15 d. With variable magnitude, all of the cultivars re-translocated P from the above ground parts to their roots under P starvation, and [P] at 44 d after transplanting was higher in developing leaves compared with developed leaves. Under P deprivation, translocation of absorbed P from metabolically inactive to active sites may have helped the tolerant cultivars to establish a better rooting system, which provided a basis for tolerance against P starvation and increased PUE. A better understanding of the extent to which changes in the flux of P absorption and re-translocation under PSIEC will help to scavenge Pi from bound P reserves and will bring more sparingly soluble P into cropping systems and obtain capitalization of P reserves.

Genetic diversity of Brassica cultivars in relation to phosphorus uptake and utilization efficiency under P-stress environment

Phosphorus (P) plays a central role in plant cell metabolism. Therefore, low P availability is one of the major constraints for plant productivity in natural and agricultural ecosystems. The addition of phospahtic fertilizers is economically not feasible for resource-poor farmers as the efficiency of added P fertilizers is often low. Plants have evolved a myriad of adaptive mechanisms to increase P uptake and P-utilization efficiency (PUE). Plant efficiency for P uptake and PUE may contribute to improve crop-yield potential in resource-poor environments and selection of P-efficient cultivars can enhance productivity on low fertility soils and reduce fertilizer requirements. A controlled-climate chamber was used to investigate the performance of 14 hydroponically grown Brassica cultivars. Cultivars differed significantly in biomass accumulation (shoot and root dry matter), root-shoot ratio, P concentrations and contents in plant parts, relative reduction in biomass accumulation due to P stress or P-stress factor (PSF) and PUE indicating considerable diversity among the tested cultivars. PUE and the proportional increases in shoot dry matter (SDM) production (SDMmax/SDMmin) in response to the P levels assisted in differentiating plants into efficient and inefficient utilizers of the absorbed P. Cultivars were classified into efficient responsive (ER), efficient non-responsive (ENR), non-efficient responsive (NER) and non-efficient non-responsive (NENR). Efficient cultivars showed the lowest shoot P concentrations and PSF, and the highest biomass accumulation and PUE.

Path and Correlation Analyses of the Factors affecting Biomass Production of Brassica Cultivars under Phosphorus‐Deficiency Stress Environment

Path analysis is a statistical technique that partitions correlations into direct and indirect effects and distinguishes between correlation and causation, whereas correlation in general measures the extent and direction (positive or negative) of a relationship occurring between two or more variables. The estimates of correlation and path coefficients can help us to understand the role and relative contribution of various plant traits in establishing growth behavior of crop cultivars under given environmental conditions. Dependence of shoot dry‐matter (SDM) production of six hydroponically grown Brassica cultivars on various growth parameters and characteristics of P metabolism was investigated using the modified Johnson's nutrient solution to maintain deficient (10 µM) and adequate (200 µM) P levels. Root dry‐matter (RDM), total dry‐matter, P content in shoot, and P‐utilization efficiency (PUE) had significant and positive effects on production of SDM in a P‐deficient environment. Root–shoot ratio (RSR), however, negatively affected SDM of cultivars exposed to P‐deficient conditions and did not show any impact on SDM production in either of the two treatments. In a pot study, six Brassica cultivars were grown in a sandy loam soil that was deficient in NaHCO3‐extractable P (3.9 mg P kg−1 soil) for 49 days. Significant positive correlations were observed between SDM and some other plant traits such as RDM, leaf area per plant, P uptake, and PUE, at both genotypic and phenotypic levels. The correlations of SDM with RSR, however, were not observed, implying that relative partitioning of biomass into roots or shoots had little role to play in SDM production by Brassica cultivars under P‐deficiency stress. Path analysis revealed that favorable impact of RDM and leaf area on SDM production was indirect through positive effect of these parameters on P uptake and PUE. Thus, under P‐deficiency stress, better P acquisition and efficient P utilization by the cultivars for biomass synthesis collectively formed the basis of higher SDM production by the cultivars, evidencing that P uptake and utilization efficiency are two important plant traits for selecting P‐deficiency‐stress‐tolerant Brassica cultivars.

Relative Phosphorus Utilization Efficiency, Growth Response, and Phosphorus Uptake Kinetics of Brassica Cultivars under a Phosphorus Stress Environment

Plants grown in highly weathered or highly alkaline calcareous soils often experience phosphorus (P) stress but never a P‐free environment. Thus, applications of mineral P fertilizers are often required to achieve maximum yield, but recovery of applied P fertilizers is notoriously low. Phosphorus deprivation elicits a complex array of morphological, physiological, and biochemical adaptations among plant species and genotypes to enhance P acquisition and utilization efficiency. Ten Brassica cultivars were grown hydroponically to investigate their relative efficiency to utilize deficiently (20‐µM) and adequately (200‐µM) supplied P, using Johnson's modified solution. Cultivars differed significantly (P<0.001) in biomass accumulation. Orthophosphate concentration and uptake in shoot and root, absolute and relative growth rate, and P‐utilization efficiency (PUE) were also significantly different among various Brassica cultivars. Root‐shoot ratio and specific absorption rate were substantially increased in plants subjected to low P supply. Shoot and root dry‐matter yield as well as total biomass production correlated significantly (P<0.01) with their total P uptake and PUE. Cultivars, which were efficient in P utilization, were also efficient accumulators of biomass under adequate as well as deficient levels of P supply. As part of the study, kinetic parameters of P uptake were evaluated for six contrasting Brassica cultivars in PUE, grown in nutrient solution. The kinetic parameters related to P influx were maximal transport rate (Vmax), the Michaelis–Menten constant (Km), and the external concentration when net uptake is zero (Cmin). Lower Km and Cmin values were indicative of P‐uptake ability of the cultivars, evidencing their adaptability to P‐stress conditions. In another experiment, six cultivars were exposed to no P nutrition for 27 days after initial feeding on optimum nutrition for 14 days. All the cultivars retranslocated P from aboveground parts to their roots during growth in P‐free conditions, the magnitude of which was variable in different cultivars. Phosphorus concentration at 41 days after transplanting was higher in developing leaves than developed leaves. Translocation of absorbed P from metabolically inactive sites to active sites in plants growing under P‐stress conditions may have helped the tolerant cultivars to establish a better rooting system, which provided basis for tolerance against P‐deficiency stress and increased PUE.

Phosphorus starvation induced root-mediated pH changes in solublization and acquisition of sparingly soluble P sources and organic acids exudation by Brassica cultivars

Plant species and cultivars elicit a diverse array of sophisticated metabolic and developmental strategies to enhance phosphorus (P) solublization and acquisition from P-deficient rooting media. Scavenging of phosphate (Pi) from extracellular sparingly soluble P sources may be aided by organic acids (OAs) exudation and root-mediated pH changes under a P-stress environment. Root exudates were collected to quantify short-term (4 h, 8 h) carboxylate exudation using hydroponically grown Brassica cultivars. Malic and citric acids were the dominant OAs and efficient cultivars exuded 2–3-fold more OAs than inefficient cultivars under P-deficient conditions. However, the exudation rate of both resistant and sensitive cultivars decreased with time. Experiments in nutrient solution were conducted to evaluate growth responses and the P solublization and acquisition ability of six genetically diverse Brassica cultivars. Pre-germinated seedlings were grown in nutrient solution containing ammonium di-hydrogen phosphate (AP), tri-calcium phosphate (TCP) and rock phosphate (RP) (TCP at 0.2 g L−1 and RP at 2 g L−1, in a bid to maintain deficiently buffered solution-P concentration) as different P sources. The cultivars exhibited substantial growth differences (P < 0.001) in terms of biomass accumulation, P acquisition and P utilization efficiency (PUE). Biomass production correlated significantly (P < 0.01) with their shoot P uptake and PUE at both P sources, indicating that cultivars efficient in P solublization accumulated more biomass. Higher P uptake by all cultivars was significantly related to the drop in root medium pH, which was presumably owing to H+ efflux from the roots supplied with TCP and RP. Higher shoot dry matter of the cultivars at TCP was related to better P acquisition ability, which in turn was related to higher Ca uptake. Thus, cultivars with efficient Ca accumulation ability can acquire higher amounts of P from P-deficient soils and can adapt well to such low-P soil conditions.

Phosphorus and Micronutrient Nutrition of Chickpea Genotypes in a Multi-Nutrient-Deficient Typic Ustochrept

ABSTRACT The chickpea breeding program in India has not yet considered the genotypic variation in phosphorus (P) efficiency, despite the fact that the largest proportion of chickpea-growing soils are P deficient. Since general P application to chickpea is at sub-optimum levels, efficient P-utilizing genotypes will perform better than others under P-deficient conditions. High levels of P application may induce zinc (Zn) deficiency in plants grown on Zn-deficient soils. Twenty chickpea genotypes were evaluated for their P efficiency at varied levels of added P, and the effect of P levels on Zn, iron (Fe), copper (Cu), and manganese (Mn) nutrition was studied in pot-culture experiments. Three criteria were used for evaluating P efficiency; shoot dry-matter yield without P, P-uptake efficiency (PUPE), and P-utilization efficiency (PUSE). Under P-deficiency conditions (control), the genotypes BG-256, HK-94-134, Phule-G-5, and Vikash produced the highest shoot biomass. However, genotypes that were found to be superior in the absence of P did not perform in a similar way under optimum P supply. Root dry weight showed a highly significant correlation with P uptake at all P levels. In the case of PUPE, genotypes KPG-59 and Pusa-209 were found to be superior to others. With increasing P levels, PUSE declined in all the genotypes. Increasing P up to 13.5 mg kg−1 soil increased Zn concentration, while further increase led to decreased concentration. Genotypes KPG-59, BG-256, RSG-888, and JG-315 showed Zn concentrations below the critical limit of 20 μg Zn g−1 dry weight (DW) at the high level of P application (27.0 mg kg−1). Iron concentration decreased with increasing P levels. Up to 13.5 mg kg−1 P application, Cu concentration increased and thereafter decreased. Manganese concentration gradually increased with the increasing P levels studied. Based on three criteria, BG-256 can be recommended for use in P-deficient conditions and can be good germplasm source material for chickpea-breeding programs for evolving P-efficient genotypes. Results also suggest that when selecting P-efficient genotypes of chickpea, it is essential to apply deficient micronutrients.

Mapping QTLs for Phosphorus-Deficiency Tolerance at Wheat Seedling Stage

Soil phosphorus (P) deficiency is one of the major limiting factors to crop production throughout the world. It is an important strategy to breed varieties with improved P-deficiency tolerance for sustainable agriculture. The objective of this study was to map QTLs for P-deficiency tolerance in wheat, and develop molecular marker assisted selection in breeding wheat with improved P-deficiency tolerance. A doubled haploid (DH) population, consisting of 92 DH lines (DHLs) derived from P-deficiency tolerant wheat variety Lovrin 10 and P-deficiency sensitive variety Chinese Spring, was developed for mapping QTLs for P-deficiency tolerance. A genetic linkage map consisting of 34 linkage groups was constructed using 253 SSR markers. Shoot dry weight (SDW), tiller number (TN), shoot P uptake (SPU), and shoot P utilization efficiency (PUE) were investigated at seedling stage under P deficiency (−P) and sufficiency (+P) condition in two pot trials in 2002 and 2003, respectively. All traits segregated continuously in the population under either −P or +P condition. Significant positive correlations were found in between TN, SDW and SPU, whereas significant negative correlations were observed between PUE and SPU and between PUE and TN. Twenty and 19 QTLs were detected under −P and +P condition, respectively. The 39 QTLs were distributed on 21 chromosomal regions. There were three clusters of QTLs, which were associated with Xgwm25l (on chromosomes 4B), Xgwm271.2 (on chromosome 5A), and Xgwm121 (on chromosome 5D), respectively. Compared to the DHLs with all Chinese Spring alleles at the three loci, those with all Lovrin 10 alleles had, on average, much higher SPU, SDW and TN under −P condition in both trials, suggesting the importance of the three loci in controlling P-deficiency tolerance. It was interesting to find that two of the above three loci were closely linked with vernalization requirement genes VRN-A1 (on chromosome 5A) and VRN-D1 (on chromosome 5D). Potential implication of the linkage between P-deficiency tolerance and VRN genes was discussed.

Impact of Arbuscular-Mycorrhizal Fungi on Phosphorus Efficiency of Wheat, Rye, and Triticale

ABSTRACT Genotypic variation and mycorrhiza play an important role in plant uptake of phosphorus (P). A pot experiment was conducted with three cereals, wheat (Triticum aestivum L. cv. PBW-34), rye (Secale cereale L. cv. R-308), and triticale (Triticale octoploide L. cv. DT-46), a hybrid of wheat and rye, to examine the genetic variation in the degree of arbuscular-mycorrhizal (AM) infection and its inheritability from parents (wheat and rye) to their progeny (triticale). The soil used for pot culture was low in available P (7.8 mg P kg−1soil). Inoculation with AM fungi showed a significant increase in extent of root colonization for all three cereals (average 70%) compared with their performance without AM (average 19.1%). However, among the three cereals, this increase was significantly greater in rye than in the other two crops, while wheat and triticale did not differ significantly. Mycorrhizal infection resulted in 1.6, 1.7, and 1.8-fold increases in shoot, root, and total plant dry matter, respectively, compared with the un-inoculated treatment. Among the three cereals, rye recorded maximum shoot, root, and total plant dry mass and P content with AM inoculation. The P uptake by wheat, rye, and triticale was 10%, 64%, and 35%, respectively, higher with rather than without mycorrhizal infection. Rye was most responsive to AM inoculation, with mycorrhizal dependency of 193%; here again, triticale followed wheat, with similar mycorrhizal dependency. Rye showed an increase in P utilization efficiency (PUE) without AM inoculation while the PUE of triticale was intermediate between wheat and rye. High efficiency of AM symbiosis in terms of P uptake exists in rye and most of these traits in triticale seem to be inherited from wheat rather than rye.

Screening Chinese Wheat Germplasm for Phosphorus Efficiency in Calcareous Soils

Twenty commonly used winter wheat genotypes collected throughout China were used in field screening for phosphorus (P)-efficient germplasm in a calcareous soil with and without fertilizer P application; the same genotypes were also evaluated for high and low P inputs in a greenhouse experiment. The overall criterion for P efficiency was the capacity to produce a relatively high yield with low P availability. Significant differences in grain yield production occurred between efficient and inefficient genotypes. Four parameters were calculated to determine which was the most useful for describing P efficiency: (1) percentage of relative yield with no applied P; (2) total P uptake; (3) P-harvest index (PHI: grain P/total P uptake); and (4) P-utilization efficiency (PUE: grain yield produced per unit of P taken up). A simple but satisfactory criterion in screening P-efficient wheat genotypes, 85% of relative grain yield at low P/high P, was recommended and proved to be more effective than the other three parameters. With this criterion, 12 out of 20 genotypes were classified as P-efficient (≤ 15% yield reduction with no P applied) from both field and pot experiments. Phosphorus efficiency may have resulted from either P uptake or P-utilization efficiency. Three parameters, namely relative yield without applied P, PHI and PUE, were found to be useful, together with P uptake, in determining overall P efficiency. Successful selection for P efficiency was found to be possible at the shooting stage (but not at tillering) by comparing P uptake and P-utilization efficiency of plants at this growth stage with those of plants at maturity.

Genotypic variability of pigeonpea in distribution of photosynthetic carbon at low phosphorus level

Pigeonpea ( Cajanus cajan L. Millsp.) is an important grain protein crop, which thrives in the P-deficient soils of tropical and subtropical Asia. The varietal differences in soil phosphorus uptake and partitioning of the crop are well documented, but the mechanism of carbon distribution between the source and sink at low P supply is not understood. In the present study, the effect of a low P supply on the distribution of photosynthetic carbon of one high-yielding improved hybrid cultivar, ICPH 8 and two low-yielding non-hybrid cultivars, ICPL 87 and UPAS 120, were compared by feeding the plants 13 CO 2 at the vegetative and reproductive stages of development. A low P supply significantly decreased plant biomass, P uptake, average leaf area and photosynthetic activity of all genotypes; the decrease was smallest in ICPH 8 and largest in UPAS 120. ICPH 8 retained more plant biomass at low P supply due to higher P-absorption capacity rather than high P-utilization efficiency. The tolerance of ICPH 8 to low P is mostly related to its maintenance of a high leaf area and rate of photosynthesis. In contrast, P deficiency severely reduced leaf initiation of the sensitive cultivar UPAS 120, and reduced its photosynthesis. Under limiting P supply, partitioning of 13 C increased in favor of the roots in all cultivars, but the resistant cultivar ICPH 8 partitioned less 13 C to roots, and invested more in shoot growth compared to the non-hybrid cultivars. Similarly, partitioning of 13 C to the raceme was greater in ICPL 87 than in the highly sensitive UPAS 120. It is concluded that P deficiency affects primarily sink activity by restricting cellulose biosynthesis in the meristematic sink cells.

Influence of native endomycorrhiza, soil flooding and nurse plant on mycorrhizal status and growth of purple nutsedge ( Cyperus rotundus L.)

A study was made to investigate the effects of native endomycorrhizal fungi, soil flooding and nurse plant (onion) on the mycorrhizal status, growth and phosphorus (P) uptake of purple nutsedge ( Cyperus rotundus L.). Above ground (AG) and below ground (BG) dry weight of mycorrhizal purple nutsedge plants were significantly lower than the non-mycorrhizal plants, but ratios of BG:AG dry weight were the same except when grown with onion. Mycorrhizal infection was characterized by vesicles and hyphae, both intraradical and extramatrical, but lacked arbuscules. Percentage root colonization of purple nutsedge and onion was significantly higher when the two grew together, but plants growing alone had less infection. Flooding of soil inhibited mycorrhizal formation in purple nutsedge, and mycorrhizal infected plants produced smaller tubers than uninfected plants. AG tissue P concentration was lower in mycorrhizal purple nutsedge but BG P concentration had no significant variations between infected and uninfected plants. P utilization efficiency (PUE) was similar for mycorrhizal and non-mycorrhizal purple nutsedge. Plants in flooded soil had the maximum AG and BG dry weights, tuber dry weight and P content, but had lower AG:BG dry weight ratio and PUE.

Rate variables associated with P uptake, utilization and growth of mycorrhizal and nonmycorrhizalLeucaena leucocephala1

Abstract A sequential harvest experiment was conducted in the greenhouse to determine relative growth rate (RGR), specific absorption rate (SAR) of P, P utilization rate (PUR) and P utilization efficiency (PUE) of vesicular‐arbuscular mycorrhizal (VAM) and nonmycorrhizal Leucaena leucocephala. Total P content, root length and total dry‐matter yield of mycorrhizal plants were significantly higher than those of nonmycorrhizal plants beginning on 15, 25 and 25 days after planting, respectively. The length of root colonized by Glomus aggregatum increased exponentially with time and leveled off 30 days after planting. In mycorrhizal plants, RGR of roots (based on total root length) was lower than those of RGR of infected roots till 30 days after planting, after which time the trend was reversed. Although, RGR based on dry‐matter yield was higher in mycorrhizal plants than in nonmycorrhizal plants, the differences observed were not statistically significant. SAR of P was higher in mycorrhizal plants than in non...