EXPLOITATION OF GENETIC VARIABILITY AMONG WHEAT GENOTYPES FOR TOLERANCE TO PHOSPHORUS DEFICIENCY STRESS

Forty six wheat genotypes from different origins were tested at stress (25 μM P) and adequate (250 μM P) levels of phosphorus (P) developed in a modified Johnson's nutrient solution. Response of wheat genotypes for tolerance to P deficiency stress was measured at two growth stages in terms of growth, P uptake, and P utilization efficiency. Substantial differences in shoot and root growth were observed among genotypes at both stress and adequate P levels in the growth medium. Reduction in shoot biomass due to P deficiency varied from >50% to 27%. Similarly P concentration in shoot and root, P uptake, specific absorption rate of P, and P utilization efficiency varied significantly at both levels of applied P. A significant negative correlation between P stress factor and root dry weight (r = ?0.396**), shoot P uptake (r = ?0.451**), and specific absorption rate of P (r = ?0.281**, P < 0.01) suggested that the genotypes with greater root biomass, higher P uptake potentials in shoots, and absorption rate of P were generally more tolerant to P deficiency in the growth medium. Wheat genotypes were grouped according to the ranking order of investigated plant characteristics and shoot dry matter yield per unit of P absorbed. Genotypes Inqlab-91, SARC-II, SARC-IV, Chakwal-86, 90627, 89626, and Parvaz-94 were P efficient, while genotypes Pak-81, Pato, 88042, 88163, 89295, 4072, 89313, and 91109 were P inefficient. All other genotypes were intermediate in P use efficiency.     

Differential Growth Performance of 15 Wheat Genotypes for Grain Yield and Phosphorus Uptake on a Low Phosphorus Soil Without and With Applied Phosphorus Fertilizer

ABSTRACT

Two field experiments were conducted to compare 15 wheat genotypes at two phosphorus (P) levels (zero-P control or low P level—without application of P fertilizer on soil with 8 mg extractable P kg^?1, and adequate P level—with P fertilizer applied at 52 kg P ha^?1) for yield, P uptake, and P utilization efficiency (P efficiency ratio—PER, P harvest index—PHI, and P physiological efficiency index—PPEI). On the average of two experiments, substantial and significant differences were observed among wheat genotypes for both grain and straw yields at both P levels. Grain yields ranged from 2636 to 4455 kg ha^?1 in the zero-P control, and from 2915 to 4753 kg ha^?1 at adequate P level. Genotype 5039 produced the maximum grain yield, while 6529-11 had the minimum grain yield at both P levels. Relative reduction in grain yield due to P deficiency stress (PSF) ranged from none to 32%, indicating differential P requirements of genotypes. Genotypes 4943, Pasban 90, Inqlab 91, PB 85, Lu 26s, 4770, Chakwal 86, 4072, 6544-6, and 5039 had little or no response to P application. Phosphorus responsive genotypes included FSD 83, Kohinoor 83, Parvaz-94, Pak 81, and 6529-11. A non-significant correlation (r = ?0.466, P > 0.05) between grain and PSF in zero-P control treatment also indicated the least effect of P deficiency on some wheat genotypes. A wide range of PPEI (270–380 kg grain kg^?1 P absorbed in grain + straw at control P level, and 210–330 kg grain kg^?1 P absorbed in grain + straw at adequate P level) indicated differential utilization of absorbed P by the genotypes for grain production. This indicated that wheat genotypes differed considerably in their P requirement for growth and responsiveness to P application. The findings also suggested that PPEI was a better parameter for measuring P efficiency than other parameters, and can be used for selecting P efficient genotypes, because it relates to the internal concentration of a nutrient and genetic makeup of plant. It is concluded that genotypes having ability to produce relatively high grain yield, good command to tune P within plant and high PPEI are suited to low P soil conditions. Genotypes 4072, Inqlab 91, 4943, Pak 81 and 5039 were P efficient and had above mentioned abilities, while genotypes FSD 83, 6544-6, and 6529-11 were P inefficient. It should be noted that traits related to P efficiency are inheritable and can be used to improve P use efficiency of a genotype through back cross breeding programs.     

Variation in Yield,Phosphorus Uptake,and Physiological Efficiency of Wheat Genotypes at Adequate and Stress Phosphorus Levels in Soil

Genetic differences among crop genotypes can be exploited for identification of genotypes more suited to a low‐input agricultural system. Twenty wheat (Triticum aestivum L.) genotypes were evaluated for their differential yield response, phosphorus (P) uptake in grain and straw, and P‐use efficiency at the zero‐P control and 52 kg P ha^?1 rates. Substantial and significant differences were obvious among genotypes for both grain and straw yields at stress (8 mg P kg^?1 soil, native soil P, no P addition) and adequate (52 kg P ha^?1) P levels. Genotype 5039 produced maximum grain yield at both P levels. Relative reduction in grain yield due to P‐deficiency stress [i.e., P stress factor (PSF)] ranged between none and 32.4%, indicating differential P requirement of these genotypes. Pasban 90, Pitic 62, Rohtas 90, Punjab 85, and line 4943 did not respond to P application and exhibited high relative yield compared to those at adequate P level. FSD 83 exhibited the best response to P with maximum value for PSF (32.4%). Genotypes were distributed into nine groups on the basis of relationship between grain yield and total P uptake. Rohtas 90 and lines 4072 and 5039 exhibited high grain yield and medium P uptake (HGY‐MP). However, line 5039 with high total index score utilized less P (12.2 kg P ha^?1) than line 4072 and Rohtas 90 (13.5 and 13.6 kg P ha^?1, respectively). Moreover, this genotype also had greater P harvest index (PHI, %) and P physiological efficiency index (PPEI) at stress P level. Pasban 90, Pitic 62, and Pak 81 had the greatest total index score (21), mainly due to high total P uptake, but yielded less grain than lines 5039 and 4072 under low available P conditions. Line 6142 had minimum total index score (15) and also produced minimum grain yield. A wide range of significant differences in PPEI (211 to 365 kg grain kg^?1 P absorbed at stress and 206 to 325 kg grain kg^?1 P absorbed by aboveground plant material at adequate P) indicated differential utilization of absorbed P by these genotypes for grain production at both P levels. It is concluded from the results that wheat genotypes differed considerably in terms of their P requirements for growth and response to P application. The findings suggest that PSF, PHI, and PPEI parameters could be useful to determine P‐deficiency stress tolerance in wheat.     

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

Abstract

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.     

Selection Criteria for Genotypes and Identification of Plant Characteristics for Phosphorus-Efficient Wheat

Most genetic analyses of wheat crops concentrate on elucidating the mode of inheritance of plant characteristics. However, it is equally important to study the genetic relationship between different characteristics so that the consequences of selection for one characteristic on the performance of another can be predicted. Three field experiments with 15 wheat genotypes were conducted at two sites with similar soil types and agroecological conditions (two experiments at site 1 and one experiment at site 2) to evaluate wheat genotypes through correlation and path analyses for identification of plant characteristics responsible for high grain yield at low phosphorus (P) (7.86–8.23 mg P kg^?1 soil; control, no application of P) and adequate P (52 kg P ha^?1) in soil. On the average of the three experiments, the genotypic and phenotypic coefficients in correlation analysis agreed closely in each case. Relatively high values of genotypic coefficient showed a masking influence of genetic factors in the grain production. Grain yield correlated significantly with P-uptake parameters, such as P uptake in grain and straw. Integration of P in grain formation varied among wheat genotypes because of differences in their abilities to absorb, translocate, distribute, accumulate, and utilize P. The integrated effect of these physiological processes appeared in the form of end product (i.e., grain). The yield potential of a genotype to produce grain can be measured directly from absolute grain yield, but when selection was made through the involvement of plant factors such as harvest index, it proved to be a good predictor of grain yield. Positive relationship of harvest index with grain yield indicated an increase in grain yield. Because grain production is an outcome of the integrated effect of many P-related physiological processes, P efficiency was measured by P harvest index, P efficiency ratio, and P physiological efficiency index. The P physiological efficiency index was found to be an appropriate measure of P-use efficiency. When the selection was made through path analysis, it was observed that the genotypes that had high harvest index, absorbed more P, accumulated more P in grain, and produced more grain per unit of absorbed P were efficient in P use and produced high grain yield under low available soil P field conditions. Wheat genotypes ‘Inqlab 91,’ ‘Pak 81,’ ‘4072,’ ‘4943,’ and ‘5039’ were capable of producing high grain yield under low soil P field conditions in this study.     

Identification of Phosphorous Efficient Germplasm in Oilseed Rape

ABSTRACT

Plant species and genotypes within one species may significantly differ in phosphorus (P) uptake and utilization when they suffer from P starvation. The objective of this research was to screen P-efficient germplasm of oilseed rape (Brassica napus L.) and analyze the possible mechanism responsible for P efficiency by two-steps screening experiments and validation of P efficiency. Phosphorus efficiency coefficient at seedling stage, namely, ratio of shoot dry weight under low P to that under adequate P (PECS) of 194 oilseed rape cultivars varied from 0.050 to 0.62 and was significantly related with shoot dry weight under low P level (r = 0.859??, P < 0.01). Oilseed rape cultivar ‘Eyou Changjia’ presented the highest P efficiency coefficient in each growth stage and had the highest seed yield at low P, whereas oilseed rape cultivar ‘B104-2’ was the most sensitive to low P stress among the 12 candidate cultivars obtained from the two-steps screening experiments. Under low P condition in validation experiments of soil and solution cultures, ‘Eyou Changjia’ could produce much more dry matter and acquire more P than ‘B104-2.’ Moreover, P efficient coefficient obtained from the pot experiment was comparable to those from the field experiment. This might be attributed to high P uptake efficiency for ‘Eyou Changjia’ when it suffered from low-P stress. Comparison of results from the hydroponics with those from the pot and field experiments led to the conclusion that the P uptake efficiency in the hydroponics is highly related to that in soil culture conditions. These results show that there are large genotypic differences in response to phosphorus deficiency in oilseed rape germplasm (Brassica napus L.) and ‘Eyou Changjia’ is P-efficient and ‘B104-2’ is P-inefficient. By comparing these results further, the mechanism responsible for P efficiency was suggested to be mainly due to high P uptake efficiency by forming larger root system, and improving the ability of mobilizing and acquiring soil P in P-efficient oilseed rape under the condition of P starvation.     

Genetic Variations of Brassica Cultivars for P Acquisition in a P Stress Environment and Comparison of P Sources for Sustainable Crop Management

To compare the growth performance of Brassica in a phosphorus (P) stress environment and response to added P, six Brassica cultivars were grown in pots for 49 days after sowing, using a soil low in P [sodium bicarbonate (NaHCO₃)–extractable P = 3.97 mg kg^?1, Mehlich III–extractable P = 6.13 mg kg^?1] with (+P = 60 mg P kg^?1 soil) or without P addition (0P). Phosphorus‐stress markedly reduced biomass accumulation and P uptake by roots and shoots. However, root–shoot ratio remained unaffected, implying that relative partitioning of biomass into roots and shoots had little role to play in shoot dry matter (SDM) production by cultivars. Biomass correlated significantly (P < 0.01) with total P uptake. Under P stress, the cultivars that produced greater root biomass were able to accumulate more total P content (r = 0.95^**), which in turn was related positively to SDM and total biomass (r > 0.89^**) and negatively to P‐stress factor (r = ?0.91^**). There was no correlation between P efficiency (PE) (relative shoot growth) and plant P, but PE showed a very significant correlation with shoot P content and SDM. Wide differences in growth and better performance of cultivars such as ‘Brown Raya’ and ‘Con‐1’ under P stress encouraged screening of more germplasm, especially in the field, to identify P‐tolerant cultivars.

In another study, potential relative agronomic effectiveness (RAE) of sparingly soluble P sources was investigated by growing two contrasting cultivars. The P sources incorporated into soil at 0, 10, 25, 50, and 100 mg P Kg^?1 were (i) powdered Jordan rock P (RP), (ii) triple superphosphate (TSP), (iii) powdered low‐grade TSP [TSP(PLG)], (iv) a mixture of RP + TSP compacted into pellets at 50:50 P ratio [RP + TSP(PelC)], and (v) a mixture of powdered RP + TSP at 50:50 P ratio [RP + TSP(PM)]. The RP was low in RAE and only 5 and 29% as effective as TSP in producing dry matter (DM) of P‐sensitive ‘B.S.A.’ and P‐tolerant ‘Brown Raya’ cultivars, respectively. There were no significant differences between TSP and RP + TSP(PelC) in DM yield of ‘Brown Raya,’ whereas, in the case of ‘B.S.A.’ RP + TSP(PM) was significantly less effective than RP + TSP(PelC) compared with TSP. Combined utilization of superior genome and P sources [such as TSP(PLG) and RP + TSP(PelC)] produced from low‐grade RP (that cannot be used either for direct application or acidulated P fertilizers) can be used as an alternative strategy for sustainable crop production, especially in resource‐poor environments. Further field trials at the level of cropping systems are needed.     

Differences in Root Exudation Among Phosphorus‐Starved Genotypes of Maize and Green Gram and Its Relationship with Phosphorus Uptake

Abstract

Availability of phosphorus (P) in soil and its acquisition by plants is affected by the release of high and low molecular weight root exudates. A study was carried out to ascertain the qualitative and quantitative differences in root exudation among the genotypes of maize (Zea mays L.) and green gram (Vigna radiata L.) under P‐stress. Results showed that both inter‐ and intra‐species differences do exist among maize and green gram in terms of root exudation, P uptake, and shoot and root P content. In general, green gram, a legume crop, had greater root exudation compared to maize. However, the amino acid content of the total root exudates in maize was two‐fold as compared to green gram. The maize and green gram genotypes possessed genetic variability in root exudation. Irrespective of the species or genotypes, a positive relationship was found among P uptake rates, total root exudation, and shoot and root ³²P content. The amount of sugars and amino acid present in the root exudates of P‐starved seedlings also add to the variation in P uptake efficiency of genotypes.     

Nitrogen Use Efficiency in Cacao Genotypes

Cacao (Theobroma cacao L) is mostly grown on soils with low natural fertility. On such soils nitrogen (N) is one of the most yield limiting nutrients for cacao. Information is lacking on N use efficiency in cacao. A greenhouse experiment was conducted to evaluate growth response and N use efficiency by two cacao genotypes. The genotypes used were TSH-565 and ICS-9 and N rates adapted were 0, 120, 240, 360, and 480 mg N /pot. In both genotypes, increasing levels of applied N improved growth (stem girth, dry weight of shoot and roots and shoot/root ratio), and concentration and uptake of N. Genotypes differed significantly for stem girth and ICS -9 produced greater stem girth compared with TSH-565. Nitrogen uptake had a linear relationship with root dry weight of the two genotypes. In both genotypes, increasing levels of applied N overall increased N-uptake efficiency (NEFF = N concentration in shoot x shoot/root), but decreased N-use efficiency by shoot and roots (NUE = g dry matter of shoot or root/mg N) and N-use efficiency of carbohydrate (NUEC = mg of total carbohydrates in shoot/mg of N in shoot). Both genotypes responded differently to applied N, despite the existence of close genetic relatedness between them. The method used here appears to be suitable method for identification of cacao genotypes that are efficient in uptake and utilization of N.     

缺磷对不同耐低磷玉米基因型酸性磷酸酶活性的影响

【目的】酸性磷酸酶活性与土壤及植株体内有机磷的分解和再利用有着密切的关系。本研究以不同耐低磷玉米自交系为材料,研究低磷胁迫下玉米叶片、根组织内以及根系分泌酸性磷酸酶活性的变化及基因型差异,探讨酸性磷酸酶与玉米耐低磷之间的关系,以期更深入地了解玉米耐低磷的生理机制。【方法】以5个典型耐低磷自交系99180T、99239T、99186T、99327T、99184T和2个磷敏感自交系99152S、99270S为试验材料,采用营养液培养方法,设正常磷和低磷两种处理,分别于缺磷处理3、8和12 d时调查取样,测定地上部干重、根干重、叶片中无机磷(Pi)含量、根和地上部磷累积量、根系分泌APase活性以及叶片中APase活性,并于缺磷处理12 d测定根系内APase活性。【结果】1)缺磷使玉米地上部干重下降,根干重、根冠比增加,随着缺磷处理(3 d→8 d→12 d)时间的延长,根干重、根冠比增加幅度增大,且耐低磷自交系根干重增加幅度普遍大于敏感自交系。2)低磷条件下,玉米自交系磷吸收、利用效率存在基因型差异,耐低磷自交系99239T、99180T和99327T磷吸收效率较高,99186T和99184T磷利用效率高,敏感自交系99152S、99270S磷吸收和利用效率均较低。3)低磷处理使玉米自交系叶片无机磷(Pi)含量显著下降,耐低磷自交系99184T、99327T和99239T下降幅度较小,相对叶片无机磷含量较高。4)缺磷诱导玉米根系分泌的APase活性升高。耐低磷自交系99184T和99186T根系分泌APase活性升高幅度较大,其余3个耐低磷自交系未表现出明显优势。缺磷处理3 d、8 d,玉米根系分泌APase活性与磷累积量显著正相关,而12 d时相关性不显著;根系分泌APase活性与磷利用效率在缺磷处理12d时达显著正相关。说明玉米根系分泌APase活性与磷吸收、利用效率相关关系不稳定。5)缺磷处理12 d,各玉米自交系根组织内APase活性与根系分泌APase活性变化情况较一致,两者相关系数r=0.755(P0.05)。6)缺磷条件下各玉米自交系叶片组织内APase活性均有升高趋势,并表现出明显的基因型差异。缺磷处理8 d,耐低磷自交系99184T和99239T叶片组织内APase活性升高幅度最大,其次是99327T和99186T,99180T、99270S和99152S升高幅度较小;缺磷处理12 d,各玉米自交系叶片APase活性仍继续增加,99239T、99184T、99327T和99186T的相对APase活性均较高,99270S和99152S的相对APase活性较低。相关性分析表明,缺磷条件下玉米自交系叶片中相对APase活性与叶片中相对无机磷(Pi)含量显著正相关,与磷吸收、利用效率不显著相关。【结论】低磷诱导玉米叶片、根组织和根系分泌APase活性升高,根组织和根系分泌APase活性的大小与玉米耐低磷能力不完全相关,叶片APase活性与玉米耐低磷能力有较好的一致性。     

Nitrogen and phosphorus nutritional interactions in a CO2 enriched environment

Nonnodulated soybean plants (Glycine max. [L.] Merr. ‘Lee') were supplied with nutrient solutions containing growth limiting concentrations of N or P to examine effects on N‐ and P‐uptake efficiencies (mg nutrient accumulated/gdw root) and utilization efficiencies in dry matter production (gdw²/mg nutrient). Nutritional treatments were imposed in aerial environments containing either 350 or 700 μL/L atmospheric CO₂ to determine whether the nutrient interactions were modified when growth rates were altered.

Nutrient‐stress treatments decreased growth and N‐ and P‐uptake and utilization efficiencies at 27 days after transplanting (DAT) and seed yield at maturity (98 DAT). Atmospheric CO₂ enrichment increased growth and N‐ and P‐utilization efficiencies at 27 DAT and seed yield in all nutritional treatments and did not affect N‐ and P‐uptake efficiencies at 27 DAT. Parameter responses to nutrient stress at 27 DAT were not altered by atmospheric CO₂ enrichment and vice versa. Nutrient‐stress treatments lowered the relative seed yield response to atmospheric CO₂ enrichment.

Decreased total‐N uptake by P‐stressed plants was associated with both decreased root growth and N‐uptake efficiency of the roots. Nitrogen‐utilization efficiency was also decreased by P‐stress. This response was associated with decreased plant growth as total‐N uptake and plant growth were decreased to the same extent by P stress resulting in unaltered tissue N concentrations. In contrast, decreased total P‐uptake by N‐stressed plants was associated with a restriction in root growth as P‐uptake efficiency of the roots was unaltered. This response was coupled with an increased root‐to‐shoot dry weight ratio; thus shoot and whole‐plant growth were decreased to a much greater extent than total‐P uptake which resulted in elevated P concentrations in the tissue. Therefore, P‐utilization efficiency was markedly reduced by N stress.     

Effect of PGPR,Phosphate sources and vermicompost on growth and nutrients uptake by lettuce in a calcareous soil

In order to study the effect of plant growth promoting rhizobacteria (PGPR), vermicompost and phosphate sources on the growth and nutrients uptake by lettuce, a greenhouse experiments was conducted. Treatments consisted of PGPR (Pseudomonas fluorescens) (with and without inoculation), vermicompost (0 and 1% w/w) and phosphate sources (control, rock phosphate (RP), tricalcium phosphate and triple super phosphate (TSP) at 25 mg P kg^?1 level). Biological fertilizers, RP and TSP significantly increased shoot dry matter (SDM) and some measured nutrients uptake. Co-application of PGPR and RP, in non-vermicompost treatments significantly increased SDM, shoot nitrogen, phosphorus (P), potassium, zinc and manganese uptake rates. Shoot P uptake had no significant difference between TSP and RP treatments. Co-application of PGPR, vermicompost and TSP significantly decreased SDM, which may be due to the P toxic levels in the plant aerial parts and/or the inhibition of the bacterial activities in the rhizosphere soil.     

Evaluation of common bean genotypes for phosphorus use efficiency

A greenhouse experiment was conducted to evaluate phosphorus (P)‐use efficiency of 10 promising genotypes of common bean (Phaseoius vulgaris L.) with short and normal growth duration. The genotypes were grown on an Oxisol at 25 mg P kg^‐1 (low P) and 150 mg P kg^‐1 (high P) of soil. Shoot and root dry weight, root length, P concentration in the shoot, and P uptake in the shoot were significantly (P<0.01) affected by soil P concentration and genotype. However, P level did not effect root length and genotype had no effect on root dry weight. On the basis of P‐use efficiency (mg dry weight of shoot/mg P accumulated in the shoot) genotypes were classified as efficient and responsive (ER), efficient and nonresponsive (ENR), nonefficient and responsive (NER), and nonefficient and nonresponsive (NENR). From a practical point of view, genotypes which produce a lot of dry matter in a soil with a low P level, and respond well to added P are the most desirable because they are able to express their high yield potential in a wide range of P environments. Novo Jalo and Pérola genotypes fall into this group. Genotypes Irai, Jalo Precoce and L93300166 fall into the ENR group. Genotypes Carioca, Rosinha G‐2, and Xamengo were classified NER, whereas, genotypes L93300176 and Diamante Negro were classified as NENR. There were no differences between short and normal growth duration genotypes in P‐use efficiency.     

Phosphorus‐use efficiency by corn genotypes

Phosphorus (P) deficiency is a principal yield‐limiting factor for annual crop production in acid soils of temperate as well as tropical regions. The objective of this study was to screen nine corn (Zea mays L.) genotypes at low (0 mg P kg^‐1), medium (75 mg P kg^‐1), and high (150 mg P kg^‐1) levels of P applied in an Oxisol. Plant height, root length, shoot dry weight, root dry weight, shoot‐root ratio, P concentration in shoot and root, P uptake in root and shoot, and P‐use efficiency parameters were significantly (P<0.01) influenced by P treatments. Significant genotype differences were found in plant height, shoot and root dry weight, P uptake in root and shoot, and P‐use efficiency. Based on dry matter production and P‐use efficiency, genotypes were classified as efficient and responsive, efficient and nonresponsive, nonefficient and responsive, and nonefficient and nonresponsive.     

Genotypic variation of potato for phosphorus efficiency and quantification of phosphorus uptake with respect to root characteristics

Potato (Solanum tuberosum L.), an important food crop, generally requires a high amount of phosphate fertilizer for optimum growth and yield. One option to reduce the need of fertilizer is the use of P‐efficient genotypes. Two efficient and two inefficient genotypes were investigated for P‐efficiency mechanisms. The contribution of root traits to P uptake was quantified using a mechanistic simulation model. For all genotypes, high P supply increased the relative growth rate of shoot, shoot P concentration, and P‐uptake rate of roots but decreased root‐to‐shoot ratio, root‐hair length, and P‐utilization efficiency. Genotypes CGN 17903 and CIP 384321.3 were clearly superior to genotypes CGN 22367 and CGN 18233 in terms of shoot–dry matter yield and relative shoot‐growth rate at low P supply, and therefore can be considered as P‐efficient. Phosphorus efficiency of genotype CGN 17903 was related to higher P‐utilization efficiency and that of CIP 384321.3 to both higher P‐uptake efficiency in terms of root‐to‐shoot ratio and intermediate P‐utilization efficiency. Phosphorus‐efficient genotypes exhibited longer root hairs compared to inefficient genotypes at both P levels. However, this did not significantly affect the uptake rate and the extension of the depletion zone around roots. The P inefficiency of CGN 18233 was related to low P‐utilization efficiency and that of CGN 22367 to a combination of low P uptake and intermediate P‐utilization efficiency. Simulation of P uptake revealed that no other P‐mobilization mechanism was involved since predicted uptake approximated observed uptake indicating that the processes involved in P transport and morphological root characterstics affecting P uptake are well described.     

RESPONSE OF MAIZE GENOTYPES TO SEVERAL MYCORRHIZAL INOCULUMS IN TERMS OF PLANT GROWTH,NUTRIENT UPTAKE AND SPORE PRODUCTION

A greenhouse experiment was conducted at the University of Çukurova, Rhisosphere Lab, Adana, Turkey, on a growth medium to assess the impact of several selected mycorrhiza including indigenous AMF-maize hybrid combinations on spore production, plant growth and nutrient uptake. In the experiment, six maize (Zea mays L.) (Luce, Vero, Darva, Pegasso, P.3394, and P.32K61) genotypes were used. Control, Glomus mossea, G. caledonium, G. etunicatum, G. clarium, G. macrocarpum, G. fasciculatum, G. intraradices, Dr. Kinkon (Japanese species), indigenous mycorrhizae (Balcal? series) and cocktail mycorrhizae species spores were used. The growth of maize genotypes was found to depend on the mycorrhizal species. For shoot and root dry weight production G. intraradices is one of the most efficient mycorrhiza species on average on all maize genotypes. Genotypes P.3394 and P.32K61 produced the highest shoot and root dry weight as well. Pagasso and Darva genotypes compared to the other genotypes have high root colonization percentages. On average G. clarium inoculated plants also have high percentages of root colonization. It has been found that the P.32K61 genotype has a high phosphorus (P)% content and Pagasso genotypes have higher zinc (Zn) content uptake than other genotypes. G. clarium inoculated maize genotype plant tissues have high P% and Zn content. G. intraradices is also efficient for P and Zn uptake. Mycorrhizal dependent maize genotypes showed variability in P efficiency from inefficient to efficient genotypes.     

Brassica genotypes differ in growth, phosphorus uptake and rhizosphere properties under P-limiting conditions

Compared to other crops, Brassicas are generally considered to grow well in soils with low P availability, however, little is known about genotypic differences within Brassicas in this respect. To assess the role of rhizosphere properties in growth and P uptake by Brassicas, three Brassica genotypes (mustard, Brassica juncea cv Chinese greens and canola, Brassica napus cvs Drum and Outback) were grown in an acidic soil with low P availability at two treatments of added P: 25 and 100 mg P kg⁻¹ as FePO₄ (P25 and P100). The plants were harvested at the 6-leaf stage, at flowering and at maturity. Shoot and root dry weight (dry weight) and root length increased with time and were lower in P25 than in P100. In P25, shoot dry weight was lowest in Outback and highest in Chinese greens. In the P100 treatment, Chinese greens had a higher shoot dry weight than the two canola cultivars. Chinese greens had a lower root dry weight and root length at flowering and maturity than the canola genotypes in both P treatments. Irrespective of P treatment, shoot P concentration was lower in Chinese greens than in the two canola genotypes. Specific P uptake (μg P m⁻¹ root length) decreased with time. In P25, Chinese greens had the lowest specific P uptake at the 6-leaf stage but it was higher than in the two canola genotypes at flowering and maturity. In P100, Outback had the lowest specific P uptake. Available P in the rhizosphere (resin P) decreased over time with the greatest decrease from the 6-leaf stage to flowering. In P25, resin P in the rhizosphere was greatest in Chinese greens at the 6-leaf stage and flowering and smallest in Outback at flowering. Microbial P and acid phosphatase activity changed little over time, were not affected by P treatment and there were only small differences between the genotypes. The rhizosphere microbial community composition [assessed by fatty acid methyl ester (FAME) analysis] of Outback and Chinese greens differed from that of the other two genotypes at the 6-leaf stage and flowering, respectively. At maturity, all three genotypes had distinct microbial communities. Plant traits such as production of high biomass at low shoot P concentrations as well as the capacity to maintain high P availability in the rhizosphere by P mobilisation can explain the observed differences in plant growth and P uptake among the Brassica genotypes.     

Growth, P uptake and rhizosphere properties of intercropped wheat and chickpea in soil amended with iron phosphate or phytate

Intercropping has been shown to increase total yield and nutrient uptake compared to monocropping. However, depending on crop combinations, one crop may dominate and decrease the growth of the other. Interactions in the soil, especially in the rhizosphere, may be important in the interactions between intercropped plant genotypes. To assess the role of the rhizosphere interactions, we intercropped a P-inefficient wheat genotype (Janz) with either the P-efficient wheat genotype (Goldmark) or chickpea in a soil with low P availability amended with 100 mg P kg⁻¹ as FePO₄ (FeP) or phytate. The plants were grown for 10 weeks in pots where the roots of the genotypes could intermingle (no barrier, NB), were separated by a 30 μm mesh (mesh barrier, MB), preventing direct root contact but allowing exchange of diffusible compounds and microorganisms, or were completely separated by a solid barrier (SB). When supplied with FeP, Janz intercropped with chickpea had higher shoot and grain dry weight (dw) and greater plant P uptake in NB and MB than in SB. Contact with roots of Janz increased shoot, grain and root dw, root length, shoot P concentration and shoot P uptake of chickpea compared to SB. Root contact between the two wheat genotypes, Janz and Goldmark, had no effect on growth and P uptake of Janz. Shoot and total P uptake by Goldmark were significantly increased in NB compared to MB or SB. In both crop combinations, root contact significantly increased total plant dw and P uptake per pot. Plant growth and P uptake were lower with phytate and not significantly affected by barrier treatment. Differences in microbial P, available P and phosphatase activity in the rhizosphere among genotypes and barrier treatments were generally small. Root contact changed microbial community structure (assessed by fatty acid methyl ester (FAME) analysis) and all crops had similar rhizosphere microbial community structure when their roots intermingled.     

Growth,P uptake and rhizosphere properties of wheat and canola genotypes in an alkaline soil with low P availability

The aim of the present study was to assess the role of soil type on growth, P uptake and rhizosphere properties of wheat and canola genotypes in an alkaline soil with low P availability. Two wheat (Goldmark and Janz) and two canola genotypes (Drum and Outback) were grown in a calcareous soil (pH 8.5) at two P levels [no P addition (0P) or addition of 200 mg kg⁻¹ P as Ca₃(PO₄)₂ (200P)] and harvested at flowering or maturity. Shoot and root dry weight, root length and shoot P content were greater in the two canola genotypes than in wheat. There were no consistent differences in available P, microbial P and phosphatase activity in the rhizosphere of the different genotypes. Shoot P content was significantly positively correlated with root length, pH and phosphatase activity in the rhizosphere. The microbial community composition, assessed by fatty acid methylester analysis, of the canola genotypes differed strongly from that of the wheat genotypes. The weight percentage bacterial fatty acids, the bacteria/fungi (b/f) ratio and the diversity of fatty acids were greater in the rhizosphere of the canolas than in the rhizosphere of the wheat genotypes. In contrast to the earlier studies in an acidic soil, only small differences in growth and P uptake between the genotypes of one crop were detected in the alkaline soil used here. The results confirmed the importance of root length for P uptake in soils with low P availability and suggest that the rhizosphere microbial community composition may play a role in the better growth of the canola compared to the wheat genotypes.     

接种菌根真菌对不同磷效率基因型大豆生长和磷吸收的影响

接种丛枝菌根真菌(AMF)能显著促进大豆生长和对磷的吸收,但不同磷效率基因型大豆对AMF接种的响应还少有报道。为探究接种AMF对不同磷效率基因型大豆生长和磷转运基因表达的影响,以磷高效大豆BX10和磷低效大豆BD2为试验材料进行盆栽试验,设置接菌和不接菌处理,对大豆干重、菌根侵染性状、氮磷养分含量、根系性状,以及菌根诱导的磷转运基因表达进行了分析。结果表明, AMF接种显著促进了大豆的磷吸收,并且接菌效果存在显著的基因型差异,接种AMF显著增加了BD2的地上部干重、磷含量以及植株总磷吸收量,但只增加了BX10的地上部磷含量和总磷吸收量,对植株地上部干重没有显著影响。无论接种与否,BD2的地上部磷含量均显著高于BX10,表明磷低效的BD2具有较高的植株体内磷转运能力。不接菌条件下,两个大豆基因型根系性状无显著差异;接种AMF后BX10的根系体积和根系平均直径均显著高于BD2。BD2的菌根生长反应(MGR)和菌根磷反应(MPR)均显著高于BX10,对菌根依赖性更高。此外,在接菌处理的BD2根系,代表菌根途径磷吸收的磷转运基因GmPT8、GmPT9和GmPT10表达均显著高于BX10;相应地,BD2的总磷吸收量也显著高于BX10。以上结果表明,接种AMF对促进磷低效大豆BD2生长和磷吸收的作用更大,这可能主要是由于BD2菌根途径的磷吸收量较高,体内磷转运效率较高。以上结果将为研究AMF接种对磷吸收的贡献提供理论依据。