CATEGORIZATION OF BRASSICA CULTIVARS FOR PHOSPHORUS ACQUISITION FROM PHOSPHATE ROCK ON BASIS OF GROWTH AND IONIC PARAMETERS

We categorized sixteen Brassica cultivars for their differential growth response and phosphorus (P) acquisition from phosphate rock (PR) and monoammonium phosphate (MAP). Plants were grown with both P sources in a nutrient solution experiment for 40 days. Cultivars differed significantly (P < 0.01) both for absolute as well as relative values of growth and physiological parameters at both P sources. Phosphorus deficiency in PR treatment significantly depressed biomass production (more than 2.5 times than control) and P concentration (about 1.5 times) in all of the cultivars. ‘Rainbow’ and ‘Poorbi Raya’ produced significantly more relative biomass than other cultivars grown with PR. Cultivars were classified into three classes on the basis of mean values of different parameters and their standard deviation viz low, medium and high. Cultivars were also classified into different classes while regressing biomass and P contents. Cultivars ‘Rainbow’ and ‘Poorbi Raya’ accumulated maximum shoot dry matter (1.21 and 1.27 g dry matter/plant, respectively) grown with phosphate rock, hence were categorized as high biomass producers. Cultivars ‘Rainbow’, ‘KS-74’, and ‘Poorbi Raya’ accumulated maximum P (5.58, 5.24, and 4.81 mg P plant^?1, respectively) from PR and were categorized as high P accumulators. Cultivars with high biomass and high P contents such as ‘Rainbow’ and ‘Poorbi Raya’ at low available P (Rock P) would be used in further screening experiments to improve P efficiency in Brassica.     

VARIATION IN PHOSPHORUS EFFICIENCY AMONG BRASSICA CULTIVARS II: CHANGES IN ROOT MORPHOLOGY AND CARBOXYLATE EXUDATION

Increased phosphorus (P) efficiency is needed to sustain agriculture productivity on soils with low available P. Significant differences were found among Brassica cultivars for growth, P utilization, and remobilization under P deficiency (see our companion paper, Aziz et al., 2011a). To identify the possible mechanisms of P acquisition from low soluble P compounds, four cultivars (‘Rainbow’, ‘CON-1’, ‘Dunkeld’, and ‘Peela Raya’) were selected to ascertain the relationship of their differential P acquisition and growth with their root length in soil and with organic acid release pattern in solution culture experiments. For this purpose their growth and P acquisition from phosphate rock (PR) was compared with calcium di-hydrogen phosphate (Ca-P) when adding uniform dose of 100 mg P kg^?1 soil separately from the two sources. Biomass accumulation, root length, root fineness, plant P uptake and ash alkalinity was significantly (P < 0.01) different in plants of all the four cultivars when supplied with PR or Ca-P in soil. Minimum biomass produced by ‘Peela Raya’ grown with either P source was followed by ‘CON-1’, ‘Dunkeld’, and ‘Rainbow’ in ascending order. Shoot dry matter production had a significant positive correlation with root dry matter production (r = 0.85, P < 0.01), root length (r = 0.59, P < 0.05) and root P uptake (r = 0.95, P < 0.01). Cultivars varied significantly for organic acid secretion in solution culture experiment. Higher quantities of secreted citric acid, malic acid and tartaric acid in solution culture experiment were measured for ‘Rainbow’ and ‘Dunkeld’ cultivars. Efficient performance of these two cultivars for growth and P uptake was associated with their longer roots and more secretion of organic acids especially citric acid.     

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.     

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.     

Effects of phosphorus and water stress levels on growth and phosphorus uptake of bean and sorghum cultivars

Primary determinants of crop production in arid/semiarid regions are lack of moisture and infertility, especially phosphorus (P) deficiency or unavailability. The effects of P and water stress (WS) levels on shoot and root dry matter (DM), leaf area, root volume, total root length, and shoot and root P concentrations and contents were determined in two bean [Phaseolus acutifolius Gray, cv ‘Tepary #21’ ("drought‐resistant") and P. vulgaris L., cv “Emerson’ ("drought‐sensitive")] and two sorghum [Sorghum bicolor (L.) Moench, cv SA7078 ("drought‐resistant") and ‘Redlan’ ("drought‐sensitive")] cultivars grown in nutrient solution. Plants were grown with different levels of P (20 and 100 μM for bean and 20, 80, and 160 μM for sorghum) when seedlings were transferred to nutrient solution, and WS levels of 0, 13.8, and 1 6.4% polyethylene glycol (PEG‐8000) introduced after plants had grown in solution 23 days (bean) and 31 days (sorghum). All growth traits were lower when bean and sorghum plants were grown with WS and low P. Growth traits were higher in cultivars grown with high compared to low P regardless of WS. Root P concentration and content and shoot content, but not shoot P concentration, were lower when bean plants were grown with WS compared to without WS. Tepary #21 bean had higher shoot DM, leaf area, total root length, and shoot P concentration than Emerson when plants were grown with WS at each level of P. Sorghum shoot and root P concentrations were higher as P level increased regardless of WS, and WS had little effect on shoot P concentration, but root P concentration was higher. Contents of P were similar for SA7078 and Redlan regardless of P or WS treatment, but SA7078 had greater P contents than Redlan over all P and WS treatments. “Drought‐resistant”; cultivars generally had better growth traits, especially total and specific root lengths, than “drought‐sensitive”; cultivars.     

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.     

Phosphorus Stress Induced Variations in Growth Behavior and P Efficiency among Brassica Cultivars Grown with Sparingly Soluble P Sources

To evaluate phosphorus (P)–stress–induced relative growth responses, P-efficiency characteristics, P remobilization, and redesign in root architectural systems, Brassica cultivars were grown with sparingly soluble rock phosphate and calcium phosphate [Ca₃(PO₄)₂] or with low/high P supply in solution and sand culture experiments. Tested cultivars showed considerable genetic diversity in biomass accumulation, concentration and contents of P, P-stress factor (PSF), and P-efficiency characteristics [P-utilization efficiency (PUE), P efficiency (PE), and P-efficiency ratio (PER)]. Statistically significant correlations were observed between P efficiency and growth parameters. Elongation rates of primary roots decreased but the length of lateral roots and branched zone elongation rates increased under P starvation. Cultivars remobilized P from metabolically inactive to active sites in P-stressed plants that may have helped low-P-tolerant cultivars to establish a better rooting system, which provided basis for enhanced P-use efficiency and tolerance against P stress. Cultivars depicting high P efficiency and low PSF values were more tolerant and are a better choice to grow under P-stress environments.     

UPLAND RICE GENOTYPES EVALUATION FOR PHOSPHORUS USE EFFICIENCY

Phosphorus (P) deficiency is one of the most yield limiting factors in crop production in Brazilian Oxisols. A greenhouse experiment was conducted to evaluate 20 upland rice genotypes at low (25 mg P kg^?1) and high (200 mg P kg^?1) P levels applied to a Brazilian Oxisol. Grain yield and yield components were significantly influenced by P level and genotype treatments. There was a significant interaction between P level and genotype treatments in relation to grain yield, indicating genotypes responded differently under two P levels. Based on grain yield efficiency index (GYEI), genotypes were classified into efficient, moderately efficient and inefficient groups. The efficient genotypes in utilizing P were ‘BRA052053’, ‘BRS Primavera’, ‘BRA052015’, ‘BRA052023’, ‘BRA01506’, ‘BRA052045’, ‘BRA032033’, ‘BRA01596’ and ‘BRA052034’. Remaining genotypes were classified as moderately efficient in P use efficiency. None of the genotypes were fall into inefficient group. Grain yield was significantly and positively related with shoot dry weight, panicle number, grain harvest index, 1000-grain weight and had a negative and significant correlation with spikelet sterility. Grain weight was having maximum contribution in total rice plant weight comparing to root and shoot, indicating improvement in harvest index of modern Brazilian upland rice cultivars by breeding.     

GENOTYPIC DIFFERENCES IN ROOT MORPHOLOGY AND PHOSPHORUS UPTAKE KINETICS IN BRASSICA NAPUS UNDER LOW PHOSPHORUS SUPPLY

Application of phosphorus (P) fertilizer is important in crop production because of the low bioavailability of phosphorus to plants in both acidic and calcareous soils. Although rapeseed (Brassica napus) is generally sensitive to P deficiency, different cultivars differ widely in this respect. Differences in P uptake and utilization between two rapeseed cultivars, one P-efficient (‘97081’) and one P-inefficient (‘97009’), were evaluated in solution culture by studying the changes in root morphology and parameters of P uptake kinetics in response to low-P stress. The P-efficient cultivar had lower Km and Cmin values and higher Vmax and developed longer and denser lateral root hair with greater number of root tips and branches under low-P stress, which resulted in a better developed root system and more efficient uptake of P. That, in turn, led to higher concentration and accumulation of P in the plants, culminating in higher biomass production. However, P utilization efficiency (biomass production per unit P accumulated in plant) of the P-efficient ‘97081’ was lower than that of ‘97009’ when P was deficient. These results suggest that P efficiency in rapeseed is due to a better developed root system as well as efficient uptake of P.     

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.     

Remobilization and utilization of phosphorus in wheat cultivars under induced phosphorus deficiency

A solution culture study was conducted to compare the phosphorus (P) remobilization efficiency of four wheat cultivars under induced P deficiency. Wheat cultivars, i.e. Sarsabz, NIA-Sunder, NIA-Amber and NIA-Saarang were initially grown on adequate P nutrition for 30 days and then exposed to P-free nutrient solution for next 15 days to study P remobilization. Completely randomized design (CRD) with ten replicates per cultivar was employed. Cultivars varied for biomass production, P concentration, P uptake, and P utilization efficiency at both harvests. Overall, more than 75% of absorbed P was mobilized from older leaves to younger leaves as well as roots of all cultivars during P-omission period. However, cultivars could not produce significant variations (P < 0.05) in P remobilization, which implied that P remobilization was only a stress response to P deficiency in wheat cultivars and it could not be related to P utilization efficiency of these cultivars.     

Solubilization and Acquisition of Phosphorus from Sparingly Soluble Phosphorus Sources and Differential Growth Response of Brassica Cultivars Exposed to Phosphorus-Stress Environment

Phosphate (Pi), the fully oxidized and assimilated form of phosphorus (P), influences virtually all developmental and biochemical processes in plants; however, its availability and distribution are widely heterogeneous. Paradoxically, although total P is abundant in lithosphere, elusive soil chemistry of Pi renders the element the most dilute and the least mobile in natural and agricultural ecosystems, resulting in P deprivation due to its low mobility and high fixation capacity in the soil. Nonmycorrhizal Brassica does not produce specialized cluster/dauciform roots but is an effective P user compared to other crops. Using a soil low in P (Mehlich 3–extractable P) with or without P fertilization, Brassica cultivars showed substantial genetic diversity in P-utilization efficiency (PUE), P efficiency (PE), P-efficiency ratio (PER), and P-stress factor (PSF). Cultivars producing greater root biomass accumulated greater total P contents, which in turn was related negatively to PSF and positively to shoot and total biomass. Plant survival and reproduction rely on efficient strategies in exploring culture media for P. Acquisition of orthophosphate from extracellular sparse P sources may be enhanced by biochemical rescue strategies such as copious H⁺ efflux and/or carboxylates exudation into rhizosphere by roots via plasmalemma H⁺-ATPase and anion channels triggered by P starvation. The P-starvation-induced solution pH changes due to H⁺ efflux, and carboxylates exudations were estimated by low-P-tolerant and low-P-sensitive cultivars in solution culture experiments. Low-P-tolerant cultivars showed more decrease in pH compared to low-P-sensitive cultivars when cultivars were grown under a P-stress environment induced by using sparingly soluble P sources (rock phosphate and tricalcium phosphate). The P contents of cultivars were inversely related to decrease in culture media pH. Low P-tolerant cultivars presented enhanced H⁺-efflux and total carboxylates exudations compared to low-P-sensitive cultivars, resulting in more rhizosphere acidification to scavenge Pi, evidencing their adaptability to P starvation. These elegant P-stress-induced rescue strategies by tested cultivars provided the basis of enhanced P solubilization and acquisition of P from sparingly soluble P sources to combat P-starved environments.     

Salt Tolerance of Canola in Relation to Accumulation and Xylem Transportation of Cations

ABSTRACT

This study was conducted in a greenhouse to evaluate the root and shoot response of canola (Brassica napus L.) to salt-stress conditions and the remobilization, deposition, and input rate of sodium (Na), potassium (K), and magnesium (Mg) at different salinity levels using two canola cultivars. A salt-tolerant (‘Kristina’) cultivar and a salt-sensitive (‘Hyola 308’) cultivar were grown in nutrient solutions with 0, 50, 100, 150, and 200 mol m^?3 NaCl for 7 d. The plants were harvested after 6, 12, 18, and 24 h and 3 and 7 d after salt treatment. The results indicated that increasing salinity significantly decreased shoot and root weights 7 d after treatment. Also, K content and K-Na selectivity decreased in both cultivars, but the changes in ‘Hyola 308’ were greater than in ‘Kristina.’ Electrolyte leakage was increased significantly by salinity, and cell-membrane stability of ‘Hyola 308’ was damaged more than that of ‘Kristina’. Sodium import, transport, and deposition was increased by salinity concentration but remobilization was decreased. The K and Mg import, deposition, and remobilization were also decreased. From this experiment we can conclude that greater K and Mg remobilization in ‘Kristina’ could be a mechanism of salt tolerance in canola.     

ADAPTABILITY MECHANISM OF NITROGEN-EFFICIENT GERMPLASM OF NATURAL VARIATION TO LOW NITROGEN STRESS IN BRASSICA NAPUS

Previous studies showed that wide genotype differences in nitrogen (N) efficiency exists among cultivars of rapeseed (Brassica napus L.), but the mechanisms behind those differences are still unknown. In the present study, our aim was to analyze the adaptability mechanism of N-efficient rapeseed to low-N stress by employing two genotypes of natural variation in N efficiency. Nitrogen-efficient genotype, ‘BG51’, and N-inefficient genotype, ‘BG88’, were grown in a solution culture experiment under conditions of high-N (6.0 mM N) and low-N (0.6 mM N) supply. After growing 30 d, roots and shoots were sampled for the analysis of dry weight, N concentration and accumulation, N use efficiency (NUE), N transport efficiency (NTE), root system vigor parameters, nitrate redutase (NR) activity, and glutamine synthetase (GS) activity. Nitrogen deficiency decreased shoot and root dry weight significantly, but ‘BG51’ exhibited a significantly lower decrease in shoot dry weight and had significantly higher biomass production than ‘BG88’. Under low N supply ‘BG51’ accumulated more N in shoot, root and whole plant than ‘BG88’, and presented higher NUE in both shoot and root. Low-N stress induced an increase in maximum root length by 28.3% for ‘BG88’ and 55.1% for ‘BG51’ compared with the high-N treatment. And ‘BG51’ presented larger root volume, higher root vigor, larger root total absorbing area and root active absorbing area than ‘BG88’ in low-N treatment. Furthermore, ‘BG51’ had significantly higher NR and GS activity in both leaf and root in low N treatment than ‘BG88’, while there was no evident difference between them in high N treatment. These results suggested that N-efficient rapeseed germplasm of natural variation involves an integrated adaptability mechanism responding to low-N stress. Namely, N-efficient genotype could form more developed root system to accumulate more N, and presented efficient N assimilation by higher NR activity and GS activity than N-inefficient genotype. These ultimately resulted in high tolerance of N-efficient genotype to low-N stress and high biomass production.     

Phosphorus Efficiency in Sunflower Cultivars and Its Relationships with Phosphorus,Calcium, Iron,Zinc and Manganese Nutrition

ABSTRACT

Phosphorus (P) efficiency (shoot dry weight at low P/shoot dry weight at high P) of a cultivar is the ability to produce a high yield in a soil that is limited in that element for a standard genotype. The large variation in P efficiency of different crops provides opportunities for screening crop species that perform well on low phosphorus soil. To explain the differences in P efficiency of sunflower (Helianthus annuus L.) cultivars a glasshouse pot experiment was conducted by using P-deficient soil [0.5 M sodium bicarbonate (NaHCO₃)-extractable P 8.54 mg kg^?1] treated with 0 (low P) and 100 mg P kg^?1 soil (high P). The relationship between P efficiency and P, calcium (Ca), iron (Fe), zinc (Zn), and manganese (Mn) nutrition and anthocyanin accumulation was investigated in ten sunflower cultivars. Phosphorus deficiency resulted in significant decreases in the shoot and root yield. Phosphorus-efficient cultivars have the ability to produce higher yield than the inefficient cultivars in a limited P conditions. Our results showed that P-efficient cultivars had lower P concentrations, but higher P content in low P conditions. Phosphorus-efficient cultivars also have lower Ca and Fe concentrations in low P conditions but not in P-sufficient conditions. Applied P resulted in significant decreases in Zn concentrations in the shoots of the cultivars. Anthocyanin concentrations showed an accumulating pattern in all cultivars under P deficiency. The results demonstrated that phosphorus efficiency of the sunflower cultivars depends on their ability to produce higher yield and take up more P, and lower the concentration of Ca and Fe in shoots under low P conditions.     

Critical Ratio of Calcium and Boron in Maize Shoot for Optimum Growth

Boron (B) deficiency is widely reported in alkaline calcareous soils of the world, including Pakistan. High calcium (Ca) content in such soils can affect the availability and utilization of B by plants. Effect of applied B at different levels of Ca addition on maize was studied in hydroponics. Four maize cultivars (‘EV-5089’, ‘SWL-2000’, ‘EV-6089’, and ‘Sultan’) were grown at three levels of Ca (0.25 mM, 1 mM, and 2 mM) and two levels of B (0 and 25 μ M). Application of both the nutrients increased shoot dry matter production. However, application of Ca antagonized the B concentration in shoot of four maize cultivars. A curvilinear relationship existed between Ca/B ratio in shoot and relative shoot dry matter of maize cultivars. Implication of using of Ca/B ratio for managing commonly occurring B deficiency in calcareous soils is suggested.     

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.     

酸性磷酸酶活性与大豆耐低磷能力的相关研究

在水培条件下研究了11个南方春大豆地方品种和育成品种对低磷胁迫反应的差异及其与酸性磷酸酶活性（APA）的相关关系。结果表明，不同大豆品种的地上部干重、根干重、植株全磷和全氮积累量差异极显著（P＜0.01），表现出品种间耐低磷的差异性。大豆品种地上部干重、根干重、植株全磷和全氮量与APA的相关性均达到显著或极显著水平。APA是大豆品种磷效率的一种机制，它可作为耐低磷品种筛选的一个生化指标。     

INFLUENCE OF ELEVATED PHOSPHORUS LEVELS IN NUTRIENT SOLUTION ON MICRONUTRIENT UPTAKE AND DEFICIENCY SYMPTOM DEVELOPMENT IN STRAWBERRY CULTURED WITH FERTIGATION SYSTEM

The relationship between the total amount of micronutrients absorbed by the above-ground plant tissue and the occurrence of visible micronutrient deficiency symptoms in two strawberry cultivars as influenced by elevated phosphorus (P) levels in fertigation solution was investigated. The plants were cultured with a fertilizer solution containing 0, 0.5, 1, 2, 4, or 6 mM P and tissue nutrient content were determined at 120 days after transplanting. Young leaves of the plants grown with nutrient solution P levels higher than 4 mM and 2 mM, respectively, in ‘Keumhyang’ and ‘Seonhong’, developed interveinal chlorosis. Tissue concentrations (mg·kg^?1 dry weight) of metallic micronutrients [iron (Fe), copper (Cu), manganese (Mn), and zinc (Zn)] in both cultivars did not decrease, but the total amount absorbed by the aboveground plant tissue decreased in the treatments in which nutrient deficiencies were observed. These results indicate that total amount of micronutrients is a better indicator of P-induced micronutrient deficiency.     

Seedling vigor and nitrogen use efficiency of Moroccan wheat as influenced by level of soil nitrogen

Abstract

One of the characteristics that can help wheat (Triticum aestivum L.) plants escape late season drought in the semiarid areas of Morocco is early stand establishment and adequate vigor. Little is known about the effect of nitrogen (N) on early seedling vigor in wheat. The objective of this study was to determine how N supply affects early root and shoot growth, N partitioning between the two parts and N use efficiency of seedlings. To reach this objective, three spring wheat cultivars were grown in pots in a growth chamber under N conditions which were low, adequate and high. Data showed that optimum N rates increased shoot and root growth but high N concentrations reduced their dry matter accumulation and inhibited root elongation. The cultivars tested behaved differently. ‘Nesma’, an older cultivar, produced 60% more dry matter and accumulated 93% more N in the shoot and root than the newer cultivars ‘Merchouch 8’ and ‘Saada’. Because of its high N uptake, ‘Nesma’ probably reduced soil N concentration at the root zone and avoided the negative effect of high N concentration on root growth. Although, ‘Nesma’ performed better and produced more dry matter, it used N less efficiently than the other two cultivars.

From this study, we can conclude that use of optimum N rates at time of seeing will result in quicker establishment and higher vigor of wheat seedlings. However, excessive N supply may retard seedling growth. The cultivars that produce more seedling dry matter with greater N accumulation are not necessarily the ones that use N more efficiently.