ROOT ZONE TEMPERATURE INFLUENCES ZINC REQUIREMENT OF MAIZE CULTIVARS ON A CALCAREOUS LOAM SOIL

The zinc (Zn) requirement of a maize (Zea mays L.) hybrid (‘FHY-396’) and an indigenous variety (‘EV-7004’) was measured at low (22.4 ± 5°C) and high (28.8 ± 5°C) root-zone temperatures (RZT). Four Zn rates (0, 3, 9 and 27 mg kg^?1 soil) were applied to a calcareous loam soil in pots for the glasshouse study. Shoot and root dry matter yields were significantly more at the higher RZT. Regardless the RZT, maximum relative shoot dry matter yield in hybrid and variety was produced, respectively, at 9 and 3 mg Zn kg^?1 soil. Zinc concentration in roots and shoots of both the cultivars increased with Zn rates and it was significantly more at the higher RZT. Cultivars differed in critical Zn concentration (C_ZnC) required for maximum shoot dry matter yield. The C_ZnC ranged from 25 to 39 μg Zn g^?1 plant tissue for optimum growth of both the cultivars at low and high RZT.     

Mineral bioavailability in grains of Pakistani bread wheat declines from old to current cultivars

Estimating variation in grain mineral concentration and bioavailability in relation to grain yield and the year of cultivar release is important for breeding wheat with increased content of bioavailable minerals. The grain yield and yield components, grain phytate concentration, and concentration and bioavailability of minerals (zinc Zn, iron Fe and calcium Ca) in wheat grains were estimated in 40 wheat cultivars released in Punjab (Pakistan) during the last five decades. Mean grain Zn and Ca concentrations in current-cultivars were significantly lower (≥14%) than in obsolete cultivars released during the Green Revolution (1965–1976). Much of this variation was related to increased grain weight in current-cultivars. There was a positive correlation among minerals (r = 0.39 or higher, n = 40) and minerals with phytate in wheat grains (r = 0.38 or higher, n = 40). The tested cultivars varied widely in grain yield and grain phytate-to-mineral molar ratios (phytate:mineral). Compared to obsolete cultivars, the current-cultivars had a higher phytate:mineral ratio in grains, indicating poor bioavailability of minerals to humans. The study revealed a non-significant relationship between grain yield and phytate:mineral ratios in grains. Therefore, breeding for lower phytate:mineral ratios in wheat grains can ensure increased mineral bioavailability without significant reduction in the yield potential. Future breeding should be focused on developing new genotypes suitable for mineral biofortification and with increased mineral bioavailability in grains.     

VARIATION IN PHOSPHORUS EFFICIENCY AMONG BRASSICA CULTIVARS I: INTERNAL UTILIZATION AND PHOSPHORUS REMOBILIZATION

Plants have adapted a number of mechanisms to cope with widespread phosphorus (P) deficiency in arable lands. Crop species and even cultivars differ widely in one or more of these adaptive mechanisms hence, in P efficiency. Identification of these mechanisms is pre-requisite for long term breeding programs. Two independent experiments were conducted to study the possible mechanisms of P efficiency in Brassica cultivars. Eight Brassica cultivars (‘B.S.A.’, ‘Toria’, ‘Toria Selection’, ‘Brown Raya’, ‘Peela Raya’, ‘Dunkeld’, ‘Rainbow’, and ‘CON-1’) were selected on the basis of differences in growth under P deficiency from preliminary experiment. In the first experiment, cultivars were grown for 40 days in sand supplied either with sparingly soluble phosphate rock (PR) or soluble mono-ammonium phosphate (MAP). Cultivars differed significantly (P<0.05) for biomass production, P contents and P use efficiency. Low P availability in PR treatment resulted in significantly lower dry weights and P contents than those grown with MAP. The cultivars ‘Rainbow’, ‘Brown Raya’ and ‘Dunkeld’ accumulated more biomass (3.2 g/pot) and P contents (3.0 mg/pot) than other cultivars when grown with PR. Root dry weight was significantly correlated with shoot dry weight, shoot P content and total P content (r > 0.65) indicating significance of improved root growth for P acquisition. While in the second experiment cultivars were grown with adequate P for 30 days and then P was withdrawn from the nutrient solution by replacing fresh P free nutrient solution for 10 days. Induced P deficiency increased P contents in young leaves by two folds indicating remobilization of P from older leaves and shoot. Nonetheless cultivars varied for remobilization but differences in P remobilization could not explain the differences in P utilization efficiency among cultivars. Hence further experimentation to study root morphology, P uptake, and organic acid exudation by these cultivars in relation to P deficiency is recommended.     

Comparison of various potting media for their influence on nutrients supply,germination, and growth of muskmelon (cucumis melo L.) seedlings

Peat moss is used as potting mix for growing muskmelon (Cucumis melo L.) seedlings. However, it is not economical for most of the farmers in developing countries. The objectives of the present study were to compare various sources of composts as substitutes for peat moss, evaluate their physicochemical properties, and their effects on germination and growth of muskmelon (Cucumis melo L.) seedlings under greenhouse conditions. The treatments included pure peat moss (control), and composts prepared from guar (Cyammopsis tetragonoloba L.), jantar (Sesbania aculeate L.), and wheat (Triticum aestivum L) straw, at three air-filled porosity (AFP) levels (10, 15, and 20%) and rice (Oryza sativa) hulls at 10% AFP level. The second factor was the addition and devoid of nitrogen (N), phosphorus (P), and potassium (K) fertilizers. The addition of fertilizers in all potting media at 10% AFP level showed a small increase in total nitrogen, extractable phosphorus, and potassium. In the guar and jantar compost at 10% AFP, the values of total N (92.43 and 85.32%), extractable P (68.13 and 76.65%), and K (63.33 and 49%) were higher than in peat moss. It is concluded that composts of guar, jantar, wheat straw, and rice hulls at 10% AFP level can be used as a substitute of peat moss for growing muskmelon seedlings, but the addition of N, P, and K fertilizers is required in wheat straw and rice hulls compost for better nutrition of muskmelon seedlings.     

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.     

Zinc Requirement of Maize Hybrids and Indigenous Varieties on Udic Haplustalf

ABSTRACT

A pot study was conducted on Gujranwala series (Udic Haplustalf) to compare zinc (Zn) requirement of maize hybrids (FHY- 456, FHY- 396, and FHY- 421) and indigenous varieties (EV-1089, Golden, and Soneri). Uniform rates of nitrogen:phosphorus:potassium (N:P:K) and four rates of Zn were applied in triplicate according to CRD. There was a significant (P < 0.05) main and interactive effect of maize genotypes and zinc application on shoot growth and Zn uptake. The three maize varieties uniformly produced maximum shoot dry weight at 3 mg Zn kg^?1 soil. The maize hybrids produced maximum shoot dry weight at 9 mg Zn applied kg^?1 soil. A 6.3 mg Zn kg^?1 plant tissue was optimum for FHY-421 (hybrid) and 9.5 mg Zn kg^?1 plant tissue was optimum for Soneri (variety). Hence, more pronounced response in maize hybrids than indigenous varieties require higher rates of Zn application. However, further verification of the results is warranted under field conditions.     

Grain phosphorus and phytate contents of wheat genotypes released during last 6 decades and categorization of selected genotypes for phosphorus use efficiency

Grain phosphorus (P) and phytate contents are important for early growth and quality of wheat, respectively. We studied seed P and phytate contents of 57 wheat genotypes released during last 6 decades. The grain total P and phytate P concentrations ranged from 2.0 to 8.9 mg g^?1 and 1.6 to 4.7 mg g^?1, respectively. Grain P was higher in genotypes released in current or last decade than pre-green revolution period and it correlated well with grain phytate contents. Indicating that breeders worked only for increased grain P and did not consider the phytate contents. Twenty-five genotypes were selected based on differences in grain P and phytate contents to observe the P use efficiency under field conditions. Genotypes differed significantly for grain P and yield at both 0 and 60 kg ha^?1 P levels. In conclusion, phytate fraction in grains of recent wheat genotypes was more as compared to old genotypes and genotype Inqlab-91 and Chakwal-86 had maximum grain total P. Moreover, number of productive tillers, spikelet per spike, grain weight, harvest index and grain P concentration and uptake were found responsible for P tolerance under P deficiency.     

High Sodium in Irrigation Water Caused B Toxicity at Low Soil Solution and Shoot B Concentration in Maize (Zea mays L.)

Sodium (Na) and calcium (Ca) in brackish water differentially affects boron (B) nutrition of plants grown on calcareous and salt-affected soils. A glasshouse experiment was conducted to evaluate the effect of brackish irrigation water with different sodium adsorption ratio (SAR_iw) [distilled-water control, 8, and 16 (mmol_c L^?1)^1/2] on B nutrition of maize. Plants were grown for 40 days with 5 levels of B (0, 1.29, 2.30, 3.22, and 4.46 mg kg^?1 soil). Boron application significantly improved plant growth at lower rates. High B rates and application of high SAR_iw decreased plant growth independently, and the reduction in growth was further aggravated due to combined effect of both B and high SAR_iw. Decreased growth was attributed mainly to increased shoot B and Na concentration, while decreased Ca concentration. These ionic changes also altered internal and external B requirements. Yield decrease was observed at lower B concentration in soil solution B and plants shoot grown with high SAR_iw than in plants grown with distilled water and low B application rates.     

Zinc bioavailability response curvature in wheat grains under incremental zinc applications

Zinc application is generally recommended to enrich wheat grains with Zn; however, its influence on Zn bioavailability to humans has not received appreciable attention from scientists. In this pot experiment, seven Zn rates (from 0 to 18 mg kg^?1 soil) were applied to two wheat cultivars (Shafaq-2006 and Auqab-2000). Application of Zn significantly increased grain yield, grain Zn concentration and estimated Zn bioavailability, and significantly decreased grain phytate concentration and [phytate]:[Zn] ratio in wheat grains. The response of grain yield to Zn application was quadratic, whereas maximum grain yield was estimated to be achieved at 10.8 mg Zn kg^?1 soil for Shafaq-2006 and 7.4 mg Zn kg^?1 soil for Auqab-2000. These estimated Zn rates were suitable for increasing grain Zn concentration and Zn bioavailability (>2.9 mg Zn in 300 g grains) to optimum levels required for better human nutrition. Conclusively, Zn fertilization for Zn biofortification may be practiced on the bases of response curve studies aimed at maximizing grain yield and optimum Zn bioavailability. Moreover, additive Zn application progressively reduced the grain Fe concentration and increased the grain [phytate]:[Fe] ratio. However, a medium Zn application rate increased grain Ca concentration and decreased the grain [phytate]:[Ca] ratio. Hence, rate of Zn application for mineral biofortification needs to be carefully selected.     

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.