Muhammad Shahbaz Naeem

NUTRIENT UPTAKE, PHYSIOLOGICAL RESPONSES, AND YIELD ATTRIBUTES OF WHEAT (TRITICUM AESTIVUM L.) EXPOSED TO EARLY AND LATE DROUGHT STRESS

The response of different wheat cultivars to drought imposed after three and six weeks of seedling emergence was evaluated in the wire house. The seeds of recommended local wheat cultivars were sown in plastic pots. The drought stress decreased the water relation, nutrient uptake and grain yield of all the wheat cultivars. The early drought stress significantly reduced the nitrogen (N) uptake by 38% while late drought stress decreased nitrogen uptake by 46%. The phosphorus (P) and potassium (K) uptake were decreased by 49% and 37% under early drought stress, respectively while their uptake was decreased by 51% each under late drought stress. Grain yield was reduced by 24% under early drought stress while it was reduced by 60% under late drought stress. Water deficit at early growth stages reduced grain weight by 10% while it was reduced by 35% under water deficit at later stages of growth.

Nano-TiO2 Is Not Phytotoxic As Revealed by the Oilseed Rape Growth and Photosynthetic Apparatus Ultra-Structural Response

Recently nano-materials are widely used but they have shown contrasting effects on human and plant life. Keeping in view the contrasting results, the present study has evaluated plant growth response, antioxidant system activity and photosynthetic apparatus physiological and ultrastructural changes in Brassica napus L. plants grown under a wide range (0, 500, 2500, 4000 mg/l) of nano-TiO2 in a pot experiment. Nano-TiO2 has significantly improved the morphological and physiological indices of oilseed rape plants under our experimental conditions. All the parameters i-e morphological (root length, plant height, fresh biomass), physiological (photosynthetic gas exchange, chlorophyll content, nitrate reductase activity) and antioxidant system (Superoxide dismutase, SOD; Guaiacol peroxidase, POD; Catalase, CAT) recorded have shown improvement in their performance by following nano-TiO2 dose-dependent manner. No significant chloroplast ultra-structural changes were observed. Transmission electron microscopic images have shown that intact & typical grana and stroma thylakoid membranes were in the chloroplast, which suggest that nano-TiO2 has not induced the stressful environment within chloroplast. Finally, it is suggested that, nano-TiO2 have growth promoting effect on oilseed rape plants.

Estimation of weed dry biomass and grain yield as a function of growth and yield traits under allelopathic weed management in maize

Growing concerns about toxicity and development of resistance against synthetic herbicides have demanded looking for alternative weed management approaches. Allelopathy has gained sufficient support and potential for sustainable weed management. Aqueous extracts of six plant species (sunflower, rice, mulberry, maize, brassica and sorghum) in different combinations alone or in mixture with 75% reduced dose of herbicides were evaluated for two consecutive years under field conditions. A weedy check and S-metolachlor with atrazine (pre emergence) and atrazine alone (post emergence) at recommended rates was included for comparison. Weed dynamics, maize growth indices and yield estimation were done by following standard procedures. All aqueous plant extract combinations suppressed weed growth and biomass. Moreover, the suppressive effect was more pronounced when aqueous plant extracts were supplemented with reduced doses of herbicides. Brassica-sunflower-sorghum combination suppressed weeds by 74-80, 78-70, 65-68% during both years of study that was similar with S-metolachlor along half dose of atrazine and full dose of atrazine alone. Crop growth rate and dry matter accumulation attained peak values of 32.68 and 1,502 g m-2 d-1 for brassica-sunflower-sorghum combination at 60 and 75 days after sowing. Curve fitting regression for growth and yield traits predicted strong positive correlation to grain yield and negative correlation to weed dry biomass under allelopathic weed management in maize crop.

Trianthema portulacastrum and Cyperus rotundus Interference in Maize and Application of Allelopathic Crop Extracts for Their Effective Management1

Horse purslane (Trianthema portulacastrum) and purple nutsedge (Cyperus rotundus) are two noxious C4 weeds of maize crop causing extensive yield losses. A two years field experiment was performed to estimate interference of T. portulacastrum and C. rotundus and to evaluate the role of allelopathic water extracts for effective weed management in maize. Five plant water extracts in ten binary combinations were foliar applied in triplicated randomized complete block design. Plots treated with commercial herbicide atrazine and weedy check (control), were also maintained for comparison. The highest density of both weed species was observed at 45 days after sowing (DAS) while weed dry biomass was higher at 60 DAS. Binary combination of sorghum-sunflower depicted greater suppression for weed density, dry biomass and persistence index (88-92% for T. portulacastrum and 65-81% for C. rotundus) as compared with weedy check. This treatment combination has also recorded an enhancement of 125% in crop resistance index, 84% in leaf area index and 41% in crop growth rate at 60-75 DAS thus, leading to 51% improvement in grain yield. Binary combination of sunflower-brassica returned maximum marginal net benefit, while sorghum-maize combination anticipated the peak value for marginal rate of return. Along with the effective weed management and higher yield, sorghum-sunflower documented the maximum net economic benefits among different plant extract combinations therefore, suggesting that exogenous application of sorghum-sunflower extract can be effectively used for controlling these weeds in maize field.

Foliar calcium spray confers drought stress tolerance in maize via modulation of plant growth, water relations, proline content and hydrogen peroxide activity

ABSTRACT Water and nutrient restrictions are the factors that limiting growth of maize in arid/semi-arid climate. Calcium (Ca2+) uptake is affected severely under drought stress (DS). The objectives of this study were to investigate the effects of DS and foliar applied Ca2+ on growth, physiological, biochemical, yield and grain-nutrient content in two maize cultivars i.e. drought-tolerantDekalb-6525 and drought-sensitive Yousafwala-hybrid. The study comprised of two phases; firstly the best rate of Ca2+ (20, 40 and 60 mg L−1) was evaluated. Secondly, optimized rate of Ca2+ (40 mg L−1) was used to assess physio-biochemical and yield responses of maize under DS. The applied DS caused significant reduction in maize growth, water-status, photosynthesis and grain nutrient contents. Foliar Ca2+ markedly improved plant growth, water-potential (18%), turgor-potential (75%), photosynthesis (45%), stomatal-conductance (47%), transpiration rate (43%) and accumulation of total soluble sugars (20%) along with decline in H2O2 content (23%) in both cultivars under DS. Furthermore, optimized rate of Ca2+ improved maize grain yield and quality under water-deficit conditions. Cultivar Dekalb-6525 presented significant response to Ca2+ over Yousafwala-hybrid. Results of the study surmise that foliar supply of Ca2+ is an effective approach to make plants vigorous to thrive under limited-water supply.

AM1 is a potential ABA substitute for drought tolerance as revealed by physiological and ultra-structural responses of oilseed rape

Abscisic acid (ABA) is an important signaling molecule for plants under drought tolerance. However, ABA itself has many limitations to be used in agriculture practically. Recently, AM1 (ABA-mimicking ligand) has been found to replace ABA. In this study, we have investigated AM1’s potential role for drought tolerance by growing two contrasting rapeseed (Brassica napus L.) genotypes: Qinyou 8 (drought sensitive) and Q2 (drought resistant) with exogenous ABA or AM1 application under well-watered and drought-stressed conditions. Results demonstrate that drought stress has hampered plant growth (relative height growth rate, plant biomass, leaf area), plant water status (leaf relative water content, root moisture content, leaf water potential), photosynthetic gas exchange attributes like net photosynthesis rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci), transpiration rate (E); chlorophyll fluorescence parameters like photosynthetic efficiency (Fv/Fm), effective quantum yield of PSII (ΦPSII), photochemical quenching coefficient (qL), electron transport rate (ETR) and chlorophyll content, especially for Qinyou 8 significantly compared to well-watered plants. Whereas increased root/shoot ratio (R/S), water use efficiency (WUE) and non-photochemical quenching (NPQ) was recorded in both genotypes under drought stress. On the other hand, exogenous ABA or AM1 treatment has regulated all the above parameters in a rational way to avoid drought stress. Chloroplast transmission electron microscope images, especially for Qinyou8, have revealed that oxidative stress induced by drought has blurred the grana thylakoids, increased the size or number of plastoglobules due to lipid peroxidation, and the presence of starch granules depict weak capacity to convert them into simple sugars for osmotic adjustment. However, intact grana thylakoid, few plastoglobules with no or very few starch granules were observed in the chloroplast from ABA- or AM1-treated plants under drought. More importantly, AM1-treated plants under drought stress have responded in an extremely similar way like ABA-treated ones. Finally, it is suggested that AM1 is a potential ABA substitute for plant drought tolerance.

Allelopathic action of parthenium and its rhizospheric soil on maize as influenced by growing conditions

A biossintese e subsequente liberacao de aleloquimicos por uma planta no ambiente e supostamente influenciada pelas condicoes de crescimento. Para aferir o efeito alelopatico de partes das plantas, bem como do solo rizosferico de losna-branca (Parthenium hysterophorus) crescendo em diferentes pontos de fazendas sob distintas condicoes na germinacao e crescimento de plântulas de milho hibrido da variedade DK 6142, um experimento foi instalado em ambiente controlado, com as sementes de milho sendo semeadas em placas de Petri sobre papel-filtro, assim como em baldes contendo substrato. Os menores valores para germinacao (30,0%), indice de germinacao (2,01), vigor de germinacao (36,3), comprimento da plântula (3,3 cm), biomassa da plântula (10 mg) e indice de vigor da plântula (99,0) de milho foram registrados sob aplicacao de extrato da folha, seguido por extrato do fruto e da planta inteira de losna-branca crescendo em Terras Altas. O solo rizosferico coletado sob plantas dessa especie crescendo proximo a canais de agua provocou maior reducao no indice de germinacao (30,8%), vigor de germinacao (40,6%), comprimento da plântula (32,6%), biomassa da plântula (35,1%) e indice de vigor da plântula (34,3%) de milho, comparado as plantas cultivadas em solo coletado em area sem vegetacao. Os efeitos fitotoxicos inibitorios tanto da losna-branca como de seu solo rizosferico foram mais pronunciados nas raizes do milho, em comparacao com a parte aerea. O maior efeito supressivo na germinacao e crescimento da plântula de milho deveu-se provavelmente a maior concentracao de fenois totais (6.678,2 e 2.549,0 mg L-1) e a presenca de compostos fenolicos, como acidos galico, cafeico, 4 hidroxy 3 methoxy benzoico, p cumarico e m cumarico, e de acido ferulico, vanilico, siringico e m cumarico no extrato aquoso das folhas de plantas coletadas em Terras Altas e de seu solo rizosferico coletado proximo a canais de agua, respectivamente.

Fullerol improves seed germination, biomass accumulation, photosynthesis and antioxidant system in Brassica napus L. under water stress

Carbon nanoparticles are widely studied for affecting crop production in agriculture. Considering their potential threats to the crops, especially under drought stress, is important for carbon nanoparticle application. However, the influence of polyhydroxy fullerene-fullerol on drought tolerance at the physiological and molecular levels in Brassica napus remains unclear. In the present study, different doses of fullerol were applied to seeds or leaves of B. napus subjected to water stress. The results showed that water stress significantly reduced the seed germination, aboveground dry weight, and photosynthesis, whereas it increased the abscisic acid (ABA) concentration, reactive oxygen species (ROS) accumulation, levels of non-enzymatic substances, and activities of antioxidant enzymes in B. napus. Priming with fullerol at 10 and 100 mg L-1 in seeds exhibited a significant promotional effect on seed germination under 15% polyethylene glycol treatment. Moreover, foliar application of fullerol raised the aboveground dry weight and photosynthesis in B. napus seedlings under soil drying. Compared with soil drying alone, the accumulation of ROS was repressed, which was concomitant with higher concentrations of non-antioxidant substances and increased activities of antioxidant enzymes in leaves of seedlings exposed to fullerol at specific concentrations addition with water shortage. Fullerol treatments at 1-100 mg L-1 dramatically increased the leaf ABA level and induced ABA biosynthesis by down-regulating the expression of the ABA catabolic gene CYP707A3 under drought. It is concluded that exogenous fullerol with seed priming or foliar application can stimulate growth in B. napus when water-stressed. The increased antioxidant ability that collectively detoxified ROS improved the drought tolerance in B. napus seedlings under foliar-applied fullerol treatment.

5-aminolevulinic acid improves salt tolerance mediated by regulation of tetrapyrrole and proline metabolism in Brassica napus L. seedlings under NaCl stress

5-aminolevulinic acid (ALA), a key biosynthetic precursor of tetrapyrroles, is vital for plant growth and adaptation to stress environments. Although exogenous ALA could enhance photosynthesis and biomass accumulation in plants under stress conditions, the underlying physiological and molecular mechanisms governed by ALA in promoting salt tolerance in Brassica napus L. are not yet clearly understood. In the present study, exogenous ALA with the concentration of 30 mg L-1 was applied to the leaves of B. napus seedlings subjected to 200 mM NaCl. The results showed that NaCl stress decreased the photosynthesis, biomass accumulation, and levels of chlorophyll and heme with the reduction of the concentrations of intermediates including ALA, protoporphyrin IX (Proto IX), Mg-Proto IX, and Pchlide in the tetrapyrrole (chlorophyll and heme) biosynthetic pathway. The transcript levels of genes encoding ALA-associated enzymes and genes encoding Mg-chelatase in the chlorophyll biosynthetic branch were down-regulated, while the expression levels of genes encoding Fe-chelatase in the heme branch were not significantly altered by NaCl stress. Foliar application with ALA enhanced the aboveground biomass, net photosynthetic rate, activities of antioxidant enzymes, accumulation of chlorophyll and heme, and concentrations of intermediates related to chlorophyll and heme biosynthesis in B. napus under 200 mM NaCl. The expression of most genes mentioned above remained constant in ALA-treated plants in comparison with non-ALA-treated plants under NaCl stress. Additionally, exogenous ALA synchronously induced the proline concentration and up-regulated the expression of genes P5CS and ProDH encoding proline metabolic enzymes in the NaCl treatment. These findings suggested that ALA improved salt tolerance through promoting the accumulation of chlorophyll and heme resulting from the increase of intermediate levels in the tetrapyrrole biosynthetic pathway, along with enhancing the proline accumulation in B. napus.

Tree species as a potential source of bio-herbicides for controlling Parthenium hysterophorus L.

To assess the herbicidal potential of Eugenia jambolana Lam., Ricinus communis L., Ziziphus jujuba L. and Ziziphus mauritiana L. against noxious weed Parthenium hysterophorus L., germination bioassay using their 1%, 2%, 3%, 4% and 5% (w/v) and seedling growth bioassay using their 5% (w/v) (on dry weight basis) aqueous leaf extracts (ALE) were conducted. ALE of R. communis showed maximum reductions in germination percentage (79%), germination index (89%) and seedling biomass (88%) as well as maximum delays in mean germination time (211%) and time to 50% germination (265%) of parthenium whereas maximum reductions in its seedling length (47%) and seedling vigour index (97%) were shown by Z. mauritiana. Reciprocal dose–response relationship by probit regression analysis revealed that LC50 values of R. communis and Z. mauritiana are 1.04% and 1.44%, respectively. Therefore, R. communis and Z. mauritiana are potential sources of bio-herbicides against this weed.