Resistance to foliage feeding aphid in wheat

Experimental trials were conducted at Integrated Pest Management Programme, National Agriculture Research Centre Islamabad, to evaluate the resistance of host plants (cereals) against Rhopalosiphum padi (L.). For evaluation of susceptibility, twenty varieties/-advanced lines of National Uniform Wheat Yield Trails (NUWYT) Normal (N) of year 2004-2005 were used. In seedling bulk tests varieties/advanced lines were grouped into three categories resistant, moderately resistant and susceptible. Data from seedling bulk tests showed that DN-47 and PR 87 lines of wheat were resistant to aphid as compared to the other varieties/-advanced lines. In antixenosis tests varieties/-advanced lines were grouped into three categories, least preferred, moderately preferred, highly preferred. Lines V-01180, DN-47 and PR-84 were least preferred, sixteen varieties/-advanced lines were moderately preferred and only one variety V-9021 was found to be highly preferred.     

A new cytotoxic xanthone from Garcinia rigida

A new xanthone, yahyaxanthone (1), was isolated from Garcinia rigida leaves. Cytotoxicity evaluation showed that 1 was inhibitory to L1210 cell, with an IC50 value 4.08 microg/ml.     

Using synergistic exogenous phytohormones to enhance somatic embryogenesis from leaf explants of a Eucalyptus grandis clone

Somatic embryogenesis (SE) in Eucalyptus spp. has been limited to germinated seeds, flowers, lignotubers or zygotic embryos. The low yield of somatic embryos from leaf explants has hampered progress, even though leaves offer a more viable source of clonal explants from superior selected genotypes. It was hypothesised that SE from leaf explants could be enhanced through pairing of synergistic exogenous plant growth regulators, such as natural auxins with natural cytokinins. Callus and embryo induction using 2,4-dichlorophenoxyacetic acid (2,4-D), α-naphthalene acetic acid (NAA), indole acetic acid (IAA), and indole butyric acid (IBA), each at either 1.0 or 3.0?mg L^?1, indicated that IAA and IBA favoured significantly higher numbers of embryos compared with 2,4-D or NAA. Hence, IAA and IBA were used for subsequent experiments, combining them (at 1.0?mg L^?1) with either the synthetic cytokinin, kinetin, or the natural cytokinin, trans-zeatin, both at 0.1?mg L?1. The combination of trans-zeatin and either IAA or IBA resulted in a significant increase in SE (e.g. 86 ± 17.2% and 23 ± 3.2% for IAA with trans-zeatin and kinetin, respectively), compared with kinetin, or with these auxins alone. Embryo maturation and plantlet regeneration was highest in those calli that were induced with IAA and trans-zeatin, indicating that maturation was dependent on auxin depletion, based on the stability of the analogue used for induction. For the E. grandis clone under study, the use of synergistic plant growth regulators significantly enhanced SE from leaf explants, thus presenting the opportunity to benefit from the advantages that SE offers over conventional organogenesis.     

Glycinebetaine mediates chromium tolerance in mung bean through lowering of Cr uptake and improved antioxidant system

A pot experiment was conducted to evaluate the role of glycinebetaine (GB) in chromium (Cr) tolerance in mung bean (Vigna radiata L.) grown in Cr-stressed soil. Three concentrations of Cr (0, 250 and 500 µM) were tested with three (0, 50 and 100 mM) concentrations of foliar-applied GB. Cr alone led to a significant decrease in plant growth, biomass, and concentrations of chlorophyll a, b and carotenoids. Cr concentration and electrolyte leakage significantly increased in plants with increasing Cr levels in the soil. Lower Cr stress enhanced the activities of superoxide dismutase (SOD), peroxidases (POD) and catalase (CAT), while higher Cr concentrations decreased the activities of these enzymes. Foliar application of GB successfully alleviated toxic effects of Cr on mung bean and increased plant growth, biomass and chlorophyll contents under Cr stress. GB application reduced Cr accumulation and electrolyte leakage in plants and enhanced the activities of antioxidant enzymes in both shoots and roots as compared with Cr treatments alone. These findings suggest that foliar-applied GB alleviated Cr-induced oxidative stress in mung bean by reducing Cr uptake. The protective effect of GB against Cr stress varies with the concentrations of GB and Cr stress applied. Thus, further studies are still needed to specify the concentrations of GB required for detoxification of specific Cr concentrations under various climatic conditions.     

Effect of NaCl-induced saline sodicity on the interpretation of soil potassium dynamics

Excess of exchangeable sodium (Na) in salt-affected soils causes ion toxicity and decrease in nutrient uptake by plants, particularly potassium (K). A number of studies have been conducted to investigate the effect of K-fertilization on plant growth under sodic and saline-sodic conditions but the results are much diverse to process for concrete recommendations. To explore the possible reasons, it was hypothesized that Na applied as NaCl to produce salinity/sodicity in the soil may release non-exchangeable K, minimizing the effect of K-fertilization. Incubation studies were conducted for 2, 4 and 6 days in the light (sandy loam) and heavy (clay loam) textured soils producing two saline/sodic levels, i.e. 20 and 30 sodium adsorption ratio (SAR) along with control (SAR 3). Potassium fertilizer applied was calculated according to 40 (general recommendations based on soil-nutrient status), 80 and 160 kg K ha^?1. Interestingly, it was observed that addition of NaCl possibly released non-exchangeable K from the soil minerals and increased the K concentration in soil solution. Total K release was more in heavy textured soil but initial release was more in light textured soil. This release may eliminate the effect of K-fertilization applied under salt stress induced by NaCl. Therefore, it is suggested that while studying Na–K interaction in salt-affected soils, NaCl should be avoided to produce salinity, and naturally occurring saline-sodic soils may be used. Soil Na–K interaction studies including ameliorating effect of K under sodic or saline-sodic conditions should be conducted carefully considering the above-stated argument.     

Population dynamics of citrus leaf miner on different varieties of citrus in correlation with abiotic environmental factors in Sargodha District,Punjab, Pakistan

From January 2010 to December 2011, samples of leaves from citrus varieties Kinnow, Musambi and Feutral were taken from the five tehsils (administrative subdivisions) of Sargodha District in Pakistan including Sargodha, Bahalwal, Silanwalli, Sahiwal and Kotmomin, to study the population trends in citrus leaf miner (CLM), Phyllocnistis citrella (Stainton) (Lepidoptera: Gracillariidae), and its correlation with various environmental factors: (temperature, humidity and rainfall); plant morphological factors: moisture contents of leaves, leaf thickness, surface area (cm ² ), and biochemical percentage of calcium, potassium and magnesium in leaves. The maximum population of CLM was observed on Kinnow and Feutral, followed by Musambi. The effect of these factors on the larval population was 8.39- 2.30(Mg)+2.73(K)-0.398(Ca)-0.100(Temp)0.038(Humidity)+0.567(Rain)+0.07(Moist) 1.01 (Thickness)-0.022(Surface area). This equation revealed that magnesium, calcium, temperature, humidity, leaf thickness and leaf surface area are negatively correlated with larvae population, whereas potassium, rainfall and moisture are positively correlated with larvae population.     

Consequences of narrow crop row spacing and delayed Echinochloa colona and Trianthema portulacastrum emergence for weed growth and crop yield loss in maize

Echinochloa colona and Trianthema portulacastrum are weeds of maize that cause significant yield losses in the Indo‐Gangetic Plains. Field experiments were conducted in 2009 and 2010 to determine the influence of row spacing (15, 25 and 35 cm) and emergence time of E. colona and T. portulacastrum (0, 15, 25, 35, 45 and 55 days after maize emergence; DAME) on weed growth and productivity of maize. A season‐long weed‐free treatment and a weedy control were also used to estimate maize yield and weed seed production. Crop row spacing as well as weed emergence time had a significant influence on plant height, shoot biomass and seed production of both weed species and grain yield of maize in both years. Delay in emergence of weeds resulted in less plant height, shoot biomass and seed production. However, increase in productivity of maize was observed by delay in weed emergence. Likewise, growth of both weed species was less in narrow row spacing (15 cm) of maize, as compared with wider rows (25 and 35 cm). Maximum seed production of both weeds was observed in weedy control plots, where there was no competition with maize crop and weeds were in rows 35 cm apart. Nevertheless, maximum plant height, shoot biomass and seed production of both weed species were observed in 35 cm rows, when weeds emerged simultaneously with maize. Both weed species produced only 3–5 seeds per plant, when they were emerged at 55 DAME in crop rows spaced at 15 cm. Infestation of both weeds at every stage of crop led to significant crop yield loss in maize. Our results suggested that narrow row spacing and delay in weed emergence led to reduced weed growth and seed production and enhanced maize grain yield and therefore could be significant constituents of integrated weed management strategies in maize.