Glyphosate hormesis in broad-leaved weeds: a challenge for weed management

Little is known of glyphosate-induced hormesis in weeds and how this might influence weed management. To test the hormetic effect of low doses of glyphosate on broad-leaved weeds, two experiments were conducted, in the laboratory and the screenhouse. The hormetic effects of glyphosate solution in growth media (0, 65, 130, 250, and 500 g acid equivalent (a.e) ha^?1) and foliar spray (0, 4, 8, 16, 32, and 64 g a.e. ha^?1) were tested on four broad-leaved weeds (Coronopus didymus, Chenopodium album, Rumex dentatus, and Lathyrus aphaca). Glyphosate solution in the range 65–250 g a.e. ha^?1 stimulated the germination and seedling growth of all tested weeds. However, at 500 g a.e. ha^?1 inhibition of germination and growth was observed. Foliarly applied glyphosate in the range 4–32 g a.e. ha^?1 increased root and shoot length, dry biomass, and seed production ability of all four weeds species; however, the stimulatory response was species dependent. These results indicate that glyphosate hormesis could play a significant role in altering crop/weed competition and might influence weed management.     

Effects of Convolvulus arvensis Water Extract on Germination of Okra Under Different Seed Sizes

Convolvulus arvensis is a toxic allelopathic weed that suppresses germination and growth of crops.The prime object of present study was to investigate effect of Convolvulus arvensis water extract on germination and performance of okra with different seed sizes.The seeds of okra variety pusa green were separated into three different sizes,viz large size(4.00-5.00 mm),medium size(3.00-3.50 mm)and small size(2.00-3.50 mm),and then soaked in allelopathic plant bindweed water extract and kept in patrisdishes for germination into the germinator at 15℃.The experiment was laid out using Complete Randomized Design(CRD)with three replications.The results showed that after sowing of 12 days the highest germination was observed in non-treated seeds as compared to seeds treated in Convolvulus arvensis water extract for 1 h,further non-treated large seeds produced maximum plants as compared to treated small seeds after sowing of 24 days.Meanwhile,root length,shoot length,root fresh and dry weight,shoot fresh and dry weight were recorded higher in non-treated large seeds as compared to small seeds soaked for 1 h in Convolvulus arvensis allelopthic water extract.It could be found that Convolvulus arvensis affected germination,seed growth and overall performance of okra,further presence Convolvulus arvensis in crops could cause negative impact on germination and integrity of okra crops.     

Studying the extent of genetic diversity among Gossypium arboreum L. genotypes/cultivars using DNA fingerprinting

Genetic diversity is an area of concern for sustaining crop yield. Information on genetic relatedness/diversity among Gossypium arboreum L. cultivars/genotypes is scanty. We have used random amplified polymorphic DNA (RAPD) analysis to assess the genetic divergence/relationship among 30 genotypes/cultivars of G. arboreum. Of 45 primers surveyed, 63% were polymorphic. Out of the total number of loci amplified, 36% were polymorphic. The calculated genetic similarity between the cultivars/genotypes was in the range of 47.05–98.73%. Two genotypes, HK-244 and Entry-17, were the most distantly related. The average genetic relatedness among all the genotypes was 80.46%. However, most of the cultivated varieties showed a close genetic relationship, indicating a narrow genetic base in comparison to the non-cultivated germplasm. The calculated coefficients were used to construct a dendrogram using the unweighted pair group of arithmetic means (UPGMA) algorithm, which grouped the genotypes/cultivars into two major and three smaller clusters. The study is the first comprehensive analysis of the genetic diversity of G. arboreum germplasm and identifies cultivars that will be useful in extending the genetic diversity of cultivated varieties and future genome mapping projects.     

Supra‐optimal growth temperature exacerbates adverse effects of low Zn supply in wheat

Rising temperatures are a major threat to global wheat production, particularly when accompanied by other abiotic stressors such as mineral nutrient deficiencies. This study aimed to quantify the effects of supra‐optimal temperature on growth, photosynthetic performance, and antioxidative responses in bread wheat cultivars grown under varied zinc (Zn) supply. Two bread wheat cultivars (Triticum aestivum L., cvs. Lasani‐2008 and Faisalabad‐2008) with varied responsiveness to Zn supply and drought tolerance were cultured in nutrient solution with low (0.1 µM) or adequate (1.0 µM) Zn under optimal (25/20°C day/night) or supra‐optimal (36/28°C day/night) temperature regimes. Supra‐optimal temperature severely reduced root but not shoot biomass, whereas low Zn reduced shoot as well as root biomass. Shoot‐to‐root biomass ratio was reduced under low Zn but increased under supra‐optimal temperature. Supra‐optimal temperature inhibited root elongation and volume particularly in plants supplied with low Zn. In both cultivars, Zn efficiency index was reduced by supra‐optimal temperature, whereas heat tolerance index was reduced by low Zn supply. Supra‐optimal temperature decreased photosynthesis, quantum yield, and chlorophyll density in low‐Zn but not in adequate‐Zn plants. In comparison, low Zn decreased specific activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) and increased glutathione reductase (GR), where supra‐optimal temperature increased SOD, decreased GR and did not change APX activity in leaves and roots. Moreover, supra‐optimal temperature severely reduced shoot Zn concentration and Zn uptake per plant specifically under adequate Zn supply. Overall, supra‐optimal temperature exacerbated adverse effects of low Zn supply, resulting in severe reductions in growth traits viz. shoot and root biomass, root length and volume, and consequently impeded Zn uptake, enhanced oxidative stress and impaired photosynthetic performance. Adequate Zn nutrition is crucial to prevent yield loss in wheat cultivated under supra‐optimal temperatures.     

Manganese nutrition improves the productivity and grain biofortification of fine grain aromatic rice in conventional and conservation production systems

Manganese (Mn) deficiency is prevalent in rice-growing regions resulting in poor paddy yield and human health. In this study, role of Mn, applied through various methods, in improving the productivity and grain biofortification of fine grain aromatic rice was evaluated. Manganese was delivered as soil application (SA) (0.5 kg ha^?1), foliar spray (FA) (0.02 M Mn), seed priming (SP) (0.1 M Mn) and seed coating (SC) (2 g Mn kg^?1 seed) in conventional (puddled transplanted flooded rice) and conservation (direct seeded aerobic rice) production systems at two different sites (Faisalabad, Sheikhupura) in Punjab, Pakistan. Manganese application, through either method, improved the grain yield and grain Mn contents of fine grain aromatic rice grown in both production systems at both sites. However, Mn application as SC and FA was the most beneficial and cost effective in improving the productivity and grain biofortification in this regard. Overall, order of improvement in grain yield was SC (3.85 t ha^?1) > FA (3.72 t ha^?1) > SP (3.61 t ha^?1) > SA (3.36 t ha^?1). Maximum net benefits and benefit–cost ratio were obtained through Mn SC in flooded field at Faisalabad, which was followed by Mn SP in direct seeded aerobic rice at the same site. However, maximum marginal rate of return was noted with Mn SC in direct seeded aerobic rice at both sites. In crux, Mn nutrition improved the productivity and grain biofortification of fine grain aromatic rice grown in both conventional and conservation production systems. However, Mn application as seed treatment (SC or SP) was the most cost effective and economical.     

Technical adaptations for mechanized SRI production to achieve water saving and increased profitability in Punjab, Pakistan

Even in a country with a large population and rapid population growth, there can be labor shortages in the agricultural sector, because of outmigration of the able-bodied work force. The System of Rice Intensification (SRI) is not necessarily more labor-intensive once the methods have been learned, but the initial labor requirements can be a barrier to adoption, and farmers with large land areas cannot find the labor needed to use these more productive methods. Recognizing this problem, a set of agricultural implements have been designed for mechanizing the operations of SRI, with a view to reducing water requirements as well as labor requirements because the current conditions for agricultural production in the Punjab region of Pakistan include water scarcity and poor water quality as well as labor shortages. This article reports on the process of mechanizing SRI production in Punjab, which has been quite successful so far. Average yield is considerably increased with a 70% reduction in water requirements and a similar reduction in labor needs. The machinery and methods have been further adapted to other crops, being grown on permanent-raised beds, so that SRI with organic fertilization is combined with Conservation Agriculture. This combination is referred to as “paradoxical agriculture” because it enables farmers to achieve higher outputs with reduced inputs.     

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.     

Low-molecular weight organic acids improve plant availability of phosphorus in different textured calcareous soils

Understanding the role of organic acids on phosphorus (P) sorption capacity of soils is very important for its economic and friendly management. Combining P application with low-molecular weight organic acids could result in its higher plant availability for prolonged time. Therefore, citric and oxalic acid (at the rate of 1.0 mM kg^?1 soil) were evaluated for their effect on P sorption capacity and its plant availability in two different textured calcareous soils. Organic acids decreased P sorption capacity and organic carbon partition coefficient (K_oc) whereas increased Gibbs free energy (ΔG) of P. Organic-acid-treated soils required lesser quantity of P fertilizer to produce soil solution P concentration optimum for plant growth (external P requirement [EPR_0.2]), that is, 0.2 mg L^?1. Citric acid was efficient than oxalic acid in the above effects. P sorption parameters of Freundlich model were negatively correlated with lime potential and ΔG whereas had positive correlation (P < 0.05) with EPR_0.2 and K_oc. Incubation with oxalic acid increased available P in loamy sand and loam soil by 20% and 30%, respectively. Thus, organic acids could help reduce application rate of P fertilizer through lowering its adsorption in highly P-fixing soils without compromise on yield.     

Soil sodicity is more detrimental than salinity for quinoa (Chenopodium quinoa Willd.): A multivariate comparison of physiological,biochemical and nutritional quality attributes

Soil salinization is a serious environmental problem worldwide. To explore the comparative effects of soil salinity and sodicity on physiological, biochemical and nutritional quality attributes of four quinoa genotypes (A1, A7, Puno, Vikinga), pot and field experiments were performed on non‐saline soil and two types of salt‐affected soils designated as SS1 (saline) and SS2 (saline‐sodic). The results of both the experiments showed similar reduction pattern in biomass (11%–44%), chlorophyll content (10%–36%), stomatal conductance (18%–32%) and grain yield (30%–47%) of four genotypes on SS2 compared with SS1. Higher sodicity level of SS2 resulted in more Na accumulation (23%–40%) and oxidative damage (12%–35% decrease in membrane stability) leading to an increase in the activities of antioxidant enzymes (SOD, POD, CAT) in all the genotypes. Grain mineral contents (except Na and Mg) were decreased more in SS2 than SS1. Multivariate analysis revealed that grain Na content has negative correlation with all the nutritional quality attributes except Mg and fibre contents. Genotypes A1 and A7 were more salt tolerant with better grain nutritional quality than Puno and Vikinga. It is concluded that soil sodicity is more detrimental than salinity, and quinoa genotypes A1 and A7 are better than Puno and Vikinga for cultivation on saline and saline‐sodic soils.