Synergistic and antagonistic interactions between potassium and magnesium in higher plants

Magnesium(Mg)affects various critical physiological and biochemical processes in higher plants,and its deficiency impedes plant growth and development.Although potassium(K)-induced Mg deficiency in agricultural production is widespread,the specific relationship of K with Mg and especially its competitive nature is poorly understood.This review summarizes current knowledge on the interactions between K and Mg with respect to their root uptake,root-to-shoot translocation and distribution in plants.Their synergistic effects on certain physiological functions are also described.The antagonistic effect of K on Mg is stronger than that of Mg on K in root absorption and transport within plants,indicating that the balanced use of K and Mg fertilizers is necessary for sustaining high plant-available Mg and alleviating K-induced Mg deficiency,especially in plant species with high K demand or in highavailable-K soil.The relationship between Mg and K in plant tissues may be antagonistic or synergistic depending on plant species,cell type,leaf age,source-and sink organs.There are synergistic effects of K and Mg on photosynthesis,carbohydrate transport and allocation,nitrogen metabolism,and turgor regulation.Definition of optimal K/Mg ratios for soils and plant tissues is desirable for maintaining proper nutritional status in plants,leading to a physiological state supporting crop production.Future research should concentrate on identifying the physiological and molecular mechanisms underlying the interactions between K and Mg in a given physiological function.     

Evaluation of bacterial biological control agents for control of root-knot nematode disease on tomato

Among 19 bacterial strains isolated in Yunnan from rhizosphere soils and plant tissues, Bacillus methylotrophicus strain R2-2 and Lysobacter antibioticus strain 13-6 exhibited the highest antagonistic activity against the tomato root-knot nematode Meloidogyne incognita in plate and greenhouse pot experiments. The two strains, when applied as soil drenches or seed treatments in greenhouse experiments, reduced root-knot severity and incidence on tomato compared to no-bacteria controls. In tomato field trials conducted in separate years, soil drench treatment with either strain reduced root-knot disease levels and increased yields compared to the control. Levels of disease control and yield enhancement provided by the strains were higher than those using the chemicals abamectin and carbofuran. This is the first report of B. methylotrophicus being used as a biocontrol agent against a plant parasitic nematode and the first demonstration that B. methylotrophicus and L. antibioticus can suppress disease caused by root-knot nematodes in the field.     

Alternative treatments for late blight control in organic potato: Antagonistic micro-organisms and compost extracts for activity againstPhytophthora infestans

Summary The effects of various fungi, bacteria and different compost extracts on foliar infection of potato (Solatium tuberosum) withPhytophthora infestans were tested in detached leaf bioassays in 2001–2003. Application of microorganism inocula and compost extracts as well as copper oxychloride to excised leaves resulted in different degrees of blight control. In general, suppression of blight lesion growth was not improved by applying the antagonists before the leaves were inoculated withPhytophthora spores. There was some evidence that extracts made from different compost feed stocks of different ages suppressed leaflet infection with blight. However, results were very limited and inconsistent. Moreover, the effects were much smaller than where copper oxychloride was used. Improved efficacy of acceptable alternatives to copper fungicides especially in organic farming is required. No promising effective alternative to the use of copper fungicides to reduce late blight infection in organic potato production systems was identified in the experiments.     

Relationship between vegetation state and bite dimensions of sheep grazing contrasting plant species and its implications for intake rate and diet selection

This study used both experimental evidence and a mathematical model to address some differences in interpretation in the literature on the relationship between sward height and the bite dimensions (bite depth, bite area and bite mass) of sheep grazing contrasting vegetation types. Individual non-fasted sheep were released onto small areas (10 × 10m) of white clover (Trifolium repens) and perennial ryegrass (Lolium perenne) and bite dimensions were measured as they grazed across patches (0·7 × 0·7 m) of predetermined sward surface height (SSH). Sward heights were 4, 7, 10, 13 and 16cm for white clover patches and 4, 6, 5, 9, 11·5 and 14cm for ryegrass patches. Four sheep were assigned to each plant species and each sheep grazed one patch of each height (five patches/sheep). Bite depth, bite area and bite mass increased linearly with SSH in both white clover and ryegrass. At a given SSH, bite depth was similar in white clover and ryegrass, but bite area and bite mass were greater in white clover than in ryegrass. The linear relationships observed between bite mass and SSH contrasted with the asymptotic relationships observed in some other studies, but it is suggested that different relationships may arise because of methodological differences between studies. Furthermore, when linear relationships for bite mass were compared with asymptotic relationships for bite mass in a mechanistic model of animals grazing from ryegrass-white clover pastures it was demonstrated that the nature of the relationship had relatively little effect on the relationship between intake rate and SSH. This was because intake rate depended on the fundamental mechanistic relationship between bite mass and prehension bite rate. This relationship meant that the greater bite masses found when linear relationship were assumed were associated with reduced prehension bite rates and thus the effect on intake rate was relatively small. In addition, the predictions of the model regarding the bases of diet selection by animals grazing ryegrass-white clover mixtures were simplified, and stabilized, when linear relationships were assumed.     

花生属栽野杂种后代抗青枯病研究

用强致病力青枯病病原菌接种花生栽野杂种后代种子 ,通过测定萎蔫指数和抗病率鉴定青枯病抗性。结果表明 ,花生栽野杂种后代存在抗青枯病新品系 ,2 7个品系的抗病率高于抗病对照协抗青 ,其中 7个高抗品系与抗病对照差异达显著或极显著水平。大部分抗病品系兼抗黑斑病和锈病     

Integration of Pseudomonas fluorescens and acibenzolar-S-methyl to control bacterial spot disease of tomato

Xanthomonas axonopodis pv. vesicatoria was isolated from infected tomato seedlings grown in an open field in Egypt. All the tested isolates infected tomato plants but with different degrees of disease severity. In an attempt to manage this disease, tomato seeds and/or seedlings were treated with an antagonistic local isolate of Pseudomonas fluorescens as a suspension or its formulation or acibenzolar-S-methyl (BTH). When the above three treatments were applied to tomato seeds under laboratory conditions, they improved seed germination and seedlings vigour relative to control seeds treated with sterile distilled water and pathogen but P. fluorescens culture was the most effective. Under greenhouse and field conditions, combinations of the above treatments were used. All treatments significantly reduced disease severity of bacterial spot in tomato relative to the infected control. The biggest disease reduction compared to seedlings inoculated with the pathogen alone resulted from a foliar application of P. fluorescens. Combined application of P. fluorescens or its formulation with BTH reduced the pathogen population and increased seedling biomass and tomato yield relative to control seedlings.     

Demand relationships and pricing implications for selected potato products

This study focused on determining retail demand relationships between tablestock potatoes, frozen french fries, and potato chips. The impact upon potato utilization resulting from independent pricing decisions was also analyzed. Bi-weekly data were obtained from five Central Maine grocery stores and analyzed using multiple linear regression Sales of tablestock potatoes appeared to be influenced more by the prices of potato chips than by their own price. The reverse was true for both french fries and potato chips, as their own prices had a greater effect on sales than did prices of other products. The inter-product analysis indicated that independent pricing decisions, while increasing utilization for the market with the reduced price, might cause utilization of potatoes in other markets to decline, possibly to the extent that total utilization was reduced from the original level To reduce or prevent widespread economic injury to the potato industry, it is recommended that a coordinated marketing system be developed to guide the industry through the transition from a predominantly fresh potato market to a market dominated by processed potato products     

Integrated effect of Glomus mosseae and selected plant oils on the control of bacterial wilt disease of tomato

This study investigated the efficacy of Glomus mosseae and thyme and peppermint oils in controlling bacterial wilt disease (BW) of tomato caused by Ralstonia solanacearum under in vitro conditions and under greenhouse and field conditions. In an in vitro study, we tested nine plant oils against R. solanacearum, and the results demonstrate that only caraway, thyme, peppermint and marjoram oils inhibited the growth of the BW pathogen with differing degrees, thyme oil caused the highest reduction of the growth of the pathogen followed by peppermint and the lowest was caraway and marjoram. We evaluated the effect of thyme and peppermint under greenhouse and field conditions. Under greenhouse conditions, the thyme treatment exhibited the highest disease reduction percentage followed by the thyme + peppermint treatment, while G. mosseae caused the least disease reduction percentage. Under field experiments, thyme oil treatment exhibited the highest ability to reduce the disease by 94.8 and 97.1% in the 2011 and 2012 growing seasons, respectively, followed by the treatment of thyme oil + peppermint oil with the reduction of 89.5 and 82.4%, respectively. G. mosseae exhibited the lowest percentage of disease reduction; however, it caused a greater yield increase percentage during both of the tested seasons.     

Molecular interactions between cereal soluble dietary fibre polymers and a model bile salt deduced from C NMR titration

Soluble dietary fibres (SDF) such as (1,3:1,4)-beta-d-glucan (βG) and arabinoxylan (AX) have been reported to lower plasma cholesterol levels in the human body, at least in part by preventing bile salts (BS) from being reabsorbed into the enterohepatic circulation. The mechanism(s) by which SDF interact with BS in the digestive tract is not known. This report describes investigations of molecular interactions between a model bile salt (taurochenodeoxycholate – TCDC) micelle with each of βG and AX using ¹³C NMR. In the presence of βG, chemical shift changes were observed for many bile salt resonances, but not βG resonances, without any apparent change in line widths. In contrast, in the presence of AX, no consistent chemical shift changes were observed for either TCDC or AX resonances, but TCDC signal intensities were reduced. This was not due to simple viscosity effects as the viscosity of the βG used was greater than that of the AX. The results suggest two different mechanisms of interaction between cereal non-starch polysaccharides and TCDC micelles: βG interacts directly on a molecular length scale with the micelles, whilst AX changes the local environment, resulting in reduced micellar mobility without direct molecular interaction.     

Evaluation of potato varieties and selections for resistance to bacterial soft rot

Potato varieties and selections were evaluated for resistance to bacterial soft rot caused byErwinia carotovora subsp. carotovora and Erwinia carotovora subsp. atroseptica in mist chamber. A randomized complete block design with a single treatment and 3 replications was used in this study. Potato lines were inoculated with bacterial suspension (10 tubers / line) using the puncture inoculation method and incubated for 4 days in a mist chamber at 21 C and 100 % relative humidity in the dark. Although there were differences in incidence of soft rot and in amount of weight reduction, most of the potato lines were susceptible to tuber soft rot. Mean incidence (%) of soft rot ranged from 10 to 100%. Mean reduction of tuber weight (%) ranged from 0.13 to 16.43 %. Among the varieties and selections tested, AF 522-5 was the most resistant to tuber weight loss, while AF 1424-7 was most susceptible. There were also significant differences between years, and a variety by year interaction. Testing over a period of years is recommended. A significant correlation coefficient of soft rot incidence (%) and reduction of tuber weight (%) was obtained (r=0.65; P=0.05), indicating that incidence was a fair measure of soft rot potential. However, the greater variability in results for incidence make weight loss a better measure of soft rot reaction. There was a significant difference among varieties in the reduction of tuber weight when potato lines were inoculated either 1 month or 2 months after harvest, but the interaction of time by year prohibits a conclusion as to which time gives a better test reaction. Late maturing varieties had slightly less weight loss than earlier maturing varieties.     

The effect of ground vegetation management on competition between the ants Oecophylla longinoda and Pheidole megacephala and implications for conservation biological control

In tropical Africa and Asia, two species of the predatory ant genus, Oecophylla, play a crucial role in protecting tree crops against pests and enhancing the quality of fruits and nuts. As predatory effectiveness is influenced by the presence of other dominant ant species, understanding the ecological factors at work in agroecosystems lies at the basis of conservation biological control. Over three and a half years, the effect of ground vegetation management on the beneficial tree-nesting ant Oecophylla longinoda (Latreille) and its competitor, the ground-nesting ant, Pheidole megacephala (Fabricius), was studied in a citrus orchard in Tanzania. When ground vegetation was present, P. megacephala tolerated O. longinoda and to some extent cohabited with this ant in citrus trees. However, after clean cultivation, P. megacephala displaced O. longinoda from tree crowns and became the sole occupant of the majority of trees. Displacement could be reversed by reversing the weed management regime, but this took time. Two years after the establishment of ground vegetation about half of the trees were colonized by Oecophylla only. Maintaining ground vegetation in tree crop plantations benefits the establishment and abundance of Oecophylla over Pheidole and is recommended in order to improve the efficiency of biological control of tree pests. The use of Amdro ant bait (hydramethylnon) to control P. megacephala is discussed. Boosting agroecological innovations, such as the one described in this paper, could benefit smallholder producers.     

Molecular interactions between cereal soluble dietary fibre polymers and a model bile salt deduced from 13C NMR titration

Soluble dietary fibres (SDF) such as (1,3:1,4)-beta-d-glucan (βG) and arabinoxylan (AX) have been reported to lower plasma cholesterol levels in the human body, at least in part by preventing bile salts (BS) from being reabsorbed into the enterohepatic circulation. The mechanism(s) by which SDF interact with BS in the digestive tract is not known. This report describes investigations of molecular interactions between a model bile salt (taurochenodeoxycholate – TCDC) micelle with each of βG and AX using ¹³C NMR. In the presence of βG, chemical shift changes were observed for many bile salt resonances, but not βG resonances, without any apparent change in line widths. In contrast, in the presence of AX, no consistent chemical shift changes were observed for either TCDC or AX resonances, but TCDC signal intensities were reduced. This was not due to simple viscosity effects as the viscosity of the βG used was greater than that of the AX. The results suggest two different mechanisms of interaction between cereal non-starch polysaccharides and TCDC micelles: βG interacts directly on a molecular length scale with the micelles, whilst AX changes the local environment, resulting in reduced micellar mobility without direct molecular interaction.     

Multifunctionality and non-trade concerns: implications for future agricultural policy in Asia

Agriculture's multifunctional role as provider of non-commodity outputs has received increased attention in the debate on the future of agricultural policy. To identify appropriate economic policies, a distinction must be made between concerns involving market failure and a consequent misallocation of resources, and those relating to distributional issues. We argue that it is essential to restrict the concept of multifunctionality to non-commodity outputs involving technical externalities or public goods and for which market failure and the misallocation of resources are important (e.g., amenity values and agricultural pollution). Other non-trade concerns, such as rural incomes and employment and food security, involve distributional issues, but no resource misallocation. This distinction makes it possible to identify different types of domestic policy measures to address them effectively and efficiently. Through reference to an empirical application to Taiwanese paddy rice policy, we illustrate that the most effective way to reconcile non-trade concerns is through policy measures that correct for market failure by valuing non-commodity outputs appropriately and a separate set of measures that address distributional issues.

Ecophysiological aspects of the interactions between Bromus kopetdaghensis and two nurse shrubs, Astragalus meschedensis and Acantholimon raddeanam in a semiarid rangeland

Plant-plant interactions are known as the main biotic drivers of the vegetation dynamics. Therefore, understanding such processes is beneficial for the applied vegetation management. The aim of this research was to investigate the type and intensity of plant-plant interaction during the time course of a growth season. We studied ecophysiological aspects of facilitation and competition between two aridland shrubs, A. meschedensis Bunge and A. raddeanam Czernjak and one perennial grass, B. kopetdaghensis Krasch. Soil and plant sampling were carried out for shrubs and the grass that were either growing alone or the grass was growing under the canopy of shrubs. In Spring (May), soil humidity weight was higher under the shrubs+grass than the grass-only site. By the beginning of Summer (July) grass consumed the common soil water and rapidly terminated its yearly growth. Therefore, in August and September, soil humidity weight was lower under the shrubs+grass than shrub-only sites. Photosynthesis rate of B. kopetdaghensis was sharply reduced from the beginning towards the end of growth season, but was not varied between the different plant combinations. Leaf proline measurement in July indicated higher stress for B. kopetdaghensis that were growing under shrubs than those of open areas. In conclusion, we found facilitation effects of shrubs on the grass at the early times of growth season, but it shifted into the competition for water during summer times. The outcome of plant interaction was positive for the grass but negative for the shrubs, especially A. meschedensis.     

Within-field variability of wheat yield and economic implications for spatially variable nutrient management

Economic justification for varying fertiliser inputs to match crop yield potential of different areas or zones in fields is limited by lack of understanding of the relationship between the extent of within-field yield variation and economic gains from zone versus uniform management. We conducted a survey of yield monitor data from 199 fields on the northern sandplain of the wheatbelt in Western Australia in order to document the extent of sub-field yield variation and test if variation is related to attributes such as yield and field area. The economic significance to zone management of the yield variation found in the survey along with variation in size of management zones, costs and prices, and soil fertility status was then assessed using a simple nutrient response model.     

Genotype x environment interactions and optimum resource allocation for sugarcane yield trials in Swaziland

To account for genotype x environment (G x E) interactions, sugarcane varieties are tested in multi-environment trials (METs) across multiple crop-years and seasons (early vs. late) under fully irrigated conditions in Swaziland. This study aimed to quantify the main sources of variation relevant to the MET network, identify mega-environments, evaluate adaptability of imported sugarcane varieties, and optimize resource use within the testing network. Nine varieties (eight imported Mauritian and one South African variety) were tested at two sites (Mhlume – M and Simunye – S), harvested early (E) and late (L) in the season across five crop-years in replicated (8) Latin square designs. A linear mixed model analysis of cane yield (tons of cane per ha; TCH), sucrose content (SUC%), sucrose yield (tons of sugar per ha; TSH), and fiber content (FIB%) showed that variety x season interactions were highly significant (P < 0.001) and larger than variety x site interactions for most traits. Genotype + genotype x environment (GGE) biplots revealed clustering of environments into two mega-environments by season rather than by site. Two Mauritian varieties were superior in each of the early and late mega-environments. Broad-sense heritability (H²) for all traits was larger than 0.79, with the highest value observed for FIB% (0.89). Resource optimization analysis, using variance components, suggested that future testing be conducted at a single site, across two seasons, with replicate numbers >5, and harvested across approximately five crop-years. Strong variety x season interactions should be exploited more aggressively in irrigated sugarcane selection programs.