Effect of moisture stress on Nitrate Reductase Activity (NRA) in PEA (Pisum sativum L.) [C3] and sorghum (Sorghum vulgare Pers.) [C4] plants

Nitrate reductase activity (NRA) was studied in pea, a C₃ plant, and sorghum, a C₄ plant, at various stages of growth and development. Influence of moisture stress and nitrogen application was also observed since these factors have profound influence on growth and development.

In pea, NRA was maximum at pod maturity stage and minimum at flowering stage. In sorghum plant there was gradual increase in NRA upto grain formation followed by a fall in activity at maturity.

Nitrogen treatment as nitrate and ammonia significantly increased nitrate reductase activity over control in both pea and sorghum. Treatment with potassium nitrate was found to stimulate more NRA in pea than with ammonium sulphate. In sorghum, both forms of nitrogen did not differ much in their influence on NRA.

Influence of moisture stress in reducing NRA was more clear in sorghum, a C₄ plant than in pea, a C₃ plant. In general, control plants recorded low NRA in both the crops when compared to nitrogen treated plants except at pod formation stage in pea.     

Inoculation treatments affect the migration and colonisation of rhizobia in alfalfa (Medicago sativa L.) plants

Purpose: The purposes of this study were to characterise the migration and the colonisation dynamics of two different fluorescent-tagged rhizobia in various alfalfa tissues (especially in seeds); and also to develop efficient inoculation treatments to promote colonisation ability of target rhizobia in elite seed varieties.

Materials and methods: Four treatments (root drench, root damaging and drench, root drench with matrine, and flower spray) were applied to inoculate alfalfa with two fluorescent-tagged rhizobia, Ensifer meliloti LZgn5f (gn5f) and Ensifer meliloti 12531f (12531f), at three different growth stages; bud, flower and pod stages. The migration and colonisation dynamics of the two fluorescent tagged rhizobia strains were monitored using UV lamp detection and a stereo fluorescence microscopy.

Results: The results showed that both rhizobia strains mainly colonised the roots and could migrate to aerial tissues. In aerial tissues, when alfalfa plants were inoculated during the bud stage, both rhizobia strains mainly colonised the leaves and stems; during the flower stage, a spray inoculation treatment resulted in more 12531f colonising reproductive tissues, while during the pod stage, more rhizobial strains gn5f colonised seeds using the root drench with matrine treatment.

Conclusions: These results indicate that endophytic rhizobia are natural inhabitants of internal regions of roots, stems, leaves and that the endophytes may arise from reproductive tissues, such as seeds. Understanding the population dynamics of endophytic rhizobia in alfalfa would considerably improve the survival of target rhizobia during seed transfer. Combining target endogenous rhizobial species with good alfalfa seed varieties may lead to the development of a novel breeding method.     

Carbohydrate status in response to ion regulation of two rice varieties (Oryza Sativa L.) grown in saline medium

Two experiments were conducted to test varietal salt tolerance differences in the growth of rice and to identify initial ion‐specific salinity effects on ion regulation and carbohydrate metabolism.

The tillering growth stage of sensitive Giza 35 was more depressed due to high NaCl salinization than tolerant Giza 159. At low external K/Na there were no significant varietal differences in ion regulation. Reducing sugars generally were little affected by salinity. Salinization increased the low sucrose level in shoots of Giza 35 considerably, whereas the high sucrose level of Giza 159 was of little change. KC1 was most stimulative; sulfate had little effect in Giza 35 but decreased sucrose in Giza 159. Salinity Increased shoot starch content more in Giza 35 than in Giza 159, KC1 was most effective, whereas there was no change due to sodium sulfate treatment.

Possible interactions of ion regulation and carbohydrate metabolism in response to varietal salt tolerance of the two rice varieties were discussed. It is assumed that differences within the carbohydrate metabolism contribute to metabolic tolerance of rice varieties when grown in saline environment.     

Book review

Trace elements in plants by M. Ya. Shkolnik

Elsevier Science Publishers P. O. Box 330 1000 AH Amsterdam The Netherlands

Elsevier Science Publishing Company 52 Vanderbilt Ave. New York, New York 10017     

Mineral oil barrier is an effective alternative for suppression of damage by white snails

Purpose: Citrus white snail, Helicella candeharica Pfeiffer (Panpulmonata: Helicidae) is one of the most important orchard pests. In this study, the effectiveness of mineral oil was compared with molluscicide baits such as metaldehyde, ferricole (iron phosphate) and a snail-repellent paint in a commercial citrus orchard in northern Iran to reduce access of citrus white snails to citrus trees.

Materials and methods: The number of snails on citrus trees was monitored and counted 10 days after the application of the treatments, and at an interval of 6–8 days up to harvest time.

Results: In the first study, the mineral oil and repellent paint treatments reduced a number of snails best. In the second study, using metaldehyde and mineral oil barrier, again the mineral oil barrier reduced snails best. The cost of each treatment during one season per hectare was calculated at 55, 153, 124 and 120?$/ha for mineral oil, iron phosphate, snail-repellent paint and metaldehyde, respectively.

Conclusions: Mineral oil is an effective alternative for chemical compounds for reducing access by H. candeharica to citrus trees.     

Low-P solution culture can be used for screening root growth vigor in soil for high nutrient uptake of spring wheat varieties

Purpose: Root and root hairs of plants have been intensively studied in solution culture; however, correlation of such measurements in solution culture with development in soil is poorly understood. Therefore, the aim of this study is to study whether root and root hairs grown in solution culture can predict their behavior in soil and their correlation with macro- and micronutrients uptake of wheat genotypes.

Materials and methods: The growth of roots and root hairs as well as uptake of macro- and micronutrients of six spring wheat varieties was compared in solution culture under P stress and P abundance and in a low fertility soil.

Results and conclusions: Root length and surface area under P stress were significantly positively correlated with that in the low fertility soil, while no such correlation was apparent for root hair length and density. In absolute terms, the root length, surface area, root hair length and density of spring wheat varieties were substantially higher in soil than in solution culture, while the concentration and uptake of macro- and micronutrients in soil differed from solution culture in a complex way. The early uptake of macro- and micronutrients was intimately associated with root length and surface area as well as root hair length and density in soil but not in solution culture. Therefore, root length rather than root hair traits in low-P solution may be used to screen early root growth vigor in soil and thereby high nutrient uptake of wheat in low fertility soil.     

The relative efficiency of ionic iron(III) and iron(II) utilization by the rice plant

Uptake of iron by rice plants was equally rapid when supplied as ionic iron(II) or iron(III) at pH 3 and 4. Iron(III) uptake was reduced at pH 5 and uptake of iron when supplied as FeEDTA was relatively low at all three pH levels.

At pH 4 in the presence of plant roots, reduction of iron(III) to iron(II) occurred as indicated by Fe²⁺ BPDS formation. BPDS in a 3:1 ratio to iron(III) suppressed iron uptake by about 70%. The reduction was observed to be located in the endodermis of young roots and exodermis of older roots.

A capacity to oxidize iron(II) at the root surface was also observed under local anaerobic and relatively high pH conditions.

The significance of these two counteracting processes in affecting the oxidation state of iron at the root surface is discussed.     

Arbuscular mycorrhizal colonization of selected herbaceous plants under arid protected area in Tunisia

Arbuscular mycorrhizal fungi (AMF) play an important role in plants growth and soils dynamic in all most ecosystems. The main objective of the present study was to evaluate the plant-AMF interactions on soil functions under arid protected area ‘Zarat-Gabès’ in Tunisia.

AMF colonization was evaluated by visual observation of AMF in fine roots of eight herbaceous plants. The level of mycorrhizal colonization varied between plants. Astragalus corrugatus and Hippocrepis areolata showed the highest mycorrhizal performance. The relative spore number was significantly different across rhizosphere soils. Statistical analysis showed a clearly positive correlation between the number of spores and plant-mycorrhizal intensity.

For microbiological parameters, our results showed that mycorrhizal plants improved significantly the various microbiological parameters. Rhizosphere soils of Astragalus corrugatus and Hippocrepis areolata presented the necessary microbial densities and microorganisms more stable compared to unplanted soil. This study allowed obtaining a new result that challenges us about the need for efficient management of natural resources in the objective of nature conservation.     

Differential zinc uptake and transport in sorghum varieties suited for different moisture regimes

Zinc absorption and transport were examined in M‐35 a drought resistant, and M‐47, a drought susceptible sorghum (Sorghum bicolor L. Moench) cultivar. Excised roots were employed to study the mechanisms of uptake at cellular level in these varieties.

The absorption over 0 to 130 μM ZnCl₂ followed a biphasic pattern with a second rise at 90 μM, a feature which was not observed in the absorption by roots of intact seedlings. While there were no differences in the patterns of absorption in the two cultivars, the transport to shoot in M‐35 followed a slower rate up to 90 μM than that in M‐47. When Zn uptake was examined for 6 hours, the absorption and transport showed a number of changes in phase, which were running parallel. The transport of Zn followed a higher rate in M‐47 than that in M‐35.

Phosphate decreased the uptake and also transport of Zn in both the varieties. However, Zn inhibited phosphate absorption and transport in intact seedlings differentially amongst the varieties. Further, the inhibition of Zn uptake was much less in M‐35 than in M‐47, a feature which will perhaps facilitate survival of M‐35 under water stress, a condition which would also limit phosphate availability.     

Comparative response of poppy (Papaver somniferum L.) and eight crop and vegetable species to manganese excess in solution culture

The relative response of poppy (Papaver somniferum L.) and eight crop and vegetable species to excess manganese was investigated in a glasshouse, solution culture experiment. Plant yields and manganese concentrations were measured after two and six weeks growth at five levels of manganese (10–800 μM).

Poppies were highly sensitive to manganese toxicity in solution culture and reductions in shoot yield occurred at lower manganese levels in solution and at lower shoot manganese concentrations than that for the following sensitive species, ranked in order of increasing tolerance : brussels sprout, barley, green beans, lucerne and grean pea. In contrast lupins, oats and sugar beet were relatively tolerant producing about 80% or more of maximum shoot yield at the highest solution manganese level (800 μM Mn).

In this study the sensitivity of poppy, and brussels sprout, to manganese excess was attributed to their low shoot manganese “toxicity threshold values”; and their capacity to partition a high proportion of total plant manganese and dry matter to the shoot at solution manganese levels ≥ 100 μM.

The application of these results to field grown poppy is discussed in relation to interactions between manganese and other elements which modify plant tolerance to manganese excess.     

Differential tolerance of bush bean cultivars to excess manganese in solution and sand culture

Nineteen bush bean cultivars were screened for tolerance to excess Mn in nutrient solution and sand culture experiments. Seven‐day‐old seedlings were treated with full strength Hoagland No. 2 nutrient solution containing different Mn concentrations for 12 days in the greenhouse.

Cultivars showing the greatest sensitivity to Mn toxicity were ‘Wonder Crop 1’ and ‘Wonder Crop 2'; those showing the greatest tolerance were ‘Green Lord’, ‘Red Kidney’ and ‘Edogawa Black Seeded’.

Leaf Mn concentration of plants grown in sand culture was higher than that for plants grown in solution culture. The lowest leaf Mn concentration at which Mn toxicity symptoms developed, was higher in tolerant than in sensitive cultivars. The Fe/Mn ratio in the leaves at which Mn toxicity symptoms developed, was higher in the sensitive cultivars than in the tolerant ones.

We concluded that Mn tolerance in certain bush bean cultivars is due to a greater ability to tolerate a high level of Mn accumulation in the leaves.     

Effect of nitrogen and sulphur fertilizers and seed inoculation with rhizobium phaseoli on the nitrogen‐sulphur relationships of bean (phaseolus vulgaris L.)

A greenhouse experiment with beans (Phaseolus vulgaris L.) was performed in order to investigate the effect of nitrogen and sulphur application and seed inoculation on the yield, leaf area, distribution of different nitrogen and sulphur fractions and N/S ratio in shoot, fruit and root.

Inoculation of plants together with nitrogen or sulphur application produces an increase in the concentration of total nitrogen and a decrease in the accumulation of nitrate‐nitrogen and sulphate‐sulphur in shoot, fruit and root. Leaf area increased more with nitrogen than with sulphur application while the highest amounts of fruit dry matter were obtained with sulphur application.

N: S ratios obtained were different according to the part of the plant tested. Sulphur fertilization decreased the N: S ratios in shoot, fruit and root. The data obtained indicate that and adequate N: S ratio can insure maximum production of yield.     

Breeding rice for rice yellow mottle virus resistance in Sub-Saharan Africa: a review

Rice is the world’s second most produced staple cereal crop after wheat. Currently, rice production and consumption have steadily increased in Sub-Saharan Africa (SSA). To date, rice is the largest imported commodity crop in the region. The low productivity is due to a number of biotic and abiotic stresses, and socio-economic constraints. Among the biotic constraints, rice yellow mottle virus (RYMV) is the most important constraint to rice in SSA. In SSA, RYMV causes yield losses ranging from 20% to 100%. Various control strategies (host resistance, cultural practices and chemicals) have been recommended to manage RYMV epidemics. RYMV disease management through generic crop protection chemicals is not economic nor is it successful due to the presence of a large number of vector species disseminating the virus. In addition, cultural practices are ineffective against RYMV because the virus is spread by several agents, including insect vectors. The use of RYMV resistant cultivars remains the most effective, economic and environmentally friendly method for resource poor farmers. However, RYMV resistant varieties have not yet been developed and deployed in SSA. The aim of this review was to present the main components in the development of rice cultivars with RYMV disease resistance. The paper provides a comprehensive review on the genetic variability of the RYMV, its epidemiology and control measures, and the gene action responsible for RYMV resistance.

The review also summarises complementary genomic tools useful in RYMV disease resistance breeding.

Successful breeding of rice for RYMV resistance depends on the availability of genes for stable resistance, knowledge of the genetics of the host and, the availability of efficient phenotyping and pathotyping methods, and understanding of the genes involved and their pattern of inheritance. Information presented in the review can serve as a reference guide for rice breeding emphasising RYMV resistance, high yields and farmers-preferred traits.     

The effect of salinity and iron application on growth and mineral uptake of sunflower (helianthus annuus L.)

In a greenhouse experiment, the effect of salinity and Fe chelate on growth and mineral uptake of sunflower (Helianthus annuus L. c.v. Record) was studied.

Sunflower plants were grown in nutrient solution with four levels of salinity (0, 1.5, 3.0 and 4.5 atm), induced by NaCl and four rates of Fe chelate (0, 0.5, 1.0 and 1.5, ppm Fe) as FeEDDHA. The experiment was a completely randomized design with treatment combinations arranged in a factorial manner with three replications.

Dry matter yield, shoot‐root ratio, leaf area, plant height and transpiration decreased as salinity increased, the effect of salinity being depressed by iron applications. Salinity reduced P, K, Ca and Mg uptake by roots as well as that of N, P, K, Ca, Mg by shoots, while Fe applications increased uptake of these elements in roots and shoots. Both salinity and iron applications increased Cl, Na and Fe uptake by roots and shoots, as expected. In most instances salinity reduced uptake of Fe, Mn and Zn by the plants while iron applications improved uptake of these elements.

The sunflower plant used in this experiment was found to be, at least partly, tolerant to salinity and decreased water availability as well as toxicity of ions. Nutritional disorders were the cause of decreased plant growth by increasing salinity of the nutrient solution. The decreased plant growth and mineral uptake, induced by salinity, were partially offset by increased iron levels in the nutrient solution.     

Influence of extreme K:Na ratios and high substrate salinity on plant metabolism of crops differing in salt tolerance.VII. Relations between carbohydrates and degradative enzymes in salt tolerant and salt sensitive cotton genotypes during initial salinity stress

The effects of salinity on carbohydrates in leaves and roots of different salt tolerant cotton genotypes Glza 45 (salt tolerant) and Dandara (salt sensitive) during the initial salinity stress are investigated. Changes of starch and sucrose in relation to soluble amylases, phosphorylase and invertase in young leaves are studied. The plants are grown in water culture under controlled conditions.

Starch and sucrose accumulation is rapidly stimulated in leaves of Dandara, particularly due to extreme potassium sulfate supply, while in Giza 45 the amount of starch and sucrose declines except for extreme potassium sulfate treatment. The low sucrose value in roots of Dandara increases extremely, especially as a result of potassium chloride treatment. In contrast, the higher sucrose content in roots of Giza 45 is little affected. Amylase activity changes considerably in positive correlation with the starch content, whereas the low specific activity of phosphorylase is little affected. The sucrose content in the leaves is directly controlled by a high level of invertase activity of both cotton varieties.

Possible interactions of carbohydrate metabolism and genotyplcal ion regulation in response to the different salt tolerance of the genotypes are discussed. It is concluded that genotypical differences in the carbohydrate metabolism could be effective mechanisms for salt tolerance in cotton.     

Assessing the impact of soil amendments made of processed biowaste digestate on soil macrofauna using two different earthworm species

Fermentation in combination with subsequent composting of biowaste is a preferred method for municipalities to recycle organic byproducts and transform them into useful end products for soil amelioration or plant fertilization. These compost products, especially if obtained from household wastes, can be a source of hazardous components, e.g. heavy metals, pathogens, synthetic chemicals or toxic organic compounds. An avoidance test with two earthworm species (Eisenia fetida and Aporrectodea caliginosa) was conducted to assess the impact of differently processed biowaste based digestate products on soil invertebrates. Body weight changes were recorded, as well as differences in effects on adult versus juvenile earthworms.

While E. fetida showed no avoidance towards the digestate products (negative avoidance, meaning that the tested products were preferred, of 80 to 100 %), A. caliginosa rejected the crude biowaste digestate compost in higher concentrations (avoidance of 45 %), but not the agglomerated or pelletized variants. A clear weight gain of up to 25 % was observed only for individuals of E. fetida. The developmental stages of the worms were not crucial for the outcome of the avoidance test.

Based on the results of this study the application of biowaste products on arable land cannot be recommended without constraints.     

Practical Applicability of Germination Index Assessed by Logistic Models

Sewage sludge management is a major challenge in environmental protection. Composting is an organic waste treatment method that is cost effective and leads to resource recovery. Composting is considered an environmentally and agriculturally friendly method of sewage sludge utilisation. The objective of this study was to evaluate maturity of three composts prepared on the basis of sewage sludge mixed with structure-forming waste materials, such as pine bark, sawdust and wheat straw. The germination index (GI) was used to assess the maturity and phytotoxicity of composts at particular composting stages (initial, mesophilic, thermophilic, cooling, maturation). Cress seeds were used to determine the GI. The logistic model, which belongs to a broad class of generalized linear models, was used to analyze experimental data. Using this model the interesting probabilities (from the point of view of the experimenter) for the occurrence of a specific root length were determined. In addition, a model was constructed providing a dependence of probability on temperature.

This work indicates a marked dependence between root length produced by cress seeds and the temperature of the composting process, which was closely related to the GI values. The longest plant roots, similarly as the highest GI values, were found at the lower temperature, which took place at the beginning and at the end of the composting process. Our findings suggest that the practical applicability of GI in the evaluation of compost maturity is limited. Additionally, the role of additional wastes being structure-forming agents in composted mixtures with sewage sludge was stressed as a sorption matrix for harmful substances released from sewage sludge.     

The influence of high salt stress on starch,sucrose and degradative enzymes of two glycine max varieties that differ in salt tolerance

Salt stress effects were investigated on growth, the carbohydrate levels and the activity of degradative enzymes amylases, phosphorylase and invertase of two soybean varieties, Jackson and the more salt tolerant Lee.

Stress depressed growth of Jackson more than of Lee. Salt stress increased leaf and root sucrose more in Jackson than it did in Lee. Root sucrose was higher in Lee. Stress reduced leaf starch in both. It decreased spec. invertase activity in close negative correlation with the sucrose. Independent from salt tolerance, increased spec. amylase activity was in some correlation with the declined starch level. Stress changed phosphorylase little in both varieties. It is concluded that salt stress‐induced restricted utilization of leaf sucrose, but not foliar starch, could partly be a result of ionic affected degradation, which may diminish survival value of soybean varieties.     

Manganese toxicity in bush bean as affected by concentration of manganese and iron in the nutrient solution

An experiment was conducted to clarify the relationship between Mn toxicity and Fe deficiency in bush snap bean (Phaseolus vulgaris L. cv. ‘Wonder Crop No. 2'). Seedlings were grown in full strength Hoagland No. 2 solution at pH 6.0 for ten days. Six concentrations of Mn as MnCl₂.4H₂O were used in combination with three concentrations of Fe as FeEDTA.

Toxicity symptoms, induced by low levels of Mn (0.1 ppm and above), included: small brown necrotic spots and veinal necrosis on primary leaves; necrosis on primary leaf petioles; interveinal chlorosis, with or without brown necrotic spots, on trifoliate leaves; and brown necrotic spots on stipules. Manganese toxicity symptoms were alleviated or prevented by increasing Fe concentration in the nutrient solution.

Manganese concentration in the leaves increased with increasing Mn and decreased with increasing Fe concentration in the nutrient solution, Iron concentration in the roots increased with increasing Fe concentration in the nutrient solution; however, Fe concentration in the leaves was not significantly affected by increasing Mn concentration in the solution culture. Manganese toxicity symptoms developed when Mn concentration in the leaves reached about 120 ppm.

A decrease in the Fe/Mn ratio in the nutrient solution resulted in a proportionate decrease in that of the leaves. Manganese toxicity symptoms occurred when the Fe/Mn ratio in the solution was 10.0 and below, or when the ratio in the leaves was less than 1.5. The ratio of Fe/Mn in the solution required for optimum growth of ‘Wonder Crop No. 2’ bean, without Mn toxicity symptoms, was in the range of 20.0 to 25.0.

Results indicate that the chlorosis on bush bean leaves induced by excessive Mn in the nutrient solution was due to excessive accumulation of Mn and not to Fe deficiency.     

Resistance breeding and biocontrol of Striga asiatica (L.) Kuntze in maize: a review

Purpose: The aims of this article are to highlight pre-breeding procedures for identifying primary sources of Striga-resistance genes and to summarize complimentary breeding techniques that enhance partial resistance of maize varieties against Striga species.

Materials and methods: The paper presented a comprehensive account of Striga screening and controlling techniques and highlighted the potential of integrating partial resistance with FOS to boost maize production and productivity in SSA.

Results: Striga infestation is a major constraint to maize production and productivity in Sub-Saharan Africa (SSA). A lack of Striga-resistant maize varieties and the limited adoption of other control methods hinder effective and integrated control of the parasitic weed in maize and related cereal crops globally. Genetic resistance of maize should be complemented with the use of Fusarium oxysporum f.sp. strigea (FOS), a biocontrol agent known to suppress Striga.

Conclusions: A combined use of genetic resistance and FOS has remained largely unutilized in controlling Striga in Africa. A combination of conventional and molecular Striga-resistance breeding tools as well as the use of FOS are promising methods to effectively control Striga in SSA.