Soil fungal isolates produce different organic acid patterns involved in phosphate salts solubilization

Phosphorus availability is a major limiting factor for yield of most crop species. The objective of this study was to compare the solubilization of three sources of phosphorus (P) by different fungal isolates and to determine the possible mechanisms involved in the process. Talaromyces flavus (S73), T. flavus var flavus (TM), Talaromyces helicus (L7b) and T. helicus (N24), Penicillium janthinellum (PJ), and Penicillium purpurogenum (POP), fungal strains isolated from the rhizosphere of crops, are known to be biocontrol agents against pathogenic fungi. The P solubilization efficiency of these fungal strains in liquid media supplemented either with tricalcium phosphate (Ca₃(PO₄)₂; PC), aluminum phosphate (AlPO₄; AP), or phosphorite (PP) depended on the source of P and the fungal species. The type and concentration of organic acids produced by each species varied according to the source of available P. In the medium supplemented with PC, the highest proportion was that of gluconic acid, whereas in the media supplemented with the other P sources, the highest proportion was that of citric and valeric acids. This suggests that the release of these organic compounds in the rhizosphere by these microorganisms may be important in the solubilization of various inorganic P compounds. Results also support the hypothesis that the simultaneous production of different organic acids by fungi may enhance their potential for solubilizing insoluble phosphate.     

Fusaproliferin effects on the photosystem in the cells of maize seedling leaves

The possible role of the fusariotoxin, fusaproliferin in plant pathology was investigated with respect to cell membrane potential. Electron microscopy was used to study both the early effect of fusaproliferin on the host’s plasma membrane and ultrastructure responses in the cells of maize leaves. The seedlings of resistant (Lucia) and susceptible (Pavla) to the fusaproliferin maize cultivars were grown in the presence of fusaproliferin at different concentrations, namely 5 and 35 μg ml⁻¹, respectively, and electrophysiological measurements were compared with those obtained using two different toxic compounds, namely fusicoccin and 3-3(3,4 dichlorophenyl)-1,1-dimethylurea (DCMU). It was observed that only the higher concentration of fusaproliferin induced the onset of visible symptoms on the leaves. Comparing the effect of fusaproliferin to that of fusicoccin and DCMU at the higher toxin concentration, it was observed that functional differences in membrane potential induced severe damage to the mesophyll and outer chloroplast membrane; the extent of changes in electrophysiology and ultrastructure disturbances depended on the toxin concentration and was greater in the susceptible cv. Pavla. Results indicated that fusaproliferin could be involved in Fusarium pathogenesis either as a virulence factor or by enhancing the activity of other toxins that might be concomitantly present in infected plants.     

The triparental triploid onion <Emphasis Type="Italic">Allium</Emphasis> × <Emphasis Type="Italic">cornutum</Emphasis> Clementi ex Visiani, 1842, possesses a sterile S-type of cytoplasm

Triploid onion, Allium × cornutum Clementi ex Visiani, 1842 (2n = 3x = 24), a vegetatively reproduced garden crop, possess a complex triparental genome organization with three putative parental species, A. cepa L., A. pskemense B. Fedtsch., and A. roylei Stearn. Two of its most studied clones are the Croatian ‘Ljutika’ and the Indian ‘Pran’, which are genetically highly similar. Earlier studies have shown that ‘Pran’ possesses some molecular markers in the chloroplast DNA (cpDNA) identical to those of the unique male-sterile (S) cytoplasm, used for onion breeding. To find out whether ‘Ljutika’ also possesses a S-type of cytoplasm, we analyzed several cpDNA and mitochondrial (mtDNA) molecular markers. The PCR amplification and RFLP analysis of the chloroplast genes accD, atpF, petB and the mitochondrial gene cob, as well as the sequence analysis of the chloroplast matK and atpB-rbcL regions showed that ‘Ljutika’ possesses the male-sterile S-type of cytoplasm. The phylogenetic analysis of the matK and atpB-rbcL sequences of A. × cornutum, its parental species and other Allium species of the section Cepa showed that none of the analyzed species had the identical type of cpDNA as A. × cornutum. Results also suggested that A. pskemense can be excluded as a donor of the S-cytoplasm and a female parent, whereas cpDNA of A. roylei, although not identical to S-cytoplasm, possessed many polymorphisms of S-type. Fluorescent in situ hybridization, using fluorescently labelled parental genomic DNAs as probes in combination with fluorescently labelled 5S and 35S rDNAs enabled simultaneous visualization of the three genomes during meiosis and confirmed their homeologus intergenomic pairing.     

The Influence of Maca (<Emphasis Type="Italic">Lepidium meyenii</Emphasis>) on Antioxidant Status,Lipid and Glucose Metabolism in Rat

This work focused on the effect of maca on lipid, anti-oxidative, and glucose parameters in hereditary hypertriglyceridemic (HHTg) rat. Maca (1%) was administred to rats as a part of a high-sucrose diet (HSD) for 2 weeks. Rosiglitazone (0.02%) was used as a positive control. Maca significantly decreased the levels of VLDL (very low density lipoproteins), LDL (low density lipoproteins), and total cholesterol, and also the level of TAG (triacylglycerols) in the plasma, VLDL, and liver. Maca, as well as rosiglitazone, significantly improved glucose tolerance, as the decrease of AUC (area under the curve) of glucose showed, and lowered levels of glucose in blood. The activity of SOD (superoxide dismutase) in the liver, the GPX (glutathione peroxidase) in the blood, and the level of GSH (glutathione) in liver increased in all cases significantly. Results demonstrate that maca seems to be promising for a positive influence on chronic human diseases (characterized by atherogenous lipoprotein profile, aggravated antioxidative status, and impaired glucose tolerance), and their prevention.     

Biochemical Properties of Red Currant Varieties in Relation to Storage

Eleven red currant varieties (Ribes rubrum L.) cultured in Serbia were evaluated for some of their biochemical properties such as total phenolics, anthocyanins, ascorbic acid, invert sugar, soluble solid content, and acidity. The average amount of ascorbic acid varied from 50.5–71.6 mg/100 g FW, while concentration of invert sugars ranged from 6.0%–9.0%. The highest amounts of total phenolics and anthocyanins were detected in variety Redpoll (153.4 mg GAE/100 g FW and 19.3 mg/100 g, respectively). Red currants were processed to juice, and the phenolic and anthocyanin contents changed as a result of processing. Berries and juices were long-term stored at −18 °C and changes in phytochemicals were monitored. In berries, storage caused the decrease of ascorbic acid content up to 49%, and a general reduction of total phenolics was also noticed. In juices, total phenolics content increased after one year of storage. In both berries and juices total anthocyanins increased during storage by up to 85% and 50%, respectively. This study demonstrates that certain varieties, namely Redpoll, Jonkheer and London Market are good source of phytochemicals, retaining the nutritional value during processing and storage.     

Toxicity of biofungicide Timorex 66 EC to Cladobotryum dendroides and Agaricus bisporus

Twenty Cladobotryum dendroides isolates from Serbian Agaricus bisporus farms collected during 2003–2007, and the F56 strain of A. bisporus were tested in vitro for sensitivity to tea tree oil (Timorex 66 EC), a biofungicide, in comparison with prochloraz–manganese (Octave WP). The efficacies of tea tree oil and prochloraz–manganese were evaluated in a mushroom growing room, after application at standard product application rates and a combination of the two at respective proportion of 20:80%. Tea tree oil was considerably less toxic than prochloraz–manganese in vitro to C. dendroides isolates (ED₅₀ 112.9–335.8 mg l⁻¹) and A. bisporus F56 strain (98.0 mg l⁻¹), although neither fungicide was lethal to the pathogen. The biological efficiency of tea tree oil was higher than in treatments with the reference formulation of prochloraz–manganese. In our in vivo trials, no negative interference of the biofungicide with A. bisporus physiology was observed. Tea tree oil applied at the standard product application rate caused a significant reduction in cobweb disease levels in the A. bisporus growing room. Timorex 66 EC should be tested further in combination with other biofungicides to investigate the effectiveness of various mixtures for A. bisporus disease control.     

Histological characteristics of sugar beet leaves potentially linked to drought tolerance

Water is becoming more and more limiting factor of sugar beet production and the productivity of the crop can be significantly improved by increased drought tolerance. It is therefore a great challenge to assess the degree of variability of anatomical and morphological traits of breeding material with respect to water use efficiency and drought, that can be used as potential markers for selection of sugar beet genotypes with better tolerance to water shortage. To achieve this, the first step is to assess the degree of genetic variability with respect to anatomical and histological features linked to water management in plants, under optimal water supply. Comparative histiological analysis of lamina and petiole was done on 12 sugar beet genotypes which previously showed divergent responses to lack of water in the field. The plants were grown in semi-controlled conditions of a glasshouse, and watered daily. Mircromorphological analyses were done to assess leaf epidermal characteristics, by both light and SEM, and lamina and petiole histological features. The measurements were used to calculate the percentage of individual tissues in relation to the thickness of the lamina, main vein area and petiole area. The general structure of sample variability was established by principal component analysis (PCA), based on correlation matrix. In majority of genotypes the ratio of the size of cells of spongy parenchyma and palisade cells in average was 80%. Low genotypic variability of the studied histological parameters of the lamina and petiole may reflect the narrow genetic base of tested breeding material. The most significant genotypic difference, considering leaf epidermal tissue, was in % of adaxial and abaxial epidermis. The highest found number of stomata per mm² on both adaxial and abaxial epidermis was 40% higher than the lowest. During water stress, when stomata are closed, plant survival depends on the amount of water lost through the cuticle. SEM analysis of adaxial epidermis of the lamina show that cuticle varies in texture. Considering the observed genotypic variability in cuticle ornamentation and the fact that plants develop various strategies of adaptation to drought, finding genotypes with increased drought tolerance could be based on the characteristics of the cuticle and epidermis.     

Grapevine rupestris stem pitting virus: a new pathogen of grapevine in Serbia

Journal of Plant Diseases and Protection - Grapevine rupestris stem pitting-associated virus (GRSPaV), a member of the genus Foveavirus, is a commonly detected grapevine virus around the world....     

Effect of <Emphasis Type="Italic">Meloidogyne ethiopica</Emphasis> parasitism on water management and physiological stress in tomato

Root-knot nematodes (RKN) are obligate endoparasites that severely damage the host root system. Nutrient and water uptake are substantially reduced in infested plants, resulting into altered physiological processes and reduced plant growth. The effect of nematode infestation on the morphological changes of roots and subsequent physiological plant responses of infested tomatoes with the RKN Meloidogyne ethiopica was studied in a pot experiment. Plants were infested with two inoculum densities (10 or 50 eggs per cm³ substrate) and its effect was evaluated 74 and 102 days post inoculation (DPI). Morphological changes and root growth was determined by analysing scanned images of the whole root system. Nematode infestation reduced the portion of fine roots and increased that of coarse roots due to gall formation. Fine roots of non-infested control plants represented around 51% of the area of the whole root system at 74 and 102 DPI. In comparison to controls, plants inoculated with low and high nematode density had 2.1 and 3.2-times lower surface area of fine roots at 102 DPI. Root analyses revealed that plants had a very limited ability to mitigate the effects of the root-knot nematodes infestation by altering root growth. Root galls had a major influence on the hydraulic conductivity of the root system, which was significantly reduced. The low leaf water potential of infested plants coincided with decreased stomatal conductivity, transpiration and photosynthesis. The latter two were reduced by 60–70% when compared to non-infested control plants.