Dragan Žnidarčič

Impact of Climate Change on Developmental Dynamics of Thrips tabaci (Thysanoptera: Thripidae): Can It Be Quantified?

Abstract We attempt to quantify the impact of future climate change on the developmental dynamics of onion thrips in Slovenia. Monthly averaged results of simulations of future climate from four different general circulation models (GCMs) were projected to local scale by empirical downscaling. The GCM simulations were based on two emission scenarios (IPCC SRES A2 and B2). Local estimates of monthly averaged air temperatures for five locations in Slovenia were adjusted for an additional four emission scenarios (SRES A1T, A1F1, A1B, and B1) using a pattern scaling technique. They were further transferred to a daily scale using a first-order autoregressive model. A simple degree-day model, based on data reported in the literature, was used to relate the development of onion thrips to temperature. Potential changes in the period with favorable developmental conditions for onion thrips (i.e., temperatures above the lower developmental threshold) and in the number of generations per season were estimated with regard to the expected future climate change in Slovenia. The changes are influenced by the magnitude of temperature increase, its asymmetry within the year, and present climate conditions. Using this approach, one can obtain quantitative estimates of the impact of climate change on the developmental dynamics of an insect pest, but one must be fully cognizant of all the assumptions made in the procedure, which introduce uncertainties in the final results. Further research is needed to evaluate the plausibility of such simplified projections.

Field efficacy of deltamethrin in reducing damage caused by Thrips tabaci Lindeman (Thysanoptera: Thripidae) on early white cabbage

Our research assessed how the number of sprayings with deltamethrin influenced the efficiency against onion thrips, Thrips tabaci, on early white cabbage. The study was performed in 2002 and 2005 using the early white cabbage cultivar Parel, which is very susceptible to the attack of onion thrips. The cabbages were planted in a block-design experiment, with percentage of damage on the exterior leaves recorded according to the positions of the leaves (i.e. outer to inner). Although the attack of thrips was much greater in 2002 than in 2005, nevertheless, control plants in both years showed much more damage than plants with at least one insecticide spraying. In 2002, there was little difference between one and two sprayings, but three sprayings showed a significantly improved result. However, three sprayings of this insecticide is generally not permitted in farming practice. In 2005, no differences in efficacy among one, two and three sprayings were recorded. We also assessed a high threshold (up to 10% damaged leaf surface) and low threshold (up to 1% damaged leaf surface) for the removal of damaged leaves. In 2002, both thresholds were exceeded for control plants, but in 2005, the attack of thrips was mild enough that neither threshold was exceeded. In this case, one spraying was sufficient to reduce leaf damage below the higher (more tolerant) threshold, but three sprayings were needed to reduce leaf damage below the lower (more stringent) threshold. Therefore, in Slovenia or other parts of the world with similar climatic conditions, we recommend one spraying as broadly effective and recommend the more tolerant threshold for leaf removal.

Field efficacy of three insecticides against cabbage stink bugs (Heteroptera: Pentatomidae) on two cultivars of white cabbage

Abstract In 2002 – 2003, three insecticidal substances were tested for their ability to reduce the damage inflicted on plants of white cabbage by cabbage stink bugs, Eurydema ventrale and E. oleracea (Heteroptera: Pentatomidae). The two cultivars of cabbage tested were: the early cultivar, ‘Tucana F1’, which requires about 60 days from transplanting to harvest, and the mid-early cultivar ‘Hinova F1’, which requires about 120 days. In a field experiment, the growth and damage on cabbage plants sprayed with malathion (two sprays), potassium soap [potassium salts of fatty acids] (five sprays), and refined rape oil (five sprays) were compared to the growth and damage on unsprayed plants. Potassium soap and refined rape oil are considered to be environmentally friendly insecticides. In 2002, plants of the cultivar ‘Tucana’, that were treated with malathion had the highest plant weights [PW], head weights [HW], HW/PW ratio, and the lowest number of frame leaves. In the drier year of 2003, there were no significant differences in damage between the three treatments for either cultivar, except during the last assessment done on 13 August. In 2003, plants of ‘Tucana’, treated with potassium soap, had the highest PW and HW. The significantly lowest PW and HW values were recorded from the untreated plants. For the cultivar ‘Hinova’, the PW and HW were heaviest from the plants treated with malathion. In both years, the HW/PW ratio of Hinova (mid-early cultivar) did not differ between treatments, while the plants of ‘Tucana’ (early cultivar) treated with malathion had the highest ratio. Of the three substances tested, malathion was the most effective at reducing the damage on white cabbage plants caused by cabbage stink bugs. However, in an attempt to reduce the use of synthetic insecticides, instead of malathion, we recommend the use of refined rape oil (49 EUR/ha), as it is as effective as potassium soap (81 EUR/ha), but much cheaper.

Yield of early white cabbage grown under mulch and non-mulch conditions with low populations of onion thrips (Thrips tabaci Lindeman)

The damage caused by Thrips tabaci to a susceptible hybrid of early white cabbage was studied in field experiments undertaken during 2004 and 2005. The three treatments tested were beds of cabbage mulched with: (1) barley straw, (2) hay, and (3) black polyethylene (PE) sheeting. Bare-soil (un-mulched) beds were used as the control treatment. One early and one late experiment were performed in both years. In the early experiments, the mulches were applied at the start of the experiment, whereas in the late experiments the soil was first covered with black polyethylene for approximately 1 month. In both years, the springs were cold and wet, and so the thrips appeared late and their numbers were low. The highest mean actual weight and trimmed weight were recorded for cabbage grown in 2005 under PE mulch (actual early: 995 g, actual late: 1184 g, trimmed early: 870 g, trimmed late: 1056 g). Year 2004 gave lower values (110g for both variables) under barley straw and hay mulch (165 g and 160 g, respectively). There was no evidence of an allelopathic effect of water extracts of either barley straw or hay.

Three natural substances for use against Alternaria cichorii on selected varieties of endive: antifungal agents, plant strengtheners, or foliar fertilizers? Drei gegenüber Alternaria cichorii an ausgewählten Endiviensorten wirkende natürliche Substanzen: antimykotische Agenzien, Pflanzenstärkungsmittel oder Blattdünger?

During 2004 and 2005 the activity of sulphur, soya lecithin, and salicylic acid on endive and on the fungus Alternaria cichorii were investigated in a field block experiment. In both years, the plants sprayed five times with soya lecithin or three times with sulphur yearly, were significantly less infected than untreated plants. In 2005, the effect of salicylic acid (five sprays) was also shown to be satisfactory. Compared to the untreated plants, the plants treated with natural substances exhibited higher total mass as well as higher net mass. In both years a significant positive correlation was established between the total mass of the plants and yield loss (r2 = 0.66 in the 2004 soya lecithin treatment, and r2 = 0.62 in the 2005 salicylic acid treatment). In 2005, when the fungus occurred to a higher extent, a lower correlation (r2 = 0.30) was confirmed between yield loss and the extent of infection on the exterior leaves. The variety Eros was the most heavily infected with the fungus in both years, while the varieties Escariol grüner, Pancalieri, Avance, and Palmira showed greater resistance to infection with A. cichorii. The varieties Perfect, Pancalieri, and Avance had the highest net mass, while only the first of them showed the highest total mass.ZusammenfassungIn den Jahren 2004 und 2005 wurde die Wirkung von Schwefel, Sojalecithin und Salicylsäure auf die Endivie und ihr pilzliches Pathogen Alternaria cichorii in Blockversuchen im Feld untersucht. In beiden Jahren waren fünfmal mit Sojalecithin oder dreimal mit Schwefel gespritzte Endivien signifikant geringer infiziert als unbehandelte Pflanzen. Im Jahr 2005 wurde eine positive Wirkung nach fünfmaliger Anwendung von Salicylsäure beobachtet. Im Vergleich zur unbehan-delten Kontrolle wiesen die behandelten Pflanzen höhere Gesamt- und Nettogewichte auf. In beiden Jahren waren Gesamtgewicht der Pflanzen und Ertragsverluste positiv korreliert (r2= 0.66 in der Sojalecithin-Behandlung 2004 und r2= 0.62 in der Salicylsäure-Behandlung 2005). Im Jahr 2005 mit höheren Infektionsraten wurde eine geringere positive Korrelation (r2 = 0.30) zwischen Ertragsverlusten und Infektionsraten der Hüllblätter beobachtet. Die Sorte Eros war in beiden Jahren am stärksten infiziert, während die Sorten Escariol grüner, Pancalieri, Avance und Palmira resistenter gegenüber A. cichorii waren. Die Sorten Perfect, Pancalieri und Avance erreichten das höchste Nettogewicht und Perfect das höchste Gesamtgewicht.

Evaluation of genetic diversity of sweet potato [Ipomoea batatas (L.) Lam.] on different ploidy levels applying two capillary platforms

ABSTRACT The genetic composition of sweet potato [Ipomoea batatas (L.) Lam.] (2n = 6x = 90) is reflected in different levels of genetic variation. The main objective of the present study was a comparison of genetic diversity parameters of different ploidy levels (2n, 4n, and 6n codominant allele determination), analyzed on two high-resolution capillary platforms. Fragment analysis was performed by applying SSR markers on a 3130XL Genetic Analyzer (ABI 3130) and QIAxcel Advanced System (QX). A high level of expected heterozygosity (He) as a measure of genetic diversity was observed for both ABI3130 (0.731) and QX (0.679). Molecular variance was 17% for ABI3130 and 10% for QX. Comparison between genetic distance matrices based on allele lengths showed a moderate Mantel correlation coefficient (rxy = 0.557) between ABI3130 and QX. Global cluster analysis using the Bayesian approach distributed the observed genotypes into two clusters on both capillary platforms. Our results show that the two high-resolution capillary electrophoreses for codominant data on 2n, 4n, and 6n levels are applicable in genetic diversity studies but their efficiency depends on in-resolution expectations, financial resources, available time, and the equipment of the laboratory.

Impact of Organic Fertilizers on Phenolic Profiles and Fatty Acids Composition: A Case Study for Cichorium intybus L.

Radicchio (Cichorium intybus L.) is an increasingly appreciated leafy vegetable that exhibits great diversity in appearance, including different colored leaves, rosettes, or heads. Varieties of radicchio (‘Treviso’, ‘Verona’ ‘Anivip’, ‘Castelfranco’, and ‘Monivip’) commonly produced in Slovenia were investigated for their phenolic and fatty acid profiles. Plants were grown under organic and/or mineral fertilizer managements in greenhouse conditions. High-performance liquid chromatography analysis was used to study phenolic compounds in radicchio leaf samples. Thirty-three phenolic com‐ pounds were quantitatively evaluated. Significant differences were found between varieties and across different fertilizer managements. The total phenolic amount (TPA) was found in a wide range from 58 to 403 mg/100 g fresh weight (FW). Between varieties, the highest TPA was observed for var. ‘Treviso’ (300 mg/100 g FW) and the lowest TPA was observed for var. ‘Castelfranco’ (125 mg/100 g FW). The main phenolic compounds in radicchio leaves were represented by phenolic acids, chlorogenic acid and cichoric acid, respectively. The fatty acid levels of radicchio leaf samples were determined by the chromatographic analysis of fatty acid methyl esters using gas chromatography with flame ionization detector. The analysis revealed the amounts of C16:0, C18:0, C18:1n9, C18:2n6, C18:3n3, and C20:0 fatty acids. The total fatty acid levels varied from 170 to 500 mg/100 g FW. The highest fatty acid quantity was represented by C18:3n3 (≤63%) followed by C18:2n6 (≤45%) and C16:0 (≤24%). All radicchio samples had a ratio of n-6/n-3 essential fatty acids below 1 and thus in accordance with the current dietary guidelines. Among different fertilizer managements, the highest total fatty acid levels were found for organic fertilizer (384 mg/100 g FW).

Yield and quality of sweet corn (Zea mays L. var. saccharata) cultivars grown on different soil types

Maize (Zea mays L.) genotypes wit It improved nitrogen utilization efficiency (NUE) are of interest to growers. Field experiments were conducted to evaluate the total N uptake in the aboveground biomass and NUE (kg grain per kg of N absorbed in the aboveground biomass). Four commercial hybrids of similar maturity ranking were grown under the high-N (200 kg N ha(-1)) and low-N (1100 kg N ha(-1)) fertilization rates over three years. Growing conditions significantly affected hybrid performance for NUE, which ranged from 42 kg grain kg N-1 in the low-yielding (dry) environment to 55 kg grain kg N-1 under higher yielding environment, When compared to the low-N rate, the average N uptake was by 32% higher at the high-N rate, whereas smaller differences occurred for the aboveground biomass (12%), grain yields (14%), stover N (28%) and grain N (13%) concentrations. Significant differences existed among tested hybrids for grain yield, aboveground biomass, grain and stover N concentration, N uptake and consequently NUE.Hairy vetch (Vicia villosa Roth) and crimson clover (Trifolium incarnatum L.) were evaluated as cover crops during two vegetation seasons in the Mediterranean and Continental area of Croatia. Better tolerance to low winter temperatures was observed for crimson clover. Higher plants (10 to 3 1 cm) before winter and in spring (67 to 117 cm) were measured for hairy vetch, while crimson clover had higher yields of fresh biomass (33.7 to 113.1 t ha(-1)). Concentrations of N (1.53 to 3.34%), P2O5 (0.55 to 1.04%) and K2O (2.02 to 5.32%) in plant tissue were higher for hairy vetch. However, due to higher yields of dry matter, crimson clover accumulated more N (105 to 239 kg ha(-1)), P2O5 (28 to 83 kg ha(-1)), and K2O (105 to 440 kg ha(-1)) than hairy vetch. According to our results crimson clover could be recommended as a cover crop in Mediterranean and Continental area of Croatia.

Bioactive compounds and macroelements of chicory plants ( Cichorium intybus L.) after hydroponic forcing in different nutrient solutions

The aim of this study was to measure the bioactive compounds and elemental composition in the leaves of different chicory (Cichoruim intybus L.) cultivars after hydroponic forcing. Five chicory cultivars were studied: three red coloured cultivars: ‘Treviso’, ‘Verona’, and ‘Anivip’; one red-spotted cultivar ‘Castelfranco’; and one green cultivar ‘Monivip’. Developing chicory roots were forced in three different nutrient solutions enriched in nitrogen (+N), enriched in potassium (+N/K), or enriched in phosphorus (+N/P/K) to obtain new vegetative apical buds called chicons, or ‘Belgian endive’. Each of the nutrient solutions was used at three concentrations: 1%, 2%, and 3%. Fifty leaf samples (5 cultivars × 10 nutrient solutions) were used for analyses. Total phenolic content, antioxidant potential, and total flavonoid content were determined using spectrophotometric methods at the appropriate wavelengths, and multi-elemental analysis (P, S, Cl, K, Ca, Fe, Zn, Mn, Rb, Br, and Sr) was conducted using energy dispersive X-ray fluorescence spectroscopy. The highest total phenolic and total flavonoid contents of the chicons were observed with the nutrient solution enriched in K, followed by the solution enriched in N, and P. The highest antioxidant potential was observed with the nutrient solution enriched in N. Multi-element analysis detected the major macroelements (> 1 g·kg-1 dry weight) as K, P, Ca, Cl, and S. The nutrient solutions enriched in K and P generally showed the highest contents of these two macroelements in the chicons. Linear discriminant analysis for 19 parameters derived from 43 samples of five cultivars of chicons showed good discrimination between cultivars and nutrient solutions used for hydroponic forcing.

Economic analysis of different sweet corn varieties production

One of the biggest challenges for the safe maize production is the yield stability in a wide range of environments with different soil fertility, weather conditions, prevailing pests and diseases as well as cultural practices. In order to achieve it, new hybrids with higher tolerance to biotic and abiotic stress are continuously being created. In order to compare performance of maize hybrids in environments with different levels and types of stress, and relate it to the stalk lodging incidence, we compared performance of 64 maize hybrids obtained by crossing 16 inbred lines with four inbred testers in three different environments. Two environments at same location (Rugvica) differed in crop rotation, and the third environment at location Botinec was considered as dry because of low water capacity of the soil. Mixed models that included all design elements and genetic background of hybrids were used to analyze the effect of lodging on yield in different environments. The results show that stalk lodging had a significant effect on yield, but significant lodging x environment interaction indicates that this effect was rather environment specific.Sweet pepper Istra F1 hybrid was grown in a greenhouse on K rich soil. For evaluation of K antagonism, two K rates (55 and 85 kg ha-1) were applied in a randomized complete block design with four replications. Total number of fruits, total number of BER affected fruits as well as average fruit mass were recorded for each harvest. Fruit and leaf K and Ca content were determined at three plant growth stages (at the stage of the first, third and fifth fruit cluster). Higher K rate gave higher : average fruit mass (169.45 g), total number of fruits per plant (7.95), number of BER affected fruits per plant (3.82), K in leaves (5.44% DM), K in fruits (6.35% DM), but negatively correlated with Ca concentration in fruits (0.57% DM) and leaves (3.24% DM). This resulted in decreased marketable yield of sweet pepper fruits.