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Destelbergen, Belgium

Parkinson J.F.,University of Sussex | Gobin B.,PCS Ornamental Plant Research | Hughes W.O.H.,University of Sussex
Entomologia Experimentalis et Applicata | Year: 2014

Mealybugs are sap-feeding insect pests that pose a serious threat to horticulture. The citrus mealybug, Planococcus citri (Risso) (Hemiptera: Pseudococcidae), like most other mealybug species, harbours two obligate maternally transmitted bacterial endosymbionts, which are essential for nutrient acquisition and host survival. These are 'Candidatus Tremblaya princeps', a member of the β-Proteobacteria, and 'Candidatus Moranella endobia', a member of the γ-Proteobacteria. The density of symbionts in the hosts is now understood to be dynamic, being influenced by the age and gender of the host and by environmental conditions during development. Here, we examine the impact of short-term heat stress treatment on the obligate symbionts and life-history parameters of P. citri, using qPCR to measure changes in symbiont density. Heat stress killed juveniles and adult males, and significantly reduced levels of 'Ca. Moranella endobia' and 'Ca. Tremblaya princeps' in adult females. However, adult females were resilient to this and it did not affect their fecundity or brood survival, although the sex ratio of their brood was slightly, but significantly, more female biased. Our results suggest that 'Ca. Tremblaya princeps' and 'Ca. Moranella endobia' are not as essential to the survival of adult mealybugs as they are to the survival of immature mealybugs and that sub-lethal heat treatment alone is unlikely to be effective as a disinfestation tactic. © 2014 The Netherlands Entomological Society.

Christiaens A.,Ghent University | Christiaens A.,PCS Ornamental Plant Research | Van Labeke M.C.,Ghent University | Gobin B.,PCS Ornamental Plant Research | Van Huylenbroeck J.,Belgium Institute for Agricultural and Fisheries Research
Acta Horticulturae | Year: 2015

Adventitious rooting is a critical process in the vegetative propagation of ornamental plants. A well-rooted cutting is essential for optimal growth and high quality plants. We investigated the use of spectral light quality to improve adventitious rooting of cuttings in three ornamental species: Chrysanthemum × morifolium, Lavandula angustifolia and Rhododendron simsii hybrids (azalea). Different combinations of red (R) and blue (B) LEDs were tested: R:B 100:0, 90:10, 80:20, 50:50, 10:90 and 0:100 at a light intensity of 60 μmol m-2 s-1 for chrysanthemum and lavender and 30 μmol m-2 s-1 for azalea. No natural light was supplied. The rooting quality was assessed by determining the rooting percentage, the amount of roots and the root dry weight. For all three species, rooting was highly efficient under 100% red light. Polar auxin transport was also influenced by the different light spectra as demonstrated by the use of auxin transport inhibitors. For chrysanthemum, rooting was most inhibited under 10:90 R:B, while for azalea the inhibition in rooting was highest under 50:50 R:B. The use of LEDs for rooting of ornamental cuttings is promising if it can be used in a multi-layered system. The controlled environment will lead to a year-round high quality rooted cutting production.

Christiaens A.,PCS Ornamental Plant Research | Christiaens A.,Ghent University | Gobin B.,PCS Ornamental Plant Research | Van Labeke M.C.,Ghent University
Acta Horticulturae | Year: 2016

Efficient adventitious rooting is a key process in the vegetative propagation of horticultural and woody species. A well-rooted cutting is essential for optimal growth and high quality plants. The use of spectral light quality to influence adventitious rooting has been studied for many years, but got a lot more attention since LEDs came on the market for horticultural practices. Contrasting results of the effect of light quality on adventitious rooting are reviewed in this paper. Even though more fundamental research is needed to easily determine which light quality can be used for a specific species, the use of LEDs for adventitious rooting is promising. For in vitro plantlets implementation can be done easily, for in vivo cuttings, the use of LEDs seems also promising in a multi-layered system. The controlled environment will lead to a year-round high quality rooted cutting production.

Moerkens R.,University of Antwerp | Leirs H.,University of Antwerp | Leirs H.,University of Aarhus | Peusens G.,Pcfruit | And 3 more authors.
Journal of Applied Entomology | Year: 2012

Beneficial arthropods are often used for suppressing specific pest outbreaks in agricultural crop systems. The European earwig, Forficula auricularia L., (Dermaptera: Forficulidae), is an important natural enemy in fruit orchards. Recently, ecological studies were published describing earwig dispersal and survival during summer, hereby revealing clear differences between populations with a single brood (SBP) and two broods a year (DBP). In this article, we will describe three potential mortality factors of earwigs during the underground winter period, namely cold temperatures, parasitoids and soil tillage. This knowledge is essential for making efficient management strategies for increasing earwig abundance in fruit orchards. The effect of cold temperatures was checked during a 3-year semi-field experiment. Parasitism rates of Triarthria spp. (Fallén) and Ocytata pallipes (Fallén) (Diptera: Tachinidae) were obtained in a rearing experiment. The negative effect of soil tillage on the survival of earwigs nests was checked in a field experiment covering a 4-year time period. A strong, negative relation between temperature [cooling day degrees (CDD)] and survival of female and male earwigs during winter was found. Male earwigs of SBP died very quickly, mimicking natural conditions. Between 60% and 90% of females do not survive winter. Survival of females in DBP was higher than in SBP. Parasitism rates vary a lot between species, generation, year and location (0-20%). During winter, we found a maximum mortality of 13%. There is a clear trend that soil tillage can reduce the number of nymphs in spring and summer by 50%. Implications for biocontrol are the following: (i) mortality owing to temperature can be predicted using CDD and if necessary preventive management actions can be undertaken to control pests; (ii) parasitism rates are negligible compared to high impact of temperature; and (iii) soil tillage can be timed more accurately using a recently developed day degree model. © 2011 Blackwell Verlag, GmbH.

Christiaens A.,Ghent University | Christiaens A.,PCS Ornamental Plant Research | De Keyser E.,Belgium Institute for Agricultural and Fisheries Research | Pauwels E.,PCS Ornamental Plant Research | And 3 more authors.
Frontiers in Plant Science | Year: 2016

Reliance on carbohydrates during flower forcing was investigated in one early and one late flowering cultivar of azalea (Rhododendron simsii hybrids). Carbohydrate accumulation, invertase activity, and expression of a purported sucrose synthase gene (RsSUS) was monitored during flower forcing under suboptimal (natural) and optimal (supplemental light) light conditions, after a cold treatment (7°C + dark) to break flower bud dormancy. Post-production sucrose metabolism and flowering quality was also assessed. Glucose and fructose concentrations and invertase activity increased in petals during flowering, while sucrose decreased. In suboptimal light conditions RsSUS expression in leaves increased as compared to optimal light conditions, indicating that plants in suboptimal light conditions have a strong demand for carbohydrates. However, carbohydrates in leaves were markedly lower in suboptimal light conditions compared to optimal light conditions. This resulted in poor flowering of plants in suboptimal light conditions. Post-production flowering relied on the stored leaf carbon, which could be accumulated under optimal light conditions in the greenhouse. These results show that flower opening in azalea relies on carbohydrates imported from leaves and is source-limiting under suboptimal light conditions. © 2016 Christiaens, De Keyser, Pauwels, De Riek, Gobin and Van Labeke.

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