Cold storage to overcome dormancy affects the carbohydrate status and photosynthetic capacity of Rhododendron simsii.

Global warming leads to increasing irregular and unexpected warm spells during autumn, and therefore natural chilling requirements to break dormancy are at risk. Controlled cold treatment can provide an answer to this problem. Nevertheless, artificial cold treatment will have consequences for carbon reserves and photosynthesis. In this paper, the effect of dark cold storage at 7 °C to break flower bud dormancy in the evergreen Rhododendron simsii was quantified. Carbohydrate and starch content in leaves and flower buds of an early ('Nordlicht'), semi-early ('M. Marie') and late ('Mw. G. Kint') flowering cultivar showed that carbon loss due to respiration was lowest in 'M. Marie', while 'Mw. G. Kint' was completely depleted of starch reserves at the end of cold treatment. Gene isolation resulted in a candidate gene for sucrose synthase (SUS) RsSus, which appears to be homologous to AtSus3 and had a clear increase in expression in leaves during cold treatment. Photosynthesis measurements on 'Nordlicht' and the late-flowering cultivar 'Thesla' showed that during cold treatment, dark respiration decreased 58% and 63%, respectively. Immediately after cold treatment, dark respiration increased and stabilised after 3 days. The light compensation point followed the same trend as dark respiration. Quantum efficiency showed no significant changes during the first days after cold treatment, but was significantly higher than in plants with dormant flower buds at the start of cold treatment. In conclusion, photosynthesis stabilised 3 days after cold treatment and was improved compared to the level before cold treatment.

MOLECULAR INSIGHTS ON THE FUNCTIONAL MICROBIAL COMMUNITY FROM ORGANIC AND MINERAL GROWING MEDIA AND ITS INTERACTION WITH AGROBACTERIUM RHIZOGENES.

Despite numerous preventative measures, the hairy roots syndrome is an increasing problem in greenhouse horticulture. A recent survey of 177 tomato, cucumber and eggplant growers in Flanders (Belgium) revealed an increase of this disease in the last two years, with about 26% of all the tomato crops showing the syndrome. In this study, we compared the physicochemical and microbial community characteristics of inorganic and organic growing media in relation to the presence of the causative agent of the hairy roots, the plant pathogen Agrobacterium rhizogenes. We aimed to identify how the microbial and environmental interactions influenced the development and spread of this disease in a soilless cultivation system. Multivariate statistical analysis performed to assess the characteristics of each growing media revealed key variables impacting the hosted microbial community. Thus, humidity, pH, potassium and conductivity were drivers of the differences among microbial community composition. High throughput sequencing analysis of the bacterial family abundance of the communities present in organic media indicated potential competitive interactions with A. rhizogenes. Based on our hypothesis that growing media hosted a particular microbiota with potential for modulating hairy roots, we determined how the environment in organic media is reshaped to avoid establishment of A. rhizogenes. Our methodology provides a comprehensive insight into the complex bacterial interactions in horticultural media, which may be potentially applied for the development of effective control strategies and decrease in economic losses.

Cold storage to overcome dormancy affects the carbon balance of azalea.

Flower bud dormancy in azalea (Rhododendron simsii) is broken by artificial cold treatment and this will have its consequences on carbon reserves and photosynthesis. The effect of cold storage at 7 °C on carbohydrate and starch content in leaves and flower buds of an early ('Nordlicht') and semi-early ('M. Marie) flowering cultivar was quantified. Carbon loss due to respiration was lowest for 'M. Marie'. Photosynthetic measurements on 'Nordlicht' showed that photosynthesis 3 days after cold treatment (plants ready to flower) was improved compared to before cold treatment (plants with dormant flower buds).

Evaluation of herbicide combinations for livid amaranth (Amaranthus blitum) control in tuberous begonia (Begonia x tuberhybrida).

In the past years livid amaranth (Amaranthus blitum) is observed increasingly in begonia production fields. Control of weeds in begonia is generally done by a combined application of the soil herbicides isoxaben + simazin followed 10 days later by application of the contact herbicide bentazone. This treatment usually controls the weed population sufficiently with exception of amaranth. In 2003 a field trial was conducted to evaluate control of livid amaranth in tuberous begonia with isoxaben, simazin. S-metolachloor, phenmedipham + desmedipham and bentazone. These herbicides were used as combinations of soil treatment and contact herbicides. The results suggest that a soil treatment of isoxaben + S-metolachloor significantly reduces livid amaranth compared to isoxaben + simazin, without a pronounced negative effect on tuber yield. Application of phenmedipham + desmedipham however did not improve control of livid amaranth compared to bentazone.

Control of the two-spotted spider mite (Tetranychus urticae Koch) in glasshouse roses.

Populations of the two-spotted spider mite, Tetranychus urticae, can increase rapidly in glasshouse production, especially during summer. Both chemical and biological control must start at low densities for effective control. The combined efficacy of Phytoseiulus persimilis and the predatory midge, Feltiella acarisuga to control T. urticae on roses was evaluated in 2002. A second year rose crop (Rosa hybrida cv. First Red) was used for this experiment. Two glasshouse compartments of 200 m2 each were used, one was assigned for integrated control and the other for chemical control. The mite populations were monitored by bi-weekly analysis of 12 randomly selected harvestable flower stems, extracted on the Berlese funnel. Sticky plates (3 yellow and 3 blue/200 m2) were used for monitoring the Feltiella adults. End of January a population of +/- 2 spider mites/flower was present in both compartments. In the integrated control, the first Phytoseiulus were released on February the 7th, while the first release of Feltiella was on February the 20th. From week 7 till 13 the population of T. urticae increased exponentially to 90 spider mites/flower stem, while Phytoseiulus population was below one/flower stem. A treatment of fenbutatinoxide + hexythiazox (Torque + Nissuron) was necessary to reduce the spider mite population. A maximum number of predatory mite (4/flower stem) and predatory midge (106 adults/sticky plate) was found only 4 weeks later. A second increase of spider mite population occurred in week 27. Although 2 weeks later 3 predatory mites/flower stem were present, additional chemical treatment was necessary to control. A third and last increase of spider mite occurred in week 39. This last raise could be controlled effectively by Phytoseiulus and Feltiella. Chemical control in the second compartment was effective all-year-round with the exception of week 23 when a major increase up to 60 spider mites/flower stem was found. The applied biocontrol agents could not efficiently control spider mite in glasshouse rose. However, combined with selective insecticides they offer possibilities for IPM in glasshouse roses.