Evaluation of three essential oils as potential sources of botanical fungicides.

In previous study, thirty essential oils were evaluated in vitro against two citrus pathogens namely Penicillium italicum Wehmer and Penicillium digitatum Sacc. Essential oils of Cinnamomum zeylanicum, Cinnamomum verum and Eugenia caryophyllus were selected because of their high inhibitory activities against both pathogens. The present study was undertaken to evaluate the in vivo activity of these essential oils. Fresh orange fruits were wounded and treated with different concentrations of essential oil (0.5, 1, and 5%) before being infected at the wound site with conidia suspensions of the tested pathogens. When applied at 5%, essential oils tested controlled totally the infections. Among the three essential oils tested, C. zeylanicum seems particularly interesting because of its high protection activity at 1% compare to the others. It reduced the disease incidence from 40 to 70% and the disease severity from 65 to 82%. Moreover no visible damage burn induced on the orange cuticle or skin was observed up to 5% of essential oil. These results strengthen the potential use of essential oils in postharvest disease management of citrus fruit as alternative to chemical fungicides.

Isolation and evaluation of bacteria and fungi as biological control agents against Rhizoctonia solani.

Rhizoctonia solani is one of the most important limiting factors for potato production and storage in Belgium and worldwide. Its management is still strongly dependent on chemical treatments. The aim of this work was to evaluate the possibility of exploiting bacteria and fungi in order to control this pathogen. Among a collection of 220 bacterial strains isolated from different organs of healthy potato plants and rhizospheric soils, 25 isolates were selected using screening methods based on in vitro dual culture assays. The mycelial growth inhibition rate of the pathogen was ranged from 59.4 to 95.0%. Also seven fungal strains isolated from the rhizospheric soil and potato roots showed a highly mycelial growth inhibition of R. solani. The mycelial growth inhibition rate obtained with these fungi was included between 60.0 and 99.4%. From this preliminary study, the further investigations will be planned to determine the bacterial isolates systematic, species of fungal strains by using molecular tools and to assess their efficacy against R. solani in greenhouse trials.

Detection and epidemiological characteristics of peach latent mosaic viroid in Tunisia.

A rapid and sensitive assay was developed for the detection and identification of Peach latent mosaic viroid (PLMVd) by reverse transcription-polymerase chain reaction (RT-PCR) in infected tissues from Tunisian orchards. The test was initially performed by using total RNA preparations from selected isolates and then applied on total RNA preparations from leaf or bark tissues of fruit trees collected in 2003 in 20 orchards in the North of Tunisia and the Sahel. PLMVd occurred in peach and pear trees. The identity of the detected viroid was confirmed by comparison of its sequence with other isolates previously characterized. The test was then simplified by direct use of diluted crude plant extracts. The results obtained from crude sap extracts of leaves or bark tissues are identical to those obtained from total RNA preparations. Epidemiological characteristics of PLMVd on peach trees have been investigated. A survey of peach trees was carried out in 32 orchards in May 2004. The obtained results showed that (1) PLMVd is highly and equally present in several regions of the north of Tunisia rather than the central, the Sahel and the southern regions, (2) infection percentage increases with the age of the tree and (3) the studied cultivars are classified into three groups of sensitivity.

Development of molecular tests for the detection of ILAR and latent viruses in fruit trees.

The detection throughout the year of latent and ILAR viruses in fruit tress by classical serological tests appear to be unreliable. We have developed RT-PCR tests for a reliable detection of latent and ILAR viruses in fruit trees. These assays were then simplified to allow the direct use of crude plant extracts instead of total RNA preparations, and the analyses of pooled samples. In this way, such RT-PCR protocols are suitable for a routine diagnosis of latent and ILAR viruses in fruit tree certification.