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.

Biocontrol of blue mold on apple fruits by Aureobasidium pullulans (strain Ach 1-1): in vitro and in situ evidence for the possible involvement of competition for nutrients.

Aureobasidium pullulans strain Ach1-1 was recently isolated for its biocontrol effectiveness against Penicillium expansum, the causal agent of blue mold on harvested apples. In the present study, strain Ach1-1 was found to be very effective in controlling P. expansum on apple wounds. For in vitro tests, strain Ach1-1 and P. expansum were cocultured in the presence of apple juice (0 - 5%) using a system preventing direct contact between both agents. The presence of the antagonist greatly reduced germination of conidia at low (0.1, 0.5 and 1%) but not at high (5%) juice concentrations. Germination of previously inhibited conidia at 0.5% apple juice was partially restored in the presence of the antagonist when fresh juice was added at a final concentration of 5%, and completely recovered at both 0.5 and 5% juice concentrations in the absence of the antagonist. These data show that P. expansum conidia are able to germinate when cocultered with strain Ach1-1 in conditions of sufficient rather than limited nutrient availability and that the antagonist does not affect the viability of these conidia, indicating that the inhibitory effect of strain Ach1-1 on conidia germination may be due to a competition for nutrients. Such observation was confirmed in situ since the application of high amounts of exogenous amino acids, vitamins or sugars on apple wounds significantly reduced the protective level of strain Ach1-1 against P. expansum, the most important effect was obtained with amino acids followed by vitamins and then by sugars. The present work provides both in vitro and in situ evidence that the biocontrol activity of strain Ach1-1 against P. expansum essentially relies on competition for apple fruit nutrients, especially amino acids.

Water deficit effects on solute contribution to osmotic adjustment as a function of leaf ageing in three durum wheat (Triticum durum Desf.) cultivars performing differently in arid conditions.

A greenhouse study was carried out using three durum wheat (Triticum durum Desf.) cultivars differing in their field performances under arid conditions (Kabir 1, poor yield stability; Omrabi 5, high yield stability and Haurani, landrace well adapted to drought). Water stress was imposed by withholding water at the seedling stage. Water potential (Psi(w)), relative water content (RWC), stomatal resistance (SR), and changes in solute concentrations were quantified: (1) as a function of leaf development during the stress period; and (2) in young expanded and growing leaves harvested at the end of the stress treatment. Psi(w), RWC and SR were almost unaffected by leaf age in controls. In contrast, solute concentrations appeared to vary in the course of leaf development. During the stress treatment, Psi(w) and RWC decreased and SR increased in all cultivars; the changes were most often largest in Omrabi 5, lowest in Haurani and intermediate in Kabir 1. Water stress also increased sugar and proline concentrations and decreased nitrate levels. Young expanded and growing leaves differed in terms of Psi(w), RWC and osmotic adjustment (OA). The capacity of OA was greater in growing than in expanded leaves, especially in the two cultivars best adapted to aridity, and allowed turgor maintenance in these genotypes. Sugars were the main solutes that contributed to OA particularly in growing leaves followed by proline and then quaternary ammonium compounds. The contributions of these organic solutes to OA tended to be higher in Omrabi 5 and in Haurani than in Kabir 1. Inorganic solutes, however, did not seem to play an important role in OA despite their high proportion in total solutes.