In vitro effect of lemon essential oil and garlic extract on Monilinia fructicola growth Efecto in vitro del aceite de limón y el extracto de ajo sobre el crecimiento de Monilinia fructicola Efeito in vitro do óleo de limão e extrato de alho no crescimento de Monilinia fructicola

Brown rot produced by Monilinia fructicola (MON) is the main disease that causes postharvest losses in peaches of Argentina. There is a public concern in reducing the use of synthetic fungicides. The objective of this work was to evaluate the effect of lemon essential oil (LO) and aqueous garlic extract (GE) on MON in vitro mycelial growth inhibition (INH). In a first trial a MON colony disc was placed in the middle of a Petri dish containing PDA 2%, or over the plate lid containing 1 mL of the following treatments: Control, LO 0.5%, LO 1%, LO 3% and Fludioxonil 0.02%. In a second trial, GE was obtained processing fresh garlic (cultivar Colorado) in a blender with tap water; 1 mL of garlic extract was placed in the cover of each plate, the treatments were: Control, GE 2.27%, GE 5.68%, GE 11.35% and Fludioxonil 0.02%, the MON colony was placed over the lid containing the extract. All concentrations of LO assayed and GE 11.35% showed INH > 90%. Following these results LO and GE could be evaluated in future trials as postharvest treatments on peach fruits for Monilinia fructicola control.


Introduction
Brown rot produced by Monilinia fructicola (Wint.) Honey (MON) is the main disease producing yield and quality losses in peaches of San Pedro (Buenos Aires, Argentina) and in other countries (Figure 1) (1) (2) . There is a public concern in reducing the use of synthetic fungicides, and several experiences have been conducted in order to study the effect of alternative compounds on postharvest pathogens (3)(4)(5) . Essential oils, also called natural volatiles, have a complex composition containing alcohols, aldehydes, ketones, phenols, esters, ethers, and terpenes in varying proportions. Some of these compounds are recognized as "Generally regarded as safe" (GRAS) chemicals, stimulating interest from postharvest scientists. In vitro studies in the vapor phase have revealed that the application of the essential oils as vapors was highly effective for the control of postharvest pathogens (6) .
In vitro and in vivo testing were carried out using essential oils in the vapor phase as a fumigant rather than by direct contact, as this application method seemed to be more practical for postharvest disease management (11) .
Fumigation with natural volatiles is promising specially in some species, like cherries, because they can be applied without wetting the fruit. The treatment of 10 mg L -1 thymol fumigation significantly reduced the incidence of brown rot, but had no effect on blue mold rot (9) and produced stem discoloration.
Results from the sensory evaluation trials after fumigation indicated that lemon myrtle essential oil treatment effect on sensory value was not significant. The association between lemon myrtle essential oil treatment and intention to purchase was also not significant (11) .
A commercial formulate containing essential oil of Melaleuca alternifolia was effective at controlling in vitro growth of Monilinia fructicola (3) . This organic formulate proved to be useful in a spraying schedule, combined with fungicides and coadjutants, in order to reduce the application of synthetic products prior to peach harvest (12) (13) .
The effect of biofumigation, through slow-release diffusors, of thyme and savory (Satureja montana) essential oils was effective in controlling postharvest rots of peaches and nectarines. Naturally contaminated peaches and nectarines were exposed to EO vapors for 28 days at 0 ºC in sealed storage cabinets and then exposed at 20 ºC for 5 days during shelf-life in normal atmosphere, simulating retail conditions. Under low disease pressure, most treatments significantly reduced fruit rot incidence during shelf-life, while under high disease pressure only vapors of thyme essential oil at the highest concentration tested (10% v/v in the diffusor) significantly reduced the rots (10) .
Citrus sinensis essential oil contains limonene; this active compound showed a potent toxicity against Penicillium expansum (14) . Citrus industry is a big scale activity in Argentina and lemon essential oils can be obtained as a residue.
Garlic production is important in Argentina and aqueous garlic extract (GE) is obtained, commercialized and applied in different horticultural crops in    Following these results, further investigations could be performed to evaluate postharvest fumigation with GE in order to reduce the presence of brown rot in peaches.

Conclusions
Several authors have obtained promising results for the in vitro and in vivo control of brown rot using natural volatiles.
This work shows that LO and GE, both natural products easily obtained in Argentina, can reach over 90% of in vitro mycelial growth inhibition of Monilinia fructicola.
Following these results, LO and GE could be evaluated in future trials as postharvest treatments to peach fruits for Monilinia fructicola control.
Methods of application should be assayed, and further assays developed, in order to evaluate these alternative compounds to synthetic fungicides.