Nine plant-volatile compounds were tested for their activity against Monilinia laxa, the cause of brown rot in stone fruit. In vitro trials on conidial germination and mycelial growth showed a consistent fungicidal activity of trans-2-hexenal, carvacrol, and citral, whereas trans-cinnamaldehyde, hexanal, (-)-carvone, eugenol, 2-nonanone, and p-anisaldehyde exhibited a progressively lower inhibition. The best inhibitor of conidial germination was trans-2-hexenal (effective dose for 50 and 90% inhibition [ED50 and ED95] = 7.53 and 9.4 μl/liter, respectively; minimal inhibitory concentration [MIC] = 12.3 μl/liter], whereas carvacrol was the best inhibitor of mycelial growth (ED50 and ED95 = 2 and 3.4 μl/liter, respectively; MIC = 6.1 μl/liter). The three most active compounds in in vitro studies also were tested in vivo as postharvest biofumigants. The best control of brown rot was with trans-2-hexenal (efficacy ranging from 46.2 to 80.3%, depending on cultivar), whereas citral and carvacrol resulte...

https://apsjournals.apsnet.org/doi/pdf/10.1094/PD-91-0030

Fungicidal Activity of Plant Volatile Compounds for Controlling Monilinia laxa in Stone Fruit

Investigations on ''natural'' cuticular cracks were conducted on nectarine fruit (Prunus persica (L.) Batsch var. nucipersica (Suckow) C.K. Schneid.). A method for quantifying the cuticular crack surface area on a whole fruit basis was proposed. By using a stratified sampling design, the spatial distribution of the cuticular cracks over three regions (stylar end, peduncle, and cheek), their morphology, and the estimation of the total proportion of cuticular cracks on the fruit were studied. These features were examined during fruit development and in response to several fruit growing conditions corresponding to various crop loads and irrigation regimes. Cuticular cracks on nectarine fruit occurred during the final rapid fruit growth stage. Larger fruit presented higher cuticular crack densities in the apical regions than in the cheek regions. Thin and larger cuticular cracks occurred continuously during fruit development. Cuticular cracks represented 10% to 12.5% of the fruit surface area for well irrigated or low crop load trees, whereas they covered less than 4.5% for the heavy crop load and water deficit treatments. Cheek regions largely contributed to the total cuticular crack surface area (>60%), regardless of the fruit growing conditions. After irrigation was restricted, cuticular crack development was limited. A positive relationship was established between the cuticular crack surface area per fruit surface area and the fruit fresh weight.

/pdf/cuticular-cracking-on-nectarine-fruit-surface-spatial-1dtez0h684.pdf

Cuticular Cracking on Nectarine Fruit Surface: Spatial Distribution and Development in Relation to Irrigation and Thinning

Brown rot (BR) caused by Monilinia spp., has been an economic problem for the stone fruit market due to dramatic losses, mainly during the postharvest period. There is much literature about basic aspects of Monilinia spp. infection, which indicates that environment significantly influences its occurrence in the orchard. However, progress is needed to sustainably limit this disease: the pathogen is able to develop resistance to pesticides, and most of BR resistance research programs in plant models perish. Solving this problem becomes important due to the need to decrease chemical treatments and reduce residues on fruit. Thus, research has recently increased, exploring a wide range of disease control strategies (e.g., genetic, chemical, physical). Summarizing this information is difficult, as studies evaluate different Monilinia and Prunus model species, with diverse strategies and protocols. Thus, the purpose of this review is to present the diversity and distribution of agents causing BR, focusing on the biochemical mechanisms of Monilinia spp. infection both of the fungi and of the fruit, and report on the resistance sources in Prunus germplasm. This review comprehensively compiles the information currently available to better understand mechanisms related to BR resistance.

https://hal.archives-ouvertes.fr/hal-01594477/document

Brown Rot Strikes Prunus Fruit: An Ancient Fight Almost Always Lost.

We applied a semi-mechanistic model of fresh matter accumulation to peach fruit during the stage of rapid mesocarp development. The model, which is based on simple hypotheses of fluid flows into and out of the fruit, assumes that solution flow into the fruit increases with fruit weight and transpiration per unit weight, and decreases with the maximum daily shrinkage of the trunk, which was used as an indicator of water stress. Fruit transpiration was assumed to increase with fruit size and with radiation. Fruit respiration was considered to be related to fruit growth and to temperature. The model simulates variability in growth among fruits according to climatic conditions, degree of water stress and weight of the fruit at the beginning of the simulation. We used data obtained from well-watered and water-stressed trees grown in containers to estimate model parameters and to test the model. There was close agreement between the simulated and measured values. A sensitivity analysis showed that initial fruit weight partly determined the variation in growth among fruits. The analysis also indicated that there was an optimal irradiance for fruit growth and that the effect of high global radiation on growth varied according to the stage of fruit development. Water stress, which was the most important factor influencing fruit growth, rapidly depressed growth, particularly when applied late in the season.

/pdf/modeling-the-response-of-peach-fruit-growth-to-water-stress-13j8lepjp5.pdf

Modeling the response of peach fruit growth to water stress.

Les pesticides font aujourd’hui l’objet d’enjeux environnementaux considerables. Des 1999, le ministere charge de l’Ecologie a mis en place le programme de recherche « Evaluation et reduction des risques lies a l’utilisation des pesticides ». Dans ce cadre, 57 projets de recherche ont ete lances afin d’accroitre la connaissance des risques et d’aider les acteurs du domaine a mettre en œuvre des actions pour les reduire.

Cet ouvrage presente les avancees majeures de ce programme a travers quatre thematiques principales : transferts de pesticides et reduction de la contamination de l'environnement ; effets des pesticides et reduction des impacts sur les organismes et les ecosystemes ; pratiques agronomiques innovantes pour reduire l’utilisation des pesticides ; accompagnement des acteurs pour reduire les risques lies aux pesticides.
Les decideurs, porteurs de politiques publiques, professionnels du monde agricole ou encore gestionnaires de l’environnement y trouveront des elements pour estimer les risques lies a l’utilisation de ces produits et agir en faveur de pratiques agricoles plus economes en pesticides. Les enseignants mais aussi les etudiants accederont a une synthese des connaissances, etoffee de nombreuses references bibliographiques. Enfin, l’ouvrage identifie certaines lacunes scientifiques de la problematique et ouvre la reflexion sur de futures pistes de recherche.

Pesticides : des impacts aux changements de pratiques

Le comportement de conidies de M. laxa et de spores de R. stolonifer deposees a la surface de nectarines non blessees, a ete suivi en microscopie electronique a balayage. Parfois des figures de penetration d'hyphes myceliens par des microfissures cuticulaires sont observees. Il n'y a aucune penetration directe a travers la cuticule

/pdf/contribution-a-l-etude-des-voies-de-penetration-de-parasites-3ka7futbun.pdf

Contribution à l'étude des voies de pénétration de parasites fongiques des nectarines Monilia laxa (Ascomycète-Discomycète) et Rhizopus stolonifer (Zygomycète-Mucorale)

R. Hugueney

Papers

Contribution à l'étude des voies de pénétration de parasites fongiques des nectarines Monilia laxa (Ascomycète-Discomycète) et Rhizopus stolonifer (Zygomycète-Mucorale)