Peach Surface Research Articles

Enhancing the adhesion of Epicoccum nigrum conidia to peach surfaces and its relationship to the biocontrol of brown rot caused by Monilinia laxa

To find a formulation of Epicoccum nigrum conidia that enhances its adhesion to peach surfaces and improves its biocontrol efficacy against brown rot caused by Monilinia laxa. The stickers, glycerol, sodium alginate and methylcellulose; the desiccants, silica powder and talc; and a commercial adhesive (NU FILM 17) were added at two different points during the production of an E. nigrum conidial formulation to improve conidial adhesion to peach surfaces. Conidial adhesion levels were determined from the number of E. nigrum conidia that adhered to glass slides or peach surfaces and conidial viability of adherent E. nigrum conidia was determined from the number of colony-forming units of glass or peach-adherent E. nigrum that grew on Petri dishes that contained potato dextrose agar. Compared to dried E. nigrum conidia without additives, the adhesion and viability of adherent E. nigrum conidia to peach surfaces were enhanced when either 1.25% sodium alginate or 2.5% methylcellulose was added to the conidial mass after fluid-bed drying, and when 2.5% methylcellulose was added to the conidial mass after its production and before fluid-bed drying. Epicoccum nigrum conidial formulations with 2.5% methylcellulose were more effective than dried E. nigrum conidia without additives in reducing the incidence of brown rot in peaches caused by M. laxa. When 2.5% methylcellulose is incorporated into an E. nigrum conidial formulation, the adhesion of E. nigrum conidia to peach surfaces improves and results in efficacious biocontrol of brown rot. A new improved formulation of a biocontrol agent has been developed to improve the control of M. laxa on peaches.

Population dynamics ofEpicoccum nigrum, a biocontrol agent against brown rot in stone fruit

To study the population dynamics of Epicoccum nigrum on peaches and nectarines and to enhance its colonization on fruit surfaces to improve its biocontrol efficacy against brown rot. Twelve surveys were performed to study E. nigrum populations and their effect on the number of the pathogenic Monilinia spp. conidia in peach orchards in Spain and Italy between 2002 and 2005. Fresh conidia and five different formulations of E. nigrum conidia were applied three to six times to peach and nectarine trees from full flowering to harvest. The size of the E. nigrum populations was determined from the number of colony-forming units and conidial numbers per flower or fruit. Treatment with all conidial formulations increased the size of the indigenous conidial population on peach surfaces. Formulations of E. nigrum having high viability are most effective against conidia of the pathogen when applied at pit hardening and during the month immediately before fruit harvest. Application of an E. nigrum conidial formulation decreased the number of conidia of Monilinia spp. on fruit surfaces during the growing season to the same extent as fungicides.

Conidial density of Monilinia spp. on peach fruit surfaces in relation to the incidences of latent infections and brown rot

To evaluate the effect of conidial density of Monilinia spp. on the fruit surface on the incidence of latent infection and brown rot in peaches, eleven field surveys were performed in commercial orchards located in Cataluna, Spain over four growing seasons from 2002 to 2005, and nine surveys were conducted to determine the sources of overwintered Monilinia spp. inoculum. There was a significant positive relationship (r = 0.69) between the numbers of conidia of Monilinia spp. on the fruit surface and the incidence of latent infections, but not with brown rot at harvest. Although mummified fruit, twigs and pits have been identified as being able to carry the pathogen from year to year in peaches grown in Spanish orchards, no relationships between any of these sources and the numbers of conidia on the fruit surface, or incidence of latent infection or brown rot were found. The effect of temperature (T), solar radiation (SR), rainfall (R) and wind speed (WS) on the area under the number of conidia of Monilinia spp. curve (AUncC) on peach surfaces was analysed. Regression analysis revealed that T, SR, R, and WS could account for 99% of the total variation in the area of the AUncC on peach surfaces. Thus, in order to reduce the incidence of latent infection and brown rot it is essential not only to remove the sources of primary inoculum but also to reduce the number of Monilinia spp. conidia on the fruit surface. Furthermore, the sources of airborne conidia of Monilinia spp. should be taken into consideration in disease management programmes in Spain.

Influence of additives on adhesion of Penicillium frequentans conidia to peach fruit surfaces and relationship to the biocontrol of brown rot caused by Monilinia laxa

Additives, such as sucrose, d-sorbitol, glycerol, sodium alginate, carboxymethyl cellulose, silica gel, gelatine, non-fat skimmed milk and a commercial adhesive were added to conidia of Penicillium frequentans at two different points in the production process of the formulation of this fungus to improve conidial adhesion. Conidial adhesion was estimated as the number of P. frequentans conidia (no. conidia cm − 2 ) and colony-forming units of P. frequentans per unit area (cfu cm − 2 ) that adhered to glass slides or to peach surfaces. The P. frequentans conidial concentration had a significant effect on conidial adhesion, while the shelf life of conidia did not have any effect. The highest adhesion of P. frequentans conidia to glass slides was observed when conidial concentrations were greater than 10 6 conidia ml − 1 . P. frequentans conidial adhesion was improved when 1.5% sodium alginate or 1.5% carboxymethyl cellulose were added to the conidial mass obtained after production and before drying by the fluid bed drying process. Conidial adhesion was also enhanced when 1.5% sodium alginate, 1.5% carboxymethyl, or 1.5% gelatine were added to conidia after fluid bed drying. P. frequentans formulations with 1.5% sodium alginate or 1.5% carboxymethyl cellulose were more effective in reducing brown rot caused by Monilinia laxa than dried P. frequentans conidia alone. Our results show that additives can improve adhesion of P. frequentans conidia to fruit surfaces, resulting in more effective control of brown rot in peaches.

Penicillium frequentans population dynamics on peach fruits after its applications against brown rot in orchards

The study provides useful information on the temporal population dynamics of the biological control agent, Penicillium frequentans, after its applications against brown rot in orchards. Population dynamics of P. frequentans were studied on peach flower and fruit surfaces after different field treatments. Eight experiments were carried out in commercial peach orchards in Spain, over four growing seasons from 2002 to 2005. Six different formulated P. frequentans conidia were applied four to six times from blossom to harvest and P. frequentans population sizes were monitored using conidial numbers and colony forming units (CFU) per flower or fruit. A consistent population of P. frequentans, ranging from 10(5) to 10(6) number of conidia or 10(3) to 10(4) CFU of P. frequentans per flower or fruit, was obtained. Colonization of peach surfaces by all P. frequentans formulation are similar and it appears to follow a general pattern: (i) higher colonization of fruits at preharvest than on the flowers at bloom; (ii) high populations just after treatments, especially after preharvest treatments; and (iii) a slight decline between treatments, especially in cool and moist springs. The exponential model was the most appropriate for fitting and comparing the P. frequentans dynamic populations on peaches and nectarines over time. The linearization of the P. frequentans population curve was essential to determine dynamic population and for population levels forecast. A positive relationship between number of blossom and preharvest applications, temperature, relative humidity and dynamic of P. frequentans population applied on peaches was studied using a multiple regression model. Blossom and preharvest applications were the most important spray times for obtaining the highest population of P. frequentans on peach surfaces. The study provides useful information on dynamic P. frequentans population and its effects on the brown rot biocontrol.

Effects of different biological formulations of Penicillium frequentans on brown rot of peaches

Abstract Four wettable powder formulations of Penicillium frequentans conidia with measurable viability of one year and an improved adherence to peach surfaces were produced by the addition of various ingredients, in two separate steps of the production and drying processes, to conidia. These formulations were then evaluated against brown rot of peach fruit caused by Monilinia spp. Formulations were applied to fruit either as postharvest treatments or before harvest in field treatments to peach trees. In the case of postharvest treatments to fruit, reductions of brown rot were obtained with all P. frequentans formulations. Treatments applied before harvest were tested in six field experiments in peach orchards in Spain. A total of 100 fruits, randomly selected in each orchard, were used as the sample unit and every treatment was repeated four times. Results showed that P. frequentans formulations significantly reduced the inoculum density of the pathogen (measured as the number of conidia on peach surface) in five trials out of the six tested, better than a chemical fungicide that only showed a reduction of the pathogen conidial in two of the six trials. The relationship between the number of conidia of the pathogen and the incidence of brown rot disease is discussed.

The germicidal and hormetic effects of UV-C light on reducing brown rot disease and yeast microflora of peaches

The application of ultraviolet light-C doses (254 nm, UV-C) was used to determine the germicidal and hormetic effects on reducing brown rot of ‘Elberta’ peaches which were naturally and artificially inoculated with Monilinia fructicola. The results showed that a negative relationship existed between UV-C doses, colony forming units of the fungus, and the number of brown rot lesions. Also, the results of our study showed that the hormetic (beneficial) effect of low UV-C dose of 7.5 kJ m −2 induced host resistance by controlling latent brown rot infection. The hormetic effects of UV-C on peaches was photoreversed with visible light and resulted in the reduction of host resistance to brown rot. Furthermore, the results indicated that UV-C doses increased phenylalanine ammonia-lyase activity, delayed ripening and suppressed ethylene production. Additionally, the population of epiphytic yeast ( Debaryomyces hansenii) increased curvilinearly on peach surfaces following UV-C irradiation up to 7.5 kJ m −2. Evaluation of the yeast population on the peach surfaces showed an antagonistic activity against M. fructicola. The possibility of the host peripheral defense by UV-C stimulation of the antagonist activity of a yeast is discussed.

Iron—Polyphenol Complex Formation and Skin Discoloration in Peaches and Nectarines

The formation of metallo-pigmentation and copigmentation as potential mechanisms of inking formation was investigated in peach and nectarine skin tissues. Cyanidin-3-glucoside, the most abundant anthocyanin in peaches and nectarines, formed very purple ferric complexes with an anthocyanin/iron molar ratio of two. Greenish metallo complexes between ferric ion and chlorogenic acid, caffeic acid, catechin, or epicatechin formed with an phenolic/iron molar ratio of one. The lack of copigmentation pointed out the importance to focus research on the metallo-phenolics reaction. High intensity of dark color formation was developed with cyanidin-3-glucoside, followed by caffeic acid, chlorogenic acid, catechin, and epicatechin on an equal molar basis. Citric acid acted as a strong iron chelator to prevent and reverse the formation of ferric cyanidin-3-glucoside complexes. The variety of dark and light colored spots observed on the surface of peaches and nectarines is explained by the formation of metallo-pigment complexes.

PLANT HORMESIS INDUCED BY ULTRAVIOLET LIGHT-C FOR INDUCING RESISTANCE OF BROWN ROT OF PEACHES

Low hormetic doses of ultraviolet light (UV-C) stress on exposed peaches (Prunus persica). reduced brown rot resulting from field and artificial inoculation from Monilinia fructicola. To test the hypothesis that UV-C induced resistance through host responses the following tests involving biochemical changes (phenlyalanine ammonia-lyase activity (PAL) and ethylene production (EP)), bioassay of antifungal activity of tissue extracts to the fungus, and latent infection of rot free peaches previously treated with and without UV-C were determined. Exposure of peaches to UV-C dose of 7.5×104 ergs/mm2 promoted an increase in PAL and EP compared to the control. As the PAL activity increased, percent storage rots decreased. Antifungal activity to the fungal conidia in UV-C treated peach extract showed that the percent conidia germination was reduced 3 folds. Preharvest infection of brown rot which indicated latent infection was significantly reduced. To test for the germicidal effect of UV-C on M. fructicola on the surface of peaches, an artificial epiphytic population of the fungus was deposited on the peaches. A negative relationship between UV-C dose of 1.3 to 40×104 ergs /mm2, colony forming units and number of decaying brown rot lesions were found.

SPECTRAL ANALYSIS OF PEACH SURFACE DEFECTS

ABSTRACT The spectral reflectance of peach surface defects (bruise, cut, scar, scale, brown rot, wormhole) in the 350 to 1200 nm range was measured. Sorting criteria which were suitable for use with a machine vision system were developed and evaluated based on their potential for discriminating between defective and normal peach surface. Separability was calculated in terms of the Mahalanobis distance between the two classes. Sorting criteria which were based on ratios of wave-lengths had good separability for some defects, but multivariate sorting criteria with at least one unnormalized component were required for good class discrimination for all peach defect types at a fixed set of wavelengths. A three-wave-length criterion with spectral sensitivities centered at 650, 720, and 815 nm had the highest Mahalanobis distances for the types of peach defects tested.

LENGTHENING THE POSTHARVEST LIFE OF PEACHES BY COATING WITH HYDROPHOBIC EMULSIONS

In this study peaches were coated with three different hydrophobic emulsions and stored at room conditions (21–24°C and 57–63% R.H). The decrease in weight and the changes in the total titratable acidity, ascorbic acid and soluble solids contents, pH and the organoleptic characteristics of the coated and uncoated (control) samples were determined periodically. The rate of the weight decrease and the changes in the chemical structure and texture of the peaches were lower with the beeswax-coconut oil emulsion coated peaches than the uncoated peaches. While the maximum acceptable shelf-life for uncoated samples was 10 days, the samples coated with this emulsion maintained their acceptability for 14 days. The coating of the peach surfaces with this emulsion decreased the water vapor and oxygen gas transfer, resulting in the diminished respiration rate thus increased the shelf-life of the fruit.

Composition and Ultrastructure of Leaf Cuticles From Fruit Trees, Relative to Differential Foliar Absorption

Differential foliar absorption of chemicals by peach, apple and orange was related to cuticle thickness, weight, surface wax and embedded wax content and to surface wax wettability, ultrastructure and composition. Surface wax concentration, especially on abaxial leaf surfaces, correlated well with resistance to foliar absorption. The abaxial surface wax on peach leaves was built up in layers around and over the guard cells (which are preferred paths of spray entry into leaves) whereas apple and orange guard cells were relatively wax-free. Peach surface waxes were more difficult to wet than orange waxes and, although more polar than orange waxes, may be more resistant to water penetration as they were rich in hydrocarbons and triterpenoids. Enhancement of foliar absorption may require improved partitioning of sprays through the surface waxes or the bypassing of the waxes via stomatal penetration.