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INTEGRATED PRODUCTION SYSTEMS IN SWITZERLAND

WEIBEL, F. P.7_{, WYSS, G. S.}8

Key words: Malus domestica Borkh., organic production, microorganisms, fungi, fungal diversity

Abstract

The eff ects of organic and integrated production systems on the cultivable mycobiota (fungal microfl ora) of stored apple fruits from fi ve matched pairs of certifi ed organic and integrated ‘Golden Delicious’ farms were studied at fi ve representative production sites in Switzerland. Isolated fungi were identifi ed morphologically. Abundance (colony numbers), colonization frequency (percentage of apples colonized), and diversity (taxon richness) were assessed for each orchard. Compared to integrated apples, organic apples had signifi cantly higher taxon diversity, abundance of total fungi, and frequencies of fi lamentous fungi. Canonical correspondence analysis (CCA) of the total fungal community revealed a clear diff erentiation among production systems and sites.

Introduction

Pathogenic microorganisms are major causes of economic losses in apple production and challenge crop protection strategies. However, the microfl ora of crops also includes a large proportion of non-pathogenic microorganisms that have been recognized as benefi cial components of the natural microfl ora of many plants, including apple, by acting as antagonists toward plant pathogens or by inducing the plant’s own defense mechanisms (Fokkema, 1976; Ippolito et al., 2000). Apple farm management practices, namely the use of pesticides, may infl uence such complex microbial interactions with substantial consequences for the microbial composition and outcome of their interaction. As an example, organic and integrated apple production diff er considerably with respect to crop management practices (e.g., no use of chemically synthesized fertilizers, herbicides, fruit thinners, and plant-protecting agents in organic apple production (Avilla and Riedl, 2003; Weibel and Häseli, 2003), but only scant information exists about the eff ects of such production systems on the microorganisms associated with apple. In a previous study, a comparison of the apple phylloplane microfl ora in organic and integrated apple orchards showed a greater abundance and diversity of microorganisms on leaves from organic trees (Waipara et al., 2002).

1 1_{Research Institute of Organic Agriculture FiBL, Ackerstrasse, 5070 Frick, Switzerland,}

E-Mail jose.granado@fi bl.org, Internet www.fi bl.org

2, 3, 5, 6, 7, 8_{as above}

Here, we focus on the mycobiota (fungal microfl ora) of stored ‘Golden Delicious’ apple fruits and compare the infl uence of organic and integrated farming practices on fungal population abundance (colony numbers), colonization frequency (percentage of apples colonized), composition, and diversity (taxon richness) with established morphological and microbiological methods.

Materials and Methods

In September 2004 we picked mature and well developed apple fruits under aseptical conditions at ten commercial fruit farms (fi ve matched pairs of certifi ed organic and integrated farms) in representative apple-producing regions in Switzerland: two sites were in the canton of Valais (VS1, VS2) and one in the canton of Vaud (VD) (both southwestern cantons); one site was in the northwestern canton of Aargau (AG) and one site was in the northeastern canton of Thurgau (TG). The apples (30 per orchard, in total 300 fruits) were stored under normal atmospheric conditions at 2°C and a relative humidity of 90–95% while preventing microbial contamination during the storage. The sampling of microorganisms from the stored apple fruits was from January until April 2005.

Epiphytic microorganisms were lifted from the edible fruit surface (excluding the non-eaten calyx, stem, and stem cavity) using a sterile swab and collected into a plastic tube containing 1.8 ml Ringers Solution and 0.005% Tween 80. Aliquots of 100 μl of 10-1 _{to 10}-2 _{dilutions of the} suspension were spread in duplicates on DG18 (Oxoid, CM 0729) isolation plates supplemented with chloramphenicol (0.01% w/v). Endophytes were sampled from the same fruits: the whole fruits were surface-sterilized and 12 discs (5 mm in diameter, including skin and a 1–2 mm layer of fl eshy tissue) per apple were taken randomly from the edible fruit surface using a sterilized cork borer. Discs were placed with the fl eshy tissue layer down on isolation plates (12 discs per plate and per apple) supplemented with chloramphenicol (0.01% w/v). Both epiphytic and endophytic colonies were counted after seven days of incubation at 25°C. Epiphytic and endophytic counts were expressed in colony forming units (CFU) and viable disc colonies (VDC), respectively. Fungal abundance was expressed in CFU per gram fresh weight and in VDC per apple, respectively. Following incubation, colonies with a distinct morphology (color, shape, size) were identifi ed at diff erent taxonomic levels (taxa), e.g., species or genera, or as recognizable groups according to color, shape or lack of spores (sterility). The number of diff erent taxa was expressed as taxon richness and the fungal diversity as taxon richness per apple.

We used the nonparametric Wilcoxon’s matched-pairs signed-ranks test (SPSS 13.0 for Windows) for pairwise comparisons of organic and integrated apples.To test the factor eff ects “site” and “production system” on the composition of fungal populations on apples we used Monte Carlo permutation tests using CANOCO 4.5 (Biometris, Plant Research International, Wageningen, NL). The ordination of samples relative to the treatment factors was performed using canonical correspondence analysis (CCA).

Results

The standard quality of the stored fruits was comparable for both organic and integrated apples and complied with national food hygiene standards. Only on apples maintained by

integrated management practices residues of contact and systemic synthetic fungicides, used to prevent pre-harvest and post-harvest diseases, were detected within permissible limits (data not shown). Yeasts (6 taxa) and Aureobasidium pullulans were the dominant epiphytes, fi lamentous fungi (21 taxa) the dominant endophytes. The most common fungi occurred at all sites and belonged to the “white” and “pink” yeasts, A. pullulans, Cladosporium spp., Alternaria spp., and sterile species.

Compared to integrated apples, organic apples had signifi cantly higher taxon diversity, abundance of total fungi, and frequencies of filamentous fungi (data not shown). Canonical correspondence analysis (CCA) of the total fungal community revealed a clear diff erentiation among production systems and sites (Fig. 1). Both inherent experimental factors, i.e., production systems and sites, were signifi cant, while the production systems are diff erentiated along the fi rst canonical axis and the sites mainly along the second canonical axis. Production systems and sites explained 35.9% of the total variation. The major part of the variability (64.1%) remained unexplained. The infl uence of the sites was highly signifi cant, explaining 23.5% of the total variation, whereas the production systems accounted for 12.4% of the total variation.

Discussion

The eff ects of the production system on the mycobiota are most likely due to the diff erent plant protection strategies. Similar eff ects on fungal populations were shown by Teixido et al. (1999) on untreated apples compared to apples treated with synthetic fungicides. The incidence of potential mycotoxin producers such as Penicillium and Alternaria species was not diff erent between production systems, and, as we worked with symptomless apples, an accumulation of harmful mycotoxin concentrations was unlikely to occur in our samples. Other fungi, for example A. pullulans, are potential biocontrol agents against post-harvest pathogens of apples (Ippolito et al., 2000; Leibinger et al., 1997). Notably, in our study A. pullulans occurred naturally at elevated population densities on organic apples at all sites tested, suggesting a benefi cial role in postharvest pathogen control on organic apples.

Fig. 1. Constrained ordination of the fi rst two canonical axes as determined by canonical correspondence analysis (CCA) of cultivable numbers of epi- phytic and endophytic fungi (CFU per gram and VDC per apple, respective- ly) on apple fruits from paired organic (Org: circles, n = 149) and integrated (Int: triangles, n = 148) orchards and fi ve geographically diff erent sites (VS1, VS2, VD, AG, TG) in Switzerland.

In conclusion, canonical correspondence analysis (CCA) of the total fungal community revealed a clear diff erentiation among production systems and sites. Fungal populations of orchards located in the northern areas (AG, TG) were clearly diff erentiated from those located in the southern areas of Switzerland (VS1, VS2, VD). This may relate to climate conditions, with warmer temperatures and less rainfall in the south than in the north of Switzerland. A higher fungal abundance and diversity on stored edible organic fruits was one eff ect relating to the type of production system. We suggest that higher fungal diversity may generally be associated with organic production and may increase the level of benefi cial and antagonistically acting species known for their potential to suppress apple pathogens, which may be an advantage to organic apples, e.g., in respect to natural disease control. The role of potential biocontrol agents on apples, however, needs to be studied.

Acknowledgments

We are grateful to Coop Naturaplan-Fonds, Switzerland, for their fi nancial support.

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ADVANCED STRATEGIES IN ASSESSMENT OF BIO-PRODUCTS